HU ISSN 2063-6792 HU ISSN 2063-6792

MATERIALS SCIENCE AND ENGINEERING MATERIALS SCIENCE AND ENGINEERING

A Publication of the University of Miskolc A Publication of the University of Miskolc

Volume 43, Number 1 Volume 43, Number 1

Miskolc University Press Miskolc University Press 2018 2018

Editor Board: Editor Board:

Chair: Prof. Dr. Árpád Bence Palotás Chair: Prof. Dr. Árpád Bence Palotás

Secretary: Dr. Ágnes Wopera Secretary: Dr. Ágnes Wopera

Members: Members:

Prof. Dr. Eric G. Eddings Prof. Dr. Eric G. Eddings Dr. György Fegyverneki Dr. György Fegyverneki Dr. László Gömze Dr. László Gömze Prof. Dr. C. Hakan Gür Prof. Dr. C. Hakan Gür Prof. Dr. Tamás Kékesi Prof. Dr. Tamás Kékesi Dr. János Lakatos Dr. János Lakatos Dr. Valéria Mertinger Dr. Valéria Mertinger Prof. Dr. Zoltán Gácsi Prof. Dr. Zoltán Gácsi Prof. Dr. András Roósz Prof. Dr. András Roósz Dr. Judit Sóvágó Dr. Judit Sóvágó Dr. Tamás Szabó Dr. Tamás Szabó Dr. Katalin Szemmelveisz Dr. Katalin Szemmelveisz

Editors: Dr. Ágnes Wopera Editors: Dr. Ágnes Wopera Gábor Nagy Gábor Nagy

CONTENTS CONTENTS

Csongor Báthory–Árpád Bence Palotás: Csongor Báthory–Árpád Bence Palotás: Balloon Based Atmospheric Stability Measurement Near the Surface ...... 5 Balloon Based Atmospheric Stability Measurement Near the Surface ...... 5

R. Zsanett Boros–István Varga–Barnabás Buzellák–Márta Harangozó– R. Zsanett Boros–István Varga–Barnabás Buzellák–Márta Harangozó– Milán Szőri–Béla Viskolcz–László Farkas: Milán Szőri–Béla Viskolcz–László Farkas: An Approach for Eliminating Phenyl Isocyanate from Solvent Used in Isocyanaate An Approach for Eliminating Phenyl Isocyanate from Solvent Used in Isocyanaate Production ...... 11 Production ...... 11

Marianna Bubenkó–Monika Tokár–György Fegyverneki: Marianna Bubenkó–Monika Tokár–György Fegyverneki: The Examination of the Grain Refining Effects of Titanium in Hypoeutectic Al-Si The Examination of the Grain Refining Effects of Titanium in Hypoeutectic Al-Si Foundry Alloys ...... 17 Foundry Alloys ...... 17

Viktória Dargai–László Varga: Viktória Dargai–László Varga: The Examination of the Mechanical Properties of Water Glass Core Sands ...... 26 The Examination of the Mechanical Properties of Water Glass Core Sands ...... 26

Attila Garami–Pál Tóth: Attila Garami–Pál Tóth: Flame Image Processing and Artificial Intelligence as a Diagnostic Tool for Flame Image Processing and Artificial Intelligence as a Diagnostic Tool for Industrial Biomass Combustion ...... 31 Industrial Biomass Combustion ...... 31

Róbert Géber–István Kocserha: Róbert Géber–István Kocserha: Current Research Trends in Foamed Construction and Building Materials: Current Research Trends in Foamed Construction and Building Materials: A Review...... 42 A Review...... 42

Gábor Gyarmati–Monika Tokár–György Fegyverneki: Gábor Gyarmati–Monika Tokár–György Fegyverneki: The Effect of Inclusions on the Tensile Properties of AlSi7Mg0.4Cu0.5 The Effect of Inclusions on the Tensile Properties of AlSi7Mg0.4Cu0.5 Casting Alloy ...... 54 Casting Alloy ...... 54

Szabolcs Jónás–Miklós Tisza: Szabolcs Jónás–Miklós Tisza: Numerical Investigation of Clinched Joints ...... 62 Numerical Investigation of Clinched Joints ...... 62

Ákos Korbács–R. Zsanett Boros–Angelica Rodrigez–László Farkas: Ákos Korbács–R. Zsanett Boros–Angelica Rodrigez–László Farkas: Reducing of DNT Content in Red Water Formed During TDI Production ...... 71 Reducing of DNT Content in Red Water Formed During TDI Production ...... 71

Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz: Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz: The Effect of Age on Combustion Properties of Energy Willows ...... 79 The Effect of Age on Combustion Properties of Energy Willows ...... 79

Krisztina Román–Tamás J. Szabó–Kálmán Marossy: Krisztina Román–Tamás J. Szabó–Kálmán Marossy: Application of Diiocyanate Additive in Rigid PVC/Wood Flour Composite ...... 92 Application of Diiocyanate Additive in Rigid PVC/Wood Flour Composite ...... 92

Patcharapon Somdee–Tímea Lassú-Kuknyó–Csaba Kónya–Kálmán Marossy: Patcharapon Somdee–Tímea Lassú-Kuknyó–Csaba Kónya–Kálmán Marossy: Influence of Chain Extender on Soft and Hard Segment of Polyurethane Elastomers ... 98 Influence of Chain Extender on Soft and Hard Segment of Polyurethane Elastomers ... 98

Yilei Xue–Zsófia Borbála Rózsa–Andrea Guljas–Béla Fiser–Anita Rágyanszki– Yilei Xue–Zsófia Borbála Rózsa–Andrea Guljas–Béla Fiser–Anita Rágyanszki– John Justine Villar–Béla Viskolcz–Imre G. Csizmadia–Milán Szőri: John Justine Villar–Béla Viskolcz–Imre G. Csizmadia–Milán Szőri: Model Aided Biofuel Design: A Case Study of C6H12O ...... 108 Model Aided Biofuel Design: A Case Study of C6H12O ...... 108

Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 5–10. Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 5–10.

BALLOON BASED ATMOSPHERIC STABILITY MEASUREMENT NEAR BALLOON BASED ATMOSPHERIC STABILITY MEASUREMENT NEAR THE SURFACE THE SURFACE

CSONGOR BÁTHORY1–ÁRPÁD BENCE PALOTÁS2 CSONGOR BÁTHORY1–ÁRPÁD BENCE PALOTÁS2

Detailed vertical temperature and humidity distribution data were collected up to 300 m above sea level Detailed vertical temperature and humidity distribution data were collected up to 300 m above sea level using a helium balloon technique. The measurement serves as a basis for research of the link between using a helium balloon technique. The measurement serves as a basis for research of the link between the mixing layer height and PM10 concentration. The balloon with the data recorder, like an aerostat, the mixing layer height and PM10 concentration. The balloon with the data recorder, like an aerostat, by its rigging was lifted and then descended. During the test measurements data were recorded and by its rigging was lifted and then descended. During the test measurements data were recorded and stored. After the experiment analysis demonstrated the instable, mixed and stable air layering as stored. After the experiment analysis demonstrated the instable, mixed and stable air layering as atmospheric stability types. atmospheric stability types. Keywords: PM10, mixing layer height, atmospheric stability, temperature gradient Keywords: PM10, mixing layer height, atmospheric stability, temperature gradient

INTRODUCTION INTRODUCTION

In Switzerland meteorological and PM10 concentration data were collected for over 15 years In Switzerland meteorological and PM10 concentration data were collected for over 15 years to analyze the connection between them [1]. The investigations revealed that on a yearly to analyze the connection between them [1]. The investigations revealed that on a yearly basis, the wiping effect of the daily precipitation [2] and the turbulent and spreading effect basis, the wiping effect of the daily precipitation [2] and the turbulent and spreading effect of the gusts typically reduce the concentration of PM10 [3]. Case studies however show that of the gusts typically reduce the concentration of PM10 [3]. Case studies however show that this is not always the case: moderate or strong winds can create a resuspension mechanism this is not always the case: moderate or strong winds can create a resuspension mechanism which increases PM10 concentration [4], or can be associated with long-range transport of which increases PM10 concentration [4], or can be associated with long-range transport of pollutants [5, 6]. pollutants [5, 6].

Table 1 Table 1 Effect of meteorological variables to PM10 concentration [1] Effect of meteorological variables to PM10 concentration [1]

Spring Summer Autumn Winter Year Spring Summer Autumn Winter Year workday- daily workday- daily wind gust (–) (–) wind gust (–) wind gust (–) (–) wind gust (–) (–) wind gust (–) wind gust (–) (–) weekday precipitation weekday precipitation MLH (–) wind gust (–) MLH (–) MLH (–) wind gust (–) MLH (–) wind gust (–) MLH (–) MLH (–) wind gust (–) yesterday afternoon yesterday workday- yesterday afternoon yesterday workday- (–) (–) (–) temperature (–) (–) (–) (–) (–) temperature (–) (–) precipitation temperature precipitation weekday precipitation temperature precipitation weekday relative daily yesterday yesterday relative daily yesterday yesterday (–) (–) (–) (–) (–) (–) (–) (–) (–) (–) humidity precipitation precipitation precipitation humidity precipitation precipitation precipitation net net (–) net irradiance (+) front effect (+) (–) net irradiance (+) front effect (+) irradiance irradiance daily daily daily daily (–) (–) MLH (–) (–) (–) MLH (–) precipitation precipitation precipitation precipitation temperature (–) temperature (–)

The effects of meteorological conditions vary with the season. On the annual level the mixing The effects of meteorological conditions vary with the season. On the annual level the mixing layer height (MLH) presented after the effect of the fronts, but in spring, autumn and winter layer height (MLH) presented after the effect of the fronts, but in spring, autumn and winter

1 Department of Combustion Technology and Thermal Energy, University of Miskolc 1 Department of Combustion Technology and Thermal Energy, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 2 Department of Combustion Technology and Thermal Energy, University of Miskolc 2 Department of Combustion Technology and Thermal Energy, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 6 Csongor Báthory–Árpád Bence Palotás 6 Csongor Báthory–Árpád Bence Palotás as the second significant PM10 concentration influencing factor. According to Table 1. MLH as the second significant PM10 concentration influencing factor. According to Table 1. MLH is a measure for the vertical turbulent exchange within the boundary layer, which is one of is a measure for the vertical turbulent exchange within the boundary layer, which is one of the controlling factors for the dilution of pollutants emitted near the ground [7], [8]. It has a the controlling factors for the dilution of pollutants emitted near the ground [7], [8]. It has a decreasing effect (see Table 1), meaning that with increasing MLH, PM10 concentrations decreasing effect (see Table 1), meaning that with increasing MLH, PM10 concentrations decrease [9], [10]. decrease [9], [10]. The easiest approach of determining MLH is the vertical temperature distribution in a The easiest approach of determining MLH is the vertical temperature distribution in a way of measurement technique. Various studies looking for a link between the MLH and PM way of measurement technique. Various studies looking for a link between the MLH and PM concentrations with different variables (see Table 2). Largeron and Staquet reported that the concentrations with different variables (see Table 2). Largeron and Staquet reported that the daily-average temperature gradient values are well-correlated with the PM10 concentration, daily-average temperature gradient values are well-correlated with the PM10 concentration, in the Alps, with a correlation coefficient of 0.68 [11], as Table 2 shows. The correlation is in the Alps, with a correlation coefficient of 0.68 [11], as Table 2 shows. The correlation is stronger if it is restricted to the persistent inversion periods (when the temperature gradient stronger if it is restricted to the persistent inversion periods (when the temperature gradient is higher than the winter average over 72 hours), reaching 0.89 [11]. Whiteman and his group is higher than the winter average over 72 hours), reaching 0.89 [11]. Whiteman and his group analyzed data for the Salt Lake Valley (Utah, USA) for the past 40 years and reported a analyzed data for the Salt Lake Valley (Utah, USA) for the past 40 years and reported a correlation coefficient of 0.65 between PM2.5 and the valley heat deficit (calculated from correlation coefficient of 0.65 between PM2.5 and the valley heat deficit (calculated from temperature gradient), for all the 40 winters [12]. Vecchi and his colleagues analyzed air temperature gradient), for all the 40 winters [12]. Vecchi and his colleagues analyzed air pollution data in Milan, Italy and have determined a correlation coefficient of 0.62 between pollution data in Milan, Italy and have determined a correlation coefficient of 0.62 between PM10 and the concentration of Radon as a measure of boundary layer stability during PM10 and the concentration of Radon as a measure of boundary layer stability during nighttime [13]. Guzman-Torres and his colleagues evaluated a correlation coefficient of 0.56 nighttime [13]. Guzman-Torres and his colleagues evaluated a correlation coefficient of 0.56 between PM10 and surface thermal inversions in Mexico [10]. between PM10 and surface thermal inversions in Mexico [10].

Table 2 Table 2 Correlation between characteristic of MLH and PM concentrations [10–13] Correlation between characteristic of MLH and PM concentrations [10–13] Largeron and Largeron and Whiteman Guzman- Largeron and Largeron and Whiteman Guzman- Author Vecci et al. Author Vecci et al. Staquet Staquet et al. Torres et al. Staquet Staquet et al. Torres et al. Grenoble, Grenoble, Salt Lake Mexico, Grenoble, Grenoble, Salt Lake Mexico, Place Milan, Italy Place Milan, Italy France France Valley, USA Mexico City France France Valley, USA Mexico City Variable A PM10 conc. PM10 conc. PM2.5 conc. PM10 conc. PM10 conc. Variable A PM10 conc. PM10 conc. PM2.5 conc. PM10 conc. PM10 conc. daily-average persistent surface daily-average persistent surface valley heat concentration valley heat concentration Variable B temperature inversion thermal Variable B temperature inversion thermal deficit of Radon deficit of Radon gradient period inversion gradient period inversion Correlation Correlation 0.68 0.89 0.65 0.62 0.56 0.68 0.89 0.65 0.62 0.56 coefficient coefficient

The importance of the atmospheric conditions in the evolution of smog periods is The importance of the atmospheric conditions in the evolution of smog periods is undisputable, especially at valley type terrain. Miskolc is located both in the Szinva Valley undisputable, especially at valley type terrain. Miskolc is located both in the Szinva Valley and in the Sajó Valley next to the varying heating habits at the suburban areas. The and in the Sajó Valley next to the varying heating habits at the suburban areas. The atmospheric stability change can be one of the main reason of the high PM10 and PM2.5 atmospheric stability change can be one of the main reason of the high PM10 and PM2.5 concentrations during the heating season. The effect of this factor is still not known. To concentrations during the heating season. The effect of this factor is still not known. To explore the effect, the temperature distribution along the vertical axis at different times of the explore the effect, the temperature distribution along the vertical axis at different times of the day were measured. The criteria for the experimental design and implementation were the day were measured. The criteria for the experimental design and implementation were the following: following: • must be cost-effective, • must be cost-effective, • reliable measurements, and automatic data collection, • reliable measurements, and automatic data collection, • the results should be reproducible in identical situation. • the results should be reproducible in identical situation.

Balloon Based Atmospheric Stability Measurement Near the Surface 7 Balloon Based Atmospheric Stability Measurement Near the Surface 7

1. MATERIALS AND METHODS 1. MATERIALS AND METHODS 1.1. Measuring device 1.1. Measuring device Sensors, power source, microcontroller, and a small display, which are part of the data Sensors, power source, microcontroller, and a small display, which are part of the data recording system, have been fixed in a test box (see Figure 1). recording system, have been fixed in a test box (see Figure 1).

Table 3 Table 3 Major components of the measuring device Major components of the measuring device Device type Device Name Key Features Device type Device Name Key Features Microcontroller Raspberry Pi 3B Power Consumption: 1.5 W–6.7 W Microcontroller Raspberry Pi 3B Power Consumption: 1.5 W–6.7 W CPU: 1.2 GHz, Memory: 1 GB CPU: 1.2 GHz, Memory: 1 GB Temperature and humidity DHT22 Humidity: 0–100%, ±2% Temperature and humidity DHT22 Humidity: 0–100%, ±2% sensor Temperature: –40–80°C, ±0,5 °C sensor Temperature: –40–80°C, ±0,5 °C Temperature, pressure and HP206C Temperature: –40–85°C, ±0.5 °C Temperature, pressure and HP206C Temperature: –40–85°C, ±0.5 °C altitude sensor Pressure: 300–1,200 mbar, ±0,01 mbar altitude sensor Pressure: 300–1,200 mbar, ±0,01 mbar Altitude: 0–9,999 m, ±0,1 m Altitude: 0–9,999 m, ±0,1 m Power source Zendure A3 Power Bank 10,000 mAh Power source Zendure A3 Power Bank 10,000 mAh

The full weights of the test box, i.e. payload was 873 g. The data recorder program was The full weights of the test box, i.e. payload was 873 g. The data recorder program was written in Python 2.7 programming language. The properties of the elements of the measuring written in Python 2.7 programming language. The properties of the elements of the measuring device is listed in Table 3. device is listed in Table 3.

1.2. Lifting method 1.2. Lifting method The test box was lifted by a 2 m diameter latex balloon, filled with helium. A cradle was The test box was lifted by a 2 m diameter latex balloon, filled with helium. A cradle was made for it of 20 m rope. Volume of the balloon was 1.18 m3, lift capacity was 4 kg. made for it of 20 m rope. Volume of the balloon was 1.18 m3, lift capacity was 4 kg.

Figure 1 Figure 1 Test box and the compiled measuring system Test box and the compiled measuring system

In addition to the 2 m diameter balloon, four small (approx. 0.5 m diameter) helium balloons In addition to the 2 m diameter balloon, four small (approx. 0.5 m diameter) helium balloons were taken as emergency reserve. The balloon loaded with a rope and a carabiner connection were taken as emergency reserve. The balloon loaded with a rope and a carabiner connection had complete lifting capacity of 3.5 kg. The test box (measurement device) was fixed to the had complete lifting capacity of 3.5 kg. The test box (measurement device) was fixed to the

8 Csongor Báthory–Árpád Bence Palotás 8 Csongor Báthory–Árpád Bence Palotás base of the cradle, and the balloon + cradle was attached to a winch base (see Figure 1). The base of the cradle, and the balloon + cradle was attached to a winch base (see Figure 1). The winch was fed with a 200 m long rope weighing 1.5 kg. winch was fed with a 200 m long rope weighing 1.5 kg.

1.3. Measurement location and time 1.3. Measurement location and time The measurements were implemented from the top roof of the building C/1 at the University The measurements were implemented from the top roof of the building C/1 at the University of Miskolc, were the height is 125 metres above the sea level (MASL). Three measurements of Miskolc, were the height is 125 metres above the sea level (MASL). Three measurements were conducted in January 2018 as shown in Table 4. were conducted in January 2018 as shown in Table 4.

Table 4 Table 4 Measurements time and maximum elevated height in MASL Measurements time and maximum elevated height in MASL No. Date Start End Max height No. Date Start End Max height #1 04. 01. 2018. p.m 03:47 p.m 06:29 185 MASL #1 04. 01. 2018. p.m 03:47 p.m 06:29 185 MASL #2 05. 01. 2018. a.m 09:57 a.m 11:28 175 MASL #2 05. 01. 2018. a.m 09:57 a.m 11:28 175 MASL #3 09. 01. 2018. a.m 07:52 a.m 09:54 105 MASL #3 09. 01. 2018. a.m 07:52 a.m 09:54 105 MASL

During measurements the test box were elevated over 305 MASL. For the second and third During measurements the test box were elevated over 305 MASL. For the second and third measurements the data are incomplete due to a hardware error. Thus, the ascend part of the measurements the data are incomplete due to a hardware error. Thus, the ascend part of the measurement #2 is incomplete from 160 to 235 MASL and for measurement #3 the measurement #2 is incomplete from 160 to 235 MASL and for measurement #3 the descending period was recorded from 230 MASL height only. Because of the lack of the data descending period was recorded from 230 MASL height only. Because of the lack of the data and to eliminate the effect of the balloon on air mixing just the decreasing periods of the and to eliminate the effect of the balloon on air mixing just the decreasing periods of the measurement were analysed in the next chapters. measurement were analysed in the next chapters.

2. RESULTS AND DISCUSSION 2. RESULTS AND DISCUSSION The air temperature data were plotted in 5 m resolution for the way of the measurement’s The air temperature data were plotted in 5 m resolution for the way of the measurement’s descending balloon periods in Figure 2. The 125 MASL altitude represents the rooftop test descending balloon periods in Figure 2. The 125 MASL altitude represents the rooftop test site, from where the measurement was started, and the balloon has returned. The full, dashed site, from where the measurement was started, and the balloon has returned. The full, dashed and dotted grey lines show the average temperature gradient of the troposphere (Γavg = and dotted grey lines show the average temperature gradient of the troposphere (Γavg = –0.65 °C/100 m), started from the temperature of the first 5 metres section above the rooftop. –0.65 °C/100 m), started from the temperature of the first 5 metres section above the rooftop. Data for measurement #1 shows a monotone decrease in temperature with increasing Data for measurement #1 shows a monotone decrease in temperature with increasing altitude, a characteristic of an instable air layering. The total temperature gradient from 125 altitude, a characteristic of an instable air layering. The total temperature gradient from 125 to 305 MASL is –1.4 °C/100 m. This suggest a presence of a convective boundary layer, to 305 MASL is –1.4 °C/100 m. This suggest a presence of a convective boundary layer, which is usual before sunset. which is usual before sunset. The measurement #2 shows, that the temperature increases by 6 °C until the height of 215 The measurement #2 shows, that the temperature increases by 6 °C until the height of 215 MASL (+6.6 °C/100 m), decrease with 4 °C until 245 MASL (–13 °C/100 m) and after a MASL (+6.6 °C/100 m), decrease with 4 °C until 245 MASL (–13 °C/100 m) and after a short (25 m) isothermal section (~0 °C/100 m) the decreasing continues. Based on these, it short (25 m) isothermal section (~0 °C/100 m) the decreasing continues. Based on these, it can be stated that the balloon was passed through an instable and stable air layer during can be stated that the balloon was passed through an instable and stable air layer during descent. The total temperature gradient from 125 to 300 MASL is –0.9 °C/100 m. This descent. The total temperature gradient from 125 to 300 MASL is –0.9 °C/100 m. This suggest a mixed boundary layer: a stable boundary layer started to spread to instable suggest a mixed boundary layer: a stable boundary layer started to spread to instable boundary layer thanks to the warming effect of the sun. boundary layer thanks to the warming effect of the sun. During measurement #3 the sensors didn’t detect temperature change until 150 MASL During measurement #3 the sensors didn’t detect temperature change until 150 MASL and an isothermal section was recorded. Above 150 MASL the temperature increases with and an isothermal section was recorded. Above 150 MASL the temperature increases with altitude, indicating a stable air layering. The temperature gradient from the starting point (at altitude, indicating a stable air layering. The temperature gradient from the starting point (at 125 MASL, with 1.6 °C) to 225 MASL (3.5 °C) is +1.8 °C/100 m. This suggest a stable 125 MASL, with 1.6 °C) to 225 MASL (3.5 °C) is +1.8 °C/100 m. This suggest a stable boundary layer or even an inversion, which is usually seen before sunrise. boundary layer or even an inversion, which is usually seen before sunrise.

Balloon Based Atmospheric Stability Measurement Near the Surface 9 Balloon Based Atmospheric Stability Measurement Near the Surface 9

325 325 300 300 275 #1 275 #1

250 #2 250 #2 225 225 #3 #3

200 200 Altitude [MASL] Altitude [MASL] 175 #1 175 #1 Average Average 150 150 125 125 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Temperature [°C] Temperature [°C]

Figure 2 Figure 2 Air temperature data in 5 m resolution for the way of the descending balloons Air temperature data in 5 m resolution for the way of the descending balloons

CONCLUSION CONCLUSION Detailed vertical temperature and humidity distribution data were collected up to 305 MASL Detailed vertical temperature and humidity distribution data were collected up to 305 MASL above the sea level using a helium balloon technique. The balloon with the data recorder, like above the sea level using a helium balloon technique. The balloon with the data recorder, like an aerostat, was lifted and then pulled back down. an aerostat, was lifted and then pulled back down.

Table 5 Table 5 Recorded temperature gradient results Recorded temperature gradient results #1 – afternoon #2 – before noon #3 – morning #1 – afternoon #2 – before noon #3 – morning Height Gradient Height Gradient Height Gradient Height Gradient Height Gradient Height Gradient MASL °C/100 m MASL °C/100 m MASL °C/100 m MASL °C/100 m MASL °C/100 m MASL °C/100 m 125 125 215 +6.6 125 150 0 125 125 215 +6.6 125 150 0 215 245 –13 150 215 245 –13 150 –1.4 –1.4 245 270 0 +1.8 245 270 0 +1.8 305 270 300 –12.3 230 305 270 300 –12.3 230 Stability: Instable Stability: Mixed Stability: Stable Stability: Instable Stability: Mixed Stability: Stable

During the test measurements data were recorded referring to instable (04. 01. 2018. – During the test measurements data were recorded referring to instable (04. 01. 2018. – afternoon), mixed (05. 01. 2018. – before noon) and stable (09. 01. 2018. – morning) air afternoon), mixed (05. 01. 2018. – before noon) and stable (09. 01. 2018. – morning) air layering as shown in Table 5. The tests were suitable for detecting faults in the data collection layering as shown in Table 5. The tests were suitable for detecting faults in the data collection system. The data recorder device must be protected against the external conditions, like system. The data recorder device must be protected against the external conditions, like humidity, rain and UV, thermal radiation. humidity, rain and UV, thermal radiation. Our plans for future are reliability test of sensors, to extend sensors with low-budget, light Our plans for future are reliability test of sensors, to extend sensors with low-budget, light weight PM10 counter and to uniform the evaluation of data while carrying out further weight PM10 counter and to uniform the evaluation of data while carrying out further measurements to have more information about the connection between the atmospheric measurements to have more information about the connection between the atmospheric stability and PM10 concentrations. Once we understand this factor, we will have a chance to stability and PM10 concentrations. Once we understand this factor, we will have a chance to reduce the pollution during the effected periods. reduce the pollution during the effected periods.

10 Csongor Báthory–Árpád Bence Palotás 10 Csongor Báthory–Árpád Bence Palotás

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Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 11–16. Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 11–16.

AN APPROACH FOR ELIMINATING PHENYL ISOCYANATE FROM AN APPROACH FOR ELIMINATING PHENYL ISOCYANATE FROM SOLVENT USED IN ISOCYANATE PRODUCTION SOLVENT USED IN ISOCYANATE PRODUCTION

R. ZSANETT BOROS1, 2–ISTVÁN VARGA1–BARNABÁS BUZELLÁK1– R. ZSANETT BOROS1, 2–ISTVÁN VARGA1–BARNABÁS BUZELLÁK1– MÁRTA HARANGOZÓ1–MILÁN SZŐRI2–BÉLA VISKOLCZ2– MÁRTA HARANGOZÓ1–MILÁN SZŐRI2–BÉLA VISKOLCZ2– LÁSZLÓ FARKAS1 LÁSZLÓ FARKAS1

Methylene diphenyl diisocyanate (MDI) is one of the most important raw materials of polyurethane Methylene diphenyl diisocyanate (MDI) is one of the most important raw materials of polyurethane industry. During its synthesis unwanted by-products might be formed such as phenyl isocyanate (PI). industry. During its synthesis unwanted by-products might be formed such as phenyl isocyanate (PI). In this laboratory work, a separation method has been developed and tested for the the elimination of In this laboratory work, a separation method has been developed and tested for the the elimination of phenyl isocyanate from the ortho-dichlorobenzene solvent purified after MDI production. This method phenyl isocyanate from the ortho-dichlorobenzene solvent purified after MDI production. This method is based on conversion of phenyl isocyanate by MDI precursor methylene diphenyl diamine (MDA). is based on conversion of phenyl isocyanate by MDI precursor methylene diphenyl diamine (MDA). The formed carbamide compounds were separated from the solvent by either distillation or filtration. The formed carbamide compounds were separated from the solvent by either distillation or filtration. As a result, the initial phenyl isocyanate content of 9,000 ppm was successfully reduced to 30 ppm by As a result, the initial phenyl isocyanate content of 9,000 ppm was successfully reduced to 30 ppm by distillation and less efficiently to 231 ppm by filtration. distillation and less efficiently to 231 ppm by filtration. Keywords: methylene diphenyl diisocyanate, ortho-dichlorobenzene, phenyl isocyanate, Keywords: methylene diphenyl diisocyanate, ortho-dichlorobenzene, phenyl isocyanate, distillation, filtration distillation, filtration

INTRODUCTION INTRODUCTION Polyurethanes are the most versatile class of polymers, used in a surprising array of Polyurethanes are the most versatile class of polymers, used in a surprising array of commercial applications such as flexible- and rigid foams, solid elastomers, thermoplastic commercial applications such as flexible- and rigid foams, solid elastomers, thermoplastic polyurethanes, coatings, adhesives, sealants and elastomers used on floors and automotive polyurethanes, coatings, adhesives, sealants and elastomers used on floors and automotive interiors [1]. They are formed by the exothermic reaction between alcohols with two or more interiors [1]. They are formed by the exothermic reaction between alcohols with two or more reactive hydroxyl and isocyanates that have more than one reactive isocyanate group. reactive hydroxyl and isocyanates that have more than one reactive isocyanate group. Methylene diphenyl diisocyanate (MDI) is one of the most significant raw material of Methylene diphenyl diisocyanate (MDI) is one of the most significant raw material of polyurethane industry [2]. Production of MDI occurs via phosgenation of the appropriate polyurethane industry [2]. Production of MDI occurs via phosgenation of the appropriate diamine, namely methylene diphenyl diamine (MDA), in a solvent such as dichlorobenzene diamine, namely methylene diphenyl diamine (MDA), in a solvent such as dichlorobenzene which is removed from the product by distillation and is reused [3]. MDA is synthetized from which is removed from the product by distillation and is reused [3]. MDA is synthetized from the reaction between aniline and formalin. In the case of MDA synthesis some aniline could the reaction between aniline and formalin. In the case of MDA synthesis some aniline could be remained in the system which might be converted to phenyl isocyanate via phosgenation be remained in the system which might be converted to phenyl isocyanate via phosgenation (Figure 1). In MDI synthesis phenyl isocyanate might be a possible source of several by- (Figure 1). In MDI synthesis phenyl isocyanate might be a possible source of several by- product due to its reactivity [4]. The reactivity of aniline derivatives with phosgene have been product due to its reactivity [4]. The reactivity of aniline derivatives with phosgene have been studied by Ulrich et al. [5]. The aromatic diamines such as the MDA are much more reactive studied by Ulrich et al. [5]. The aromatic diamines such as the MDA are much more reactive amines than others. The reactivity of different aromatic amines with diisocyanates have been amines than others. The reactivity of different aromatic amines with diisocyanates have been measured [6]. Beside the phenyl isocyanate formation, numerous other side-reactions can measured [6]. Beside the phenyl isocyanate formation, numerous other side-reactions can occur via the MDI synthesis producing several unwanted by-products which might cause occur via the MDI synthesis producing several unwanted by-products which might cause problems. For instance, the isocyanates can easily react with amines forming carbamides due problems. For instance, the isocyanates can easily react with amines forming carbamides due to the high reactivity of isocyanate group. Callison et al. investigated the reactions between to the high reactivity of isocyanate group. Callison et al. investigated the reactions between carbamides and phosgene producing precursor to chlorine radicals, which could form carbamides and phosgene producing precursor to chlorine radicals, which could form

1 Wanhua-BorsodChem Ltd., Bolyai tér 1. 1 Wanhua-BorsodChem Ltd., Bolyai tér 1. H-3700 Kazincbarcika, Hungary H-3700 Kazincbarcika, Hungary [email protected] [email protected] 2 Institute of Chemistry, Faculty of Materials Science and Engineering, University of Miskolc 2 Institute of Chemistry, Faculty of Materials Science and Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary

12 Boros–Varga–Buzellák–Harangozó–Szőri–Viskolcz–Farkas 12 Boros–Varga–Buzellák–Harangozó–Szőri–Viskolcz–Farkas conjugated systems with the MDI backbone promoting discoloration [7]. The formation of conjugated systems with the MDI backbone promoting discoloration [7]. The formation of the by-products is substantial. The elimination of them encounters difficulties. the by-products is substantial. The elimination of them encounters difficulties.

aniline phosgene phenyl isocyanate hydrochloric-acid aniline phosgene phenyl isocyanate hydrochloric-acid

Figure 1 Figure 1 Phenyl-isocyanate formation via phosgenation of aniline Phenyl-isocyanate formation via phosgenation of aniline

This study focusses only on one possible by-product, phenyl isocyanate. The aim of this This study focusses only on one possible by-product, phenyl isocyanate. The aim of this research was to find out an appropriate method for phenyl isocyanate removal. Our research was to find out an appropriate method for phenyl isocyanate removal. Our exploration was based on the reaction of phenyl isocyanates with amines [8]. The phenyl exploration was based on the reaction of phenyl isocyanates with amines [8]. The phenyl isocyanate was converted to carbamide (Figure 2) and then eliminated from the solvent. isocyanate was converted to carbamide (Figure 2) and then eliminated from the solvent.

phenyl-isocyanate amine carbamide phenyl-isocyanate amine carbamide

Figure 2 Figure 2 Reaction of phenyl-isocyanate with amine Reaction of phenyl-isocyanate with amine

1. APPLIED METHODS AND REAGENTS 1. APPLIED METHODS AND REAGENTS Distillations were carried out using distillation apparatus set up in the laboratory. Three- Distillations were carried out using distillation apparatus set up in the laboratory. Three- necked, round-bottom 250 ml of glass flask was used as reaction vessel while a 100 ml of necked, round-bottom 250 ml of glass flask was used as reaction vessel while a 100 ml of one-necked round-bottom glass flask was used as volumetric flask for the distillate. The one-necked round-bottom glass flask was used as volumetric flask for the distillate. The flasks were connected by a distillation head and a Liebig-cooler. Heating was provided by flasks were connected by a distillation head and a Liebig-cooler. Heating was provided by melted metal bath heated by laboratory heater. The head- and bottom temperatures were melted metal bath heated by laboratory heater. The head- and bottom temperatures were controlled using thermometers. In the case of vacuum distillation, the reduced pressure was controlled using thermometers. In the case of vacuum distillation, the reduced pressure was set up by oil-ring pump produced by Leybold. About 100 ml of ODCB sample – arisen from set up by oil-ring pump produced by Leybold. About 100 ml of ODCB sample – arisen from the plant – was used mixed with phenyl isocyanate purchased by Sigma Aldrich. For the the plant – was used mixed with phenyl isocyanate purchased by Sigma Aldrich. For the filtration Whatman glass vacuum membrane filtration device was applied. The vacuum was filtration Whatman glass vacuum membrane filtration device was applied. The vacuum was adjusted using water suction pump. The grain size of the filter was 1.4 µm. adjusted using water suction pump. The grain size of the filter was 1.4 µm. The phenyl isocyanate content of the samples was analyzed by Agilent 6890N gas The phenyl isocyanate content of the samples was analyzed by Agilent 6890N gas chromatograph applying Zebron Inferno capillary column, using flame ionization detector chromatograph applying Zebron Inferno capillary column, using flame ionization detector (FID). Scanning electron microscopy (Joel T220 SEM) was used for mapping the structure (FID). Scanning electron microscopy (Joel T220 SEM) was used for mapping the structure of the formed carbamides. of the formed carbamides.

2. RESULTS AND DISCUSSION 2. RESULTS AND DISCUSSION Distillation was the first type of phenyl isocyanate removal method which was tried. The first Distillation was the first type of phenyl isocyanate removal method which was tried. The first idea was that the ortho-dichlorobenzene will be purified this by-product via simple idea was that the ortho-dichlorobenzene will be purified this by-product via simple An Approach for Eliminating Phenyl Isocyanate from Solvent… 13 An Approach for Eliminating Phenyl Isocyanate from Solvent… 13 distillation. The phenyl isocyanate content was measured before and after the distillation. The distillation. The phenyl isocyanate content was measured before and after the distillation. The results are summarized in Table 1. results are summarized in Table 1.

Table 1 Table 1 Phenyl isocyanate content before and after distillation Phenyl isocyanate content before and after distillation

PI content (ppm) PI content (ppm)

Before distillation After distillation Before distillation After distillation 1,800 2,979 1,800 2,979 1,800 2,870 1,800 2,870 1,800 2,596 1,800 2,596

The initial 1,800 ppm was not decreased but increased after the distillation without using any The initial 1,800 ppm was not decreased but increased after the distillation without using any reagent. Due to the similar boiling points of the ortho-dichlorobenzene (180 °C) and phenyl- reagent. Due to the similar boiling points of the ortho-dichlorobenzene (180 °C) and phenyl- isocyanate (166 °C) the separation of the compounds is difficult. The accumulation of the isocyanate (166 °C) the separation of the compounds is difficult. The accumulation of the isocyanate in the distillate can be explained by the lower boiling point, although the isocyanate in the distillate can be explained by the lower boiling point, although the difference in boiling points are not large enough to ensure complete separation. difference in boiling points are not large enough to ensure complete separation. MDA was tested as a reagent for converting phenyl isocyanate into a non-volatile MDA was tested as a reagent for converting phenyl isocyanate into a non-volatile compound before the distillation. Samples with different phenyl isocyanate content was compound before the distillation. Samples with different phenyl isocyanate content was reacted with MDA and then distilled. The starting phenyl isocyanate content was greatly reacted with MDA and then distilled. The starting phenyl isocyanate content was greatly reduced (<100 ppm). The results are summarized in Table 2. The amino group of the MDA reduced (<100 ppm). The results are summarized in Table 2. The amino group of the MDA was reacted with the isocyanate group of the phenyl isocyanate producing carbamide bond. was reacted with the isocyanate group of the phenyl isocyanate producing carbamide bond. The product carbamide was remained in the bottom of the flask while the ortho- The product carbamide was remained in the bottom of the flask while the ortho- dichlorobenzene was distilled. The phenyl isocyanate content was reduced efficiently. dichlorobenzene was distilled. The phenyl isocyanate content was reduced efficiently.

Table 2 Table 2 Phenyl isocyanate content before and after distillation using MDA as reactant Phenyl isocyanate content before and after distillation using MDA as reactant PI content (ppm) PI content (ppm) After distillation After distillation Before distillation Before distillation (using MDA as reagent before) (using MDA as reagent before) 1,800 89 1,800 89 700 20 700 20 500 10 500 10

The other main advantage of using MDA as reactant is that it is a familiar material in MDI The other main advantage of using MDA as reactant is that it is a familiar material in MDI synthesis. Any MDA residues in the solvent will never cause problems because it can be synthesis. Any MDA residues in the solvent will never cause problems because it can be easily eliminated from the system. In addition, MDA is one of the raw materials produced so easily eliminated from the system. In addition, MDA is one of the raw materials produced so that using it will be obvious. that using it will be obvious. Vacuum distillation – performed under reduced pressure – was also tested for solvent Vacuum distillation – performed under reduced pressure – was also tested for solvent purification after MDA was added to the solvent to react with the phenyl isocyanate. The purification after MDA was added to the solvent to react with the phenyl isocyanate. The efficiency of the simple and vacuum distillation is compared in Table 3. The initial phenyl efficiency of the simple and vacuum distillation is compared in Table 3. The initial phenyl isocyanate content was 9,000 ppm. The final phenyl isocyanate content was <40 ppm. The isocyanate content was 9,000 ppm. The final phenyl isocyanate content was <40 ppm. The vacuum distillation seemed to be more effective than the simple distillation, although the vacuum distillation seemed to be more effective than the simple distillation, although the difference in removal efficiency is minimal. This phenomenon could be explained by the fact difference in removal efficiency is minimal. This phenomenon could be explained by the fact that at higher temperature carbamides can be decomposed into amine and isocyanate. In the that at higher temperature carbamides can be decomposed into amine and isocyanate. In the

14 Boros–Varga–Buzellák–Harangozó–Szőri–Viskolcz–Farkas 14 Boros–Varga–Buzellák–Harangozó–Szőri–Viskolcz–Farkas case of the simple distillation higher temperature was used which was favorable for the case of the simple distillation higher temperature was used which was favorable for the decomposition of the product facilitating phenyl isocyanate formation, while in the case of decomposition of the product facilitating phenyl isocyanate formation, while in the case of vacuum distillation lower temperature resulted in less isocyanate release. vacuum distillation lower temperature resulted in less isocyanate release.

Table 3 Table 3 Phenyl isocyanate content before and after simple- and vacuum distillation Phenyl isocyanate content before and after simple- and vacuum distillation Type of PI content (ppm) Type of PI content (ppm) distillation Before distillation After distillation distillation Before distillation After distillation 29 29 simple 30 simple 30 29 29 9,000 9,000 18 18 vacuum 17 vacuum 17 19 19

Filtration of impurities is a frequently used method in the industry for purification. The Filtration of impurities is a frequently used method in the industry for purification. The applicability of it was tested for phenyl isocyanate elimination, too. Ortho-dichlorobenzene applicability of it was tested for phenyl isocyanate elimination, too. Ortho-dichlorobenzene samples with high phenyl isocyanate content were mixed with the appropriate amount of samples with high phenyl isocyanate content were mixed with the appropriate amount of MDA at room temperature and at higher temperatures as well. Beside the influence of the MDA at room temperature and at higher temperatures as well. Beside the influence of the temperature the effect of the stirring was also studied. temperature the effect of the stirring was also studied. The results are summarized in Table 4. The results are summarized in Table 4.

Table 4 Table 4 Phenyl isocyanate content before and after filtration using MDA as reagent Phenyl isocyanate content before and after filtration using MDA as reagent PI content (ppm) PI content (ppm) Temperature Temperature Sample Stirring Sample Stirring [°C] Before After [°C] Before After filtration filtration filtration filtration 1 25–30 No 58 1 25–30 No 58 2 25–30 Yes 57 2 25–30 Yes 57 3 70–90 Yes 9,000 110 3 70–90 Yes 9,000 110 4 110–120 Yes 128 4 110–120 Yes 128 5 120–130 Yes 231 5 120–130 Yes 231

The starting 9,000 ppm was significantly decreased <300 ppm. It was surprising that without The starting 9,000 ppm was significantly decreased <300 ppm. It was surprising that without stirring (for 1 hour) and at room temperature the phenyl isocyanate was reduced from 9,000 stirring (for 1 hour) and at room temperature the phenyl isocyanate was reduced from 9,000 ppm to 58 ppm. As the temperature was higher the phenyl isocyanate reduction efficiency of ppm to 58 ppm. As the temperature was higher the phenyl isocyanate reduction efficiency of the MDA was lower. The structures of the filtrated solid sediments were different. They were the MDA was lower. The structures of the filtrated solid sediments were different. They were examined by scanning electron microscopy. According to the microscopic views (Figure 3) examined by scanning electron microscopy. According to the microscopic views (Figure 3) the particle sizes of the formed carbamides are different. the particle sizes of the formed carbamides are different.

An Approach for Eliminating Phenyl Isocyanate from Solvent… 15 An Approach for Eliminating Phenyl Isocyanate from Solvent… 15

25–30 °C 70–90 °C 25–30 °C 70–90 °C

110–120 °C 120–130 °C 110–120 °C 120–130 °C Figure 3 Figure 3 Microscopic views of the filtrated carbamide compounds Microscopic views of the filtrated carbamide compounds

At lower temperature the reaction between the MDA and phenyl isocyanate resulted smaller At lower temperature the reaction between the MDA and phenyl isocyanate resulted smaller particle sized (<10µm) carbamide sediment, while at higher temperature bigger sized particle sized (<10µm) carbamide sediment, while at higher temperature bigger sized (>10µm) particles were formed. At higher temperature the decomposition of the carbamide (>10µm) particles were formed. At higher temperature the decomposition of the carbamide into phenyl isocyanate and amine could also occur such as in the case of the simple into phenyl isocyanate and amine could also occur such as in the case of the simple distillation. Therefore, more phenyl isocyanate was found in the solvent after the filtration at distillation. Therefore, more phenyl isocyanate was found in the solvent after the filtration at higher temperature. Considering the filtration method, the phenyl isocyanate content can be higher temperature. Considering the filtration method, the phenyl isocyanate content can be reduced significantly. The efficiency of the filtration is as adequate as the distillation’s. This reduced significantly. The efficiency of the filtration is as adequate as the distillation’s. This procedure can be feasible even in the technology. The filtrate was also examined and it was procedure can be feasible even in the technology. The filtrate was also examined and it was found that it has a little MDA content. If this method will be applied for phenyl isocyanate found that it has a little MDA content. If this method will be applied for phenyl isocyanate removing, it is necessary to take care about this MDA content of the ortho-dichlorobenzene removing, it is necessary to take care about this MDA content of the ortho-dichlorobenzene as well. as well.

CONCLUSION CONCLUSION This study was focused on removing of a possible by-product – phenyl isocyanate – of MDI This study was focused on removing of a possible by-product – phenyl isocyanate – of MDI synthesis from the solvent. Useful methods were found for phenyl isocyanate elimination: synthesis from the solvent. Useful methods were found for phenyl isocyanate elimination: distillation or filtration. distillation or filtration. Simple distillation of the ortho-dichlorobenzene was not effective because the phenyl Simple distillation of the ortho-dichlorobenzene was not effective because the phenyl isocyanate co-distilled with ortho-dichlorobenzene. It was essential to convert this isocyanate isocyanate co-distilled with ortho-dichlorobenzene. It was essential to convert this isocyanate into another compound which is easier to separate from the solvent. The idea was to find a into another compound which is easier to separate from the solvent. The idea was to find a reactant which can easily react with the phenyl isocyanate. Using MDA as a reagent appeared reactant which can easily react with the phenyl isocyanate. Using MDA as a reagent appeared to be obvious as it is the precursor of MDI synthesis. Applying it as a reagent will never cause to be obvious as it is the precursor of MDI synthesis. Applying it as a reagent will never cause any problems even if it remains in the system. The results confirmed that phenyl isocyanate any problems even if it remains in the system. The results confirmed that phenyl isocyanate can be reduced significantly from the ortho-dichlorobenzene using MDA. can be reduced significantly from the ortho-dichlorobenzene using MDA. Filtration seemed to be also a quite good method for a possible phenyl isocyanate Filtration seemed to be also a quite good method for a possible phenyl isocyanate reduction. MDA was used as a reagent in this way, too. The efficiency of this method is lower reduction. MDA was used as a reagent in this way, too. The efficiency of this method is lower than the distillation, however it is effective enough. than the distillation, however it is effective enough.

16 Boros–Varga–Buzellák–Harangozó–Szőri–Viskolcz–Farkas 16 Boros–Varga–Buzellák–Harangozó–Szőri–Viskolcz–Farkas

Considering the experimental results, it could be said that both distillation and filtration Considering the experimental results, it could be said that both distillation and filtration could be suggested for a possible technological application after MDA was used as a reagent could be suggested for a possible technological application after MDA was used as a reagent for converting phenyl isocyanate to carbamide. Some disadvantages need to be noted as well for converting phenyl isocyanate to carbamide. Some disadvantages need to be noted as well such as during the filtration the filter packages must be cleaned frequently causing some such as during the filtration the filter packages must be cleaned frequently causing some difficulties and in the case of distillation high energy is requires for evaporation of the difficulties and in the case of distillation high energy is requires for evaporation of the solvent. solvent.

ACKNOWLEDGMENTS ACKNOWLEDGMENTS This research was supported by the European Regional Development Fund in the framework of the This research was supported by the European Regional Development Fund in the framework of the GINOP-2.3.4-15-2016-00004 project. The authors would like to thank Tamás Purzsa,Vice President of GINOP-2.3.4-15-2016-00004 project. The authors would like to thank Tamás Purzsa,Vice President of BorsodChem, for his helpful contribution. BorsodChem, for his helpful contribution.

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Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 17–25. Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 17–25.

THE EXAMINATION OF THE GRAIN REFINING EFFECTS OF THE EXAMINATION OF THE GRAIN REFINING EFFECTS OF TITANIUM IN HYPOEUTECTIC AL-SI FOUNDRY ALLOYS TITANIUM IN HYPOEUTECTIC AL-SI FOUNDRY ALLOYS

MARIANNA BUBENKÓ1–MONIKA TOKÁR2–GYÖRGY FEGYVERNEKI3 MARIANNA BUBENKÓ1–MONIKA TOKÁR2–GYÖRGY FEGYVERNEKI3

Grain refining is an important technological step for the nucleus growth of the melt, in order to Grain refining is an important technological step for the nucleus growth of the melt, in order to increase the number of nuclei, to improve mechanical properties (tensile strength, yield strength, increase the number of nuclei, to improve mechanical properties (tensile strength, yield strength, hardness, elongation), feeding conditions and to decrease the tendency of hot tearing and the degree hardness, elongation), feeding conditions and to decrease the tendency of hot tearing and the degree of sintering. [1], [2] The aim of the experiments was the determination of the grain refining effects of of sintering. [1], [2] The aim of the experiments was the determination of the grain refining effects of titanium (Ti) addition in the form of AlTi5B1 master alloy to the examined alloys (AlSi7MgCu0.5 – titanium (Ti) addition in the form of AlTi5B1 master alloy to the examined alloys (AlSi7MgCu0.5 – AC 42 000, AlSi9Cu3Fe0.5 – 46 500; AlSi9Cu1 – AC 46 400). AC 42 000, AlSi9Cu3Fe0.5 – 46 500; AlSi9Cu1 – AC 46 400). Keywords: Al-Si alloys, grain refinement, titanium, thermal analysis, nucleus formation Keywords: Al-Si alloys, grain refinement, titanium, thermal analysis, nucleus formation

INTRODUCTION INTRODUCTION Providing the uniaxial dendritic structure for cast alloys in fine – grained cast state is Providing the uniaxial dendritic structure for cast alloys in fine – grained cast state is necessary. Thus, the regulation of the nucleus formation of the melt via grain refinement is necessary. Thus, the regulation of the nucleus formation of the melt via grain refinement is an essential step to achieve the required quality and mechanical properties [1], [2], [3]. an essential step to achieve the required quality and mechanical properties [1], [2], [3]. Grain refining is one of the strengthening mechanisms which provide higher mechanical Grain refining is one of the strengthening mechanisms which provide higher mechanical properties to an alloy. Grain refinement would increase the number of grains and their properties to an alloy. Grain refinement would increase the number of grains and their boundaries, therefore, increase the yield strength of the material. [4] The addition of grain boundaries, therefore, increase the yield strength of the material. [4] The addition of grain refiner increases the number of nucleation sites, thus, promoting equiaxed grain growth refiner increases the number of nucleation sites, thus, promoting equiaxed grain growth rather than columnar. Large grains of α-Al in the microstructure are responsible for a rather than columnar. Large grains of α-Al in the microstructure are responsible for a number of defects, like scattered porosity, microcracks, deterioration of mechanical number of defects, like scattered porosity, microcracks, deterioration of mechanical properties, etc. For many years, grain refinement of α-Al has been obtained by the properties, etc. For many years, grain refinement of α-Al has been obtained by the controlled addition of intermetallic compounds of the type: Al3Ti, TiB2, TiC, to the liquid controlled addition of intermetallic compounds of the type: Al3Ti, TiB2, TiC, to the liquid metal. For this purpose, master alloys, like AlTi5B1, AlTi3B1 or AlTi3C015 can be used, metal. For this purpose, master alloys, like AlTi5B1, AlTi3B1 or AlTi3C015 can be used, or the newly developed alloys of AlTi1.7B1.4, AlTi1.2 B0.5 or AlSr5Ti0.8B0.7. [5] There or the newly developed alloys of AlTi1.7B1.4, AlTi1.2 B0.5 or AlSr5Ti0.8B0.7. [5] There are several theories describing the process of grain refinement which are available in are several theories describing the process of grain refinement which are available in numerous publications. The most frequently adopted one claim that in the case of Al–Ti–B numerous publications. The most frequently adopted one claim that in the case of Al–Ti–B refiner, the main compound responsible for the grain refining effect is TiB2. [5] According refiner, the main compound responsible for the grain refining effect is TiB2. [5] According to the duplex nucleation theory (Mohanty and Gruzleski [6]), in case of the use of Al–Ti–B to the duplex nucleation theory (Mohanty and Gruzleski [6]), in case of the use of Al–Ti–B master alloys, a Ti rich melt layer is formed surrounding the TiB2 particles in the melt. If master alloys, a Ti rich melt layer is formed surrounding the TiB2 particles in the melt. If the local Ti content is higher than 0.15 wt%, a solid TiAl3 layer is formed on the surface of the local Ti content is higher than 0.15 wt%, a solid TiAl3 layer is formed on the surface of TiB2 particles (Figure 1). Then, the aluminium particles are formed through peritectic TiB2 particles (Figure 1). Then, the aluminium particles are formed through peritectic reactions on the TiAl3 layer. reactions on the TiAl3 layer.

1 Institute of Foundry Engineering, University of Miskolc 1 Institute of Foundry Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 2 Institute of Foundry Engineering, University of Miskolc 2 Institute of Foundry Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 3 Institute of Foundry Engineering, University of Miskolc 3 Institute of Foundry Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 18 Marianna Bubenkó–Monika Tokár–György Fegyverneki 18 Marianna Bubenkó–Monika Tokár–György Fegyverneki

Figure 1 Figure 1 Duplex nucleation theory. (a) Excess Ti (Ti > 2.21) in solution, (b) Ti segregated to the Duplex nucleation theory. (a) Excess Ti (Ti > 2.21) in solution, (b) Ti segregated to the TiB2 – melt interface, (c) formation of TiA13 layer on TiB2, (d) Nucleation of α-Al by TiB2 – melt interface, (c) formation of TiA13 layer on TiB2, (d) Nucleation of α-Al by peritectic reaction [7] peritectic reaction [7]

1. EXPERIMENTAL CONDITIONS AND RESULTS 1. EXPERIMENTAL CONDITIONS AND RESULTS The three examined foundry alloy melts (AlSi7MgCu0.5 – 1st alloy; AlSi9Cu1 – 2nd alloy; The three examined foundry alloy melts (AlSi7MgCu0.5 – 1st alloy; AlSi9Cu1 – 2nd alloy; AlSi9Cu3Fe0.5 – 3rd alloy) were alloyed with AlTi5B1 master alloy during the rotary AlSi9Cu3Fe0.5 – 3rd alloy) were alloyed with AlTi5B1 master alloy during the rotary degassing process [with nitrogen (N2) inert gas]. The initial Ti contents were between 900– degassing process [with nitrogen (N2) inert gas]. The initial Ti contents were between 900– 1,200 ppm. Based on the recommendation of the alloy manufacturer (Trimet GmbH), 750 g 1,200 ppm. Based on the recommendation of the alloy manufacturer (Trimet GmbH), 750 g AlTi5B1 master alloy was added to 1,000 kg melt (37.5 ppm Ti content in function of total AlTi5B1 master alloy was added to 1,000 kg melt (37.5 ppm Ti content in function of total amount). The effect of additional Ti content (in the form of AlTi5B1 master alloy) on the amount). The effect of additional Ti content (in the form of AlTi5B1 master alloy) on the nucleus formation properties of the aluminium melt was examined. nucleus formation properties of the aluminium melt was examined. Optical Emission Analyzer technique was used to determine the chemical compositions Optical Emission Analyzer technique was used to determine the chemical compositions of the alloys and the amount of the beneficial AlTi5B1 master alloy. Thermal analysis was of the alloys and the amount of the beneficial AlTi5B1 master alloy. Thermal analysis was carried out to examine the degree of grain refinement. The equipment used for the thermal carried out to examine the degree of grain refinement. The equipment used for the thermal analysis and the dimensions of the casted test bar can be seen in Figure 2. The test bar was analysis and the dimensions of the casted test bar can be seen in Figure 2. The test bar was casted in a steel crucible preheated to 200 °C. casted in a steel crucible preheated to 200 °C.

Figure 2 Figure 2 Thermal analysis equipment and casted test bar Thermal analysis equipment and casted test bar The Examination of the Grain Refining Effects of Titanium… 19 The Examination of the Grain Refining Effects of Titanium… 19

For the examination of the mechanical properties, so-called Diez-test bars were casted after For the examination of the mechanical properties, so-called Diez-test bars were casted after melt treatment in a Diez-die, which die was prepared according to a German standard. [8] melt treatment in a Diez-die, which die was prepared according to a German standard. [8] Tensile test specimens were made from the Diez-test bars according to industrial standard. Tensile test specimens were made from the Diez-test bars according to industrial standard. The test bars were cylindrical, 5 mm in diameter and 50 mm long. The test bars were cylindrical, 5 mm in diameter and 50 mm long. Diez-test bars are technological test bars which were used to examine the grain refining Diez-test bars are technological test bars which were used to examine the grain refining effect of AlTi5B1 master alloy on the alloys. In this case, certain external influences that effect of AlTi5B1 master alloy on the alloys. In this case, certain external influences that emerge during casting and the affect the mechanical properties can be eliminated. emerge during casting and the affect the mechanical properties can be eliminated. To examine the mechanical properties, the test bars were heat treated (1st alloy-T5, 2nd To examine the mechanical properties, the test bars were heat treated (1st alloy-T5, 2nd alloy-T6, 3rd alloy-was not heat treated) under operating conditions. The Diez-die and test alloy-T6, 3rd alloy-was not heat treated) under operating conditions. The Diez-die and test bar with their locations where the tensile specimens were taken can be seen in Figure 3. bar with their locations where the tensile specimens were taken can be seen in Figure 3.

Figure 3 Figure 3 The Diez-die and test bar with the locations of the tensile specimens The Diez-die and test bar with the locations of the tensile specimens

1.1. Composition 1.1. Composition The titanium concentration before and after the addition of AlTi5B1 master alloy, The titanium concentration before and after the addition of AlTi5B1 master alloy, determined by compositional analysis, can be seen in Table 1. determined by compositional analysis, can be seen in Table 1.

Table 1 Table 1 The titanium concentrations based on the compositional analysis The titanium concentrations based on the compositional analysis Difference of Difference of Titanium Titanium Casting Titanium Titanium Casting Techno- Titanium Techno- Titanium Alloys concentra- concentra- temperature Alloys concentra- concentra- temperature logical step concentration logical step concentration tion (wt%) tion (ppm) (°C) tion (wt%) tion (ppm) (°C) (ppm) (ppm) Before Ti Before Ti (1st) addition 0.11935 1,193.5 (1st) addition 0.11935 1,193.5 AlSi7MgCu0.5 (series) 35.9 728 AlSi7MgCu0.5 (series) 35.9 728 After Ti After Ti 0.12294 1,229.4 0.12294 1,229.4 addition addition Before Ti Before Ti addition 0.10766 1,076.6 addition 0.10766 1,076.6 (2nd) (2nd) (series) 11.9 737 (series) 11.9 737 AlSi9Cu1 AlSi9Cu1 After Ti After Ti 0.10885 1,088.5 0.10885 1,088.5 addition addition Before Ti Before Ti addition 0.08911 891.1 addition 0.08911 891.1 (3rd) (3rd) (series) 37.5 716 (series) 37.5 716 AlSi9Cu3Fe0.5 AlSi9Cu3Fe0.5 After Ti After Ti 0.09286 928.6 0.09286 928.6 addition addition 20 Marianna Bubenkó–Monika Tokár–György Fegyverneki 20 Marianna Bubenkó–Monika Tokár–György Fegyverneki

In case of the 2nd alloy, only 31.73% of the 37.5 ppm additional titanium was dissolved in In case of the 2nd alloy, only 31.73% of the 37.5 ppm additional titanium was dissolved in 1,000 kg melt. The cause of this might be the presence of other alloying elements which 1,000 kg melt. The cause of this might be the presence of other alloying elements which formed intermetallic phases with titanium. Thus, the titanium content of the additional formed intermetallic phases with titanium. Thus, the titanium content of the additional AlTi5B1 master alloy could not have any beneficial effects on grain refinement [9]. AlTi5B1 master alloy could not have any beneficial effects on grain refinement [9].

1.2. Thermal analysis 1.2. Thermal analysis By thermal analysis, the efficiency of grain refinement can be determined by the evaluation By thermal analysis, the efficiency of grain refinement can be determined by the evaluation of the cooling curves of the solidifying melt. The thermal analyser is equipped with a of the cooling curves of the solidifying melt. The thermal analyser is equipped with a thermocouple which is connected to a signal processing data logger. The data logger thermocouple which is connected to a signal processing data logger. The data logger produces the temperature – time cooling curves from which the various processes in the produces the temperature – time cooling curves from which the various processes in the solidifying metal can be determined. solidifying metal can be determined. The cooling curves of test bars in case of 1st alloy (AlSi7MgCu0.5) are shown in Figure The cooling curves of test bars in case of 1st alloy (AlSi7MgCu0.5) are shown in Figure 4. As it can be seen on the curve with dotted line, the starting temperature of the nucleus 4. As it can be seen on the curve with dotted line, the starting temperature of the nucleus formation is 3.03 °C higher after AlTi5B1 addition. formation is 3.03 °C higher after AlTi5B1 addition.

Figure 4 Figure 4 The liquidus temperature ranges of the cooling curves of the 1st (AlSiMgCu0.5) alloy The liquidus temperature ranges of the cooling curves of the 1st (AlSiMgCu0.5) alloy

The differences of the starting temperature of nucleation before and after AlTi5B1 addition The differences of the starting temperature of nucleation before and after AlTi5B1 addition are shown in Table 2. are shown in Table 2.

Table 2 Table 2 The differences of the starting temperature of nucleation before and after AlTi5B1 addition The differences of the starting temperature of nucleation before and after AlTi5B1 addition Titanium concentration after Titanium concentration after Alloys ∆TLmin (°C) Alloys ∆TLmin (°C) AlTi5B1 addition (ppm) AlTi5B1 addition (ppm) (1st) AlSi7MgCu0.5 1,229.4 3.03 (1st) AlSi7MgCu0.5 1,229.4 3.03 (2nd) AlSi9Cu1 1,088.5 4.87 (2nd) AlSi9Cu1 1,088.5 4.87 (3rd) AlSi9Cu3Fe0.5 928.6 0.17 (3rd) AlSi9Cu3Fe0.5 928.6 0.17

The addition of extra 750 g AlTi5B1 master alloy had a positive effect (mainly in case of 1st The addition of extra 750 g AlTi5B1 master alloy had a positive effect (mainly in case of 1st nd nd and 2 alloys) on the nucleus formation and increased the ∆TLmin, cause the starting and 2 alloys) on the nucleus formation and increased the ∆TLmin, cause the starting temperatures of the nucleation were increased. temperatures of the nucleation were increased. The Examination of the Grain Refining Effects of Titanium… 21 The Examination of the Grain Refining Effects of Titanium… 21

1.3. Grain numbers – thermal analysis test bars 1.3. Grain numbers – thermal analysis test bars The thermal analysis test bars were cut horizontally, polished and Barker etched before The thermal analysis test bars were cut horizontally, polished and Barker etched before further microstructure analysis. On the etched test specimen 15 microstructural images further microstructure analysis. On the etched test specimen 15 microstructural images (226.8 mm2 examined area/specimen) were taken from each one test bar, using an optical (226.8 mm2 examined area/specimen) were taken from each one test bar, using an optical microscope with 25× magnification. The number of grains was determined on each image. microscope with 25× magnification. The number of grains was determined on each image. The number of (α)Al grains on the surfaces of the test bars can be counted due to the The number of (α)Al grains on the surfaces of the test bars can be counted due to the various colours caused by polarised light. The Barker colour etched micrographs in case of various colours caused by polarised light. The Barker colour etched micrographs in case of 3rd alloy can be seen in Figure 5. 3rd alloy can be seen in Figure 5.

Figure 5 Figure 5 The Barker colour etched micrographs: (a) 3rd alloy before grain refinement, (b) after the The Barker colour etched micrographs: (a) 3rd alloy before grain refinement, (b) after the addition of AlTi5B1 grain refining master alloy addition of AlTi5B1 grain refining master alloy

The average grain number in case of the thermal analysis test bars are illustrated in Figure The average grain number in case of the thermal analysis test bars are illustrated in Figure 6. The examination of the thermal analysis test bars revealed that the increased titanium 6. The examination of the thermal analysis test bars revealed that the increased titanium concentration led to increased grain number. The grain number of the test bars with higher concentration led to increased grain number. The grain number of the test bars with higher ΔTLmin (3.03 °C and 4.87 °C) temperature after AlTi5B1 addition was 2.8–2.9× higher. ΔTLmin (3.03 °C and 4.87 °C) temperature after AlTi5B1 addition was 2.8–2.9× higher. Based on the cooling curves and the microscopic particle analysis it can be stated that grain Based on the cooling curves and the microscopic particle analysis it can be stated that grain refinement occured in all three alloys. The objective of further research is to determine if refinement occured in all three alloys. The objective of further research is to determine if the solved titan concentration of the second alloy was enough to achieve such effect. the solved titan concentration of the second alloy was enough to achieve such effect.

Figure 6 Figure 6 Average grain number in case of the thermal analysis test bars Average grain number in case of the thermal analysis test bars 22 Marianna Bubenkó–Monika Tokár–György Fegyverneki 22 Marianna Bubenkó–Monika Tokár–György Fegyverneki

1.4. The examination of Diez-test bars 1.4. The examination of Diez-test bars Mechanical test and microstructure analysis were carried out on test specimens prepared Mechanical test and microstructure analysis were carried out on test specimens prepared from standard Diez-test bars. We determined the effect of extra 750 g AlTi5B1 master alloy from standard Diez-test bars. We determined the effect of extra 750 g AlTi5B1 master alloy addition on the mechanical properties and on the efficiency of the grain refinement. addition on the mechanical properties and on the efficiency of the grain refinement. Figure 7 shows the average grain numbers of the tensile test specimens made out of Figure 7 shows the average grain numbers of the tensile test specimens made out of Diez-test bars. The AlTi5B1 addition resulted higher grain number. Diez-test bars. The AlTi5B1 addition resulted higher grain number.

Figure 7 Figure 7 The average grain numbers of the tensile test specimens made out of Diez-test bars The average grain numbers of the tensile test specimens made out of Diez-test bars

During mechanical tests, the tensile strength, the yield strength and the elongation were During mechanical tests, the tensile strength, the yield strength and the elongation were determined. Three Diez-test bars were casted from each alloy, and two tensile test determined. Three Diez-test bars were casted from each alloy, and two tensile test specimens were prepared from each Diez-test bars. The average values of six tensile specimens were prepared from each Diez-test bars. The average values of six tensile specimens for each alloy can be observed in Figures 8–10. The results were compared to specimens for each alloy can be observed in Figures 8–10. The results were compared to the required operational strength values. the required operational strength values.

Figure 8 Figure 8 The average tensile strength of the specimens from the Diez-test bars The average tensile strength of the specimens from the Diez-test bars The Examination of the Grain Refining Effects of Titanium… 23 The Examination of the Grain Refining Effects of Titanium… 23

It can be observed that after the addition of the extra master alloy, the tensile strength It can be observed that after the addition of the extra master alloy, the tensile strength (Figure 8) and yield point values (Figure 9) increased by a few percentage. In case of the (Figure 8) and yield point values (Figure 9) increased by a few percentage. In case of the 2nd alloy, the grain number of which was almost two times higher (1.88×), the average 2nd alloy, the grain number of which was almost two times higher (1.88×), the average tensile strength increased with almost 4.79%. The average elongation after the AlTi5B1 tensile strength increased with almost 4.79%. The average elongation after the AlTi5B1 master alloy addition increased with 7% in case of the 2nd alloy. In case of 1st and 3rd alloys master alloy addition increased with 7% in case of the 2nd alloy. In case of 1st and 3rd alloys the elongation values were decreased. the elongation values were decreased. The average standard deviation of the elongation values was rather high. In order to The average standard deviation of the elongation values was rather high. In order to determine the reason for the low strength values, the fracture surfaces of the tensile determine the reason for the low strength values, the fracture surfaces of the tensile specimens were examined. specimens were examined. In case of all three alloys, the fracture surfaces of the specimens prepared from the Diez- In case of all three alloys, the fracture surfaces of the specimens prepared from the Diez- test bars with mechanical properties below the limit values were examined with a stereo test bars with mechanical properties below the limit values were examined with a stereo microscope. The following observations can be made based on the micrographs. microscope. The following observations can be made based on the micrographs.

Figure 9 Figure 9 The average yield strength of the specimens from the Diez-test bars The average yield strength of the specimens from the Diez-test bars

Figure 10 Figure 10 The average elongation of the specimens from the Diez-test bars The average elongation of the specimens from the Diez-test bars 24 Marianna Bubenkó–Monika Tokár–György Fegyverneki 24 Marianna Bubenkó–Monika Tokár–György Fegyverneki

The stereo microscopic image of the test bar with the Al2O3 oxide inclusion can be seen in The stereo microscopic image of the test bar with the Al2O3 oxide inclusion can be seen in Figure 11. Figure 11.

Figure 11 Figure 11 The surface of test bar prepared from the Diez-test bar of the melt of the 1st alloy before Ti The surface of test bar prepared from the Diez-test bar of the melt of the 1st alloy before Ti addition, with large Al2O3 oxide inclusion addition, with large Al2O3 oxide inclusion

CONCLUSIONS CONCLUSIONS Based on the evaluation of the experimental test bars and the prepared diagrams, it can be Based on the evaluation of the experimental test bars and the prepared diagrams, it can be concluded that the extra 750 g AlTi5B1 master alloy addition to the three Al-Si alloy melts concluded that the extra 750 g AlTi5B1 master alloy addition to the three Al-Si alloy melts (AlSi7MgCu0.5; AlSi9Cu; AlSi9CuFe0.5) had a positive effect on the nucleus formation (AlSi7MgCu0.5; AlSi9Cu; AlSi9CuFe0.5) had a positive effect on the nucleus formation and increased the starting temperature of the crystallization. and increased the starting temperature of the crystallization. The additional titanium concentration resulted in increased average grain number. The The additional titanium concentration resulted in increased average grain number. The grain number was 2.8–2.9 times higher of the thermal test bars after AlTi5B1 addition, in grain number was 2.8–2.9 times higher of the thermal test bars after AlTi5B1 addition, in case of the alloys with higher ΔTLmin (3.03 °C and 4.87 °C) temperatures. case of the alloys with higher ΔTLmin (3.03 °C and 4.87 °C) temperatures. The effect of the additional 750 g AlTi5B1 master alloy on the mechanical properties The effect of the additional 750 g AlTi5B1 master alloy on the mechanical properties could be observed on the Diez-test bars. A correlation can be observed between the average could be observed on the Diez-test bars. A correlation can be observed between the average tensile strength, yield strength and grain number of the series and the test bars with higher tensile strength, yield strength and grain number of the series and the test bars with higher titanium concentration: the increased grain number resulted in higher tensile strength and titanium concentration: the increased grain number resulted in higher tensile strength and yield strength value. However, the elongation values were greatly affected by the inclusion yield strength value. However, the elongation values were greatly affected by the inclusion content of the melt. The parameters influencing melt quality (e. g. the efficiency of the melt content of the melt. The parameters influencing melt quality (e. g. the efficiency of the melt cleaning) should be reviewed, as the decreased mechanical properties cannot be attributed cleaning) should be reviewed, as the decreased mechanical properties cannot be attributed to the addition of AlTi5B1 master alloy, but the inclusion content of the melt. to the addition of AlTi5B1 master alloy, but the inclusion content of the melt.

ACKNOWLEDGEMENT ACKNOWLEDGEMENT The authors are grateful to Árpád Kovács for carrying out the tests with scanning electron microscope. The authors are grateful to Árpád Kovács for carrying out the tests with scanning electron microscope. The authors are grateful to Mária Ambrus for her advice. The authors are grateful to Mária Ambrus for her advice.

The described article/presentation/study was carried out as part of the EFOP-3.6.1-16-2016-00011 The described article/presentation/study was carried out as part of the EFOP-3.6.1-16-2016-00011 Younger and Renewing University – Innovative Knowledge City – institutional development of the Younger and Renewing University – Innovative Knowledge City – institutional development of the University of Miskolc aiming at intelligent specialisation project implemented in the framework of the University of Miskolc aiming at intelligent specialisation project implemented in the framework of the Szechenyi 2020 program. The realization of this project is supported by the European Union, co- Szechenyi 2020 program. The realization of this project is supported by the European Union, co- financed by the European Social Fund. financed by the European Social Fund.

The Examination of the Grain Refining Effects of Titanium… 25 The Examination of the Grain Refining Effects of Titanium… 25

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THE EXAMINATION OF THE MECHANICAL PROPERTIES OF WATER THE EXAMINATION OF THE MECHANICAL PROPERTIES OF WATER GLASS CORE SANDS GLASS CORE SANDS

VIKTÓRIA DARGAI1–LÁSZLÓ VARGA2 VIKTÓRIA DARGAI1–LÁSZLÓ VARGA2

One of the main challenges for environmentally responsible foundries that keep the health of One of the main challenges for environmentally responsible foundries that keep the health of the employees in mind is the decrease of emission values. The use of inorganic binders, i.e. the employees in mind is the decrease of emission values. The use of inorganic binders, i.e. water glass systems, in core production plays a significant role in the prevention of the release water glass systems, in core production plays a significant role in the prevention of the release of toxic materials during production. The various developments in binder systems during the of toxic materials during production. The various developments in binder systems during the past years showed that the use of conventional organic binders can be an economically valid past years showed that the use of conventional organic binders can be an economically valid alternative to replace water glass binders. These developments almost solely focused on the alternative to replace water glass binders. These developments almost solely focused on the fully modified water glass systems. Various researches and developments have been carried fully modified water glass systems. Various researches and developments have been carried out for the successful use of inorganic binders. out for the successful use of inorganic binders. Keywords: Inorganic binder, water glass solutions, regeneration, new sand Keywords: Inorganic binder, water glass solutions, regeneration, new sand

1. ALKALI-SILICATE SOLUTIONS 1. ALKALI-SILICATE SOLUTIONS Water glass is not considered a standard compound but a collective term for various alkali- Water glass is not considered a standard compound but a collective term for various alkali- silicate melts and compounds that forms a glassy solid. The alkali salts of silica are also silicate melts and compounds that forms a glassy solid. The alkali salts of silica are also considered water glass. Water glass can be characterised with its module (SiO2: Na2O ratio), considered water glass. Water glass can be characterised with its module (SiO2: Na2O ratio), density and viscosity [1]. density and viscosity [1]. The module means the silica and alkali-oxide ratio of water glass. The general water glass The module means the silica and alkali-oxide ratio of water glass. The general water glass composition can be described as: xSiO2 • yM2O • zH2O, where M represents the alkali metals, composition can be described as: xSiO2 • yM2O • zH2O, where M represents the alkali metals, such as sodium, potassium or lithium. The module of the most common sodium water glass such as sodium, potassium or lithium. The module of the most common sodium water glass used in the foundry industry, i.e. the SiO2: Na2O ratio, is 2.0–3.3. Certain technological used in the foundry industry, i.e. the SiO2: Na2O ratio, is 2.0–3.3. Certain technological properties of the moulding mixture and the binder system are influenced by the module [1], [2]. properties of the moulding mixture and the binder system are influenced by the module [1], [2].

2. CORE PRODUCTION TECHNOLOGIES 2. CORE PRODUCTION TECHNOLOGIES Water glass binders have been successfully used during various manufacturing processes in Water glass binders have been successfully used during various manufacturing processes in the past. Water glass – CO2 and water glass – ester methods are considered classic inorganic the past. Water glass – CO2 and water glass – ester methods are considered classic inorganic core-production technologies, during which various chemical processes are responsible for core-production technologies, during which various chemical processes are responsible for the setting [1]. Cores produced with these methods are not suitable for the modern market, the setting [1]. Cores produced with these methods are not suitable for the modern market, because of their low strength, yield properties, knock-out ability and the limited reusability because of their low strength, yield properties, knock-out ability and the limited reusability of the regenerated materials. New inorganic binder systems have been developed during the of the regenerated materials. New inorganic binder systems have been developed during the last 15 years, due to the new manufacturing processes and the developments in silicate last 15 years, due to the new manufacturing processes and the developments in silicate chemistry. Chemical binding and drying are combined in most of the newly developed chemistry. Chemical binding and drying are combined in most of the newly developed inorganic water glass based binding processes. The two main components of such systems inorganic water glass based binding processes. The two main components of such systems are a liquid modified water glass binder and a powder-based additive [1], [2]. The are a liquid modified water glass binder and a powder-based additive [1], [2]. The commercially available binder systems are the following: Cordis binder system, Inotec binder commercially available binder systems are the following: Cordis binder system, Inotec binder

1 Nemak Linz GmbH 1 Nemak Linz GmbH Zeppelinstrasse 24, Linz, Upper-Austria 4030, Austria Zeppelinstrasse 24, Linz, Upper-Austria 4030, Austria [email protected] [email protected] 2 Institute of Foundry, University of Miskolc 2 Institute of Foundry, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] The Examination of the Mechanical Properties of Water Glass Core Sands 27 The Examination of the Mechanical Properties of Water Glass Core Sands 27 system, AWB method, Laempe and Hydrobond processes. Inorganic binders can be used system, AWB method, Laempe and Hydrobond processes. Inorganic binders can be used mostly for aluminium castings because of the low casting temperature. However, foundries mostly for aluminium castings because of the low casting temperature. However, foundries are carrying out researches on the successful application of inorganic binders for iron casting are carrying out researches on the successful application of inorganic binders for iron casting production [1], [6]. production [1], [6].

3. REGENERATION TECHNOLOGIES 3. REGENERATION TECHNOLOGIES The aim of regeneration is to produce sand with similar properties to new sand which is The aim of regeneration is to produce sand with similar properties to new sand which is reusable for core and form production [1], [3]. The regeneration of inorganic water glass reusable for core and form production [1], [3]. The regeneration of inorganic water glass bound core-sand mixtures poses a great challenge for foundries, as, dissimilarly to organic bound core-sand mixtures poses a great challenge for foundries, as, dissimilarly to organic binders, the binder is not burnt out after casting. Various regeneration methods can be used binders, the binder is not burnt out after casting. Various regeneration methods can be used for core-sand mixtures with inorganic binders. I.e. moist, thermal, mechanical and thermal- for core-sand mixtures with inorganic binders. I.e. moist, thermal, mechanical and thermal- mechanical regeneration. mechanical regeneration. During moist regeneration, the used sand is washed in several steps. This technology is During moist regeneration, the used sand is washed in several steps. This technology is the most effective, as the silicate binder can be washed off of the sand particles. However, the most effective, as the silicate binder can be washed off of the sand particles. However, the technology is not in compliance with the ecological consideration of inorganic binders the technology is not in compliance with the ecological consideration of inorganic binders due to the high water and space demand, the issues of wastewater cleaning and the disposal due to the high water and space demand, the issues of wastewater cleaning and the disposal of sludge. Furthermore, the sand needs to be dried as well. The industrial used of the of sludge. Furthermore, the sand needs to be dried as well. The industrial used of the technology is rather rare and no further developments have been made [1], [4]. technology is rather rare and no further developments have been made [1], [4]. Thermal regeneration can be used in case of water glass- ester binders. During burning, the Thermal regeneration can be used in case of water glass- ester binders. During burning, the organic components are burnt off of the surface of the sand. This regeneration method has high organic components are burnt off of the surface of the sand. This regeneration method has high energy and space demand. Thus, the technology can be economic only for high volume energy and space demand. Thus, the technology can be economic only for high volume production. It is used mostly for the regeneration of organic binder systems [1], [4], [5]. production. It is used mostly for the regeneration of organic binder systems [1], [4], [5]. Lately, the use of mechanical regeneration equipment for the regeneration of inorganic Lately, the use of mechanical regeneration equipment for the regeneration of inorganic binder based sands is getting more and more widespread. Mechanical abrasion is caused by binder based sands is getting more and more widespread. Mechanical abrasion is caused by either the different crusher balls or because of the friction between the particles. The space either the different crusher balls or because of the friction between the particles. The space need of these devices is low, the operation is cheap and they can be easily incorporated into need of these devices is low, the operation is cheap and they can be easily incorporated into the system of any foundry [1], [4]. the system of any foundry [1], [4]. Furthermore, the combination of thermal and mechanical systems is also used by Furthermore, the combination of thermal and mechanical systems is also used by companies such as BMW [5], [6]. In these systems, a thermal step is included beside companies such as BMW [5], [6]. In these systems, a thermal step is included beside mechanical regeneration. This combination is also distributed by Scheuchel as a mass- mechanical regeneration. This combination is also distributed by Scheuchel as a mass- production device. The investment costs are rather high because of the thermal regeneration production device. The investment costs are rather high because of the thermal regeneration block. block.

4. RESULTS AND DISCUSSION 4. RESULTS AND DISCUSSION During the experiments, new and reclaimed sand (from the first regeneration cycle) with During the experiments, new and reclaimed sand (from the first regeneration cycle) with similar inorganic binder and additive content, and mechanically reclaimed sand (from the similar inorganic binder and additive content, and mechanically reclaimed sand (from the first regeneration cycle) with various binder and additive content were used for the first regeneration cycle) with various binder and additive content were used for the production of mixtures to compare. The inorganic binder system was made out of water glass production of mixtures to compare. The inorganic binder system was made out of water glass binder and a powder additive. Measurement of three-point bending strength is commonly binder and a powder additive. Measurement of three-point bending strength is commonly used as a basic characteristic property for moulding materials. Bending strength depends on used as a basic characteristic property for moulding materials. Bending strength depends on the binder system used, its dosage as well as on properties of the base material used the binder system used, its dosage as well as on properties of the base material used (chemical, mineralogical, grain shape, grain size). Three-point bending tests were carried out (chemical, mineralogical, grain shape, grain size). Three-point bending tests were carried out on test bars (170 × 22.5 × 22.5 mm) with various holding times and binder contents. The on test bars (170 × 22.5 × 22.5 mm) with various holding times and binder contents. The holding times were 30 sec, 1 hour and 24 hours after the production of test bars with a core holding times were 30 sec, 1 hour and 24 hours after the production of test bars with a core shooter. shooter. The bending strength of the mixtures from new and reclaimed sand with same binder and The bending strength of the mixtures from new and reclaimed sand with same binder and additive content is illustrated in Figure 1. additive content is illustrated in Figure 1.

28 Viktória Dargai–László Varga 28 Viktória Dargai–László Varga

Newsand Newsand 300 300 Reclaimed sand Reclaimed sand 250 250 High binder content High binder content 200 with 0.9% additive 200 with 0.9% additive

150 150

100 100

50 50

0 0 Bending strengthas a percentage Bending strengthas a percentage 30 s 1 h 24 h 30 s 1 h 24 h Storage time Storage time Figure 1 Figure 1 The bending strength of the mixtures from new sand and reclaimed sand with same binder The bending strength of the mixtures from new sand and reclaimed sand with same binder and additive content and additive content

It can be observed that the bending strength values of the samples from regenerated sand with It can be observed that the bending strength values of the samples from regenerated sand with the same binder and additive content increased in all cases: with 20% at 30 s and 29% at 1 the same binder and additive content increased in all cases: with 20% at 30 s and 29% at 1 and 24 h. There was no significant difference between the bending strength in case of 1 and and 24 h. There was no significant difference between the bending strength in case of 1 and 24 h holding time. 24 h holding time. The bending strength values of mixtures from reclaimed sand with similar additive and The bending strength values of mixtures from reclaimed sand with similar additive and various binder content at different holding times can be seen in Figure 2. various binder content at different holding times can be seen in Figure 2.

Reclaimed sand with low binder content Reclaimed sand with low binder content 300 300 Reclaimed sand with medium binder content Reclaimed sand with medium binder content 250 250 Reclaimed sand with high binder content Reclaimed sand with high binder content 200 200 0.9% additive content 0.9% additive content 150 150

100 100

50 50 Bending strength as a percentage Bending strength as a percentage 0 0 30 s 1 h 24 h 30 s 1 h 24 h Storage time Storage time Figure 2 Figure 2 The bending strength values of mixtures from reclaimed sand with similar additive and The bending strength values of mixtures from reclaimed sand with similar additive and various binder content various binder content

The Examination of the Mechanical Properties of Water Glass Core Sands 29 The Examination of the Mechanical Properties of Water Glass Core Sands 29

The decreased binder content led to lower bending strength. In case of the initial bending The decreased binder content led to lower bending strength. In case of the initial bending strength with the highest additive content, the bending strength of test bars decreased with strength with the highest additive content, the bending strength of test bars decreased with 10% with medium binder content and 20% with low binder content. At 1 h holding time, the 10% with medium binder content and 20% with low binder content. At 1 h holding time, the decrease in bending strength was 2% with medium and 18% with low binder content. The decrease in bending strength was 2% with medium and 18% with low binder content. The test bars with 24 h holding time exhibited 9% decrease in bending strength with medium test bars with 24 h holding time exhibited 9% decrease in bending strength with medium binder content and 20% decrease with low binder content. binder content and 20% decrease with low binder content. Figure 3 illustrates the bending strength values of mixtures form the mechanically Figure 3 illustrates the bending strength values of mixtures form the mechanically reclaimed sands with similar binder and decreased additive content. reclaimed sands with similar binder and decreased additive content. In case of the various additive contents, the mixtures with 30 s holding time exhibited In case of the various additive contents, the mixtures with 30 s holding time exhibited significant differences. With 0.7% additive, the bending strength decreased with 8% and significant differences. With 0.7% additive, the bending strength decreased with 8% and using 0.5% additive resulted in 17% bending strength decrease. The 1 h holding time resulted using 0.5% additive resulted in 17% bending strength decrease. The 1 h holding time resulted in approximately 3% strength decrease, and 7% in case of 24 h holding time. in approximately 3% strength decrease, and 7% in case of 24 h holding time.

Reclaimed sand + 0,5% additiv Reclaimed sand + 0,5% additiv 300 300 Reclaimed sand + 0,7% additiv Reclaimed sand + 0,7% additiv 250 250 Reclaimed sand + 0,9% additiv Reclaimed sand + 0,9% additiv 200 200 High binder content High binder content 150 150

100 100

50 50 Bending strengthas a percentage Bending strengthas a percentage 0 0 30 s 1 h 24 h 30 s 1 h 24 h Storage time Storage time Figure 3 Figure 3 The bending strength of mechanically reclaimed sands with similar binder and decreased The bending strength of mechanically reclaimed sands with similar binder and decreased additive content additive content

SUMMARY SUMMARY In case of mixtures with the same binder and additive content, the use of reclaimed sand In case of mixtures with the same binder and additive content, the use of reclaimed sand resulted in 29% higher bending strength, compared to the use of new sand. The bending resulted in 29% higher bending strength, compared to the use of new sand. The bending strength values reach a maximum at 1 h holding time and decrease after 24 h. The decreased strength values reach a maximum at 1 h holding time and decrease after 24 h. The decreased binder content had a greater effect on the bending strength values then the decreased additive binder content had a greater effect on the bending strength values then the decreased additive content. content.

ACKNOWLEDGEMENT ACKNOWLEDGEMENT The authors are grateful to Mária Ambrus for her advice. The authors are grateful to Mária Ambrus for her advice.

30 Viktória Dargai–László Varga 30 Viktória Dargai–László Varga

REFERENCES REFERENCES [1] H. Polzin (2014). Inorganic binders for mould and core production in the foundry. Germany, [1] H. Polzin (2014). Inorganic binders for mould and core production in the foundry. Germany, Schiele &Schön. Schiele &Schön. [2] Tóth L. (2011). Forma és magkészítési ismeretek. Oktatási segédlet. [2] Tóth L. (2011). Forma és magkészítési ismeretek. Oktatási segédlet. [3] E. Flemming and W. Tilch (1993). Formstoffe und Formverfahren. Stuttgart, Deutscher Verlauf [3] E. Flemming and W. Tilch (1993). Formstoffe und Formverfahren. Stuttgart, Deutscher Verlauf für Grundstoffindustrie, Leipzig. für Grundstoffindustrie, Leipzig. [4] H. Polzin, P. Jaruszewski and J. Müller-Späth (2012). Die Regenerierung von Wasserglas- [4] H. Polzin, P. Jaruszewski and J. Müller-Späth (2012). Die Regenerierung von Wasserglas- Ester-altsanden in einer mittelständischen Aluminium Gießerei. Gießerei, 99 S.70–81, 04/2012. Ester-altsanden in einer mittelständischen Aluminium Gießerei. Gießerei, 99 S.70–81, 04/2012. [5] Schwickal H., Hoffman H., Blümlhuber N. and Weissenbek E. (2009). Regenerierung von [5] Schwickal H., Hoffman H., Blümlhuber N. and Weissenbek E. (2009). Regenerierung von anorganisch gebundenen Gießereikernsanden. Gießerei, 96 S. 40–44, 11/2009. anorganisch gebundenen Gießereikernsanden. Gießerei, 96 S. 40–44, 11/2009. [6] C. Wallenhorst (2010). Chemische Grundlagen der Anorganischen Bindemittel-Betrachtung [6] C. Wallenhorst (2010). Chemische Grundlagen der Anorganischen Bindemittel-Betrachtung der Kernherstellung auf molekularer Ebene. Gießerei-Rundschau, 57 S. 50–52. der Kernherstellung auf molekularer Ebene. Gießerei-Rundschau, 57 S. 50–52.

Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 31–41. Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 31–41.

FLAME IMAGE PROCESSING AND ARTIFICIAL INTELLIGENCE AS FLAME IMAGE PROCESSING AND ARTIFICIAL INTELLIGENCE AS A DIAGNOSTIC TOOL FOR INDUSTRIAL BIOMASS COMBUSTION A DIAGNOSTIC TOOL FOR INDUSTRIAL BIOMASS COMBUSTION

ATTILA GARAMI1–PÁL TÓTH1,2 ATTILA GARAMI1–PÁL TÓTH1,2

The main objective of this work was to minimize emission levels and optimize thermal The main objective of this work was to minimize emission levels and optimize thermal efficiency of a 3 MW, grate-fired biomass boiler without on-line fuel analysis systems by efficiency of a 3 MW, grate-fired biomass boiler without on-line fuel analysis systems by applying novel combustion process control based on routinely measured operating applying novel combustion process control based on routinely measured operating parameters and real-time flame image processing and machine learning. Two important tasks parameters and real-time flame image processing and machine learning. Two important tasks of image based combustion monitoring systems are providing alerts and predictions of image based combustion monitoring systems are providing alerts and predictions regarding the state of the system. The system issues alerts based on the location of the reaction regarding the state of the system. The system issues alerts based on the location of the reaction zone and predicts boiler performance based on image and operating data. zone and predicts boiler performance based on image and operating data. Keywords: biomass, combustion, step-grate boiler, grate monitoring, flame imaging, Keywords: biomass, combustion, step-grate boiler, grate monitoring, flame imaging, machine learning machine learning

INTRODUCTION INTRODUCTION Biomass is the oldest energy source in the history of mankind. Due to global climate change Biomass is the oldest energy source in the history of mankind. Due to global climate change and depleting fossil fuel reserves, the incentive to move towards sustainable energy and depleting fossil fuel reserves, the incentive to move towards sustainable energy production has defined the last decade. Biomass is considered to be the only viable option production has defined the last decade. Biomass is considered to be the only viable option for renewable energy generation that can meet global demand in the short-term – the annual for renewable energy generation that can meet global demand in the short-term – the annual availability of biomass is believed to be approximately equal to that of coal [5]. Considering availability of biomass is believed to be approximately equal to that of coal [5]. Considering forestry alone, the annually harvested 530 billion m3 biomass has the potential to cover 10% forestry alone, the annually harvested 530 billion m3 biomass has the potential to cover 10% of the world’s power demand [18]. In the EU27 in 2010, of the approximately 3000 PJ of of the world’s power demand [18]. In the EU27 in 2010, of the approximately 3000 PJ of renewable energy generation for heating and cooling, biomass had a dominating share of renewable energy generation for heating and cooling, biomass had a dominating share of approximately 91% – this decisive role is projected to remain in and after 2020 [2]. For heat approximately 91% – this decisive role is projected to remain in and after 2020 [2]. For heat and electricity generation from biomass, combustion is by far the most widespread and electricity generation from biomass, combustion is by far the most widespread technology, holding a share of over 90% [14]. technology, holding a share of over 90% [14]. Grate firing is the most widely used method for biomass combustion. When used for heat Grate firing is the most widely used method for biomass combustion. When used for heat generation, grate-fired systems are normally limited to an output power of approximately 150 generation, grate-fired systems are normally limited to an output power of approximately 150 MWth, which is not a disadvantage in certain decentralized industry segments. Flexibility in MWth, which is not a disadvantage in certain decentralized industry segments. Flexibility in terms of fuel type and granularity further popularize the technology in smaller scale applications terms of fuel type and granularity further popularize the technology in smaller scale applications [22]. Grate-fired boilers are known to have lower efficiency compared to e. g., fluidized bed [22]. Grate-fired boilers are known to have lower efficiency compared to e. g., fluidized bed combustors [18], therefore, given the share of the technology in global renewable energy combustors [18], therefore, given the share of the technology in global renewable energy production, it is important to optimize their operation. Due to climate change and environmental production, it is important to optimize their operation. Due to climate change and environmental issues, using low-quality and heterogeneous fuels or fuel blends has become a global trend [1]. issues, using low-quality and heterogeneous fuels or fuel blends has become a global trend [1]. Grate-firing technologies can potentially meet these requirements; however, the problems Grate-firing technologies can potentially meet these requirements; however, the problems caused by using such fuels – such as reduced efficiency, increased emissions, slagging and caused by using such fuels – such as reduced efficiency, increased emissions, slagging and fouling issues and poor flame stability – must be resolved [17]. fouling issues and poor flame stability – must be resolved [17]. The main objective of this work is to minimize emission levels and optimize thermal The main objective of this work is to minimize emission levels and optimize thermal efficiency of a 3 MW, grate-fired biomass boiler without on-line fuel analysis systems by efficiency of a 3 MW, grate-fired biomass boiler without on-line fuel analysis systems by applying novel combustion process control based on routinely measured operating applying novel combustion process control based on routinely measured operating

1 Department of Combustion Technology and Thermal Energy, University of Miskolc 1 Department of Combustion Technology and Thermal Energy, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 2 RISE Bioekonomi / SP Energy Technology Center AB, Box 726, SE-941 28 Piteå, Sweden 2 RISE Bioekonomi / SP Energy Technology Center AB, Box 726, SE-941 28 Piteå, Sweden 32 Attila Garami–Pál Tóth 32 Attila Garami–Pál Tóth parameters and real-time flame image processing and machine learning. Two important tasks parameters and real-time flame image processing and machine learning. Two important tasks of image based combustion monitoring systems are providing alerts and predictions of image based combustion monitoring systems are providing alerts and predictions regarding the state of the system. The system issues alerts based on the location of the reaction regarding the state of the system. The system issues alerts based on the location of the reaction zone and predicts boiler performance based on image and operating data. zone and predicts boiler performance based on image and operating data. Historically, the reaction zone in step-grate combustors has not been monitored. Locating Historically, the reaction zone in step-grate combustors has not been monitored. Locating the reaction zone has several advantages. It provides information on the distribution of fuel the reaction zone has several advantages. It provides information on the distribution of fuel over the grate, helps guarantee equal primary air supply to different regions of the grate and over the grate, helps guarantee equal primary air supply to different regions of the grate and avoid the formation of “holes”, the elutriation of fly ash and unburned particles. The merits avoid the formation of “holes”, the elutriation of fly ash and unburned particles. The merits of a reliable boiler performance prediction system are obvious: operators can finetune of a reliable boiler performance prediction system are obvious: operators can finetune parameters based on predicted future data. A prediction system can also alert for faulty parameters based on predicted future data. A prediction system can also alert for faulty operation as soon as it can be reliably predicted. To the best of the authors’ knowledge, no operation as soon as it can be reliably predicted. To the best of the authors’ knowledge, no reports are available on the on-line monitoring and prediction of grate-fired biomass reports are available on the on-line monitoring and prediction of grate-fired biomass combustion. combustion.

1. MATERIALS AND METHODS 1. MATERIALS AND METHODS In this section, the boiler used for the experiments, the instrumentation and imaging system In this section, the boiler used for the experiments, the instrumentation and imaging system and the details of the data processing algorithms are discussed. and the details of the data processing algorithms are discussed. The approach can be best described as a combination of hardware and software elements. The approach can be best described as a combination of hardware and software elements. The hardware elements consisted of a camera and protective housing with a cooling system, The hardware elements consisted of a camera and protective housing with a cooling system, an image acquisition and data transfer system and data processing hardware. The software an image acquisition and data transfer system and data processing hardware. The software component consisted of different modules for image processing, 3D reconstruction of the component consisted of different modules for image processing, 3D reconstruction of the reaction zone and neural network prediction. reaction zone and neural network prediction.

1.1. Boiler 1.1. Boiler Figure 1 shows a schematic drawing of the boiler used for the experiments. The boiler was a Figure 1 shows a schematic drawing of the boiler used for the experiments. The boiler was a 3 MW nominal capacity, counter-current, inclined, stepping grate type combustor. The boiler 3 MW nominal capacity, counter-current, inclined, stepping grate type combustor. The boiler was integrated into a sawmill process, producing heat for steaming timber products. Wood was integrated into a sawmill process, producing heat for steaming timber products. Wood chips, by-products of the sawing process were used as fuel. chips, by-products of the sawing process were used as fuel.

Figure 1 Figure 1 A schematic drawing of the 3 MW grate-fired biomass boiler used for the experiments. The A schematic drawing of the 3 MW grate-fired biomass boiler used for the experiments. The location and field of view of the camera used for imaging is shown by the light gray area. location and field of view of the camera used for imaging is shown by the light gray area. Flame Image Processing and Artificial Intelligence as a Diagnostic Tool... 33 Flame Image Processing and Artificial Intelligence as a Diagnostic Tool... 33

1.2. Instrumentation and imaging 1.2. Instrumentation and imaging The boiler was equipped with an on-line measurement system integrated into a distributed The boiler was equipped with an on-line measurement system integrated into a distributed control system (DCS) that monitored several operational parameters, including chamber control system (DCS) that monitored several operational parameters, including chamber temperature, return and output water temperatures, fan speeds, boiler capacity and hydraulic temperature, return and output water temperatures, fan speeds, boiler capacity and hydraulic pressures of the step-grate, fuel feeding and de-ashing systems. Additionally, high accuracy pressures of the step-grate, fuel feeding and de-ashing systems. Additionally, high accuracy Vario Plus Industrial type continuous emission monitoring system (CEM) was used as a tool Vario Plus Industrial type continuous emission monitoring system (CEM) was used as a tool to monitor flue gas for simultaneous measurements of: O2, CO2, CO, NOx components, gas to monitor flue gas for simultaneous measurements of: O2, CO2, CO, NOx components, gas temperature, differential pressure. Flame images were acquired by the current state-of-art, temperature, differential pressure. Flame images were acquired by the current state-of-art, single CCD camera with response in the visible range of the spectrum [12]. The digital single CCD camera with response in the visible range of the spectrum [12]. The digital camera was a Basler Ace acA1300-22gc model. The camera utilized a global shutter CCD camera was a Basler Ace acA1300-22gc model. The camera utilized a global shutter CCD sensor. Images were acquired at a rate of 13 Hz. The duration of sampling was the same in sensor. Images were acquired at a rate of 13 Hz. The duration of sampling was the same in all cases, 12 hours. all cases, 12 hours. A high-temperature industrial pinhole lens was used for imaging the flame. The focal A high-temperature industrial pinhole lens was used for imaging the flame. The focal length of the lens was set at 3.6 mm, resulting in a field of view of approximately 80°. The length of the lens was set at 3.6 mm, resulting in a field of view of approximately 80°. The lens had a 323 mm long stainless steel housing which enabled monitoring the combustion lens had a 323 mm long stainless steel housing which enabled monitoring the combustion chamber by leading the lens through a hole in the refractory wall. The lens and the camera chamber by leading the lens through a hole in the refractory wall. The lens and the camera were protected by a tube-in-a-tube type cooling system. Compressed air was used as a were protected by a tube-in-a-tube type cooling system. Compressed air was used as a coolant. Small holes in the front-end piece of the stainless-steel housing, outside of the first coolant. Small holes in the front-end piece of the stainless-steel housing, outside of the first optical element in the lens, ensured positive pressures inside the pinhole lens, therefore optical element in the lens, ensured positive pressures inside the pinhole lens, therefore avoiding dust deposition. The cooling system of the camera maintained lens and camera avoiding dust deposition. The cooling system of the camera maintained lens and camera temperatures below 30 °C – the amount of air injected into the combustion chamber through temperatures below 30 °C – the amount of air injected into the combustion chamber through the cooler was negligible. Figure 2.a shows an example flame image acquired by the installed the cooler was negligible. Figure 2.a shows an example flame image acquired by the installed camera with the locations of the fuel feeder and the grate. camera with the locations of the fuel feeder and the grate.

Figure 2 Figure 2 Localization of the reaction zone: a) located boundaries of the reaction zone with the fuel Localization of the reaction zone: a) located boundaries of the reaction zone with the fuel feeder and grate shown by white outlines; b) transformed coordinates of the reaction zone feeder and grate shown by white outlines; b) transformed coordinates of the reaction zone boundary in the coordinate frame of the grate. Dashed lines indicate the approximate boundary in the coordinate frame of the grate. Dashed lines indicate the approximate location of grate elements; c) 3D reconstruction of the reaction zone in schematic drawing location of grate elements; c) 3D reconstruction of the reaction zone in schematic drawing of the boiler. of the boiler. 34 Attila Garami–Pál Tóth 34 Attila Garami–Pál Tóth

1.3. Reaction zone monitoring: Image segmentation 1.3. Reaction zone monitoring: Image segmentation As a first step, the raw image data was demosaicked [7] and the color channels (red, green As a first step, the raw image data was demosaicked [7] and the color channels (red, green and blue) were separated into different data vectors. and blue) were separated into different data vectors. After that to locate the boundaries of the reaction zone, where the intensive burning takes After that to locate the boundaries of the reaction zone, where the intensive burning takes place, the images were processed by segmentation algorithm. Since there may be some noise place, the images were processed by segmentation algorithm. Since there may be some noise in flame images and sometimes the edge of the flame image is not very clear, it was detected in flame images and sometimes the edge of the flame image is not very clear, it was detected by so called customized active contour model instead of conventional operators [23]. It is an by so called customized active contour model instead of conventional operators [23]. It is an energy minimizing, deformable spline influenced by constraint and image forces [13]. energy minimizing, deformable spline influenced by constraint and image forces [13]. A typical result of this segmentation procedure is also shown in Figure 2.a. As demonstrated, A typical result of this segmentation procedure is also shown in Figure 2.a. As demonstrated, the algorithm proved to be a robust and reliable method for the purpose of locating the the algorithm proved to be a robust and reliable method for the purpose of locating the reaction zone. reaction zone. Then the acquired image, along with the coordinates of the reaction zone boundary, was Then the acquired image, along with the coordinates of the reaction zone boundary, was transformed spatially to remove the effects of perspective distortion. This step ensured that transformed spatially to remove the effects of perspective distortion. This step ensured that the obtained spatial coordinates are in the coordinate frame of the grate (Figure 2.b). Figure 2 the obtained spatial coordinates are in the coordinate frame of the grate (Figure 2.b). Figure 2 illustrates the spatial transformation step. Therefore, real distance from feeder port can be illustrates the spatial transformation step. Therefore, real distance from feeder port can be easily defined by operator or control system. As seen, the obtained coordinates fit realistically easily defined by operator or control system. As seen, the obtained coordinates fit realistically into the coordinate frame of the grate. Finally, the 3D reconstruction of the reaction zone was into the coordinate frame of the grate. Finally, the 3D reconstruction of the reaction zone was carried out to visually be able to see where the reaction zone is located compared to the other carried out to visually be able to see where the reaction zone is located compared to the other parts of the chamber (Figure 2.c). parts of the chamber (Figure 2.c).

1.4. Prediction system: Image and operational parameter features 1.4. Prediction system: Image and operational parameter features Since the images had a pixel resolution of 488 × 582 with an RGB bit depth of 24 bit, and Since the images had a pixel resolution of 488 × 582 with an RGB bit depth of 24 bit, and the camera operated at 13 Hz, the image data rate was approximately 11 million 8-bit integers the camera operated at 13 Hz, the image data rate was approximately 11 million 8-bit integers per second (which corresponds to 88 Mbit/s as opposed to the 1000 Mbit/s limit of the GigE per second (which corresponds to 88 Mbit/s as opposed to the 1000 Mbit/s limit of the GigE standard). standard). Due to limited computing resources, an input space with a dimension of 488 × 582 × 3 Due to limited computing resources, an input space with a dimension of 488 × 582 × 3 cannot be handled in real time, therefore data reduction steps were necessary before feeding cannot be handled in real time, therefore data reduction steps were necessary before feeding the inputs to the neural network. The data reduction process derives image features from the the inputs to the neural network. The data reduction process derives image features from the raw image data, namely from the ordered sets of pixel intensities corresponding to the color raw image data, namely from the ordered sets of pixel intensities corresponding to the color channels of the sensor. The parameters derived by the data reduction process are channels of the sensor. The parameters derived by the data reduction process are conventionally called learning features [3]. These features must be defined in a way so that conventionally called learning features [3]. These features must be defined in a way so that the resulting feature set can be computed efficiently, while also conserving most of the the resulting feature set can be computed efficiently, while also conserving most of the information content of the images. information content of the images. For the sake of simplicity, an image can be considered as a collection of radiometric For the sake of simplicity, an image can be considered as a collection of radiometric measurements. Each pixel carries radiometric and spectral information (due to the selective measurements. Each pixel carries radiometric and spectral information (due to the selective color filters used in Bayer arrays), but also spatial information, since the spatial location from color filters used in Bayer arrays), but also spatial information, since the spatial location from where a given sensor element collects data is known [10]. where a given sensor element collects data is known [10]. Several options for data reduction can be considered. In this study, statistical description Several options for data reduction can be considered. In this study, statistical description was adapted as the data reduction method. To circumvent the loss of spatial data, features was adapted as the data reduction method. To circumvent the loss of spatial data, features from the image gradient were also computed and added to the feature set. from the image gradient were also computed and added to the feature set. After image pre-processing, the matrix form of the red channel was reconstructed in order After image pre-processing, the matrix form of the red channel was reconstructed in order to compute its smoothed spatial gradient [8]. From the spatial gradient, the gradient to compute its smoothed spatial gradient [8]. From the spatial gradient, the gradient magnitude and orientation were computed and stored as vector data representing two virtual magnitude and orientation were computed and stored as vector data representing two virtual channels. In the second step, the first four statistical moments (the mean, variance, skewness channels. In the second step, the first four statistical moments (the mean, variance, skewness and kurtosis) of each channel, including the two virtual channels, were computed. These and kurtosis) of each channel, including the two virtual channels, were computed. These statistical moments were used as image features, part of the feature set fed into the artificial statistical moments were used as image features, part of the feature set fed into the artificial neural network. neural network. Flame Image Processing and Artificial Intelligence as a Diagnostic Tool... 35 Flame Image Processing and Artificial Intelligence as a Diagnostic Tool... 35

In the application described in this paper, the prediction scheme used was hybrid in the In the application described in this paper, the prediction scheme used was hybrid in the sense that it used features from both image and non-image data. The “non-image” part of the sense that it used features from both image and non-image data. The “non-image” part of the feature set consisted of routinely measured operational parameters by DCS. Previous studies feature set consisted of routinely measured operational parameters by DCS. Previous studies reported the usage of similar hybrid schemes [21, 16, 15, 19]. reported the usage of similar hybrid schemes [21, 16, 15, 19]. Seven of the many recorded parameters were selected as inputs for the machine learning Seven of the many recorded parameters were selected as inputs for the machine learning system: boiler capacity, output water temperature, return water temperature, flue gas O2 system: boiler capacity, output water temperature, return water temperature, flue gas O2 content and the capacities of primary and secondary air fans. Operational parameters were content and the capacities of primary and secondary air fans. Operational parameters were collected at slower rates, therefore a piecewise constant extrapolation scheme was used to collected at slower rates, therefore a piecewise constant extrapolation scheme was used to produce operational parameter values before a new set of measurements became available. produce operational parameter values before a new set of measurements became available.

1.5. Prediction system: Artificial neural network 1.5. Prediction system: Artificial neural network The artificial neural network (ANN) implementation used in this work was a type of fully The artificial neural network (ANN) implementation used in this work was a type of fully connected, feedforward deep neural network. The role of the neural network was making connected, feedforward deep neural network. The role of the neural network was making predictions of the output water temperature. The predictions were made in a continuous predictions of the output water temperature. The predictions were made in a continuous multistep-ahead prediction scheme [6]. The predictions were computed for times-ahead up multistep-ahead prediction scheme [6]. The predictions were computed for times-ahead up to approximately 28 minutes. to approximately 28 minutes. The set of inputs (27 learning features, as discussed in Section 2.4) were fed to a number The set of inputs (27 learning features, as discussed in Section 2.4) were fed to a number of “blocks”, each of which outputs a prediction for a given time-ahead. Each block can be of “blocks”, each of which outputs a prediction for a given time-ahead. Each block can be considered as a separate deep multi-layer perceptron (MLP), independent of the other blocks. considered as a separate deep multi-layer perceptron (MLP), independent of the other blocks. Since the combustion process is assumed to be non-linear, non-unity activation functions Since the combustion process is assumed to be non-linear, non-unity activation functions were used in the presented ANN. Rectifiers were used as activation functions in all blocks. were used in the presented ANN. Rectifiers were used as activation functions in all blocks. Neurons with the rectifier as their activation function are called rectified linear units Neurons with the rectifier as their activation function are called rectified linear units (ReLU’s). (ReLU’s). The ANN implemented in this work can be considered a deep neural network. Deep The ANN implemented in this work can be considered a deep neural network. Deep neural networks are usually defined as MLP’s that have more than one hidden layer and all neural networks are usually defined as MLP’s that have more than one hidden layer and all neuron have non-linear activation functions. neuron have non-linear activation functions. In the ANN described in this paper, each block consisted of 5 hidden layers resulting in In the ANN described in this paper, each block consisted of 5 hidden layers resulting in a total of 7 layers per block. Each layer contained 50 neurons. The width of the lines a total of 7 layers per block. Each layer contained 50 neurons. The width of the lines represents the weights associated with the connections. The network can be regarded as a represents the weights associated with the connections. The network can be regarded as a collection of fully connected deep subnetworks, or blocks. Each input was connected to every collection of fully connected deep subnetworks, or blocks. Each input was connected to every top-level neuron of every block. The inputs were a set of 27 learning features. The outputs top-level neuron of every block. The inputs were a set of 27 learning features. The outputs were predictions at different times ahead of the current instance. A total of 200 outputs were were predictions at different times ahead of the current instance. A total of 200 outputs were used, representing 200 discrete time bins ahead of the current time. Consequently, the number used, representing 200 discrete time bins ahead of the current time. Consequently, the number of blocks was also 200. of blocks was also 200. Several ANN architectures were implemented and tested, among which the presented Several ANN architectures were implemented and tested, among which the presented architecture proved to be a good balance of architecture complexity and computational cost. architecture proved to be a good balance of architecture complexity and computational cost. The presented architecture can be trained and evaluated reasonably quickly, while still The presented architecture can be trained and evaluated reasonably quickly, while still maintaining fairly low error. maintaining fairly low error. In the present study, the training dataset was obtained in a 12-hour test campaign. The In the present study, the training dataset was obtained in a 12-hour test campaign. The dataset contained all measured operational and image features. To train the network, “future” dataset contained all measured operational and image features. To train the network, “future” values of the output water temperature were paired with “present” values of the 27 learning values of the output water temperature were paired with “present” values of the 27 learning features – in other words, a time lag between the input feature set and outputs was introduced features – in other words, a time lag between the input feature set and outputs was introduced representing the time-ahead values. The dataset acquired in the 12-hour campaign was split representing the time-ahead values. The dataset acquired in the 12-hour campaign was split in half. One half was used for training, and the other was used for testing the predictive power in half. One half was used for training, and the other was used for testing the predictive power of the ANN. of the ANN. The neural network was trained using the stochastic gradient descent method (SGD) [4], The neural network was trained using the stochastic gradient descent method (SGD) [4], with mean square error as a loss function and a sample size of 50,000. The learning rate was with mean square error as a loss function and a sample size of 50,000. The learning rate was set to 0.01. In order to avoid overfitting, L2 regularization was used. Learning rate decay and set to 0.01. In order to avoid overfitting, L2 regularization was used. Learning rate decay and 36 Attila Garami–Pál Tóth 36 Attila Garami–Pál Tóth momentum strategies were not used [11]. The neural network was implemented in Python momentum strategies were not used [11]. The neural network was implemented in Python 2.7, using the Theano machine learning framework [20]. 2.7, using the Theano machine learning framework [20].

2. RESULTS AND DISCUSSION 2. RESULTS AND DISCUSSION 2.1. Validation of the segmentation algorithm 2.1. Validation of the segmentation algorithm In this section the robust and reliable operation of the proposed algorithm were demonstrated In this section the robust and reliable operation of the proposed algorithm were demonstrated by observing the changes of the obtained reaction zone coordinates. by observing the changes of the obtained reaction zone coordinates. Figure 3 illustrates the capability of the proposed system to follow quick changes in the Figure 3 illustrates the capability of the proposed system to follow quick changes in the reaction zone location following fuel feeding or grate motion events. reaction zone location following fuel feeding or grate motion events.

Figure 3 Figure 3 Changes in 50th (p50) and 100th (p100) percentile of the y coordinates of the reaction zone Changes in 50th (p50) and 100th (p100) percentile of the y coordinates of the reaction zone boundaries with binary fuel feeding and grate motion signals as a function of time. Marked boundaries with binary fuel feeding and grate motion signals as a function of time. Marked points indicate time instances at which the images of the second row were captured. The points indicate time instances at which the images of the second row were captured. The snapshots demonstrate typical issues encountered in the operation of the monitoring snapshots demonstrate typical issues encountered in the operation of the monitoring system: a) reduced flame luminosity caused by a momentary cutoff in combustion air supply system: a) reduced flame luminosity caused by a momentary cutoff in combustion air supply due to grate motion; b)–c) a displacement of a small portion of the bed due to grate due to grate motion; b)–c) a displacement of a small portion of the bed due to grate motion; d) this event signifies the complete extinction of the flame due to the temporarily motion; d) this event signifies the complete extinction of the flame due to the temporarily diminished dynamic load of the boiler; e)–g) these events are shown to demonstrate that diminished dynamic load of the boiler; e)–g) these events are shown to demonstrate that although sharp changes are observed in the percentile values, the algorithm correctly although sharp changes are observed in the percentile values, the algorithm correctly detected the reaction zone boundary. detected the reaction zone boundary. Flame Image Processing and Artificial Intelligence as a Diagnostic Tool... 37 Flame Image Processing and Artificial Intelligence as a Diagnostic Tool... 37

In the top row of the Figure 3, the motion of the grate elements, fuel feeding, 50th (p50) and In the top row of the Figure 3, the motion of the grate elements, fuel feeding, 50th (p50) and 100th (p100) percentile of the y coordinates of the reaction zone boundaries and the boiler 100th (p100) percentile of the y coordinates of the reaction zone boundaries and the boiler capacity are shown as a function of given time period during the measurements. The grate capacity are shown as a function of given time period during the measurements. The grate motion and the fuel feeding signals are logical signals, thus they only represent on/off events. motion and the fuel feeding signals are logical signals, thus they only represent on/off events. As seen, the reaction zone coordinates followed the signals. The reaction zone migrated away As seen, the reaction zone coordinates followed the signals. The reaction zone migrated away from the feeding port when fuel was fed or the grate was moved, and receded towards the from the feeding port when fuel was fed or the grate was moved, and receded towards the feeding port when there were no signals. Consequently, the calculated boiler capacity signal feeding port when there were no signals. Consequently, the calculated boiler capacity signal was zero at these times, indicating no injection of combustion air. was zero at these times, indicating no injection of combustion air. In the second row of the Figure 3, a)–g) show snapshots of the combustion chamber, In the second row of the Figure 3, a)–g) show snapshots of the combustion chamber, taken at times indicated by markers in the time histories. The purpose of these snapshots is taken at times indicated by markers in the time histories. The purpose of these snapshots is to illustrate and explain typical detection issues encountered during operation: a) reduced to illustrate and explain typical detection issues encountered during operation: a) reduced flame luminosity caused by a momentary cutoff in combustion air supply due to grate motion; flame luminosity caused by a momentary cutoff in combustion air supply due to grate motion; b)–c) a displacement of a small portion of the bed due to grate motion; d) this event signifies b)–c) a displacement of a small portion of the bed due to grate motion; d) this event signifies the complete extinction of the flame due to the temporarily diminished dynamic load of the the complete extinction of the flame due to the temporarily diminished dynamic load of the boiler; e)–g) these events are shown to demonstrate that although sharp changes are observed boiler; e)–g) these events are shown to demonstrate that although sharp changes are observed in the percentile values, the algorithm correctly detected the reaction zone boundary. in the percentile values, the algorithm correctly detected the reaction zone boundary. In summary, the proposed system reliably captured the motion of the reaction zone, with In summary, the proposed system reliably captured the motion of the reaction zone, with minor issues that could be easily identified and filtered out. Furthermore, the system was able minor issues that could be easily identified and filtered out. Furthermore, the system was able to identify extreme operating states and undesirable fuel distribution that may lead to to identify extreme operating states and undesirable fuel distribution that may lead to decreased efficiency and reduced grate lifetime. decreased efficiency and reduced grate lifetime.

2.2. Further research on the reaction zone location 2.2. Further research on the reaction zone location Relationships between image flame features and combustion performance parameters are Relationships between image flame features and combustion performance parameters are receiving added attention because of their potential in monitoring and control applications. receiving added attention because of their potential in monitoring and control applications. Based on the observed empirical correlations, model-based controllers can be realized [9]. Based on the observed empirical correlations, model-based controllers can be realized [9]. The relevance of locating the reaction zone coordinates was further demonstrated by The relevance of locating the reaction zone coordinates was further demonstrated by exploring the correlation between selected, relevant operational parameters and the reaction exploring the correlation between selected, relevant operational parameters and the reaction zone location. zone location. When computing the linear correlation coefficient between the percentile measures of the When computing the linear correlation coefficient between the percentile measures of the reaction zone boundary coordinates and selected parameters, it was found that the reaction zone boundary coordinates and selected parameters, it was found that the coefficients were above 0.8 for most percentiles and the major flue gas constituents. The coefficients were above 0.8 for most percentiles and the major flue gas constituents. The correlation coefficients between the flue gas and combustion chamber temperature and correlation coefficients between the flue gas and combustion chamber temperature and reaction zone boundary coordinate percentiles were between 0.6 and 0.2, respectively, while reaction zone boundary coordinate percentiles were between 0.6 and 0.2, respectively, while the correlation was approximately or weaker than 0.2 for the pollutant concentrations. the correlation was approximately or weaker than 0.2 for the pollutant concentrations. However, when recomputing the correlation coefficients with the time lag between signals However, when recomputing the correlation coefficients with the time lag between signals removed via cross correlation analysis, the correlation coefficients increase to above 0.8 in removed via cross correlation analysis, the correlation coefficients increase to above 0.8 in the case of flue gas temperature, above 0.6 in the case of combustion chamber temperature the case of flue gas temperature, above 0.6 in the case of combustion chamber temperature and to approximately 0.3 in the case of pollutants (Figure 4). This suggests that the percentile and to approximately 0.3 in the case of pollutants (Figure 4). This suggests that the percentile values of the obtained reaction zone coordinates can be used for estimating other, relevant values of the obtained reaction zone coordinates can be used for estimating other, relevant operational parameters or for control purposes, based on the selected operational or emission operational parameters or for control purposes, based on the selected operational or emission parameters. Since the time lags are mostly functions of the inherent properties of the parameters. Since the time lags are mostly functions of the inherent properties of the monitored system and persistent operating practices, they can be estimated easily during monitored system and persistent operating practices, they can be estimated easily during operation and the signals can be adjusted accordingly. In this case, the obtained correlation operation and the signals can be adjusted accordingly. In this case, the obtained correlation coefficients suggest that even the relationship between the pollutants and reaction zone coefficients suggest that even the relationship between the pollutants and reaction zone boundary coordinates can be sufficient for monitoring or control purposes. boundary coordinates can be sufficient for monitoring or control purposes.

38 Attila Garami–Pál Tóth 38 Attila Garami–Pál Tóth

Figure 4 Figure 4 Absolute linear correlation coefficients between emission parameters and reaction zone Absolute linear correlation coefficients between emission parameters and reaction zone location percentile values. Stems show correlation coefficients recomputed after the location percentile values. Stems show correlation coefficients recomputed after the estimated time lag between signals had been removed. estimated time lag between signals had been removed.

2.3. Evaluation of the prediction 2.3. Evaluation of the prediction To assess the usefulness of the presented deep ANN learning scheme in predicting the output To assess the usefulness of the presented deep ANN learning scheme in predicting the output of the grate-fired biomass combustion system, the accuracy of the predictions can be of the grate-fired biomass combustion system, the accuracy of the predictions can be evaluated by calculating deviations relative to measured outputs. The deviations can be evaluated by calculating deviations relative to measured outputs. The deviations can be expressed in terms of standard errors. The magnitude of these standard errors provide insight expressed in terms of standard errors. The magnitude of these standard errors provide insight on the achievable fidelity of predictions. on the achievable fidelity of predictions. Figure 5 shows typical prediction results obtained in an experimental campaign. Each Figure 5 shows typical prediction results obtained in an experimental campaign. Each plot shows a different, approximately 28 minutes-long scenarios. The solid black lines show plot shows a different, approximately 28 minutes-long scenarios. The solid black lines show the actual measurements in 20 scenarios. Shaded areas indicate the probability density of the actual measurements in 20 scenarios. Shaded areas indicate the probability density of predictions made at time = 0 up to a time-ahead of approximately 28 minutes. Note that all predictions made at time = 0 up to a time-ahead of approximately 28 minutes. Note that all shown time-ahead predictions were available at time = 0 in every given scenario. Bars show shown time-ahead predictions were available at time = 0 in every given scenario. Bars show the feature spaces at time = 0. As seen, the predictions are fairly accurate and reproduce the feature spaces at time = 0. As seen, the predictions are fairly accurate and reproduce general trends. The errors and thus uncertainty increase with the time-ahead. general trends. The errors and thus uncertainty increase with the time-ahead. After training the ANN, the prediction performance was evaluated by using a test dataset After training the ANN, the prediction performance was evaluated by using a test dataset acquired in the experimental campaign described. The accuracy of prediction was evaluated acquired in the experimental campaign described. The accuracy of prediction was evaluated based on the root mean square error (RMSE) of predictions compared to the test dataset, as based on the root mean square error (RMSE) of predictions compared to the test dataset, as a function of time-ahead. a function of time-ahead. Figure 5 shows the RMSE of predictions as a function of time-ahead. As seen, the errors Figure 5 shows the RMSE of predictions as a function of time-ahead. As seen, the errors remain very low at time-ahead below 5 minutes – however, in this region, the accuracy of remain very low at time-ahead below 5 minutes – however, in this region, the accuracy of prediction decreases quickly. After a time-ahead of 5 minutes, the errors increase slowly up prediction decreases quickly. After a time-ahead of 5 minutes, the errors increase slowly up to an RMSE of approximately +/–1 °C at a time-ahead of 28 minutes. to an RMSE of approximately +/–1 °C at a time-ahead of 28 minutes. After a time-ahead of approximately 28 minutes, the RMSE of predictions was found to After a time-ahead of approximately 28 minutes, the RMSE of predictions was found to increase rapidly, with the predictions becoming unrealistic, in some cases unable to follow increase rapidly, with the predictions becoming unrealistic, in some cases unable to follow general trends. This is probably due to the typical cycle time of the boiler in the training data, general trends. This is probably due to the typical cycle time of the boiler in the training data, which was 20–50 minutes. Most likely, the ANN learns typical operation patterns including which was 20–50 minutes. Most likely, the ANN learns typical operation patterns including cycle times. The ANN utilizes these learned patterns for producing long-term predictions. cycle times. The ANN utilizes these learned patterns for producing long-term predictions.

Flame Image Processing and Artificial Intelligence as a Diagnostic Tool... 39 Flame Image Processing and Artificial Intelligence as a Diagnostic Tool... 39

Figure 5 Figure 5 Deep ANN-based prediction of output water temperatures Deep ANN-based prediction of output water temperatures

SUMMARY SUMMARY The main objective of this work is to minimize emission levels and optimize thermal The main objective of this work is to minimize emission levels and optimize thermal efficiency of a 3 MW nominal capacity, step-grate fired biomass boiler without an on-line efficiency of a 3 MW nominal capacity, step-grate fired biomass boiler without an on-line fuel analysis system by applying novel combustion process control based on routinely fuel analysis system by applying novel combustion process control based on routinely measured operating parameters and real-time flame image processing and machine learning. measured operating parameters and real-time flame image processing and machine learning. Two important tasks of image based combustion monitoring systems are providing alerts and Two important tasks of image based combustion monitoring systems are providing alerts and predictions regarding the state of the system. The system issues alerts based on the location predictions regarding the state of the system. The system issues alerts based on the location of the reaction zone and predicts boiler performance based on image and operating data. of the reaction zone and predicts boiler performance based on image and operating data. Using image processing of the acquired flame images, the edge of the reaction zone inside Using image processing of the acquired flame images, the edge of the reaction zone inside the boiler can be monitored. The accuracy of the system was demonstrated. We showed that the boiler can be monitored. The accuracy of the system was demonstrated. We showed that there is strong correlation between the location of the reaction zone and emission and there is strong correlation between the location of the reaction zone and emission and operating parameters. Using image data and a trained deep neural network, the results operating parameters. Using image data and a trained deep neural network, the results indicate that the proposed learning scheme can reliably predict output water temperatures indicate that the proposed learning scheme can reliably predict output water temperatures with errors +/–1%, up to roughly 30 minutes ahead of the current time. The error depends on with errors +/–1%, up to roughly 30 minutes ahead of the current time. The error depends on the time-ahead of the predictions. Without including image data, the errors were around +/–5%. the time-ahead of the predictions. Without including image data, the errors were around +/–5%. To the authors’ knowledge, neither reaction zone monitoring, nor neural network prediction To the authors’ knowledge, neither reaction zone monitoring, nor neural network prediction methods were applied to optimize step-grate combustion, thus the custom algorithms are all methods were applied to optimize step-grate combustion, thus the custom algorithms are all part of the novelty of the work. part of the novelty of the work.

ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS The described study was supported by the UNKP-17-3 New National Excellence Program of the The described study was supported by the UNKP-17-3 New National Excellence Program of the Ministry of Human Capacities and carried out as part of the EFOP-3.6.1-16-00011 “Younger and Ministry of Human Capacities and carried out as part of the EFOP-3.6.1-16-00011 “Younger and Renewing University – Innovative Knowledge City – institutional development of the University of Renewing University – Innovative Knowledge City – institutional development of the University of 40 Attila Garami–Pál Tóth 40 Attila Garami–Pál Tóth

Miskolc aiming at intelligent specialisation” project implemented in the framework of the Szechenyi Miskolc aiming at intelligent specialisation” project implemented in the framework of the Szechenyi 2020 program. The realization of this project is supported by the European Union, co-financed by the 2020 program. The realization of this project is supported by the European Union, co-financed by the European Social Fund. European Social Fund.

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Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 42–53. Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 42–53.

CURRENT RESEARCH TRENDS IN FOAMED CONSTRUCTION AND CURRENT RESEARCH TRENDS IN FOAMED CONSTRUCTION AND BUILDING MATERIALS: A REVIEW BUILDING MATERIALS: A REVIEW

RÓBERT GÉBER1–ISTVÁN KOCSERHA2 RÓBERT GÉBER1–ISTVÁN KOCSERHA2

Concrete is the most widely used building material in the world today. Thanks to its excellent Concrete is the most widely used building material in the world today. Thanks to its excellent properties (mechanical strength, workability, durability) and long service life it can be used properties (mechanical strength, workability, durability) and long service life it can be used as a building material in various forms (for example as frame structure, wall unit, beams, as a building material in various forms (for example as frame structure, wall unit, beams, blocks). Special foaming techniques and curing methods can be used to produce low density blocks). Special foaming techniques and curing methods can be used to produce low density lightweight concretes, and excellent thermal insulating materials, as well. lightweight concretes, and excellent thermal insulating materials, as well. At the same time for the production of cement, which is the binder material of concrete, At the same time for the production of cement, which is the binder material of concrete, not only a large quantity of mineral deposit, but high energy consumption is needed. The not only a large quantity of mineral deposit, but high energy consumption is needed. The quantity of raw materials available is limited and the production of cement evolves significant quantity of raw materials available is limited and the production of cement evolves significant amount of CO2 which contributes to the greenhouse effect. Therefore, researches are undergo amount of CO2 which contributes to the greenhouse effect. Therefore, researches are undergo to develop materials and technologies that offer solutions to reduce raw material consumption to develop materials and technologies that offer solutions to reduce raw material consumption and energy consumption, and to increase the use of secondary raw materials and different and energy consumption, and to increase the use of secondary raw materials and different waste materials. One possible application area could be geopolymers, which can be produced waste materials. One possible application area could be geopolymers, which can be produced mainly from secondary raw materials. mainly from secondary raw materials. The aim of this paper is to review the research trend of foamed construction and building The aim of this paper is to review the research trend of foamed construction and building materials and materials systems used today with autoclaving technology. This paper also materials and materials systems used today with autoclaving technology. This paper also contributes to the research work of foamed thermal insulating materials which is currently contributes to the research work of foamed thermal insulating materials which is currently undergo with the co-operation of Institute of Ceramics and Polymer Engineering and Institute undergo with the co-operation of Institute of Ceramics and Polymer Engineering and Institute of Raw Material Preparation and Environmental Processing at the University of Miskolc. of Raw Material Preparation and Environmental Processing at the University of Miskolc. Keywords: autoclave, construction material, concrete, geopolymer, geopolymer foam Keywords: autoclave, construction material, concrete, geopolymer, geopolymer foam

1. INTRODUCTION 1. INTRODUCTION 1.1. The most common building material: concrete 1.1. The most common building material: concrete Concrete is the largest quantity of building material produced in the world. Cement is the Concrete is the largest quantity of building material produced in the world. Cement is the binder material of concrete, the largest producing countries are China, India, the USA, binder material of concrete, the largest producing countries are China, India, the USA, Vietnam, Turkey, respectively. China is responsible for more than half of the world cement Vietnam, Turkey, respectively. China is responsible for more than half of the world cement production [1]. However, the quantity of raw materials, which are needed to produce cement, production [1]. However, the quantity of raw materials, which are needed to produce cement, is limited. According to the report Cement production in vertical shaft kilns in China – Status is limited. According to the report Cement production in vertical shaft kilns in China – Status and opportunities for improvement [2] the quantity of limestone available for the production and opportunities for improvement [2] the quantity of limestone available for the production exclusively of cement, taking into account the current growth in cement production, is exclusively of cement, taking into account the current growth in cement production, is sufficient for 59 years in China. However, there are some difficulties of cement production: sufficient for 59 years in China. However, there are some difficulties of cement production: • the quantity of raw minerals available (clay, sand, limestone) is limited; • the quantity of raw minerals available (clay, sand, limestone) is limited; • a significant amount of energy consumption is needed for the production of cement; • a significant amount of energy consumption is needed for the production of cement;

1 Institute of Ceramics and Polymer Engineering, University of Miskolc 1 Institute of Ceramics and Polymer Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 2 Institute of Ceramics and Polymer Engineering, University of Miskolc 2 Institute of Ceramics and Polymer Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected]

Current Research Trends in Foamed Construction and Building Materials… 43 Current Research Trends in Foamed Construction and Building Materials… 43

• during the production of cement evolves a large quantity of CO2 (about 8% of global • during the production of cement evolves a large quantity of CO2 (about 8% of global CO2 emissions). CO2 emissions).

The classification of concrete is possible on the basis of its physical and mechanical (e. g. bulk The classification of concrete is possible on the basis of its physical and mechanical (e. g. bulk density, consistency, compressive strength, environmental exposure) properties. According to density, consistency, compressive strength, environmental exposure) properties. According to its bulk density concrete can be classified as [3]: its bulk density concrete can be classified as [3]: • Lightweight concrete, LC: ρ = 800–2,000 kg/m3 • Lightweight concrete, LC: ρ = 800–2,000 kg/m3 • Concrete, C: ρ = 2,001–2,600 kg/m3 • Concrete, C: ρ = 2,001–2,600 kg/m3 • Heavy concrete, HC: ρ > 2,600 kg/m3 • Heavy concrete, HC: ρ > 2,600 kg/m3 As this paper focuses only on concrete and other types of building materials produced by As this paper focuses only on concrete and other types of building materials produced by foaming technology, the Authors would like to focus on the construction of lightweight foaming technology, the Authors would like to focus on the construction of lightweight concrete and other foamed or aerated building materials in more detail. concrete and other foamed or aerated building materials in more detail. Table 1 contains the comparison of conventional concrete (C) and other artificial Table 1 contains the comparison of conventional concrete (C) and other artificial construction materials [aerated concrete (AC), autoclaved aerated concrete (AAC), construction materials [aerated concrete (AC), autoclaved aerated concrete (AAC), geopolymers and geopolymer foams] on the basis of raw materials, manufacturing geopolymers and geopolymer foams] on the basis of raw materials, manufacturing technology, curing conditions and application areas. technology, curing conditions and application areas.

Table 1 Table 1 Comparison of ordinary and artificial construction materials and their foams Comparison of ordinary and artificial construction materials and their foams

Construction Manufacturing Curing Application Construction Manufacturing Curing Application Raw materials Raw materials material technology conditions areas material technology conditions areas in water or in in water or in water, cement, sand, casting, moulding, buildings, water, cement, sand, casting, moulding, buildings, Concrete steam; curing Concrete steam; curing aggregates pumping roads aggregates pumping roads time: 28 days time: 28 days thermal thermal water, cement/lime, mechanical foaming: water, cement/lime, mechanical foaming: insulation insulation foaming agent (Al • in-mixed foaming foaming agent (Al • in-mixed foaming material, material, powder, H2O2, calcium pre-foamed method; powder, H2O2, calcium pre-foamed method; • in ambient filling voids, • in ambient filling voids, Aerated carbide liberate chemical foaming: Aerated carbide liberate chemical foaming: conditions, ground conditions, ground Concrete, hydrogen, • air-entraining Concrete, hydrogen, • air-entraining stabilization, stabilization, AC oxygen and acetylene, method (gas • in steam at AC oxygen and acetylene, method (gas • in steam at 70 °C buildings, 70 °C buildings, synthetic foam, concrete); synthetic foam, concrete); shock- shock- enzyme-based foaming enzyme-based foaming • casting into mould, absorbing • casting into mould, absorbing agent) agent) • pumping buildings • pumping buildings insulation insulation in autoclave under in autoclave under Autoclaved Water, cement, lime, material, Autoclaved Water, cement, lime, material, high temperature high temperature aerated sand/fly ash type F, building aerated sand/fly ash type F, building casting into mould (~T = 190 °C) and casting into mould (~T = 190 °C) and concrete, foaming agent (Al block, concrete, foaming agent (Al block, pressure pressure AAC powder or paste) building AAC powder or paste) building (0.8–1.2 MPa) (0.8–1.2 MPa) beam beam Aluminosilicate building Aluminosilicate building minerals blocks, minerals blocks, (metakaolinite/fly ash, insulation (metakaolinite/fly ash, insulation granulated blast in air, T = 25 °C– materials, granulated blast in air, T = 25 °C– materials, casting into mould, casting into mould, Geopolymer furnace slag, waste 95 °C, curing time geopolymer Geopolymer furnace slag, waste 95 °C, curing time geopolymer vibration vibration glass, red mud, max.: 7 days cement, glass, red mud, max.: 7 days cement, construction and tiles, fire- construction and tiles, fire- demolition waste), proof demolition waste), proof alkaline activator coatings alkaline activator coatings 44 Róbert Géber–István Kocserha 44 Róbert Géber–István Kocserha

Construction Manufacturing Curing Application Construction Manufacturing Curing Application Raw materials Raw materials material technology conditions areas material technology conditions areas Aluminosilicate Aluminosilicate minerals • high temperature minerals • high temperature (metakaolinite/fly ash, processing; (metakaolinite/fly ash, processing; granulated blast • low temperature in air, T = 20 °C– granulated blast • low temperature in air, T = 20 °C– furnace slag, waste mixing method; 150 °C; furnace slag, waste mixing method; 150 °C; insulation insulation Geopolymer glass, red mud, • chemical foaming high pressure, Geopolymer glass, red mud, • chemical foaming high pressure, materials, materials, foam construction and technique; high vacuum; foam construction and technique; high vacuum; tiles, bricks tiles, bricks demolition waste), • silica fume in situ curing time max.: demolition waste), • silica fume in situ curing time max.: alkaline activator, foaming technique; 7 days alkaline activator, foaming technique; 7 days foaming agent (Al • mechanical pre- foaming agent (Al • mechanical pre- powder; diluted foaming technique powder; diluted foaming technique surfactant solution) surfactant solution)

1.2. Lightweight concretes 1.2. Lightweight concretes Lightweight concretes can be classified according to several criteria. The most commonly Lightweight concretes can be classified according to several criteria. The most commonly used method is the classification of concrete according to its raw materials and manufacturing used method is the classification of concrete according to its raw materials and manufacturing technology. Thus, we differentiate [4], [5]: technology. Thus, we differentiate [4], [5]: • lightweight aggregate concrete (LAC); • lightweight aggregate concrete (LAC); • cellular lightweight concrete (CLC); • cellular lightweight concrete (CLC); • no-fines concrete. • no-fines concrete. Cellular Lightweight Concrete (also known as aerated, foamed or gas concrete) is a Cellular Lightweight Concrete (also known as aerated, foamed or gas concrete) is a lightweight concrete which, according to its manufacturing technology, is classified into two lightweight concrete which, according to its manufacturing technology, is classified into two groups: 1. foamed concrete, or non-autoclaved aerated concrete (NAAC) and 2. autoclaved groups: 1. foamed concrete, or non-autoclaved aerated concrete (NAAC) and 2. autoclaved aerated concrete (AAC) [5]. aerated concrete (AAC) [5]. NAAC: this type of lightweight concrete (cement paste or mortar) produced by the use NAAC: this type of lightweight concrete (cement paste or mortar) produced by the use of organic, or synthetic foams or protein-based foams. Depending on the quantity of foam of organic, or synthetic foams or protein-based foams. Depending on the quantity of foam used, bulk density of the foam concrete may vary between wide limits (between 500 and used, bulk density of the foam concrete may vary between wide limits (between 500 and 1,600 kg/m3) [6], [7]. Two different method is known for producing NAAC: 1,600 kg/m3) [6], [7]. Two different method is known for producing NAAC: • In-mixed foaming: the foaming agent is mixed in the mixer by adjusting high rotation • In-mixed foaming: the foaming agent is mixed in the mixer by adjusting high rotation to generate air bubbles. All of the raw materials are added to this prepared foam, then to generate air bubbles. All of the raw materials are added to this prepared foam, then mixing is continued. This method, thanks to its simple implementation, is widely used mixing is continued. This method, thanks to its simple implementation, is widely used [8]. The disadvantage of this method is that, there are a lot of fractured pores within [8]. The disadvantage of this method is that, there are a lot of fractured pores within the foam concrete, therefore it cannot be prepare a homogenous foam structure. the foam concrete, therefore it cannot be prepare a homogenous foam structure. • Pre-foamed: during the method a water-soluble foam material is produced by • Pre-foamed: during the method a water-soluble foam material is produced by compressed air and the foam is added to the concrete. This is a costly technique, than compressed air and the foam is added to the concrete. This is a costly technique, than the in-mixed foaming technique, but a more stable and homogenous foam structure can the in-mixed foaming technique, but a more stable and homogenous foam structure can be achieved [9]. be achieved [9]. AAC: manufactured by chemically expansion. For the production of AAC cement and AAC: manufactured by chemically expansion. For the production of AAC cement and lime are used as binders, high silica sources (mainly quartz sand or fly ash), water and pore- lime are used as binders, high silica sources (mainly quartz sand or fly ash), water and pore- forming agent (mainly aluminum powder or paste) are used, as well. In the aspect of the forming agent (mainly aluminum powder or paste) are used, as well. In the aspect of the quality of the AAC product, chemical composition, quantity and the particle size of raw quality of the AAC product, chemical composition, quantity and the particle size of raw materials are of particular importance. materials are of particular importance. During the production of AAC a dilute concrete slurry, which are made from the above During the production of AAC a dilute concrete slurry, which are made from the above mentioned raw materials, poured into a mould, after that the pore-forming agent (Al powder mentioned raw materials, poured into a mould, after that the pore-forming agent (Al powder or paste) is added to the slurry. At this time aluminum reacts with water and hydrated lime or paste) is added to the slurry. At this time aluminum reacts with water and hydrated lime (1) and due to the evolved hydrogen gas a specific foam structure is generated. (1) and due to the evolved hydrogen gas a specific foam structure is generated. Current Research Trends in Foamed Construction and Building Materials… 45 Current Research Trends in Foamed Construction and Building Materials… 45

2 Al + Ca(OH)2 + 6 H2O = Ca(Al(OH)4)2 + 3 H2 (1) 2 Al + Ca(OH)2 + 6 H2O = Ca(Al(OH)4)2 + 3 H2 (1) In order to achieve the proper strength of AAC it is also necessary to use autoclaving In order to achieve the proper strength of AAC it is also necessary to use autoclaving technology. After a pre-curing method AAC samples are placed in a pressure vessel (so-called technology. After a pre-curing method AAC samples are placed in a pressure vessel (so-called autoclave), where high temperature (T ≈ 190 °C) and high pressure (p ≈ 1.0–1.2 MPa) are used autoclave), where high temperature (T ≈ 190 °C) and high pressure (p ≈ 1.0–1.2 MPa) are used to cure the sample. Thanks to this curing method, crystals of tobermorite mineral, which give to cure the sample. Thanks to this curing method, crystals of tobermorite mineral, which give the required strength of AAC, are formed. AAC is environmentally friendly, acts as an inert the required strength of AAC, are formed. AAC is environmentally friendly, acts as an inert material, non-toxic and it does not contribute to the indoor air pollution syndrome [10]. material, non-toxic and it does not contribute to the indoor air pollution syndrome [10]. CLC have an edge on AAC, that it does not require autoclave curing, making it CLC have an edge on AAC, that it does not require autoclave curing, making it economically advantageous. However, according to Panesar [11] the properties and application economically advantageous. However, according to Panesar [11] the properties and application areas are highly effected on the type and manufacturing method of foam and its properties. areas are highly effected on the type and manufacturing method of foam and its properties.

1.3. Geopolymers, as alternatives to conventional concrete 1.3. Geopolymers, as alternatives to conventional concrete Geopolymers can be alternative materials for substituting conventional concrete [12], [13], Geopolymers can be alternative materials for substituting conventional concrete [12], [13], [14]. In fact, these materials are inorganic polymer-structured artificial binders. For the [14]. In fact, these materials are inorganic polymer-structured artificial binders. For the production of geopolymers aluminosilicate materials and alkali activator are required. production of geopolymers aluminosilicate materials and alkali activator are required. Mixing these raw materials and activators together, during an exothermic reaction “artificial Mixing these raw materials and activators together, during an exothermic reaction “artificial stone” is formed. Beside metakaolinite numerous industrial wastes, construction & stone” is formed. Beside metakaolinite numerous industrial wastes, construction & demolition wastes (e. g. cuttings, fly ash, blast furnace slag, brick powder) can be used [15], demolition wastes (e. g. cuttings, fly ash, blast furnace slag, brick powder) can be used [15], [16], [17], [18], [19], [20], [21]. Geopolymers are very popular materials today, because of [16], [17], [18], [19], [20], [21]. Geopolymers are very popular materials today, because of their excellent properties (fire and heat resistance, excellent mechanical strength, low their excellent properties (fire and heat resistance, excellent mechanical strength, low shrinkage, excellent immobilising capability of heavy metals). shrinkage, excellent immobilising capability of heavy metals). Similarly in concrete foaming technologies, these methods can also be used to produce Similarly in concrete foaming technologies, these methods can also be used to produce heat-insulating materials from geopolymers [15], [16], [17], [18], [19], [22], [23]. As it was heat-insulating materials from geopolymers [15], [16], [17], [18], [19], [22], [23]. As it was formerly mentioned, in the case of different types of concrete, the improvement of the formerly mentioned, in the case of different types of concrete, the improvement of the insulating capacity has been suggested to widen the scope of application of geopolymers. insulating capacity has been suggested to widen the scope of application of geopolymers. Table 2 summarizes some researches, which are carried out on the production of foamed Table 2 summarizes some researches, which are carried out on the production of foamed geopolymers. geopolymers.

Table 2 Table 2 Researches dealing with the foaming of geopolymers Researches dealing with the foaming of geopolymers

Ref. Material Raw materials Foaming agent Ref. Material Raw materials Foaming agent Geopolymer foam Metakaolinite, Geopolymer foam Metakaolinite, [15] Al paste [15] Al paste concrete, GFC Fly ash concrete, GFC Fly ash

Geopolymer foam, Metakaolinite, H2O2, olive oil, sunflower oil, Geopolymer foam, Metakaolinite, H2O2, olive oil, sunflower oil, [16] [16] GF potassium hydroxide canola oil as stabilizer GF potassium hydroxide canola oil as stabilizer

Diluted aqueous surface Diluted aqueous surface Fly ash (class F), granulated blast Fly ash (class F), granulated blast Geopolymer foam active concentrate; foaming Geopolymer foam active concentrate; foaming [17] furnace slag, sodium hydroxide, [17] furnace slag, sodium hydroxide, concrete, GFC with air pressure foam concrete, GFC with air pressure foam sodium silicate sodium silicate generator generator Geopolymer eco- ordinary portland cement (OPC), Commercial aluminium Geopolymer eco- ordinary portland cement (OPC), Commercial aluminium [18] cellular concrete fluid catalytic catalyst (FCC), powder, recycled aluminium [18] cellular concrete fluid catalytic catalyst (FCC), powder, recycled aluminium (GECC) sodium hydroxide, sodium silicate foil (GECC) sodium hydroxide, sodium silicate foil 46 Róbert Géber–István Kocserha 46 Róbert Géber–István Kocserha

Ref. Material Raw materials Foaming agent Ref. Material Raw materials Foaming agent Aerated Aerated metakaolinite-based metakaolinite, waterglass, sodium Al powder, incinerator bottom metakaolinite-based metakaolinite, waterglass, sodium Al powder, incinerator bottom [19] [19] geopolymers hydroxide ash (IBA) geopolymers hydroxide ash (IBA) (AMKG) (AMKG) incinerator bottom ash (IBA), incinerator bottom ash (IBA), IBA aerated IBA aerated [22] mixture of sodium hydroxide Incinerator bottom ash (IBA) [22] mixture of sodium hydroxide Incinerator bottom ash (IBA) geopolymer geopolymer solution and waterglass solution and waterglass

Alkali-activated fly Fly ash (class F), sodium Alkali-activated fly Fly ash (class F), sodium [23] Al powder [23] Al powder ash foam (FAF) hydroxide ash foam (FAF) hydroxide

Fly ash (class F), palm oil fuel ash Fly ash (class F), palm oil fuel ash Oil palm shell Sika AER-50/50 (blend of Oil palm shell Sika AER-50/50 (blend of (POFA), sodium hydroxide, (POFA), sodium hydroxide, [24] foamed geopolymer synthetic surfactants and [24] foamed geopolymer synthetic surfactants and polycarboxylate ether polycarboxylate ether concrete polymer) concrete polymer) (superplasticizer) (superplasticizer)

Geopolymer fly-ash Fly ash (class F), waterglass, Geopolymer fly-ash Fly ash (class F), waterglass, [25] Al powder and H2O2 [25] Al powder and H2O2 based foam sodium hydroxide based foam sodium hydroxide

As described in Table 2, beside the raw materials of traditional geopolymers (metakaolinite, As described in Table 2, beside the raw materials of traditional geopolymers (metakaolinite, fly ash), researches are focus on the utilization of other secondary raw materials, industrial fly ash), researches are focus on the utilization of other secondary raw materials, industrial wastes [incinerator bottom ash (IBA), ground granulated blast furnace slag (GBFS), wastes [incinerator bottom ash (IBA), ground granulated blast furnace slag (GBFS), recycled aluminum foil] as geopolymer raw materials, or as foaming agents (IBA, recycled recycled aluminum foil] as geopolymer raw materials, or as foaming agents (IBA, recycled aluminum foil or other commercial foaming agents). In the aforementioned researches, aluminum foil or other commercial foaming agents). In the aforementioned researches, autoclaving has not been used for curing foamed geopolymers. It should be noted that the autoclaving has not been used for curing foamed geopolymers. It should be noted that the designation of foamed geopolymers are not yet standardized, the names of the developed designation of foamed geopolymers are not yet standardized, the names of the developed materials are arbitrarily selected by researchers (e. g. GF, GFC, GECC, AMKG). materials are arbitrarily selected by researchers (e. g. GF, GFC, GECC, AMKG).

2. AUTOCLAVING OF BUILDING MATERIALS 2. AUTOCLAVING OF BUILDING MATERIALS 2.1. Autoclaved aerated concretes 2.1. Autoclaved aerated concretes Different industrial raw materials can be used for the production of aerated concrete with the Different industrial raw materials can be used for the production of aerated concrete with the use of autoclaving technology, through hydrothermal reactions. Autoclaving is a crucial use of autoclaving technology, through hydrothermal reactions. Autoclaving is a crucial technological step in the formation of crystalline tobermorite mineral, which responsible for technological step in the formation of crystalline tobermorite mineral, which responsible for the proper strength of AAC. the proper strength of AAC. According to Mostafa [26] the intensity of formation of tobermorite phase is not change According to Mostafa [26] the intensity of formation of tobermorite phase is not change after 2 hours of autoclave curing anymore. However, Kunchariyakun et al. [27] also after 2 hours of autoclave curing anymore. However, Kunchariyakun et al. [27] also demonstrated that increasing the curing time in autoclave from 8 hours to 18 hours does not demonstrated that increasing the curing time in autoclave from 8 hours to 18 hours does not increase the quantity of tobermorite phase. Thus, material structure and mechanical increase the quantity of tobermorite phase. Thus, material structure and mechanical properties of AAC are no longer improved after 8 hours of autoclave curing. properties of AAC are no longer improved after 8 hours of autoclave curing. Shrinkage of AAC is influenced both by curing method and curing time, autoclaving Shrinkage of AAC is influenced both by curing method and curing time, autoclaving pressure, the fineness and mineral composition of SiO2, the geometry and dimensions of pressure, the fineness and mineral composition of SiO2, the geometry and dimensions of prepared sample and storage time [26]. Researchers also found that the presence of Al3+ used prepared sample and storage time [26]. Researchers also found that the presence of Al3+ used to foam AAC accelerates the formation of tobermorite crystals, and a lower curing to foam AAC accelerates the formation of tobermorite crystals, and a lower curing temperature and a shorter curing time are sufficient to produce the corresponding crystal temperature and a shorter curing time are sufficient to produce the corresponding crystal structure. structure. Current Research Trends in Foamed Construction and Building Materials… 47 Current Research Trends in Foamed Construction and Building Materials… 47

Table 3 Table 3 Raw materials and autoclave conditions of some AACs Raw materials and autoclave conditions of some AACs

Autoclave conditions Autoclave conditions Ref. Used materials Other curing method Temperature Pressure Curing Ref. Used materials Other curing method Temperature Pressure Curing [°C] [MPa] time [h] [°C] [MPa] time [h] S, L, OPC, W, after autoclaving: S, L, OPC, W, after autoclaving: [26] air-cooled slag, T = 50 °C for 24 183 1 2, 6, 12, 24 [26] air-cooled slag, T = 50 °C for 24 183 1 2, 6, 12, 24 Al powder hours Al powder hours (a) 0.115, (a) 0.115, FA (class F), after casting: FA (class F), after casting: 0.4, 0.8 (a) 8 and 0.4, 0.8 (a) 8 and [29] SF, OPC, G, L, T = 60–70 °C no data [29] SF, OPC, G, L, T = 60–70 °C no data and (b) (b) 12 and (b) (b) 12 W, Al powder for 1 hour W, Al powder for 1 hour 1.15 1.15 after autoclaving: after autoclaving: immersing the immersing the OPC, L, RS, FA OPC, L, RS, FA specimens in water for specimens in water for [30] (class F), Al no data 0.98 10 [30] (class F), Al no data 0.98 10 72 hours then 72 hours then powder powder T = 30 °C and relative T = 30 °C and relative humidity set to 45% humidity set to 45% FA (high FA (high calcium high calcium high after casting: after casting: [31] sulfate), L, no data no data 10 [31] sulfate), L, no data no data 10 T = 40 °C for 4 hours T = 40 °C for 4 hours OPC, G, W, Al OPC, G, W, Al paste, modifier paste, modifier CT, BFS, QS, CT, BFS, QS, cement clinker, cement clinker, after casting: after casting: G, W, Al G, W, Al [32] T = 48 °C for 12 no data 1.35 8 [32] T = 48 °C for 12 no data 1.35 8 powder, powder, hours in steam hours in steam naphtalene as naphtalene as superplasticizer superplasticizer after after OPC, RS, BA, OPC, RS, BA, autoclaving:specimen autoclaving:specimen [33] W, Al powder, 126 0.14 6 [33] W, Al powder, 126 0.14 6 s were cured in air s were cured in air Ca(OH)2 Ca(OH)2 until 7 days until 7 days

cement, carbide cement, carbide slag, RS, W, Al after casting: slag, RS, W, Al after casting: paste, T = 50 °C for 4 hours; paste, T = 50 °C for 4 hours; [34] naphthalene- after autoclaving: 145–220 no data 8–18 [34] naphthalene- after autoclaving: 145–220 no data 8–18 high efficiency T = 105 °C high efficiency T = 105 °C water reducing for 2 hours water reducing for 2 hours agent agent

GBFS; OPC, GBFS; OPC, [35] waterglass none 100, 200, 300 no data 24 [35] waterglass none 100, 200, 300 no data 24 activator, W activator, W 48 Róbert Géber–István Kocserha 48 Róbert Géber–István Kocserha

Autoclave conditions Autoclave conditions Ref. Used materials Other curing method Temperature Pressure Curing Ref. Used materials Other curing method Temperature Pressure Curing [°C] [MPa] time [h] [°C] [MPa] time [h] GBFS (alkali- GBFS (alkali- activated), 0.5; 1; 4; 6; activated), 0.5; 1; 4; 6; [36] none 170 0.8 [36] none 170 0.8 waterglass, QP, 10 waterglass, QP, 10 W W OPC, L, QS, G, OPC, L, QS, G, W, water after autoclaving: W, water after autoclaving: hyacinth fiber, T = 75 °C for 24 hyacinth fiber, T = 75 °C for 24 [37] 180–190 1.0–1.2 8 [37] 180–190 1.0–1.2 8 polypropylene hours (drying the polypropylene hours (drying the fiber, Al specimens) fiber, Al specimens) powder powder after casting: after casting: T = 40 °C for 3 T = 40 °C for 3 OPC, QL, S, OPC, QL, S, hours; after hours; after [38] rice husk ash, 180 no data 8; 18 [38] rice husk ash, 180 no data 8; 18 autoclaving: autoclaving: W, Al powder W, Al powder T = 40 °C for 24 T = 40 °C for 24 hours hours

FA, G, OPC, L, FA, G, OPC, L, After casting: After casting: W, Al powder, W, Al powder, [39] T = 50 °C in steam for 180 1 12 [39] T = 50 °C in steam for 180 1 12 polycarboxylic polycarboxylic 3 hours 3 hours admixture admixture

OPC, clayish OPC, clayish [40] crushed stone, none 180 1.0 12 [40] crushed stone, none 180 1.0 12 W, Al powder W, Al powder

1.5 + 1.5 + 1.5 + 1.5 + 6 + 1.5 h 6 + 1.5 h (preliminar (preliminar y heating, y heating, OPC, SL, ash- vacuuming OPC, SL, ash- vacuuming [41] slag mixture, none 185 1.2 + rise of [41] slag mixture, none 185 1.2 + rise of W, Al powder temperature W, Al powder temperature + + isothermal isothermal holding + holding + cooling) cooling)

[42] no data none 180–190 1.0–1.2 8 [42] no data none 180–190 1.0–1.2 8

CBP, OPC, S, After casting: CBP, OPC, S, After casting: [43] 180–200 1.2 18 [43] 180–200 1.2 18 L, Al powder T = 40 °C for 3 hours L, Al powder T = 40 °C for 3 hours Current Research Trends in Foamed Construction and Building Materials… 49 Current Research Trends in Foamed Construction and Building Materials… 49

Autoclave conditions Autoclave conditions Ref. Used materials Other curing method Temperature Pressure Curing Ref. Used materials Other curing method Temperature Pressure Curing [°C] [MPa] time [h] [°C] [MPa] time [h] OPC, BL, S, G, OPC, BL, S, G, waste glass waste glass (CRT cullet, after casting: (CRT cullet, after casting: [44] 190 1.2 6 [44] 190 1.2 6 glass cullet, T = 60 °C for 5 hours glass cullet, T = 60 °C for 5 hours calsiglass), W, calsiglass), W, Al powder Al powder

Z, OPC, L, QS, Z, OPC, L, QS, [45] none 200 1.15 12 [45] none 200 1.15 12 W, Al powder W, Al powder

Abbreviations: FA: fly ash; SF: silica fume, OPC: ordinary portland cement; G: gypsum; W: water, L: Abbreviations: FA: fly ash; SF: silica fume, OPC: ordinary portland cement; G: gypsum; W: water, L: lime; RS: river sand; CT: copper tailings; BFS: blast furnace slag; QS: quartz sand; QP: quartz lime; RS: river sand; CT: copper tailings; BFS: blast furnace slag; QS: quartz sand; QP: quartz powder; BA: bottom ash; GBFS: ground granulated blast furnace slag; QL: quick lime; S: sand, SL: powder; BA: bottom ash; GBFS: ground granulated blast furnace slag; QL: quick lime; S: sand, SL: slaked lime; CBP: clay brick powder; BL: burnt lime; Z: zeolite slaked lime; CBP: clay brick powder; BL: burnt lime; Z: zeolite

2.2. Autoclaving of geopolymer foams 2.2. Autoclaving of geopolymer foams Till today, according to the references few researches are found in the relevant literature Till today, according to the references few researches are found in the relevant literature concerning the production of foamed geopolymer cured with autoclave. Table 4 summarize concerning the production of foamed geopolymer cured with autoclave. Table 4 summarize the curing methods, curing conditions and some results of autoclaved geopolymers. the curing methods, curing conditions and some results of autoclaved geopolymers.

Table 4 Table 4 Curing method, conditions and some results of autoclaved geopolymers Curing method, conditions and some results of autoclaved geopolymers

Ref. Curing method Curing conditions Result of curing Ref. Curing method Curing conditions Result of curing Climatic chamber or Climatic chamber or furnace or autoclave can be furnace or autoclave can be curing time of curing time of [46] used for harden the Tmin = 40 °C [46] used for harden the Tmin = 40 °C geopolymer is shorter geopolymer is shorter geopolymer at higher geopolymer at higher temperatures. temperatures. density of geopolymer density of geopolymer T = 80 °C–120 °C; p = 0.1 MPa; T = 80 °C–120 °C; p = 0.1 MPa; [47] Autoclave curing can be achieve: [47] Autoclave curing can be achieve: curing time: 4–48 hours curing time: 4–48 hours 1,000–1,700 kg/m3 1,000–1,700 kg/m3 T = 150 °C; p = 2 MPa; compressive strength T = 150 °C; p = 2 MPa; compressive strength [48] Autoclave curing [48] Autoclave curing curing time: 3 hours was increased curing time: 3 hours was increased increase in compressive increase in compressive Heating chamber or hot air T = 80 °C; p = 2.05 MPa; Heating chamber or hot air T = 80 °C; p = 2.05 MPa; [49] strength; decrease in [49] strength; decrease in oven or autoclave curing time: 1–24 hours oven or autoclave curing time: 1–24 hours thermal conductivity thermal conductivity increase in compressive increase in compressive [50] Autoclave curing T = 150 °C; curing time: 2 hours [50] Autoclave curing T = 150 °C; curing time: 2 hours strength strength

Keulen and Kakebeeke [46] patented a preparation method that suitable for producing Keulen and Kakebeeke [46] patented a preparation method that suitable for producing geopolymers with the use of sugar and/or organic acids (curing time = 24 hours, curing geopolymers with the use of sugar and/or organic acids (curing time = 24 hours, curing temperature: minimum 40 °C). As the curing temperature increases, hardening of geopolymers temperature: minimum 40 °C). As the curing temperature increases, hardening of geopolymers can be reduced and, according to their opinion, this can be achieved by using an oven, a climate can be reduced and, according to their opinion, this can be achieved by using an oven, a climate chamber or an autoclave. chamber or an autoclave. 50 Róbert Géber–István Kocserha 50 Róbert Géber–István Kocserha

Hao and Qin [47] patented the preparation method of geopolymer-based fiberboard. As Hao and Qin [47] patented the preparation method of geopolymer-based fiberboard. As raw material red mud was used. According to their method geopolymer paste is placed into raw material red mud was used. According to their method geopolymer paste is placed into an autoclave using the following conditions: T = 80 °C–120 °C; p = 0.1 MPa; curing time: an autoclave using the following conditions: T = 80 °C–120 °C; p = 0.1 MPa; curing time: 4–48 hours. Using this method they achieved a final product of 1,700 kg/m3 of bulk density. 4–48 hours. Using this method they achieved a final product of 1,700 kg/m3 of bulk density. Bondar et al. [48] carried out tests on geopolymer cements, which were produced by Bondar et al. [48] carried out tests on geopolymer cements, which were produced by various mineral additives (kaolinite, hydrated lime, pozzolanic materials and andesite) as various mineral additives (kaolinite, hydrated lime, pozzolanic materials and andesite) as raw materials. Their results have shown that mineral additives improve the mechanical raw materials. Their results have shown that mineral additives improve the mechanical strength of geopolymers. It has also been observed that autoclave curing has also resulted in strength of geopolymers. It has also been observed that autoclave curing has also resulted in an increase in the compressive strength values (45.6 MPa). an increase in the compressive strength values (45.6 MPa). Narayanan and Shanmugasundaram [49] investigated thermal (heat resistance and Narayanan and Shanmugasundaram [49] investigated thermal (heat resistance and thermal conductivity) and mechanical properties of fly ash-based geopolymer mortars. Fly thermal conductivity) and mechanical properties of fly ash-based geopolymer mortars. Fly ash (class F), river sand as raw materials, sodium hydroxide and sodium silicate as alkali ash (class F), river sand as raw materials, sodium hydroxide and sodium silicate as alkali activators were used. Different curing methods and curing conditions were used during the activators were used. Different curing methods and curing conditions were used during the research. The effect of curing time (1 h–24 h) was also investigated. research. The effect of curing time (1 h–24 h) was also investigated. • ambient curing, • ambient curing, • heating chamber, 1,200 W; T = 80 °C; • heating chamber, 1,200 W; T = 80 °C; • hot air oven, 1,000 W; T = 80 °C; • hot air oven, 1,000 W; T = 80 °C; • autoclave: p = 2.05 MPa; T = 80 °C; • autoclave: p = 2.05 MPa; T = 80 °C;

According to the tests among all curing conditions, hot air oven curing shows the best result According to the tests among all curing conditions, hot air oven curing shows the best result (T = 80 °C; curing time: 6 hours). In this case compressive strength of the geopolymer was (T = 80 °C; curing time: 6 hours). In this case compressive strength of the geopolymer was increased by 36 percent and coefficient of thermal conductivity was decreased by 6.34 increased by 36 percent and coefficient of thermal conductivity was decreased by 6.34 percent. percent. Yunsheng et al. [50] prepared slag based geopolymers using metakaolinite precursor. Yunsheng et al. [50] prepared slag based geopolymers using metakaolinite precursor. Their aims were the improvement of mechanical strength and to study the immobilization Their aims were the improvement of mechanical strength and to study the immobilization behaviour of heavy metals (mainly Pb and and Cu). Geopolymer mixtures were prepared behaviour of heavy metals (mainly Pb and and Cu). Geopolymer mixtures were prepared with 4 different slag contents (10%, 30%, 50%, 70% by weight) and 3 different curing with 4 different slag contents (10%, 30%, 50%, 70% by weight) and 3 different curing methods (conventional curing, curing in steam, autoclave curing) were also applied. methods (conventional curing, curing in steam, autoclave curing) were also applied. During the study of the effects of curing methods and curing time it was found that During the study of the effects of curing methods and curing time it was found that autoclave curing is the most effective method to increase the mechanical strength autoclave curing is the most effective method to increase the mechanical strength (compressive and flexural strengths reach 70 MPa and 8.82 MPa, respectively) of slag-based (compressive and flexural strengths reach 70 MPa and 8.82 MPa, respectively) of slag-based geopolymers. geopolymers.

CONCLUSIONS CONCLUSIONS As this review attempted to present, the development of conventional and artificial materials As this review attempted to present, the development of conventional and artificial materials produced by foaming technology is continuous. Researchers try to develop more and more produced by foaming technology is continuous. Researchers try to develop more and more foamed materials, mainly with the use of secondary raw materials and other waste materials, foamed materials, mainly with the use of secondary raw materials and other waste materials, with better properties and performance. Therefore, both raw materials and foaming with better properties and performance. Therefore, both raw materials and foaming technologies are required to develop. technologies are required to develop.

ACKNOWLEDGEMENT ACKNOWLEDGEMENT The described article was carried out as part of the Sustainable Raw Material Management Thematic The described article was carried out as part of the Sustainable Raw Material Management Thematic Network – RING 2017, EFOP-3.6.2-16-2017-00010 project in the framework of the Széchenyi2020 Network – RING 2017, EFOP-3.6.2-16-2017-00010 project in the framework of the Széchenyi2020 Program. The realization of this project is supported by the European Union, co-financed by the Program. The realization of this project is supported by the European Union, co-financed by the European Social Fund. European Social Fund.

Current Research Trends in Foamed Construction and Building Materials… 51 Current Research Trends in Foamed Construction and Building Materials… 51

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THE EFFECT OF INCLUSIONS ON THE TENSILE PROPERTIES THE EFFECT OF INCLUSIONS ON THE TENSILE PROPERTIES OF AlSi7Mg0.4Cu0.5 CASTING ALLOY OF AlSi7Mg0.4Cu0.5 CASTING ALLOY

GÁBOR GYARMATI1–MONIKA TOKÁR2–GYÖRGY FEGYVERNEKI3 GÁBOR GYARMATI1–MONIKA TOKÁR2–GYÖRGY FEGYVERNEKI3

In this study, the effects of different melt cleaning fluxes on the inclusion content and tensile properties In this study, the effects of different melt cleaning fluxes on the inclusion content and tensile properties of an aluminum casting alloy were compared. Melt treatments, consisting of rotary degassing with N2 of an aluminum casting alloy were compared. Melt treatments, consisting of rotary degassing with N2 gas, and flux addition were executed using four different fluxes. The inclusion content of the melts was gas, and flux addition were executed using four different fluxes. The inclusion content of the melts was investigated with the evaluation of K-mold samples. In order to get information about the impact of the investigated with the evaluation of K-mold samples. In order to get information about the impact of the differences of melt quality on the mechanical properties of final products, cylindrical tensile specimens differences of melt quality on the mechanical properties of final products, cylindrical tensile specimens were machined from heat treated castings and tensile tests were carried out. The fracture surfaces of were machined from heat treated castings and tensile tests were carried out. The fracture surfaces of tensile specimens and K-mold samples were inspected with stereomicroscope and scanning tensile specimens and K-mold samples were inspected with stereomicroscope and scanning electronmicroscope. electronmicroscope. Keywords: aluminum casting alloys, inclusions, rotary degassing, flux treatment, tensile properties Keywords: aluminum casting alloys, inclusions, rotary degassing, flux treatment, tensile properties

INTRODUCTION INTRODUCTION Inclusions are discontinuities of the material which are non-metallic or sometimes Inclusions are discontinuities of the material which are non-metallic or sometimes intermetallic phases embedded in a metallic matrix [1], [2]. Inclusions can occur in the form intermetallic phases embedded in a metallic matrix [1], [2]. Inclusions can occur in the form of solid particles, films or liquid droplets in the molten alloys [3]. The quantity and type of of solid particles, films or liquid droplets in the molten alloys [3]. The quantity and type of inclusions in the melt are determined by the quality of charge and alloying materials, as well inclusions in the melt are determined by the quality of charge and alloying materials, as well as the melting and melt handling processes. The most common inclusions in aluminum alloys as the melting and melt handling processes. The most common inclusions in aluminum alloys are non-metallic compounds: oxides, nitrides, carbides, and borides. Inclusions can be are non-metallic compounds: oxides, nitrides, carbides, and borides. Inclusions can be observed in the form of single particles, clusters and agglomerates [4]. observed in the form of single particles, clusters and agglomerates [4]. Inclusions reduce mechanical properties by detracting from the effective cross-sectional Inclusions reduce mechanical properties by detracting from the effective cross-sectional area when stress is applied and because of the concentration of stresses at the inclusion area when stress is applied and because of the concentration of stresses at the inclusion interface. Figure 1 shows an example of the property reduction effect of inclusions. interface. Figure 1 shows an example of the property reduction effect of inclusions.

Figure 1 Figure 1 The fracture surface of tensile specimens with different inclusion contents [7] The fracture surface of tensile specimens with different inclusion contents [7]

1 Foundry Institute, University of Miskolc 1 Foundry Institute, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 2 Foundry Institute, University of Miskolc 2 Foundry Institute, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 3 Foundry Institute, University of Miskolc 3 Foundry Institute, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] The Effect of Inclusions on the Tensile Properties of AlSi7Mg0.4Cu0.5 Casting Alloy 55 The Effect of Inclusions on the Tensile Properties of AlSi7Mg0.4Cu0.5 Casting Alloy 55

The three tensile specimens shown have different inclusion contents on the fracture The three tensile specimens shown have different inclusion contents on the fracture surface. It can also be observed that the larger the oxide films on the fracture surface are, the surface. It can also be observed that the larger the oxide films on the fracture surface are, the lower the tensile properties of the test bar become. Properties such as elongation, yield lower the tensile properties of the test bar become. Properties such as elongation, yield strength, and ultimate tensile strength decrease with the increased inclusion content in the strength, and ultimate tensile strength decrease with the increased inclusion content in the metallic matrix. Inclusions in the melt can negatively influence melt fluidity and can prevent metallic matrix. Inclusions in the melt can negatively influence melt fluidity and can prevent interdendritic feeding [5], [6]. interdendritic feeding [5], [6]. Flux treatment usually includes the addition of a solid blend of inorganic compounds to the Flux treatment usually includes the addition of a solid blend of inorganic compounds to the melt. These compounds may perform several functions, such as the removal of non-metallic melt. These compounds may perform several functions, such as the removal of non-metallic impurities from the melt, the protection of the melt surface, or the refinement, and/or impurities from the melt, the protection of the melt surface, or the refinement, and/or degassing of the molten alloy [8]. The effect of fluxes is determined by their chemical degassing of the molten alloy [8]. The effect of fluxes is determined by their chemical composition, morphology, added quantity, as well as the temperature of the melt, and the composition, morphology, added quantity, as well as the temperature of the melt, and the method of flux addition [9]. Modern melt treatment stations can automatically add flux blends method of flux addition [9]. Modern melt treatment stations can automatically add flux blends to the melt during the first stages of rotary degassing. During the first part of the treatment, to the melt during the first stages of rotary degassing. During the first part of the treatment, the rotor is lowered to the melt and a vortex is created around the shaft by the rotor, which is the rotor is lowered to the melt and a vortex is created around the shaft by the rotor, which is rotating at a higher speed during this stage of the cycle. At this part of the treatment, the rotating at a higher speed during this stage of the cycle. At this part of the treatment, the baffle plate remains in the upper position. Then, the hopper feed system adds the required baffle plate remains in the upper position. Then, the hopper feed system adds the required amount of flux to the vortex. The flux is taken to the bottom of the melt by the vortex and amount of flux to the vortex. The flux is taken to the bottom of the melt by the vortex and effectively mixed throughout the melt by the rotor. After flux addition, the baffle plate is effectively mixed throughout the melt by the rotor. After flux addition, the baffle plate is lowered into the melt, and the rotor speed is decreased in order to terminate the vortex. lowered into the melt, and the rotor speed is decreased in order to terminate the vortex. Finally, a controlled degassing and floatation treatment takes place [10–12]. Finally, a controlled degassing and floatation treatment takes place [10–12].

1. EXPERIMENTAL 1. EXPERIMENTAL 1.1. Melt preparation 1.1. Melt preparation

Melt treatment, consisting of rotary degassing with N2 gas and flux addition, was executed Melt treatment, consisting of rotary degassing with N2 gas and flux addition, was executed on an AlSi7Mg0.4Cu0.5 alloy melt using four different fluxes (A, B, C, and D). Each flux on an AlSi7Mg0.4Cu0.5 alloy melt using four different fluxes (A, B, C, and D). Each flux was used in 8 treatment cycles. The quantity of metal treated in one cycle was approximately was used in 8 treatment cycles. The quantity of metal treated in one cycle was approximately 1 ton. The metal was melted in a stack smelter then transported by a transport ladle to a 1 ton. The metal was melted in a stack smelter then transported by a transport ladle to a resistance heated holding furnace where the melt treatments were performed (Figure 2). In resistance heated holding furnace where the melt treatments were performed (Figure 2). In each case, the melt was poured over a lesser quantity of melt (ca. 200 kg) which remained in each case, the melt was poured over a lesser quantity of melt (ca. 200 kg) which remained in the holding furnace from the previous cycle. The treatment parameters and the quantity of the holding furnace from the previous cycle. The treatment parameters and the quantity of flux added (400 g) were the same in each cycle. The N2 gas flow rate was 20 L/min; the rotor flux added (400 g) were the same in each cycle. The N2 gas flow rate was 20 L/min; the rotor revolution was 500 RPM during vortex formation and 250 RPM in the degassing phase. The revolution was 500 RPM during vortex formation and 250 RPM in the degassing phase. The treatment time was 10 minutes in each case. The molten metal temperature in the holding treatment time was 10 minutes in each case. The molten metal temperature in the holding furnace was maintained between 740 oC and 750 oC. furnace was maintained between 740 oC and 750 oC.

Figure 2 Figure 2 The stages of melt preparation: a) pouring from melting furnace, b) melt transport to The stages of melt preparation: a) pouring from melting furnace, b) melt transport to holding furnace, and c) melt processing holding furnace, and c) melt processing 56 Gábor Gyarmati–Monika Tokár–György Fegyverneki 56 Gábor Gyarmati–Monika Tokár–György Fegyverneki

1.2. Inclusion analysis 1.2. Inclusion analysis The inclusion content of the melts treated with different fluxes was investigated by the The inclusion content of the melts treated with different fluxes was investigated by the evaluation of K-mold samples, which were prepared in the gravity die illustrated in Figure evaluation of K-mold samples, which were prepared in the gravity die illustrated in Figure 3. The sample itself is a flat plate with four notches that act as fracture points. The fracture 3. The sample itself is a flat plate with four notches that act as fracture points. The fracture surface of the samples can be examined either by visual inspection or with microscope. Based surface of the samples can be examined either by visual inspection or with microscope. Based on the number of inclusions, a K-value can be determined which can be used for the on the number of inclusions, a K-value can be determined which can be used for the quantitative characterization of the melt purity: quantitative characterization of the melt purity: S S K = (1) K = (1) n n where K is the K-value, n is the number of examined samples, and S is the total number of where K is the K-value, n is the number of examined samples, and S is the total number of inclusions found in n pieces [6]. inclusions found in n pieces [6].

Figure 3 Figure 3 K-mold apparatus K-mold apparatus

During each melt preparation, K-mold samples were cast from the melt in the transport During each melt preparation, K-mold samples were cast from the melt in the transport ladle, and from the melt in the holding furnace before and after the melt treatments. Five ladle, and from the melt in the holding furnace before and after the melt treatments. Five samples were cast at each stage. The fracture surfaces of K-mold samples were inspected samples were cast at each stage. The fracture surfaces of K-mold samples were inspected with a stereomicroscope at a magnification of 25×. The inclusions found on the fracture with a stereomicroscope at a magnification of 25×. The inclusions found on the fracture surfaces were examined with SEM combined with EDS analysis. surfaces were examined with SEM combined with EDS analysis. The effect of different fluxes on the melt purity was evaluated using the comparison of The effect of different fluxes on the melt purity was evaluated using the comparison of K-values determined before and after the melt treatments. The percentage of change in K- K-values determined before and after the melt treatments. The percentage of change in K- values (ΔK) was calculated using the following equation: values (ΔK) was calculated using the following equation: 퐾 −퐾 퐾 −퐾 ∆퐾 = 2 1 ∙ 100 [%] (2) ∆퐾 = 2 1 ∙ 100 [%] (2) 퐾1 퐾1 where K1 is the K-value determined before the melt treatment and K2 is the K-value where K1 is the K-value determined before the melt treatment and K2 is the K-value determined after the melt treatment. determined after the melt treatment.

1.3. Tensile testing 1.3. Tensile testing In order to study the effect of melt treatments on the tensile properties of castings, tensile tests In order to study the effect of melt treatments on the tensile properties of castings, tensile tests were executed on cylindrical specimens (with a diameter of 5 mm) machined from T5 heat were executed on cylindrical specimens (with a diameter of 5 mm) machined from T5 heat treated castings with a Zwick Z010 testing machine. Altogether, 12 castings were investigated treated castings with a Zwick Z010 testing machine. Altogether, 12 castings were investigated (3 casting/flux blend), the number of specimens machined from a casting was 3. The castings (3 casting/flux blend), the number of specimens machined from a casting was 3. The castings were made with Rotacast® technology. The inclusions found on the fracture surface of were made with Rotacast® technology. The inclusions found on the fracture surface of specimens were examined with stereomicroscope. The area fraction of the inclusions on the specimens were examined with stereomicroscope. The area fraction of the inclusions on the fracture surfaces was calculated by MATLAB® Image Processing ToolboxTM. fracture surfaces was calculated by MATLAB® Image Processing ToolboxTM. The Effect of Inclusions on the Tensile Properties of AlSi7Mg0.4Cu0.5 Casting Alloy 57 The Effect of Inclusions on the Tensile Properties of AlSi7Mg0.4Cu0.5 Casting Alloy 57

2. RESULTS AND DISCUSSION 2. RESULTS AND DISCUSSION The average K-values of the melts at the different stages of melt preparation can be observed The average K-values of the melts at the different stages of melt preparation can be observed in Figure 4. It can be seen that melts had different inclusion contents even in the transport in Figure 4. It can be seen that melts had different inclusion contents even in the transport ladle which was the result of the differences in the quality of charge materials. In each case, ladle which was the result of the differences in the quality of charge materials. In each case, the melt in the transport ladle was poured onto a small quantity of melt remaining in the the melt in the transport ladle was poured onto a small quantity of melt remaining in the holding furnace from the previous cycle. Thus, the inclusion content of the melt was holding furnace from the previous cycle. Thus, the inclusion content of the melt was influenced by the quality of the residual melt. This way, the applied flux blends had an influenced by the quality of the residual melt. This way, the applied flux blends had an indirect effect on the average K-values of the melts even before the treatments were executed. indirect effect on the average K-values of the melts even before the treatments were executed.

Figure 4 Figure 4 Average K-values at different stages of melt preparation Average K-values at different stages of melt preparation

The average ΔK values for each flux blends are illustrated in Figure 5. The treatments The average ΔK values for each flux blends are illustrated in Figure 5. The treatments executed with flux C were the most effective in reducing the K-values and flux B was the executed with flux C were the most effective in reducing the K-values and flux B was the second most efficient. Flux blend A had the poorest results. The melt treatments performed second most efficient. Flux blend A had the poorest results. The melt treatments performed with flux A resulted in the increased inclusion content of the melt, which caused a positive with flux A resulted in the increased inclusion content of the melt, which caused a positive change in the average K-value. change in the average K-value.

Figure 5 Figure 5 Average change in K-values (ΔK) Average change in K-values (ΔK) 58 Gábor Gyarmati–Monika Tokár–György Fegyverneki 58 Gábor Gyarmati–Monika Tokár–György Fegyverneki

Some examples of inclusions found during the examination of K-mold samples can be seen Some examples of inclusions found during the examination of K-mold samples can be seen in Figure 6. In most cases, creased film-like inclusions were found on the fracture surfaces. in Figure 6. In most cases, creased film-like inclusions were found on the fracture surfaces.

Figure 6 Figure 6 Inclusions found on fracture surfaces of K-mold samples Inclusions found on fracture surfaces of K-mold samples

The inclusions found on the fracture surfaces of K-mold samples were investigated with The inclusions found on the fracture surfaces of K-mold samples were investigated with SEM. The composition of inclusions was determined by EDS microanalysis. Figure 7 shows SEM. The composition of inclusions was determined by EDS microanalysis. Figure 7 shows some examples of the SEM images of the inclusions. Based on the EDS analysis, the some examples of the SEM images of the inclusions. Based on the EDS analysis, the inclusions found are nonmetallic compounds like Al2O3, AlN, MgO∙Al2O3 and various inclusions found are nonmetallic compounds like Al2O3, AlN, MgO∙Al2O3 and various strontium-oxides. strontium-oxides. Figure 8 summarizes the results of the tensile tests. There is no significant difference Figure 8 summarizes the results of the tensile tests. There is no significant difference between the ultimate tensile strength (UTS) and the yield strength (YS) results. Some between the ultimate tensile strength (UTS) and the yield strength (YS) results. Some differences can be observed between the elongation results, but there is no clear relationship differences can be observed between the elongation results, but there is no clear relationship between the determined K-values and the elongation values. It can be concluded that the between the determined K-values and the elongation values. It can be concluded that the effect of melt treatments with different fluxes on the tensile properties of castings cannot be effect of melt treatments with different fluxes on the tensile properties of castings cannot be determined from the tensile test results. The reason might be that the tensile test results of determined from the tensile test results. The reason might be that the tensile test results of species machined from heat treated castings depend not only on the inclusion content of the species machined from heat treated castings depend not only on the inclusion content of the melt but several other technological parameters as well, like casting technology and the melt but several other technological parameters as well, like casting technology and the parameters of the heat treating process. parameters of the heat treating process.

Figure 7 Figure 7 SEM images of inclusions: a) Al2O3 inclusion with numerous different strontium-oxide SEM images of inclusions: a) Al2O3 inclusion with numerous different strontium-oxide particles (white phases), b) MgO∙Al2O3 film with some strontium-oxide particles, c) creased particles (white phases), b) MgO∙Al2O3 film with some strontium-oxide particles, c) creased Al2O3 film Al2O3 film The Effect of Inclusions on the Tensile Properties of AlSi7Mg0.4Cu0.5 Casting Alloy 59 The Effect of Inclusions on the Tensile Properties of AlSi7Mg0.4Cu0.5 Casting Alloy 59

It can be seen in Figure 8 that there is a significant scatter in the elongation at the fracture It can be seen in Figure 8 that there is a significant scatter in the elongation at the fracture values of the samples, regardless of the type of flux blend used during the melt treatments. values of the samples, regardless of the type of flux blend used during the melt treatments. In order to explore the reason for the high standard deviation in elongation values, the fracture In order to explore the reason for the high standard deviation in elongation values, the fracture surfaces of tensile test specimens were examined with a stereomicroscope. It was found that surfaces of tensile test specimens were examined with a stereomicroscope. It was found that all tensile specimens with lower elongation value had inclusions on the fracture surfaces. all tensile specimens with lower elongation value had inclusions on the fracture surfaces. In order to investigate the relationship between the size of inclusions and the extent of In order to investigate the relationship between the size of inclusions and the extent of reduction in the elongation values, the area of inclusions was measured by quantitative image reduction in the elongation values, the area of inclusions was measured by quantitative image analysis. The area fraction of inclusions was determined by the following equation: analysis. The area fraction of inclusions was determined by the following equation:

Ai Ai Af = ∙ 100 [%] (3) Af = ∙ 100 [%] (3) Afs Afs where Af is the area fraction of inclusions, Ai is the total area of inclusions, and Afs is the area where Af is the area fraction of inclusions, Ai is the total area of inclusions, and Afs is the area of the fracture surface. of the fracture surface.

Figure 8 Figure 8 Tensile test results of specimens machined from castings Tensile test results of specimens machined from castings

Figure 9 shows the steps of the applied binary image making process. Figure 9 shows the steps of the applied binary image making process.

Figure 9 Figure 9 Production of binary image: a) original, b) segmented, and c) binary image Production of binary image: a) original, b) segmented, and c) binary image 60 Gábor Gyarmati–Monika Tokár–György Fegyverneki 60 Gábor Gyarmati–Monika Tokár–György Fegyverneki

The total number of specimens with inclusion on the fracture surface was 9. The average The total number of specimens with inclusion on the fracture surface was 9. The average elongation of samples with no inclusions was 11.74 ± 0.78%. The results of the image elongation of samples with no inclusions was 11.74 ± 0.78%. The results of the image analysis of specimens with inclusions are given in Table 1. Based on the results, an inclusion analysis of specimens with inclusions are given in Table 1. Based on the results, an inclusion contributing to 1% of the fracture area can cause the reduction of the elongation value by contributing to 1% of the fracture area can cause the reduction of the elongation value by 55% compared to the average elongation of samples with no inclusions. Figure 10 55% compared to the average elongation of samples with no inclusions. Figure 10 summarizes the results of tensile testing and image analysis. It can be seen, that the results of summarizes the results of tensile testing and image analysis. It can be seen, that the results of the specimens can be divided into three groups: specimens with Af > 1%, Af < 1%, and the specimens can be divided into three groups: specimens with Af > 1%, Af < 1%, and samples with no detected inclusions (Af = 0%). Where Af > 1%, the elongation values are samples with no detected inclusions (Af = 0%). Where Af > 1%, the elongation values are significantly lower compared to the cases when inclusions are not present. The inclusions significantly lower compared to the cases when inclusions are not present. The inclusions found on samples with Af < 1% are much smaller and the elongation values of these found on samples with Af < 1% are much smaller and the elongation values of these specimens are better. specimens are better.

Table 1 Table 1 Area fraction of inclusions (Af) and elongation values of specimens Area fraction of inclusions (Af) and elongation values of specimens Elongation [%] 5.236 5.894 8.537 5.603 5.234 8.670 9.310 9.230 8.426 Elongation [%] 5.236 5.894 8.537 5.603 5.234 8.670 9.310 9.230 8.426

Af [%] 2.262 1.121 1.913 2.021 1.043 0.224 0.544 0.193 0.180 Af [%] 2.262 1.121 1.913 2.021 1.043 0.224 0.544 0.193 0.180

Figure 10 Figure 10 Comparison of the area fraction of inclusions (Af) and tensile test results Comparison of the area fraction of inclusions (Af) and tensile test results

CONCLUSION CONCLUSION In this study, the effects of different melt cleaning fluxes on the inclusion content and tensile In this study, the effects of different melt cleaning fluxes on the inclusion content and tensile properties of an AlSi7Mg0.4Cu0.5 casting alloy were compared. properties of an AlSi7Mg0.4Cu0.5 casting alloy were compared. There was a significant difference between the melt cleaning efficiency of the applied There was a significant difference between the melt cleaning efficiency of the applied fluxes. The effect of melt treatments on the tensile properties of castings could not be fluxes. The effect of melt treatments on the tensile properties of castings could not be determined from the tensile test results because there were no significant differences between determined from the tensile test results because there were no significant differences between the results of samples made from melts treated with different fluxes. It was found that all the results of samples made from melts treated with different fluxes. It was found that all The Effect of Inclusions on the Tensile Properties of AlSi7Mg0.4Cu0.5 Casting Alloy 61 The Effect of Inclusions on the Tensile Properties of AlSi7Mg0.4Cu0.5 Casting Alloy 61 tensile specimens with lower elongation value had inclusions on their fracture surfaces. tensile specimens with lower elongation value had inclusions on their fracture surfaces. Based on the image analysis results, the size of inclusions is an important factor because an Based on the image analysis results, the size of inclusions is an important factor because an inclusion contributing to 1% of the fracture area can cause the reduction of an elongation inclusion contributing to 1% of the fracture area can cause the reduction of an elongation value by 55%, as compared to the average elongation of samples with no inclusions. value by 55%, as compared to the average elongation of samples with no inclusions. The results clearly indicate that the presence of inclusions (especially oxide-films) can The results clearly indicate that the presence of inclusions (especially oxide-films) can lead to a significant scatter in the elongation values of the cast alloy due to early initiation of lead to a significant scatter in the elongation values of the cast alloy due to early initiation of fracture. The removal of inclusions is essential in order to achieve more consistent fracture. The removal of inclusions is essential in order to achieve more consistent mechanical properties and to prevent unpredicted failure of cast components. mechanical properties and to prevent unpredicted failure of cast components.

ACKNOWLEDGMENT ACKNOWLEDGMENT The main author is thankful for the rest of the authors’ help, patience and advice to make the realization The main author is thankful for the rest of the authors’ help, patience and advice to make the realization of this article possible. of this article possible. The authors are grateful to Árpád Kovács from the Institute of Physical Metallurgy, Metal Forming and The authors are grateful to Árpád Kovács from the Institute of Physical Metallurgy, Metal Forming and Nanotechnology at the University of Miskolc for carrying out the tests with scanning electron microscope. Nanotechnology at the University of Miskolc for carrying out the tests with scanning electron microscope. Supported by the ÚNKP-18-2 New National Excellence Program of the Ministry of Human Capacities. Supported by the ÚNKP-18-2 New National Excellence Program of the Ministry of Human Capacities.

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NUMERICAL INVESTIGATION OF CLINCHED JOINTS NUMERICAL INVESTIGATION OF CLINCHED JOINTS

SZABOLCS JÓNÁS1–MIKLÓS TISZA2 SZABOLCS JÓNÁS1–MIKLÓS TISZA2

This paper studies the clinch joints. After the material testing and model validations the different This paper studies the clinch joints. After the material testing and model validations the different influencers were examined. The different types of hardening laws have a high effect on the undercut of influencers were examined. The different types of hardening laws have a high effect on the undercut of the joints, so should always be considered which is the appropriate for the task. The frictional condition the joints, so should always be considered which is the appropriate for the task. The frictional condition during forming processes is interesting topic and has a high impact on the results. The knowledge of during forming processes is interesting topic and has a high impact on the results. The knowledge of the effect of the geometrical variations is useful for designers, therefore it was studied. the effect of the geometrical variations is useful for designers, therefore it was studied. Keywords: clinch joint, simulation, FEA, DP600 steel Keywords: clinch joint, simulation, FEA, DP600 steel

INTRODUCTION INTRODUCTION Clinch joints are used mostly in automotive, computer and aircraft industries, but for instance Clinch joints are used mostly in automotive, computer and aircraft industries, but for instance according to the standards not allowed to use in food industry [3], [4], [5]. The clinch joints according to the standards not allowed to use in food industry [3], [4], [5]. The clinch joints are quite new types of joints; the first patent has been accepted in 1989. This joint can be are quite new types of joints; the first patent has been accepted in 1989. This joint can be done between 2-3 thin sheets. The cross section of a joint can be seen in Figure 1. This figure done between 2-3 thin sheets. The cross section of a joint can be seen in Figure 1. This figure shows the main geometrical parameters of a joint (2 sheets were joined). The undercut size shows the main geometrical parameters of a joint (2 sheets were joined). The undercut size (C value) and the size of the neck thickness (tN value) are highly affecting the strength of the (C value) and the size of the neck thickness (tN value) are highly affecting the strength of the joints. In optimal case both of them are as high as possible. joints. In optimal case both of them are as high as possible.

Figure 1 Figure 1 Cross section of a clinched joint and the main geometrical sizes Cross section of a clinched joint and the main geometrical sizes

1 Institute of Materials Science and Technology, Department of Mechanical Technology, University 1 Institute of Materials Science and Technology, Department of Mechanical Technology, University of Miskolc of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 2 Institute of Materials Science and Technology, Department of Mechanical Technology, University 2 Institute of Materials Science and Technology, Department of Mechanical Technology, University of Miskolc of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] Numerical Investigation of Clinched Joints 63 Numerical Investigation of Clinched Joints 63

The material of the sheets can be ferrous or non-ferrous at the same time, so there is a possibility The material of the sheets can be ferrous or non-ferrous at the same time, so there is a possibility to realize dissimilar joints without any added material (weld material or glue). The joint made to realize dissimilar joints without any added material (weld material or glue). The joint made by metal plastic forming by a special tool. After the patent the increasing industrial needs of by metal plastic forming by a special tool. After the patent the increasing industrial needs of clinching led the researchers to analyse the joint much more deeply. Several studies carried out clinching led the researchers to analyse the joint much more deeply. Several studies carried out the geometry optimization of the clinching tool to get better joints by different optimization the geometry optimization of the clinching tool to get better joints by different optimization methods [7], [8]. Other studies were carried out on the so-called hybrid joints. This variant has methods [7], [8]. Other studies were carried out on the so-called hybrid joints. This variant has an adhesive layer between the sheets. The hybrid joints have higher strength but need much an adhesive layer between the sheets. The hybrid joints have higher strength but need much more time because of the adhesive layer’s drying is a time-consuming process [1], [2]. more time because of the adhesive layer’s drying is a time-consuming process [1], [2]. In this study some influencers of the clinch joint were studied through a 2D axisymmetrical In this study some influencers of the clinch joint were studied through a 2D axisymmetrical FE model with an advanced high strength steel type (DP600). FE model with an advanced high strength steel type (DP600).

1. IDENTIFICATION OF THE MATERIAL 1. IDENTIFICATION OF THE MATERIAL For the simulations the used material type is the DP600 type of steel. The DP600 is an For the simulations the used material type is the DP600 type of steel. The DP600 is an advanced high strength steel, which is a multiphase (ferrite and martensite) steel with advanced high strength steel, which is a multiphase (ferrite and martensite) steel with excellent combination of strength and formability. The dual phase steels (DP) consist of a excellent combination of strength and formability. The dual phase steels (DP) consist of a soft ferrite matrix with disperse, hard second phase in a form of islands. It has got high soft ferrite matrix with disperse, hard second phase in a form of islands. It has got high strength, high work hardening rates and high strain energy absorption properties. strength, high work hardening rates and high strain energy absorption properties.

Figure 2 Figure 2 Microstructure of the DP600 (light: ferrite, grey: martensite) Microstructure of the DP600 (light: ferrite, grey: martensite)

Figure 2 shows the microstructure of the used steel. 100-200-600-1,200 μm series of grind Figure 2 shows the microstructure of the used steel. 100-200-600-1,200 μm series of grind paper, 3 μm polish pasta and 3% Nital was used for the specimen preparation. The paper, 3 μm polish pasta and 3% Nital was used for the specimen preparation. The measurements were done with a Carl Zeiss microscope with an image recognition software measurements were done with a Carl Zeiss microscope with an image recognition software module. According to the measurements, this steel contains ~23% of martensite, and the module. According to the measurements, this steel contains ~23% of martensite, and the average grain size is 5 μm. For the chemical composition a 60 μm grind paper was used. The average grain size is 5 μm. For the chemical composition a 60 μm grind paper was used. The measurements were performed with Oxford Instruments Foundry Master Pro spectroscopy measurements were performed with Oxford Instruments Foundry Master Pro spectroscopy machine. The chemical composition can be seen in Table 1. machine. The chemical composition can be seen in Table 1. Table 1 Table 1 Chemical composition Chemical composition Fe C Si Mn P S Cr Mo Fe C Si Mn P S Cr Mo wt% [%] 98.6 0.16 0.171 0.876 <0.005 <0.005 0.262 0.077 wt% [%] 98.6 0.16 0.171 0.876 <0.005 <0.005 0.262 0.077 Al Co Cu Nb Ti V W Pb Al Co Cu Nb Ti V W Pb wt% [%] 0.0553 0.0125 0.074 0.0214 <0.005 00124 0.0103 0.0114 wt% [%] 0.0553 0.0125 0.074 0.0214 <0.005 00124 0.0103 0.0114 64 Szabolcs Jónás–Miklós Tisza 64 Szabolcs Jónás–Miklós Tisza

To determine the mechanical properties tensile tests were performed with an MTS electro- To determine the mechanical properties tensile tests were performed with an MTS electro- hydraulic testing machine. The results can be seen in Table 2. The values show quite high hydraulic testing machine. The results can be seen in Table 2. The values show quite high difference between the orientations. difference between the orientations. Table 2 Table 2 Mechanical properties Mechanical properties

Mean value 0° 45° 90° Mean value 0° 45° 90°

2 2 Ultimate tensile strength Rm N/mm 680 669 679 691 Ultimate tensile strength Rm N/mm 680 669 679 691 2 2 Yield strength Rp0.2 N/mm 451 448 451 454 Yield strength Rp0.2 N/mm 451 448 451 454

Fracture elongation A80 % 19 19 20 18 Fracture elongation A80 % 19 19 20 18 Hardening exponent n – 0.14 0.14 0.14 0.14 Hardening exponent n – 0.14 0.14 0.14 0.14 Anisotropy r – 0.81 0.71 0.73 0.98 Anisotropy r – 0.81 0.71 0.73 0.98

2. CLINCHING PROCESS 2. CLINCHING PROCESS

The TOX produced clinching tool was set up in an MTS servo-hydraulic testing machine. The TOX produced clinching tool was set up in an MTS servo-hydraulic testing machine. The maximum load which the tool can survive is 50 kN. The set up can be seen in Figure 3. The maximum load which the tool can survive is 50 kN. The set up can be seen in Figure 3.

Figure 3 Figure 3 Clinching test set up Clinching test set up

During the forming process the force-displacement curves were recorded in each case. During the forming process the force-displacement curves were recorded in each case.

3. FE MODEL BUILDING 3. FE MODEL BUILDING The FE simulation model was built in ANSYS WB 18.2 [11]. The geometry of the model The FE simulation model was built in ANSYS WB 18.2 [11]. The geometry of the model was built up in ANSYS Design Modeler as a parametric model. A 2D axisymmetric model was built up in ANSYS Design Modeler as a parametric model. A 2D axisymmetric model is presented below (Figure 4). The tools were taken into consideration as linear-elastic is presented below (Figure 4). The tools were taken into consideration as linear-elastic materials, the two sheets were simulated with elastic-plastic behaviour with multilinear materials, the two sheets were simulated with elastic-plastic behaviour with multilinear isotropic hardening rule. The two sheets were 1-1 mm thick. The tool has a spring row which isotropic hardening rule. The two sheets were 1-1 mm thick. The tool has a spring row which was taken into consideration as an elastic body with 57 GPa of Young’s modulus. The mesh was taken into consideration as an elastic body with 57 GPa of Young’s modulus. The mesh Numerical Investigation of Clinched Joints 65 Numerical Investigation of Clinched Joints 65 was built up by 2nd order axisymmetrical quadrilateral and triangular elements (PLANE183). was built up by 2nd order axisymmetrical quadrilateral and triangular elements (PLANE183). Both of the sheets contain 10 elements in thickness which provides adequate results. For Both of the sheets contain 10 elements in thickness which provides adequate results. For better solution the edges in the contact zones were finer. The contact definition between the better solution the edges in the contact zones were finer. The contact definition between the parts is Augmented Lagrange formulation with a frictional coefficient of μ = 0.12 between parts is Augmented Lagrange formulation with a frictional coefficient of μ = 0.12 between the parts. Between the punching tool and the simplified spring row the contact definition was the parts. Between the punching tool and the simplified spring row the contact definition was bonded with MPC algorithm. There are 3 time steps in the simulation. The simulation is bonded with MPC algorithm. There are 3 time steps in the simulation. The simulation is performed as a displacement controlled model. According to the final, measured bottom performed as a displacement controlled model. According to the final, measured bottom thickness and the measured piston displacement, the vertical movement of the clinching tool thickness and the measured piston displacement, the vertical movement of the clinching tool was 3.25 mm. The holder was constrained in vertical direction by a compression only support was 3.25 mm. The holder was constrained in vertical direction by a compression only support and in the 1st step a force (F = 1000 N) was applied which is constant in the 2nd and 3rd steps. and in the 1st step a force (F = 1000 N) was applied which is constant in the 2nd and 3rd steps. In the 3rd step the tool was removed from the joint. In the 3rd step the tool was removed from the joint. The distribution of the equivalent plastic strain was checked with the unaveraged display The distribution of the equivalent plastic strain was checked with the unaveraged display option. The unaveraged distribution of the plastic strain can be seen in Figure 5. The high option. The unaveraged distribution of the plastic strain can be seen in Figure 5. The high (greater than 2 mm/mm) plastic strains are acceptable, according to the literature [10]. (greater than 2 mm/mm) plastic strains are acceptable, according to the literature [10].

Figure 4 Figure 5 Figure 4 Figure 5 FE mesh and boundary conditions Equivalent plastic strain distribution after FE mesh and boundary conditions Equivalent plastic strain distribution after of the model forming process (unaveraged) of the model forming process (unaveraged)

4. MODEL VALIDATION 4. MODEL VALIDATION In this study the formed geometry and the forming force – relative punch displacement (F-d) In this study the formed geometry and the forming force – relative punch displacement (F-d) curves were used to validate the FE results. The geometry comparison can be seen in Figure curves were used to validate the FE results. The geometry comparison can be seen in Figure 6. The forming force – displacement results of the FE model can be compared after the 6. The forming force – displacement results of the FE model can be compared after the correction of the measured values (Figure 7). The difference between the model and the correction of the measured values (Figure 7). The difference between the model and the measurement is acceptable. The simulated curve shows a very good agreement with the measurement is acceptable. The simulated curve shows a very good agreement with the measured one. measured one.

66 Szabolcs Jónás–Miklós Tisza 66 Szabolcs Jónás–Miklós Tisza

Figure 6 Figure 6 Cross section of the clinched and the simulated sheets (FE: eq. plastic strain) Cross section of the clinched and the simulated sheets (FE: eq. plastic strain)

According to [3] the measured curve can be divided into 3 main phases and 5 steps. In Phase According to [3] the measured curve can be divided into 3 main phases and 5 steps. In Phase I. the testing machine starts to work, the punching tool moves down, the holder moves I. the testing machine starts to work, the punching tool moves down, the holder moves downward to fix the sheets, the tool comes into contact with the upper sheet (punch side) and downward to fix the sheets, the tool comes into contact with the upper sheet (punch side) and the joining process is started (Step I.). The tool punches the sheets and they move together the joining process is started (Step I.). The tool punches the sheets and they move together (Step I. – Step II.) and this part of the process continues until the first bending point (Step (Step I. – Step II.) and this part of the process continues until the first bending point (Step II.). The lower sheet (die side) reaches the die; that is why the slope of the curve changes II.). The lower sheet (die side) reaches the die; that is why the slope of the curve changes after Phase I. In Phase II. the sheets start to flow around the punching tool and start to flow after Phase I. In Phase II. the sheets start to flow around the punching tool and start to flow inside the free space of the die (Step III.). The last part of the process needs more deformation inside the free space of the die (Step III.). The last part of the process needs more deformation force; the curve raises with the highest slope. In Step IV. the punching tool reaches the end force; the curve raises with the highest slope. In Step IV. the punching tool reaches the end position. In this phase the setting force reaches the maximum also. After this point the tool position. In this phase the setting force reaches the maximum also. After this point the tool starts to remove from the joint with a certain slope depeding on the stiffness of the machine. starts to remove from the joint with a certain slope depeding on the stiffness of the machine. After Step V. the joint is totally released. After Step V. the joint is totally released.

Figure 7 Figure 7 Comparison of the forming force-relative punching tool displacements Comparison of the forming force-relative punching tool displacements Numerical Investigation of Clinched Joints 67 Numerical Investigation of Clinched Joints 67

5. INFLUENCE OF MATERIAL PARAMETERS 5. INFLUENCE OF MATERIAL PARAMETERS Severe plastic deformation occurs during the forming process (Step III. according to Figure Severe plastic deformation occurs during the forming process (Step III. according to Figure 7). As already stated, true plastic strains of the order of 2-3 are not unusual and stress-strain 7). As already stated, true plastic strains of the order of 2-3 are not unusual and stress-strain data far beyond the maximum uniform strain have to be available for the analysis [10]. For data far beyond the maximum uniform strain have to be available for the analysis [10]. For better simulation results the use of extrapolation methods is necessary. In this section the better simulation results the use of extrapolation methods is necessary. In this section the influence of the different hardening laws are presented through the comparison of the influence of the different hardening laws are presented through the comparison of the undercuts. The parameter identification was done by the least-squares method. The kf is the undercuts. The parameter identification was done by the least-squares method. The kf is the true stress in MPa, φ is the true plastic strain, K is the strength coefficient in MPa, n is the true stress in MPa, φ is the true plastic strain, K is the strength coefficient in MPa, n is the strain hardening exponent and m is a material coefficient. The used hardening laws follow strain hardening exponent and m is a material coefficient. The used hardening laws follow the equations (1–4): the equations (1–4): 푁á푑푎푖 푛 푁á푑푎푖 푛 푘푓 = 퐾 ∙ 휑 (1) 푘푓 = 퐾 ∙ 휑 (1)

푆푤푖푓푡 푛 푆푤푖푓푡 푛 푘푓 = 퐾 ∙ (푚 + 휑) (2) 푘푓 = 퐾 ∙ (푚 + 휑) (2)

푉표푐푒 −푛휑 푉표푐푒 −푛휑 푘푓 = 퐾 ∙ (1 − 푚 ∙ 푒 ) (3) 푘푓 = 퐾 ∙ (1 − 푚 ∙ 푒 ) (3)

푆푤푖푓푡−푉표푐푒 푆푤푖푓푡 푉표푐푒 푆푤푖푓푡−푉표푐푒 푆푤푖푓푡 푉표푐푒 푘푓 = 훼 ∙ 푘푓 + (1 − 훼) ∙ 푘푓 (4) 푘푓 = 훼 ∙ 푘푓 + (1 − 훼) ∙ 푘푓 (4)

Constants of the equations can be seen in the following table (Table 3): Constants of the equations can be seen in the following table (Table 3):

Table 3 Table 3 Parameters of the models Parameters of the models K [MPa] m[-] n [-] K [MPa] m[-] n [-] Nádai 1,013.1 – 0.1329 Nádai 1,013.1 – 0.1329 Swift 1,063.9 0.0023 0.1533 Swift 1,063.9 0.0023 0.1533 Voce 772.13 26.17 0.4149 Voce 772.13 26.17 0.4149

In case of the mixed or combined model (Swift-Voce) the α = 0.7495, which is a weighting In case of the mixed or combined model (Swift-Voce) the α = 0.7495, which is a weighting factor of the two laws. Figure 8 shows the curves fitted to the measured one. factor of the two laws. Figure 8 shows the curves fitted to the measured one. Figure 10 shows the undercuts with the different methods. The Nádai and the mixed Figure 10 shows the undercuts with the different methods. The Nádai and the mixed equations resulted nearly in the same sized undercut as it can be presumed according to the equations resulted nearly in the same sized undercut as it can be presumed according to the extrapolated curves (Figure 9). The difference is quite large (~14%) between the Voce and extrapolated curves (Figure 9). The difference is quite large (~14%) between the Voce and the Swift strain-hardening models in the undercut region. the Swift strain-hardening models in the undercut region.

Figure 8 Figure 9 Figure 8 Figure 9 Parameter identification Extrapolated flow curves Parameter identification Extrapolated flow curves 68 Szabolcs Jónás–Miklós Tisza 68 Szabolcs Jónás–Miklós Tisza

Figure 10 Figure 10 Influence of the hardening laws to the undercut Influence of the hardening laws to the undercut

6. INFLUENCE OF THE TOOL GEOMETRY AND FRICTIONAL CONDITIONS 6. INFLUENCE OF THE TOOL GEOMETRY AND FRICTIONAL CONDITIONS For a better understanding of the clinch joints a sensitivity analysis has been performed. The For a better understanding of the clinch joints a sensitivity analysis has been performed. The basis of the comparison is the size of the undercut (C) depending on the punching tool’s basis of the comparison is the size of the undercut (C) depending on the punching tool’s geometry. In this case the tip angle and tip radius of the tool were taken into consideration. geometry. In this case the tip angle and tip radius of the tool were taken into consideration. The Table 4 contains the analysed geometry variations and the calculated undercut sizes. The Table 4 contains the analysed geometry variations and the calculated undercut sizes. Table 4 Table 4 Analysed sizes Analysed sizes tip radius tip radius tip angle [°] C [mm] tip angle [°] C [mm] [mm] [mm] 1 0.2 0.213 1 0.2 0.213 1 0.3 0.175 1 0.3 0.175 1 0.4 0.141 1 0.4 0.141 2 0.2 0.162 2 0.2 0.162 2 0.3 0.117 2 0.3 0.117 2 0.4 0.110 2 0.4 0.110 3 0.2 0.154 3 0.2 0.154 3 0.3 0.112 3 0.3 0.112 3 0.4 0.101 3 0.4 0.101

Figure 11 Figure 11 Influence of the punching tool’s geometry on the undercut (fitted surface) Influence of the punching tool’s geometry on the undercut (fitted surface) Numerical Investigation of Clinched Joints 69 Numerical Investigation of Clinched Joints 69

The fitted surface (Figure 11) shows the calculated data. It can be seen how the given The fitted surface (Figure 11) shows the calculated data. It can be seen how the given parameter affect the undercut if there are only two variables. For tool designers Figure 11 parameter affect the undercut if there are only two variables. For tool designers Figure 11 can be a helpful tool. This map can use for optimization procedures because its function can can be a helpful tool. This map can use for optimization procedures because its function can be easily calculated. be easily calculated. The frictional behaviour of a forming process is always a problematic question. In this The frictional behaviour of a forming process is always a problematic question. In this subsection the effect of the frictional conditions between the sheets and tools were analysed subsection the effect of the frictional conditions between the sheets and tools were analysed through a few cases. The basic case is the μ = 0.12. For comparison a higher one and a lower through a few cases. The basic case is the μ = 0.12. For comparison a higher one and a lower one of frictional coefficients were taken into consideration as a global and constant variable. one of frictional coefficients were taken into consideration as a global and constant variable. It means that all of the contacts have the same frictional coefficient during the given It means that all of the contacts have the same frictional coefficient during the given simulation. The figures (Figure 12) show the different force need and different undercut simulation. The figures (Figure 12) show the different force need and different undercut formation after forming. As it can be seen the higher (μ = 0.2) frictional coefficient has formation after forming. As it can be seen the higher (μ = 0.2) frictional coefficient has ~10 kN higher forming force need compared to the lower (μ = 0.05) case and the shape and ~10 kN higher forming force need compared to the lower (μ = 0.05) case and the shape and the size of the undercuts are also different. The too high forming forces can easily lead to the the size of the undercuts are also different. The too high forming forces can easily lead to the failure of the tools; the use of monitoring systems is highly recommended. failure of the tools; the use of monitoring systems is highly recommended.

Figure 12 Figure 12 Influence of frictional coefficients (F-d curves and undercuts) Influence of frictional coefficients (F-d curves and undercuts)

CONCLUSION CONCLUSION In this study the different influencers of DP600 clinch joints were analysed with a 2D In this study the different influencers of DP600 clinch joints were analysed with a 2D axissymmetrical FE model. The appropriate hardening law is a key to have an accurate axissymmetrical FE model. The appropriate hardening law is a key to have an accurate enough result. Next step in this research is the consideration of changing frictional behaviour enough result. Next step in this research is the consideration of changing frictional behaviour of sliding surfaces in the FE simulation during the clinching process. of sliding surfaces in the FE simulation during the clinching process.

REFERENCES REFERENCES [1] T. Sadowski, T. Balawender and P. Golewski (2015). Technological aspects of manufacturing [1] T. Sadowski, T. Balawender and P. Golewski (2015). Technological aspects of manufacturing and numerical modelling of clinch-adhesive joints. Springer, 2015 and numerical modelling of clinch-adhesive joints. Springer, 2015 [2] L. Kascák and E. Spisák(2012). Clinching as a non-standard method for joining materials of [2] L. Kascák and E. Spisák(2012). Clinching as a non-standard method for joining materials of dissimilar properties. Zeszyty naukowe politechniki rzeszowskiej, Nr. 284. Mechanika z. 84, pp. dissimilar properties. Zeszyty naukowe politechniki rzeszowskiej, Nr. 284. Mechanika z. 84, pp. 31–41. 31–41. [3] Y. Tan, O. Han and F. Du (2005). Process Monitoring Method with Window Technique for [3] Y. Tan, O. Han and F. Du (2005). Process Monitoring Method with Window Technique for Clinch Jointing. ISIJ International, Vol. 45, No. 5. pp. 723–729. Clinch Jointing. ISIJ International, Vol. 45, No. 5. pp. 723–729. [4] M. Tisza, G. Gaszton, A. Kiss, P. Z. Kovács and Zs. Lukács (2014). Alakítható nagyszilárdságú [4] M. Tisza, G. Gaszton, A. Kiss, P. Z. Kovács and Zs. Lukács (2014). Alakítható nagyszilárdságú lemezanyagok klincs kötése. Multidiszciplináris tudományok, Vol 4. pp. 49–58. lemezanyagok klincs kötése. Multidiszciplináris tudományok, Vol 4. pp. 49–58. [5] Kovács P. Z. and Tisza M. (2016). Klincs kötés technológiai paramétereinek vizsgálata, [5] Kovács P. Z. and Tisza M. (2016). Klincs kötés technológiai paramétereinek vizsgálata, végeselemes modellezésel. Anyagmérnöki Tudományok, Vol. 39, No. 1, pp. 7–18. végeselemes modellezésel. Anyagmérnöki Tudományok, Vol. 39, No. 1, pp. 7–18. 70 Szabolcs Jónás–Miklós Tisza 70 Szabolcs Jónás–Miklós Tisza

[6] Béres G., Danyi J. and Végvári F. (2015). Clinching of steel sheets used in automotive industry. [6] Béres G., Danyi J. and Végvári F. (2015). Clinching of steel sheets used in automotive industry. Modern Technologies in Manufacturing, Vol. 808, pp. 75–79. Modern Technologies in Manufacturing, Vol. 808, pp. 75–79. [7] Eshtayeh, M. M., Hrairi, M. Mohiuddin, A. K. M. (2016). Clinching process for joining [7] Eshtayeh, M. M., Hrairi, M. Mohiuddin, A. K. M. (2016). Clinching process for joining dissimilar materials: state of the art. Int J Adv Manuf Technol, Vol. 82, p. 179. dissimilar materials: state of the art. Int J Adv Manuf Technol, Vol. 82, p. 179. [8] F. Lambiase and A. Di Ilio (2014). An experimental study on clinched joints relized with [8] F. Lambiase and A. Di Ilio (2014). An experimental study on clinched joints relized with different dies. Thin-Walled Structures, Vol. 85, pp. 71–80. different dies. Thin-Walled Structures, Vol. 85, pp. 71–80. [9] S. Coppieters, S. Cooreman, H. Sol and D. Debruyne (2011). Reproducing the experimental [9] S. Coppieters, S. Cooreman, H. Sol and D. Debruyne (2011). Reproducing the experimental strength of clinched connections with finite element methods. International Journal of Material strength of clinched connections with finite element methods. International Journal of Material Forming, Vol. 4, No. 4, p. 429. Forming, Vol. 4, No. 4, p. 429. [10] S. Coppieters (2012). Experimental and numerical study of clinched connections. Ph.D [10] S. Coppieters (2012). Experimental and numerical study of clinched connections. Ph.D dissertation, KU Leuven. dissertation, KU Leuven. [11] ANSYS 18.2 User’s manual. [11] ANSYS 18.2 User’s manual.

Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 71–78. Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 71–78.

REDUCING OF DNT CONTENT REDUCING OF DNT CONTENT IN RED WATER FORMED DURING TDI PRODUCTION IN RED WATER FORMED DURING TDI PRODUCTION

ÁKOS KORBÁCS1, 2–R. ZSANETT BOROS1, 3–ANGELICA RODRIGUEZ4– ÁKOS KORBÁCS1, 2–R. ZSANETT BOROS1, 3–ANGELICA RODRIGUEZ4– LÁSZLÓ FARKAS1 LÁSZLÓ FARKAS1

A well-known reagent was tested for industrial cleaning and extracting of dinitrotoluene (DNT) (80/20) A well-known reagent was tested for industrial cleaning and extracting of dinitrotoluene (DNT) (80/20) from red water which is a waste water of the toluene-diisocyanate (TDI) production. The capability of from red water which is a waste water of the toluene-diisocyanate (TDI) production. The capability of different extraction agents, such as 1-methyl-2-nitro benzene and 1-methyl-4-nitro benzene mixture MNT different extraction agents, such as 1-methyl-2-nitro benzene and 1-methyl-4-nitro benzene mixture MNT (60/40) and methylbenzene (toluene) was studied. The toluene seemed to have a great efficiency, and only (60/40) and methylbenzene (toluene) was studied. The toluene seemed to have a great efficiency, and only a low amount was needed for the extraction process and less DNT (60/40) remained in the water after the a low amount was needed for the extraction process and less DNT (60/40) remained in the water after the extraction. The red water contains infinitesimal toluene after the extraction which can be distilled easily extraction. The red water contains infinitesimal toluene after the extraction which can be distilled easily with small quantity of introduced heat at the distillation column, because of the toluene-water azeotrope with small quantity of introduced heat at the distillation column, because of the toluene-water azeotrope behavior. Nevertheless, heat integration is also a possibility at the distillation step. behavior. Nevertheless, heat integration is also a possibility at the distillation step. Keywords: DNT, MNT, toluene, extraction, distillation, CAD simulation Keywords: DNT, MNT, toluene, extraction, distillation, CAD simulation

INTRODUCTION INTRODUCTION Polyurethanes (PUR) are widely used nowadays. There are five main areas of the PUR Polyurethanes (PUR) are widely used nowadays. There are five main areas of the PUR market: (1) the furniture and mattress sector, which uses almost exclusively flexible foams, market: (1) the furniture and mattress sector, which uses almost exclusively flexible foams, (2) the automotive industry which provides a market for flexible foams, filling foams, rigid (2) the automotive industry which provides a market for flexible foams, filling foams, rigid and flexible integral skin foams as well as elastomers for engineering components, (3) the and flexible integral skin foams as well as elastomers for engineering components, (3) the consumer sector, which is diversified in a manner similar to the automotive industry, (4) the consumer sector, which is diversified in a manner similar to the automotive industry, (4) the building industry, which is by far the largest consumer of rigid foams as insulation materials, building industry, which is by far the largest consumer of rigid foams as insulation materials, and (5) refrigeration engineering, which represents the second largest area for use of rigid and (5) refrigeration engineering, which represents the second largest area for use of rigid polyurethane foams as insulation materials [1]. polyurethane foams as insulation materials [1].

Figure 1 Figure 1 2,4-TDI (on the left) and 2,6 TDI are the two components of commercial TDI (80/20) where 2,4-TDI (on the left) and 2,6 TDI are the two components of commercial TDI (80/20) where 80:20 is the mass ratio of the two isomers 80:20 is the mass ratio of the two isomers

1 Wanhua-BorsodChem Ltd., Bolyai tér 1. 1 Wanhua-BorsodChem Ltd., Bolyai tér 1. H-3700 Kazincbarcika, Hungary H-3700 Kazincbarcika, Hungary [email protected] [email protected] 2 Department of Chemical and Environmental Process Engineering, Faculty of Chemical Technology 2 Department of Chemical and Environmental Process Engineering, Faculty of Chemical Technology and Biotechnology, Budapest University of Technology and Economics and Biotechnology, Budapest University of Technology and Economics H-1111 Budapest, Hungary H-1111 Budapest, Hungary 3 Institute of Chemistry, Faculty of Materials Science and Engineering, University of Miskolc 3 Institute of Chemistry, Faculty of Materials Science and Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary 4 Kalamazoo College, Kalamazoo, 4 Kalamazoo College, Kalamazoo, US MI 49006, United States of America US MI 49006, United States of America 72 Ákos Korbács–R. Zsanett Boros–Angelica Rodriguez–László Farkas 72 Ákos Korbács–R. Zsanett Boros–Angelica Rodriguez–László Farkas

Toluene diisocyanate (TDI) (Figure 1) is one of the most important raw material of Toluene diisocyanate (TDI) (Figure 1) is one of the most important raw material of polyurethane industry. The main isomers of TDI are the 2,4 and 2,6; IUPAC: [2,4- polyurethane industry. The main isomers of TDI are the 2,4 and 2,6; IUPAC: [2,4- diisocyanato-1-methylbenzene, (80 m/m%)] and [2,6-diisocyanato-1-methyl-benzene, (20 diisocyanato-1-methylbenzene, (80 m/m%)] and [2,6-diisocyanato-1-methyl-benzene, (20 m/m%)]. It is formed by the phosgenation of the appropriate amine (toluene-diamine, TDA). m/m%)]. It is formed by the phosgenation of the appropriate amine (toluene-diamine, TDA). In the first step of TDA synthesis toluene reacts with acid (HNO3/H2SO4) resulting in the In the first step of TDA synthesis toluene reacts with acid (HNO3/H2SO4) resulting in the formation of mono-nitrobenzene (MNT) mixture (1-methyl-2-nitro benzene and 1-methyl-4- formation of mono-nitrobenzene (MNT) mixture (1-methyl-2-nitro benzene and 1-methyl-4- nitro benzene, MNT [60/40]). The sulphuric acid-nitric acid mixture, which is responsible nitro benzene, MNT [60/40]). The sulphuric acid-nitric acid mixture, which is responsible for nitration is used at the second nitration step first, where nitration of MNT to DNT for nitration is used at the second nitration step first, where nitration of MNT to DNT occurred, and after that, this acid mixture circulates to the first nitration step, where nitration occurred, and after that, this acid mixture circulates to the first nitration step, where nitration of toluene to MNT (this first nitration needs milder, less acidic condition) happen [2]. After of toluene to MNT (this first nitration needs milder, less acidic condition) happen [2]. After a catalytic hydrogenation of MNT an isomer mixture of dinitro toluene is produced (1- a catalytic hydrogenation of MNT an isomer mixture of dinitro toluene is produced (1- methyl-2,4-dinitro benzene-ones and 1-methyl-2,6-dinitro benzene-ones, DNT [80/20]) methyl-2,4-dinitro benzene-ones and 1-methyl-2,6-dinitro benzene-ones, DNT [80/20]) (Figure 2) [3]. (Figure 2) [3].

Figure 2 Figure 2 2,4-TDI transformation from toluene, industrial method 2,4-TDI transformation from toluene, industrial method

In terms of economy, a two-step nitration of toluene to DNT in mixed acid is still the most In terms of economy, a two-step nitration of toluene to DNT in mixed acid is still the most favorable procedure for manufacturing DNT. During this process methyl-(di)nitrophenols favorable procedure for manufacturing DNT. During this process methyl-(di)nitrophenols and its derivatives, so called (di)nitrocresols are formed which can be found in the DNT and its derivatives, so called (di)nitrocresols are formed which can be found in the DNT product [4]. It is important to get pure DNT, so this contaminated product is washed with product [4]. It is important to get pure DNT, so this contaminated product is washed with water that contains NH3 which makes these (di)nitro-cresols water soluble. Due to the colour water that contains NH3 which makes these (di)nitro-cresols water soluble. Due to the colour of this water it is known as red water. of this water it is known as red water.

Search for solutions Search for solutions This red water also contains DNT (1,100–1,500 mg/l) which is responsible for its This red water also contains DNT (1,100–1,500 mg/l) which is responsible for its characteristic colour. It is relatively easy to extract this chemical out of water with organic characteristic colour. It is relatively easy to extract this chemical out of water with organic solvents, due to DNT’s low water solubility, which increases with temperature (Table 1). solvents, due to DNT’s low water solubility, which increases with temperature (Table 1).

Table 1 Table 1 Water solubility data for different toluene derivates related with this extration [5]–[7] Water solubility data for different toluene derivates related with this extration [5]–[7] Temperature 2,4-dinitrotoluene 2,6-dinitrotolene 2-nitrotoluene 4-nitrotoluene toluene Temperature 2,4-dinitrotoluene 2,6-dinitrotolene 2-nitrotoluene 4-nitrotoluene toluene

20 °C 1.03E-03 mol/l 8.07E-04 mol/l 4.44E-03 mol/l 2.12E-03 mol/l 6.37E-03 mol/l 20 °C 1.03E-03 mol/l 8.07E-04 mol/l 4.44E-03 mol/l 2.12E-03 mol/l 6.37E-03 mol/l 30 °C 1.48E-03 mol/l 1.46E-03 mol/l 4.74E-03 mol/l 2.35E-03 mol/l 5.07E-03 mol/l 30 °C 1.48E-03 mol/l 1.46E-03 mol/l 4.74E-03 mol/l 2.35E-03 mol/l 5.07E-03 mol/l 40 °C 2.28E-03 mol/l 2.32E-03 mol/l 5.64E-03 mol/l 3.05E-03 mol/l – 40 °C 2.28E-03 mol/l 2.32E-03 mol/l 5.64E-03 mol/l 3.05E-03 mol/l – 62 °C 5.35E-03 mol/l – – – 1.73E-02 mol/l 62 °C 5.35E-03 mol/l – – – 1.73E-02 mol/l

Reaction intermediate MNT can be used as extraction agent, however, it contains a quite high Reaction intermediate MNT can be used as extraction agent, however, it contains a quite high amount of DNT because of the technology. As the basis and starter reagent of TDI amount of DNT because of the technology. As the basis and starter reagent of TDI Reducing of DNT Content in Red Water Formed During TDI Production 73 Reducing of DNT Content in Red Water Formed During TDI Production 73 production, the toluene can be considered also as extraction material, since it does not have production, the toluene can be considered also as extraction material, since it does not have any dissolved DNT, yet more water soluble (Table 1). Toluene could be a better choice for any dissolved DNT, yet more water soluble (Table 1). Toluene could be a better choice for this DNT recovery step. this DNT recovery step. Our goal is to examine the capability of toluene and intermediate MNT as extracting Our goal is to examine the capability of toluene and intermediate MNT as extracting agents, to measure its capacity and compare its partition coefficient results. To maximize the agents, to measure its capacity and compare its partition coefficient results. To maximize the information about this DNT recovery technology, data were gathered from ChemCAD information about this DNT recovery technology, data were gathered from ChemCAD simulations which were based on the distillation step. simulations which were based on the distillation step.

1. APPLIED METHODS 1. APPLIED METHODS It was necessary to develop a method that can be appropriately used for demonstrating the It was necessary to develop a method that can be appropriately used for demonstrating the technology where MNT or toluene is applied as an extracting agent. On one hand a laboratory technology where MNT or toluene is applied as an extracting agent. On one hand a laboratory system was set up for carrying out experiments and providing data, on the other hand system was set up for carrying out experiments and providing data, on the other hand simulation was used so as to calculate the efficiency of the suggested extracting agents. simulation was used so as to calculate the efficiency of the suggested extracting agents.

1.1. Experimental method for extraction step 1.1. Experimental method for extraction step Our laboratory system was based on a 1,500 ml reactor vessel with duplicated wall for its Our laboratory system was based on a 1,500 ml reactor vessel with duplicated wall for its temperature control. A mixer was put inside the vessel to mix-up the two phases and help temperature control. A mixer was put inside the vessel to mix-up the two phases and help with even homogenization. Julabo® thermostat and Digi-Sense® thermometer have been with even homogenization. Julabo® thermostat and Digi-Sense® thermometer have been used. Temperature was set to 65 °C. For the quantitative analytical measurements HPLC used. Temperature was set to 65 °C. For the quantitative analytical measurements HPLC equipment was used. equipment was used. The schema on which our experiments are based requires fresh extracting agents at each The schema on which our experiments are based requires fresh extracting agents at each step (Figure 3). Only a small amount of agent is needed, however the quality of this method step (Figure 3). Only a small amount of agent is needed, however the quality of this method gives great yields of extract at the end. During the experiments 1,000 ml red water was added gives great yields of extract at the end. During the experiments 1,000 ml red water was added into the reactor vessel with 27 g of extracting agent. After an hour of intense mixing, the two into the reactor vessel with 27 g of extracting agent. After an hour of intense mixing, the two phases were separated from which samples were taken. phases were separated from which samples were taken.

Figure 3 Figure 3 The schema of this multi-step extraction The schema of this multi-step extraction

The red water was fed back to the vessel with fresh extracting agent restarting the experiment. The red water was fed back to the vessel with fresh extracting agent restarting the experiment. This procedure was repeated four times with MNT and toluene extracting agents. As a result, This procedure was repeated four times with MNT and toluene extracting agents. As a result, the DNT content in red water appeared constant. One of the targets was to gather accurate the DNT content in red water appeared constant. One of the targets was to gather accurate data for plant equipment’s design. data for plant equipment’s design.

1.2. Simulation method for distillation step 1.2. Simulation method for distillation step Data were collected by analyzing the samples that were taken giving the possibility to obtain Data were collected by analyzing the samples that were taken giving the possibility to obtain more information about the extracted red water quality in relation with solved extracting more information about the extracted red water quality in relation with solved extracting 74 Ákos Korbács–R. Zsanett Boros–Angelica Rodriguez–László Farkas 74 Ákos Korbács–R. Zsanett Boros–Angelica Rodriguez–László Farkas agents. By using this data, simulations could have been set up in Chemstations™ ChemCAD agents. By using this data, simulations could have been set up in Chemstations™ ChemCAD environment, to check the heat needs for the extracting agents and water distillation process. environment, to check the heat needs for the extracting agents and water distillation process. Through knowledge of these results, the economic factors of the whole technology also could Through knowledge of these results, the economic factors of the whole technology also could have been examined. have been examined.

1.3. Combination of methods 1.3. Combination of methods The best way is to see the extraction and distillation technological steps as a whole process. The best way is to see the extraction and distillation technological steps as a whole process. In this study the authors first obtained information about each step separately and then tried In this study the authors first obtained information about each step separately and then tried to conclude the main points. Finding the best extracting agent is good for the extraction step to conclude the main points. Finding the best extracting agent is good for the extraction step as well as for the after cleaning distillation procedure, which has a rather great heat need. as well as for the after cleaning distillation procedure, which has a rather great heat need.

2. RESULTS OF EXTRACTION 2. RESULTS OF EXTRACTION 2.1. MNT 2.1. MNT The extraction of red water (initial DNT content: 135,350 mg/l) by the use of MNT seems The extraction of red water (initial DNT content: 135,350 mg/l) by the use of MNT seems inadequate because notable amount of DNT remained in the red water with 150 mg/l inadequate because notable amount of DNT remained in the red water with 150 mg/l concentration. This DNT concentration in red water became constant and did not go lower. concentration. This DNT concentration in red water became constant and did not go lower. The MNT’s DNT content was raised up to 155,000 mg/l (Table 2). After the experiments The MNT’s DNT content was raised up to 155,000 mg/l (Table 2). After the experiments 1,100 mg/l of MNT was remained in the red water requiring to be distilled. 1,100 mg/l of MNT was remained in the red water requiring to be distilled.

Table 2 Table 2 MNT and toluene extraction results when different amount of extraction MNT and toluene extraction results when different amount of extraction agents with variant quality were used agents with variant quality were used

DNT content after the steps, starting with used water DNT content after the steps, starting with used water and fresh extracting agents [mg/l] and fresh extracting agents [mg/l] First Second Third Fourth First Second Third Fourth extraction extraction extraction extraction extraction extraction extraction extraction MNT (27 g) MNT (27 g) Red water 214 163 158 151 Red water 214 163 158 151 K-value 711 867 881 935 K-value 711 867 881 935 Toluene (27 g) Toluene (27 g) Red water 92 11 2 0.2* Red water 92 11 2 0.2* K-value 499 571 254 221 K-value 499 571 254 221 Toluene (14 g) Toluene (14 g) Red water 141 48 8 2 Red water 141 48 8 2 K-value 647 466 515 383 K-value 647 466 515 383 Toluene° (14 g) Toluene° (14 g) Red water 246 191 179 161 Red water 246 191 179 161 K-value 737 549 547 566 K-value 737 549 547 566

2.2. Toluene 2.2. Toluene The same amount of toluene was measured (27 g) as in the case of MNT for the extraction The same amount of toluene was measured (27 g) as in the case of MNT for the extraction of 1,000 ml red water. After the extraction DNT concentration in toluene was 45,786 mg/l. of 1,000 ml red water. After the extraction DNT concentration in toluene was 45,786 mg/l. The remaining DNT in the red water was infinitesimal and it was out of our proper measuring The remaining DNT in the red water was infinitesimal and it was out of our proper measuring range* (it was under 0.2 mg/l) (Table 2). The residual toluene concentration was measured, range* (it was under 0.2 mg/l) (Table 2). The residual toluene concentration was measured, its content in the red water was 260 mg/l. This amount needs to be distilled out from the its content in the red water was 260 mg/l. This amount needs to be distilled out from the system. In another experiment less toluene (14 g) was added as extracting agent. The system. In another experiment less toluene (14 g) was added as extracting agent. The extraction efficiency was worse, more steps were required for the cleaning process (Table 2). extraction efficiency was worse, more steps were required for the cleaning process (Table 2). This experiment was repeated with model toluene, where the DNT concentration was set to This experiment was repeated with model toluene, where the DNT concentration was set to Reducing of DNT Content in Red Water Formed During TDI Production 75 Reducing of DNT Content in Red Water Formed During TDI Production 75

82,750 mg/l in the toluene. This experiment showed that the efficiency was already decreased 82,750 mg/l in the toluene. This experiment showed that the efficiency was already decreased when significant amount of DNT was solved in the extracting agent because DNT content in when significant amount of DNT was solved in the extracting agent because DNT content in the red water lower less (Table 2). the red water lower less (Table 2).

2.3. K-value – partition coefficient 2.3. K-value – partition coefficient The partition coefficient numbers were determined by the following equation (1). The partition coefficient numbers were determined by the following equation (1).

(1) (1)

The results are demonstrated by the following diagrams. According to Figure 4 the DNT The results are demonstrated by the following diagrams. According to Figure 4 the DNT concentration in water stayed relatively high until the end of the process (up to 150 mg/l) concentration in water stayed relatively high until the end of the process (up to 150 mg/l) when intermediate MNT has been used. This phenomenon can be explained by the fact that when intermediate MNT has been used. This phenomenon can be explained by the fact that MNT already contained DNT which reduced its extraction capacity. However, until the MNT already contained DNT which reduced its extraction capacity. However, until the second extraction step the K-values were increased and afterwards the K-values remained second extraction step the K-values were increased and afterwards the K-values remained constant and high (935). constant and high (935). In the case of Figure 5 the highest K-value was achieved after the second step (571) and In the case of Figure 5 the highest K-value was achieved after the second step (571) and then it was decreased, which could be explained by decreased amount of DNT in water in then it was decreased, which could be explained by decreased amount of DNT in water in function of extraction steps. The water’s DNT content was decreased as well, to 0.2 mg/l at function of extraction steps. The water’s DNT content was decreased as well, to 0.2 mg/l at the end of the fourth extraction step. According to the results, both intermediate MNT (27 g) the end of the fourth extraction step. According to the results, both intermediate MNT (27 g) and toluene (27 g) are favorable because intermediate MNT has higher K-values. Yet, toluene and toluene (27 g) are favorable because intermediate MNT has higher K-values. Yet, toluene also works since there is less DNT remaining in the red water. also works since there is less DNT remaining in the red water.

2.4. Extracting agent in red water 2.4. Extracting agent in red water After the experiments the data were collected and evaluated. The content of the remaining After the experiments the data were collected and evaluated. The content of the remaining extraction agents in water were determined in mg/l concentration. These amounts of extraction agents in water were determined in mg/l concentration. These amounts of extracting agents need to be distilled. extracting agents need to be distilled. • MNT in red water 1,100 mg/l • MNT in red water 1,100 mg/l • Toluene in red water 260 mg/l • Toluene in red water 260 mg/l

Figure 4 Figure 4 Partition coefficient and DNT’s water concentration change in the function of extraction Partition coefficient and DNT’s water concentration change in the function of extraction steps, with MNT extracting agent steps, with MNT extracting agent 76 Ákos Korbács–R. Zsanett Boros–Angelica Rodriguez–László Farkas 76 Ákos Korbács–R. Zsanett Boros–Angelica Rodriguez–László Farkas

Figure 5 Figure 5 Partition coefficient and DNT’s water concentration change in the function of extraction Partition coefficient and DNT’s water concentration change in the function of extraction steps, with toluene extracting agent steps, with toluene extracting agent

3. RESULTS OF DISTILLATION 3. RESULTS OF DISTILLATION First of all, a simulation in Chemstations™ ChemCAD environment has been set up. First of all, a simulation in Chemstations™ ChemCAD environment has been set up. UNIFAC global K-value model and model vapor/liquid/liquid/solid global phase option have UNIFAC global K-value model and model vapor/liquid/liquid/solid global phase option have been chosen because of the azeotrope (toluene-water). been chosen because of the azeotrope (toluene-water).

Figure 6 Figure 6 The basic design of the distillation step, created in Chemstations™ ChemCAD environment The basic design of the distillation step, created in Chemstations™ ChemCAD environment where equipment 1: distillation column, 2 and 3: heat exchangers; stream 1: red water, 2: where equipment 1: distillation column, 2 and 3: heat exchangers; stream 1: red water, 2: heated red water, 3: top product, 4: bottom product, 5: cooled bottom product heated red water, 3: top product, 4: bottom product, 5: cooled bottom product

3.1. MNT 3.1. MNT The boiling point (bp.) of MNT is 222 °C, the water’s is 100 °C if p = 101.3 kPa [8]. Due to The boiling point (bp.) of MNT is 222 °C, the water’s is 100 °C if p = 101.3 kPa [8]. Due to this difference steam distillation is needed. This means to remove the MNT, a relative large this difference steam distillation is needed. This means to remove the MNT, a relative large volume of water needs to be boiled in order to eliminate all of the MNT. volume of water needs to be boiled in order to eliminate all of the MNT. Reducing of DNT Content in Red Water Formed During TDI Production 77 Reducing of DNT Content in Red Water Formed During TDI Production 77

This steam distillation was modelled as packed column (Pall ring tower packing was This steam distillation was modelled as packed column (Pall ring tower packing was used), where the pressure was set to 0.040 bar and it boils 32.2 liter/hour for each cubic meter used), where the pressure was set to 0.040 bar and it boils 32.2 liter/hour for each cubic meter of red water to sprout the MNT out. The reflux ratio is 2.5. Less than 3E-05% of all MNT of red water to sprout the MNT out. The reflux ratio is 2.5. Less than 3E-05% of all MNT remained in the red water. Based on these data, it was calculated that this system needs remained in the red water. Based on these data, it was calculated that this system needs 558,438.5 kJ/h/m3, if the heat exchangers’ efficiencies are 90% (Table 3). This setup is the 558,438.5 kJ/h/m3, if the heat exchangers’ efficiencies are 90% (Table 3). This setup is the optimum for this distillation. optimum for this distillation. In this case heat integration is possible, but not efficient, because the pre-heater (Figure In this case heat integration is possible, but not efficient, because the pre-heater (Figure 6, equipment number 2) needs to heat up the red water to 100 °C, and there are not enough 6, equipment number 2) needs to heat up the red water to 100 °C, and there are not enough ΔT temperature difference between the two streams. The red water could condensate the ΔT temperature difference between the two streams. The red water could condensate the bottom column product water to increase its temperature a little bit, but also needs to go bottom column product water to increase its temperature a little bit, but also needs to go through in the pre-heater, which works with steam to reach the 100 °C. Building a pre-heater through in the pre-heater, which works with steam to reach the 100 °C. Building a pre-heater is considered to have low efficient. is considered to have low efficient. According to the results the MNT distillation is highly energy consuming. According to the results the MNT distillation is highly energy consuming.

3.2. Toluene 3.2. Toluene Toluene creates azeotrope with water, bp. of toluene: 110.9 °C, bp. of the toluene-water Toluene creates azeotrope with water, bp. of toluene: 110.9 °C, bp. of the toluene-water azeotrope: 84.1 °C, (p = 101.3 kPa) [9], which helps to eliminate it more easily than the MNT. azeotrope: 84.1 °C, (p = 101.3 kPa) [9], which helps to eliminate it more easily than the MNT. Due to the azeotrope property the distillation became more energy efficient. For this Due to the azeotrope property the distillation became more energy efficient. For this distillation tray columns could be more suitable [10], therefore a model was created. distillation tray columns could be more suitable [10], therefore a model was created. After the optimization process of this column the number of trays were set to 6 (actual After the optimization process of this column the number of trays were set to 6 (actual trays 4) and feed stream for red water was set to the second tray. The optimal working trays 4) and feed stream for red water was set to the second tray. The optimal working pressure value of the column was 0.5 bar using at least 75 °C feed stream (Figure 6 stream pressure value of the column was 0.5 bar using at least 75 °C feed stream (Figure 6 stream “Red Water”). This adjusted pressure gave us the best results for heat demand. “Red Water”). This adjusted pressure gave us the best results for heat demand. The 0.5 bar pressure column also requires an 80 °C input temperature, which means a The 0.5 bar pressure column also requires an 80 °C input temperature, which means a small pre-heater is needed. In this case, a pre-heater cannot be integrated because the bottom small pre-heater is needed. In this case, a pre-heater cannot be integrated because the bottom product was only 81 °C, but, if 1 bar pressure is used the bottom product is 99 °C and can product was only 81 °C, but, if 1 bar pressure is used the bottom product is 99 °C and can heat up the feed stream including red water. Reflux ratio is 1 in both cases. heat up the feed stream including red water. Reflux ratio is 1 in both cases. The energy required for these circumstances can be seen in Table 3. For both 0.5 bar and The energy required for these circumstances can be seen in Table 3. For both 0.5 bar and 1 bar pressures, the system could distillate all toluene, only less than 2.7E-05% of all toluene 1 bar pressures, the system could distillate all toluene, only less than 2.7E-05% of all toluene remained in the water, and 0.4 l/h for each cubic meter of toluene-water mixture would be remained in the water, and 0.4 l/h for each cubic meter of toluene-water mixture would be distilled. distilled. Table 3 Table 3 Distillation pressures and heat needs for the extracting agents Distillation pressures and heat needs for the extracting agents

Pressure [bar] Needed heat [kJ/kg/m3] Is heat integration possible? Pressure [bar] Needed heat [kJ/kg/m3] Is heat integration possible? MNT (1,100mg/l) 0.040 5.6E05 No MNT (1,100mg/l) 0.040 5.6E05 No Toluene (260mg/l) 0.5 0.3E05 No Toluene (260mg/l) 0.5 0.3E05 No Toluene (260mg/l) 1 1.1E05 Yes Toluene (260mg/l) 1 1.1E05 Yes

CONCLUSION CONCLUSION According to the experiments it can be seen that the pure fresh toluene can dissolve more According to the experiments it can be seen that the pure fresh toluene can dissolve more DNT than the intermediate MNT. Less toluene remains in the water after the extraction than DNT than the intermediate MNT. Less toluene remains in the water after the extraction than MNT extracting agent. Even more DNT can be withdrawn from the red water whether MNT extracting agent. Even more DNT can be withdrawn from the red water whether toluene is chosen to be used in the extraction step. Less energy is needed to distillate red toluene is chosen to be used in the extraction step. Less energy is needed to distillate red water in the case of toluene extraction and recover the useful organic materials of the water water in the case of toluene extraction and recover the useful organic materials of the water (toluene and MNT and DNT) which can be reused in order to create less organic chemical (toluene and MNT and DNT) which can be reused in order to create less organic chemical 78 Ákos Korbács–R. Zsanett Boros–Angelica Rodriguez–László Farkas 78 Ákos Korbács–R. Zsanett Boros–Angelica Rodriguez–László Farkas waste. By two-step extractions with 2% of toluene more than 99.9% DNT recoveries can be waste. By two-step extractions with 2% of toluene more than 99.9% DNT recoveries can be reached. reached. Heat integration is also a possible process in the case of toluene distillation using 1 bar Heat integration is also a possible process in the case of toluene distillation using 1 bar pressure in the column. However, the heating energy needs drops by more than 80% without pressure in the column. However, the heating energy needs drops by more than 80% without heat integration, and by 85% with heat integration. If 0.5 bar pressure is applied the energy heat integration, and by 85% with heat integration. If 0.5 bar pressure is applied the energy need of heating decreases by more than 93%. The vacuum pump at the top of the column need of heating decreases by more than 93%. The vacuum pump at the top of the column would need less energy as well than in case of MNT distillation, where 0.040 bar pressure is would need less energy as well than in case of MNT distillation, where 0.040 bar pressure is required. required. To summarize this series of experiments, it is suggested to choose toluene over intermedia To summarize this series of experiments, it is suggested to choose toluene over intermedia MNT as extracting agent in TDI technology. MNT as extracting agent in TDI technology.

ACKNOWLEDGMENTS ACKNOWLEDGMENTS The authors acknowledge the research possibility for Wanhua-BorsodChem Ltd. and the support for The authors acknowledge the research possibility for Wanhua-BorsodChem Ltd. and the support for Tamás Purzsa Vice President of Chief General Engineering. This research was supported by the Tamás Purzsa Vice President of Chief General Engineering. This research was supported by the European Regional Development Fund in the framework of the GINOP-2.3.4-15-2016-00004 project. European Regional Development Fund in the framework of the GINOP-2.3.4-15-2016-00004 project.

REFERENCES REFERENCES [1] I. Boustead (2005). Tolylene diisocyanate (TDI). Eco-profiles Eur. Plast. Ind., No. March, pp. [1] I. Boustead (2005). Tolylene diisocyanate (TDI). Eco-profiles Eur. Plast. Ind., No. March, pp. 1–20. 1–20. [2] W. J. Mazzafro, S. I. Clarke, M. S. Simpson, and R. Van Court Carr (2003). Weak acid process [2] W. J. Mazzafro, S. I. Clarke, M. S. Simpson, and R. Van Court Carr (2003). Weak acid process for producing dinitrotoluene – EP 0 903 336 B1. for producing dinitrotoluene – EP 0 903 336 B1. [3] H. Hermann, J. Gebauer, and P. Konieczny (1996). Industrial Nitration of Toluene to [3] H. Hermann, J. Gebauer, and P. Konieczny (1996). Industrial Nitration of Toluene to Dinitrotoluene. Josef Meissner GmbH Co., No. 5, pp. 234–249. Dinitrotoluene. Josef Meissner GmbH Co., No. 5, pp. 234–249. [4] F. Fiedler, H.-J. Schöbel, and M. Otto (2000). Identification of Nitrogen Compounds from [4] F. Fiedler, H.-J. Schöbel, and M. Otto (2000). Identification of Nitrogen Compounds from Degradation of Dinitrotoluene and Toluylenediamine Isomers Within an Industrial Degradation of Dinitrotoluene and Toluylenediamine Isomers Within an Industrial Purification Plant. Microchim. Acta, Vol. 135, No. 1–2, pp. 1–7. Purification Plant. Microchim. Acta, Vol. 135, No. 1–2, pp. 1–7. [5] D. J. L. Prak and D. W. O. Sullivan (2007). Solubility of 4-Nitrotoluene, 2,6-Dinitrotoluene, [5] D. J. L. Prak and D. W. O. Sullivan (2007). Solubility of 4-Nitrotoluene, 2,6-Dinitrotoluene, 2,3-Dinitrotoluene, and 1,3,5-Trinitrobenzene in Pure Water and Seawater. J. Chem. Eng., pp. 2,3-Dinitrotoluene, and 1,3,5-Trinitrobenzene in Pure Water and Seawater. J. Chem. Eng., pp. 2446–2450. 2446–2450. [6] J. M. Phelan and J. L. Barnett (2001). Solubility of 2,4-Dinitrotoluene and 2,4,6- [6] J. M. Phelan and J. L. Barnett (2001). Solubility of 2,4-Dinitrotoluene and 2,4,6- Trinitrotoluene in Water. J. Chem. Eng., Vol. 46, pp. 375–376. Trinitrotoluene in Water. J. Chem. Eng., Vol. 46, pp. 375–376. [7] S. H. Yalkowsky, Y. He, and P. Jain (2010). Handbook Of Aqueous Solubility Data. [7] S. H. Yalkowsky, Y. He, and P. Jain (2010). Handbook Of Aqueous Solubility Data. [8] D. R. Lide (2005). CRC Handbook of Chemistry and Physics, 85th Edition. Vol. 53. [8] D. R. Lide (2005). CRC Handbook of Chemistry and Physics, 85th Edition. Vol. 53. [9] J. Gmehling, J. Menke, J. Krafczyk, K. Fischer, J. Fontaine, and H. V Kehiaian (1996). [9] J. Gmehling, J. Menke, J. Krafczyk, K. Fischer, J. Fontaine, and H. V Kehiaian (1996). Azeotropic Data for Binary Mixtures. Handb. Chem. Phys., pp. 6-210–6-228. Azeotropic Data for Binary Mixtures. Handb. Chem. Phys., pp. 6-210–6-228. [10] M. Siegert, J. Stichlmair, J. U. Repke, and G. Wozny (2000). Heterogeneous azeotropic [10] M. Siegert, J. Stichlmair, J. U. Repke, and G. Wozny (2000). Heterogeneous azeotropic distillation in packed columns: experimental results. Chem. Eng. Technol., Vol. 23, No. 12, distillation in packed columns: experimental results. Chem. Eng. Technol., Vol. 23, No. 12, pp. 1047–1050. pp. 1047–1050.

Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 79–91. Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 79–91.

THE EFFECT OF AGE ON COMBUSTION PROPERTIES THE EFFECT OF AGE ON COMBUSTION PROPERTIES OF ENERGY WILLOWS OF ENERGY WILLOWS

DÓRA MENTES1–CSABA PÓLISKA2–TAMÁSNÉ SZEMMELVEISZ3 DÓRA MENTES1–CSABA PÓLISKA2–TAMÁSNÉ SZEMMELVEISZ3

In this study, we investigated the conditions of combustion of one- and two-year-old Energo twigs. We In this study, we investigated the conditions of combustion of one- and two-year-old Energo twigs. We were inquired into the answer how the age of the Energo willow influences its combustion properties. were inquired into the answer how the age of the Energo willow influences its combustion properties. During the research we have determined that some properties may be significantly affected by the age. During the research we have determined that some properties may be significantly affected by the age. Keywords: energy willows, combustion, higher heating value, moisture, ash Keywords: energy willows, combustion, higher heating value, moisture, ash

INTRODUCTION INTRODUCTION Due to the fight against climate change and the ever-increasing energy needs, renewable Due to the fight against climate change and the ever-increasing energy needs, renewable energy sources have come into view. Using of them, we can replace the fossil fuels and energy sources have come into view. Using of them, we can replace the fossil fuels and reduce the release of greenhouse gases that cause climate change. reduce the release of greenhouse gases that cause climate change. Renewable energy sources include biomass. A large group of it is the woody energy Renewable energy sources include biomass. A large group of it is the woody energy crops. We have many examples of setting up and operating energy woodcutters in the world. crops. We have many examples of setting up and operating energy woodcutters in the world. In Europe we find intensive experimentation in Sweden, Germany, Great Britain, Croatia, In Europe we find intensive experimentation in Sweden, Germany, Great Britain, Croatia, Serbia and Montenegro, Finland, and Hungary. In these countries, studies are carried out Serbia and Montenegro, Finland, and Hungary. In these countries, studies are carried out primarily with willow, poplar, acacia, birch and alder clones [1]. primarily with willow, poplar, acacia, birch and alder clones [1]. The woody plants of acacia, willow and poplar have favorable cultivation conditions The woody plants of acacia, willow and poplar have favorable cultivation conditions because of the continental climate in Hungary. The range of wood species and breeds that because of the continental climate in Hungary. The range of wood species and breeds that can be used for the production of woody plantations in Hungary is set out in the MARD can be used for the production of woody plantations in Hungary is set out in the MARD 45/2007. number decree. According to this, planting technology can only be used for the 45/2007. number decree. According to this, planting technology can only be used for the aforementioned plants [1], [2]. aforementioned plants [1], [2]. In researches on energy crops found in international literature, the same plant variety may In researches on energy crops found in international literature, the same plant variety may exhibit different properties. These differences can be explained by dissimilar climatic exhibit different properties. These differences can be explained by dissimilar climatic conditions, soil quality and planting systems in different European countries. Besides the above conditions, soil quality and planting systems in different European countries. Besides the above mentioned parameters, the combustion properties can be influenced by the different genotypes mentioned parameters, the combustion properties can be influenced by the different genotypes and age of the plants as well. For example, the willow calorific value change widely, depending and age of the plants as well. For example, the willow calorific value change widely, depending on the above-mentioned factors, up to 16.2 to 22.6 MJ/kg [3], [4], [5], [6], [7]. on the above-mentioned factors, up to 16.2 to 22.6 MJ/kg [3], [4], [5], [6], [7]. Investigations on woody energy plantations focus primarily on harvesting methods and Investigations on woody energy plantations focus primarily on harvesting methods and their economic, energetic and environmental impacts. their economic, energetic and environmental impacts. The aim of our work is to determine how the age of the Energo willow influences its The aim of our work is to determine how the age of the Energo willow influences its combustion properties. combustion properties.

1 Department of Combustion Technology and Thermal Energy, University of Miskolc 1 Department of Combustion Technology and Thermal Energy, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 2 Department of Combustion Technology and Thermal Energy, University of Miskolc 2 Department of Combustion Technology and Thermal Energy, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 3 Department of Combustion Technology and Thermal Energy, University of Miskolc 3 Department of Combustion Technology and Thermal Energy, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 80 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz 80 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz

1. LABORATORY EXPERIMENTS 1. LABORATORY EXPERIMENTS During our research we examined in detail the combustion properties of one- and two-year- During our research we examined in detail the combustion properties of one- and two-year- old Energo willow. This will help to ascertain how the age of the plant affects the conditions old Energo willow. This will help to ascertain how the age of the plant affects the conditions of its firing. of its firing. The pictures of the twig from the examined willows are shown in Figure 1. The pictures of the twig from the examined willows are shown in Figure 1.

Figure 1 Figure 1 Twigs of the one-year-old (right) and two-year-old (left) Energo willow Twigs of the one-year-old (right) and two-year-old (left) Energo willow

1.1. Moisture content 1.1. Moisture content Determination of the hygroscopic moisture content of the biomass happens in drying oven at Determination of the hygroscopic moisture content of the biomass happens in drying oven at 105 ± 5 ºC by mass constant, according to MSZ EN 14774:2010 standard. The final results 105 ± 5 ºC by mass constant, according to MSZ EN 14774:2010 standard. The final results were calculated with the following formula [8]: were calculated with the following formula [8]:

푚 푚 푊 = 1 × 100, % m/m (1) 푊 = 1 × 100, % m/m (1) 푚 푚 where where W hygroscopic moisture content [% m/m], W hygroscopic moisture content [% m/m], m1 weight loss (of the sample) on drying [g], m1 weight loss (of the sample) on drying [g], m the initial weight of the sample [g]. m the initial weight of the sample [g].

One of the most important combustion parameter is the moisture content. The moisture One of the most important combustion parameter is the moisture content. The moisture content of willow sample can be influenced by several factors: what time of the year was it content of willow sample can be influenced by several factors: what time of the year was it harvested, how much diameter it has and what genome it has. harvested, how much diameter it has and what genome it has.

1.2. Ash content 1.2. Ash content Ash is the solid burnings residues left from the complete combustion of fuel. Determination Ash is the solid burnings residues left from the complete combustion of fuel. Determination of it happens in closed chamber at 815 ± 15 ºC by mass constant, according to MSZ EN of it happens in closed chamber at 815 ± 15 ºC by mass constant, according to MSZ EN 14775:2010 standard. All results are reported relative to the oven dry weight of the sample, 14775:2010 standard. All results are reported relative to the oven dry weight of the sample, according to the formula [8]: according to the formula [8]:

푚 −푚 푚 −푚 퐴 = 3 1 × 100, % m/m (2) 퐴 = 3 1 × 100, % m/m (2) 푚2−푚1 푚2−푚1 The Effect of Age on Combustion Properties of Energy Willows 81 The Effect of Age on Combustion Properties of Energy Willows 81 where where A ash content [% m/m], A ash content [% m/m], m1 the weight of the crucible [g], m1 the weight of the crucible [g], m2 the initial weight of the crucible and the sample together [g], m2 the initial weight of the crucible and the sample together [g], m3 the weight of the crucible and the ash produced [g]. m3 the weight of the crucible and the ash produced [g].

The ash content of the samples, as well as their moisture content, can be influenced by a The ash content of the samples, as well as their moisture content, can be influenced by a number of factors such as the breed of willow (genotype), the environment where it grew, number of factors such as the breed of willow (genotype), the environment where it grew, the way and the time of harvest, and other conditions. the way and the time of harvest, and other conditions. One of the studies examined a sample of 19 different genotype in five different One of the studies examined a sample of 19 different genotype in five different environments. The samples with different genotype had an ash content between 1.27 and environments. The samples with different genotype had an ash content between 1.27 and 2.57% m/m. In the case of environmental impact analysis, the range of the ash content of the 2.57% m/m. In the case of environmental impact analysis, the range of the ash content of the samples is smaller: 1.37–2.16% m/m. So the environment has less impact on ashes than the samples is smaller: 1.37–2.16% m/m. So the environment has less impact on ashes than the genotype of the samples [9]. genotype of the samples [9]. In another study, two types of willow samples were investigated. It was found that the In another study, two types of willow samples were investigated. It was found that the age of the samples significantly influenced their ash content. While one breed of willow the age of the samples significantly influenced their ash content. While one breed of willow the one-year-old samples – in the case of the other breed the three-year-old sample had the largest one-year-old samples – in the case of the other breed the three-year-old sample had the largest ash content. The difference between the tree and bark part was also examined. For both ash content. The difference between the tree and bark part was also examined. For both species, the tree part contained less ash than the bark part [6]. species, the tree part contained less ash than the bark part [6]. The ash content of the plants harvested by the machine is also lower than that of manually The ash content of the plants harvested by the machine is also lower than that of manually harvested plants, which is explained by the fact that several pollutants may adhere to the harvested plants, which is explained by the fact that several pollutants may adhere to the surface of the plants when they are harvesting by hand [10]. surface of the plants when they are harvesting by hand [10].

1.3. Ultimate analysis 1.3. Ultimate analysis In this study, a Carlo Erba EA1108 type elemental analyser was used for the measurement of In this study, a Carlo Erba EA1108 type elemental analyser was used for the measurement of the a C-, H-, N-, S-, O- content in the biomass, according to MSZ EN 15104:2011 standard. the a C-, H-, N-, S-, O- content in the biomass, according to MSZ EN 15104:2011 standard. The elemental analysis is based on the perfect combustion of the fuel. From the composition of The elemental analysis is based on the perfect combustion of the fuel. From the composition of the resulting flue gas, we can deduce the quantity of elements forming the sample. The flue gas the resulting flue gas, we can deduce the quantity of elements forming the sample. The flue gas is driven by helium carrier gas through the oxidizing and reducing parts to a chromatographic is driven by helium carrier gas through the oxidizing and reducing parts to a chromatographic column where the thermal conductivity sensor detects the CO2, H2O, N2, SO2 gas components. column where the thermal conductivity sensor detects the CO2, H2O, N2, SO2 gas components. From these data, the amount of elements in biomass can be calculated [11]. From these data, the amount of elements in biomass can be calculated [11].

1.4. Determination of higher heating value (HHV) 1.4. Determination of higher heating value (HHV) Calorific test were performed using a Parr 6200 type isoperibol oxygen bomb calorimeter Calorific test were performed using a Parr 6200 type isoperibol oxygen bomb calorimeter according to MSZ EN 14918:2010 standard. according to MSZ EN 14918:2010 standard. The higher heating value of the samples were automatically computed by the data The higher heating value of the samples were automatically computed by the data processing system. The principle of the measurement was based on a substitution procedure processing system. The principle of the measurement was based on a substitution procedure in which the heat obtained from the sample was compare with the heat obtained from in which the heat obtained from the sample was compare with the heat obtained from combustion of a similar amount of calibration material (benzoic acid) whose calorific value combustion of a similar amount of calibration material (benzoic acid) whose calorific value was known [12]. was known [12]. Measurement were obtained by burning the representative sample in high pressure Measurement were obtained by burning the representative sample in high pressure oxygen atmosphere within a metal pressure vessel or bomb. The energy released by the oxygen atmosphere within a metal pressure vessel or bomb. The energy released by the combustion. The amount of heat released during combustion is absorbed by distilled water. combustion. The amount of heat released during combustion is absorbed by distilled water. During the process, the device records the temperature change of the distilled water. During the process, the device records the temperature change of the distilled water. Multiplication of this data and calorimeter heat capacity, we can calculate the heat released Multiplication of this data and calorimeter heat capacity, we can calculate the heat released during combustion. By dividing this value, the mass of the sample is obtained by releasing during combustion. By dividing this value, the mass of the sample is obtained by releasing heat from the unit weight mass [12]. heat from the unit weight mass [12]. 82 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz 82 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz

In several studies the correlation between the age and calorific value of the willow In several studies the correlation between the age and calorific value of the willow samples was studied. In the samples of 15 genomes of nine breeds of willow, the correlation samples was studied. In the samples of 15 genomes of nine breeds of willow, the correlation was found that the calorific value of one-year-old samples was higher than that of the three- was found that the calorific value of one-year-old samples was higher than that of the three- year-old [7]. year-old [7]. In another study, the calorific value of wood and bark of two breed of willow was studied. In another study, the calorific value of wood and bark of two breed of willow was studied. In the case of both willow it can be stated that the heating values of one-year-old wood parts In the case of both willow it can be stated that the heating values of one-year-old wood parts are in all cases greater than the calorific values of the two- or three-year-old wood parts. The are in all cases greater than the calorific values of the two- or three-year-old wood parts. The bark tests showed different results between the two breeds. In one case, one-year-old bark bark tests showed different results between the two breeds. In one case, one-year-old bark samples, while the other one, three-years-old bark samples had higher calorific value [6]. samples, while the other one, three-years-old bark samples had higher calorific value [6].

1.5. Ash softening characteristics 1.5. Ash softening characteristics The softening and melting parameters of the ashes and slags were determined with a Sylab The softening and melting parameters of the ashes and slags were determined with a Sylab IF 2000G type ash fusion analyzer and an IRF 1500 furnace attached to it. The morphological IF 2000G type ash fusion analyzer and an IRF 1500 furnace attached to it. The morphological changes of the ash and slag samples were recorded with a digital camera. The instrument changes of the ash and slag samples were recorded with a digital camera. The instrument allows for the execution of standardized measurements according to CEN/TS 15370-1-2006, allows for the execution of standardized measurements according to CEN/TS 15370-1-2006, ISO 540 1995, ASTM E 953-8 (2004), AFNOR M03048, BRITISH1016-70, AS 1038.15, ISO 540 1995, ASTM E 953-8 (2004), AFNOR M03048, BRITISH1016-70, AS 1038.15, DIN 51730. DIN 51730. Cylindrical specimens of 3 mm height and 3 mm diameter were made of ashes, which Cylindrical specimens of 3 mm height and 3 mm diameter were made of ashes, which were placed on a sample holder and slid into the furnace. The device registers the image of were placed on a sample holder and slid into the furnace. The device registers the image of the test specimen placed in the furnace using the digital camera as a function of the the test specimen placed in the furnace using the digital camera as a function of the temperature of the samples and the softening parameters can be determined from the series temperature of the samples and the softening parameters can be determined from the series of images. The softening point meter is made up of the following parts: of images. The softening point meter is made up of the following parts: • furnace heated up to 1,600 °C, with a tubular working surface comprising a sample • furnace heated up to 1,600 °C, with a tubular working surface comprising a sample and a furnace atmosphere during the measurement; and a furnace atmosphere during the measurement; • a softening point meter incorporating the external control equipment of the furnace • a softening point meter incorporating the external control equipment of the furnace atmosphere and the furnace temperature, which is built with computer data atmosphere and the furnace temperature, which is built with computer data collection software; collection software; • a digital camera for photographing samples of willow. • a digital camera for photographing samples of willow.

Melting features were characterized with the specific temperature points given below. Melting features were characterized with the specific temperature points given below. • Initial Deformation Temperature (IT): the temperature at which the tip of the test • Initial Deformation Temperature (IT): the temperature at which the tip of the test sample shows 5% shrinkage in height as compared to the original height of the test sample shows 5% shrinkage in height as compared to the original height of the test sample. sample. • Deformation Temperature (DT): the temperature at which the test sample starts to • Deformation Temperature (DT): the temperature at which the test sample starts to fuse into a hemispherical shape with edges and corners starting to round off. fuse into a hemispherical shape with edges and corners starting to round off. • Softening temperature (ST): the temperature at which signs of softening (change in • Softening temperature (ST): the temperature at which signs of softening (change in surface, rounding of edges) start appearing, the test sample starts blowing up. surface, rounding of edges) start appearing, the test sample starts blowing up. • Hemispherical temperature (HT): the temperature at which the shape of the test • Hemispherical temperature (HT): the temperature at which the shape of the test sample resembles a hemisphere, the hight of the test sample is equal to 1/2 of the sample resembles a hemisphere, the hight of the test sample is equal to 1/2 of the width of the base. width of the base. • Fluid temperature (FT): the temperature at which the sample height shrinks to 1/3 • Fluid temperature (FT): the temperature at which the sample height shrinks to 1/3 of the original height, i.e. the sample melts. of the original height, i.e. the sample melts.

1.6. Ash characterization 1.6. Ash characterization The scanning electronic microscopy and energy dispersive spectroscopy (SEM/EDS) The scanning electronic microscopy and energy dispersive spectroscopy (SEM/EDS) analyses were applied to the ash and slag samples were observed experimentally, confirming analyses were applied to the ash and slag samples were observed experimentally, confirming prediction using the fusibility properties. prediction using the fusibility properties. The Effect of Age on Combustion Properties of Energy Willows 83 The Effect of Age on Combustion Properties of Energy Willows 83

This type of preparation allows to observe the morphology of the agglomerates, and to This type of preparation allows to observe the morphology of the agglomerates, and to identify the major elements that may be responsible for the melting effects. It was used a high identify the major elements that may be responsible for the melting effects. It was used a high resolution Zeiss Evo MA10 scanning electron microscope. Samples were coated with a thin resolution Zeiss Evo MA10 scanning electron microscope. Samples were coated with a thin golden layer, in order to obtain the conductivity needed for SEM observation. Software golden layer, in order to obtain the conductivity needed for SEM observation. Software included in the equipment allowed data acquisition for semi-quantitative analysis. included in the equipment allowed data acquisition for semi-quantitative analysis.

1.7. Thermoanalytical examination 1.7. Thermoanalytical examination Thermal analysis contains a group of techniques in which the property of the sample is Thermal analysis contains a group of techniques in which the property of the sample is monitored against temperature and time. Due to the temperature increase, the structural monitored against temperature and time. Due to the temperature increase, the structural composition of the sample and the process of the drying, the disappearance of volatile composition of the sample and the process of the drying, the disappearance of volatile substances and oxidation can be determined. Thermoanalytical methods are shown in Table 1 substances and oxidation can be determined. Thermoanalytical methods are shown in Table 1 [14]. [14]. Table 1 Table 1 Major Thermoanalytical Methods [14] Major Thermoanalytical Methods [14] The measured property as a function of The measured property as a function of The name of the method Applied device The name of the method Applied device temperature temperature Thermogravimetry (TG) mass Thermobalance Thermogravimetry (TG) mass Thermobalance Differential Manufactured with a Differential Manufactured with a speed of mass change speed of mass change Thermogravimetry (DTG) computer Thermogravimetry (DTG) computer Differential temperature difference between the Differential temperature difference between the DTA equipment DTA equipment Thermoanalysis (DTA) sample and the reference material Thermoanalysis (DTA) sample and the reference material speed of change in the temperature speed of change in the temperature Dual Differential Manufactured with a Dual Differential Manufactured with a difference between the sample and the difference between the sample and the Thermoanalysis (DDTA) computer Thermoanalysis (DDTA) computer reference material reference material

A derivatography is a complex thermoanalytical method, by which heat energy and weight A derivatography is a complex thermoanalytical method, by which heat energy and weight changes that accompany transformations during the heating of the test sample can be changes that accompany transformations during the heating of the test sample can be determined simultaneously with one sample. The suitable instrument for this measurement is determined simultaneously with one sample. The suitable instrument for this measurement is a derivatograph that automatically picks up the TG, DTA, DTA and DDTA curves at the a derivatograph that automatically picks up the TG, DTA, DTA and DDTA curves at the same time. With this method, the slightest mass change or heat change can be detected with same time. With this method, the slightest mass change or heat change can be detected with the highest sensitivity and precision. The equipment we use is MOM Q1500D type the highest sensitivity and precision. The equipment we use is MOM Q1500D type derivatograph [8], [15]. derivatograph [8], [15].

There are four curves on the derivatogram, which are the following [8]. There are four curves on the derivatogram, which are the following [8]. • Thermogravimetry (TG): this curve shows the mass change of the sample as a result • Thermogravimetry (TG): this curve shows the mass change of the sample as a result of a rise in temperature. of a rise in temperature. • Differential Thermogravimetry (DTG): where the TG curve has an inflection point, • Differential Thermogravimetry (DTG): where the TG curve has an inflection point, there is a peak on the DTG curve, which makes it an accurate picture of mass-change there is a peak on the DTG curve, which makes it an accurate picture of mass-change processes in the sample. processes in the sample. • Differential Thermoanalysis (DTA): the minium of the resulting curve refers to • Differential Thermoanalysis (DTA): the minium of the resulting curve refers to endothermic process and the maximum of it refers to exothermic process. endothermic process and the maximum of it refers to exothermic process. • Dual Differential Thermoanalysis (DDTA): where the DTA curve has an inflection • Dual Differential Thermoanalysis (DDTA): where the DTA curve has an inflection point, there is a DDTA curve peak to give an accurate picture of the thermal point, there is a DDTA curve peak to give an accurate picture of the thermal processes occurring in the sample. processes occurring in the sample.

84 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz 84 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz

2. RESULTS AND DISCUSSION 2. RESULTS AND DISCUSSION 2.1. Characterization of fuels 2.1. Characterization of fuels The hygroscopic moisture content in air-dry state, while the ash content, the elemental The hygroscopic moisture content in air-dry state, while the ash content, the elemental composition and the calorific value in dry state of the examined energywillows are shown in composition and the calorific value in dry state of the examined energywillows are shown in Table 2. Table 2. Table 2 Table 2 Proximate analysis, ultimate analysis (% m/m) and calorific values of the fuels Proximate analysis, ultimate analysis (% m/m) and calorific values of the fuels W Ash C H N O S HHV W Ash C H N O S HHV Sample Sample % m/m % m/m % m/m % m/m % m/m % m/m % m/m MJ/kg % m/m % m/m % m/m % m/m % m/m % m/m % m/m MJ/kg Energo 1 year 7.31 1.81 49.84 5.47 0.73 42.12 0.05 19.0 Energo 1 year 7.31 1.81 49.84 5.47 0.73 42.12 0.05 19.0 Energo 2 year 7.39 1.9 48.06 5.49 0.04 44.46 0.05 18.6 Energo 2 year 7.39 1.9 48.06 5.49 0.04 44.46 0.05 18.6

The hygroscopic moisture content of the different ages of energy willows are 7.3 and 7.4% The hygroscopic moisture content of the different ages of energy willows are 7.3 and 7.4% m/m. Ashes of energy willows are also similar: 1.8–1.9% m/m. The ultimate analysis shows m/m. Ashes of energy willows are also similar: 1.8–1.9% m/m. The ultimate analysis shows that the percentage of carbon, hydrogen and oxygen are comparable for all samples. All that the percentage of carbon, hydrogen and oxygen are comparable for all samples. All willow breeds are characterized by very low sulphur content (0.05% m/m), implying that willow breeds are characterized by very low sulphur content (0.05% m/m), implying that SOx emissions during combustion are not of concern for these fuels. Because of the similar SOx emissions during combustion are not of concern for these fuels. Because of the similar hygroscopic moisture-, carbon, hydrogen- and oxygen content, there is no significant hygroscopic moisture-, carbon, hydrogen- and oxygen content, there is no significant difference between the calorific value of one- and two-year-old samples. In the two-year-old difference between the calorific value of one- and two-year-old samples. In the two-year-old samples, the nitrogen content is lower compared to one-year-old. This is due to the fact that samples, the nitrogen content is lower compared to one-year-old. This is due to the fact that nitrogen is found in those parts of the biomass that are still growing. The willow shows a nitrogen is found in those parts of the biomass that are still growing. The willow shows a stronger growth in the first year, the nitrogen content decreases in the second year, so the stronger growth in the first year, the nitrogen content decreases in the second year, so the growth rate of the willow is also decreasing. The decreasing nitrogen content of the two years growth rate of the willow is also decreasing. The decreasing nitrogen content of the two years and increasing oxygen content means improving the combustion properties. and increasing oxygen content means improving the combustion properties.

2.2. Softening characteristics 2.2. Softening characteristics The pictures of the softening test of the ash molds of twigs of energy willow made under The pictures of the softening test of the ash molds of twigs of energy willow made under laboratory conditions are shown in Figure 2. laboratory conditions are shown in Figure 2.

Figure 2 Figure 2 Pictures of the softening test of one-year-old Energo sample Pictures of the softening test of one-year-old Energo sample at 401 °C (left) and 1,541 °C (right) at 401 °C (left) and 1,541 °C (right)

From the five typical temperature points, only two temperature points can be detected during From the five typical temperature points, only two temperature points can be detected during the test [sintering temperature (IT) and deformation temperature (DT)]. The samples showed the test [sintering temperature (IT) and deformation temperature (DT)]. The samples showed only a small shrinkage, which is due to the high Ca content found in ash. We couldn’t do the only a small shrinkage, which is due to the high Ca content found in ash. We couldn’t do the The Effect of Age on Combustion Properties of Energy Willows 85 The Effect of Age on Combustion Properties of Energy Willows 85 softening test of the ash of the two-year old willow because of the available little amount of softening test of the ash of the two-year old willow because of the available little amount of ash. There is also a high amount of Ca in the ashes of two-year-old Energo willow, so the ash ash. There is also a high amount of Ca in the ashes of two-year-old Energo willow, so the ash would probably be the same behavior during the test. would probably be the same behavior during the test.

The Figure 3 shows the degree of change in the size of ash samples from one-year-old twigs The Figure 3 shows the degree of change in the size of ash samples from one-year-old twigs of willow. of willow. 100 100

80 80

60 60

40 40

Degree of change [%]change of Degree [%]change of Degree 20 20

0 0 400 600 800 1000 1200 1400 1600 400 600 800 1000 1200 1400 1600 Temperature [°C] Temperature [°C] height width height width

Figure 3 Figure 3 The degree of change in ash samples (one-year-old twigs of willow) The degree of change in ash samples (one-year-old twigs of willow)

It can be seen that the height and width of the samples remain unchanged up to 1,000 °C. It can be seen that the height and width of the samples remain unchanged up to 1,000 °C. Between 1,000 °C and 1,550 °C, the rate of decrease in height and width is the same. At Between 1,000 °C and 1,550 °C, the rate of decrease in height and width is the same. At 1,541 °C, the height and width of the ash sample were approximately 60% of the original 1,541 °C, the height and width of the ash sample were approximately 60% of the original height and width. height and width.

2.3. Ash characterization using scanning electronic microscopy – energy dispersive 2.3. Ash characterization using scanning electronic microscopy – energy dispersive spectroscopy spectroscopy It can be found below the SEM recordings of the samples and the avarage compositions of It can be found below the SEM recordings of the samples and the avarage compositions of the recordings and the composition of the selected points. the recordings and the composition of the selected points. We homogenized the one-year-old ashes with mortar. It can be seen that several particles We homogenized the one-year-old ashes with mortar. It can be seen that several particles in the sample are drawn, mainly CaO particles. The avarage compositions of the recordings in the sample are drawn, mainly CaO particles. The avarage compositions of the recordings and the composition of the selected points shown in Figure 4 are shown in Table 3. and the composition of the selected points shown in Figure 4 are shown in Table 3.

Table 3 Table 3 Semi-quantitative analysis of Energo 1 year willow Semi-quantitative analysis of Energo 1 year willow Ashes of Energo 1 Elements [% m/m] Ashes of Energo 1 Elements [% m/m] year willow year willow C O Na Mg Al Si P S Cl K Ca Ti Mn Fe C O Na Mg Al Si P S Cl K Ca Ti Mn Fe (see Fig. 4.) (see Fig. 4.) a) picture average 9.5 30.66 1.09 4.87 0.56 0.73 6.28 2.36 0.25 16.24 26.68 0.13 0.29 0.38 a) picture average 9.5 30.66 1.09 4.87 0.56 0.73 6.28 2.36 0.25 16.24 26.68 0.13 0.29 0.38 b) picture average 12.15 35.89 0.43 4.48 0.13 0.52 5.78 1.88 0.08 15.20 22.40 0.08 0.41 0.57 b) picture average 12.15 35.89 0.43 4.48 0.13 0.52 5.78 1.88 0.08 15.20 22.40 0.08 0.41 0.57 b) picture, point 1 4.96 28.83 1.12 6.56 0.78 0.85 8.10 1.88 0.39 19.72 25.90 0.06 0.48 0.38 b) picture, point 1 4.96 28.83 1.12 6.56 0.78 0.85 8.10 1.88 0.39 19.72 25.90 0.06 0.48 0.38 b) picture, point 2 7.99 33.58 0.68 1.02 0.70 0.75 1.03 1.60 0.58 3.54 46.92 0.46 0.54 0.62 b) picture, point 2 7.99 33.58 0.68 1.02 0.70 0.75 1.03 1.60 0.58 3.54 46.92 0.46 0.54 0.62 c) picture average 15.75 35.36 0.53 3.69 0.07 0.46 5.10 1.49 0.00 14.76 22.11 0.00 0.30 0.38 c) picture average 15.75 35.36 0.53 3.69 0.07 0.46 5.10 1.49 0.00 14.76 22.11 0.00 0.30 0.38 d) picture average 9.50 30.66 1.09 4.87 0.56 0.73 6.28 2.36 0.25 16.24 26.68 0.13 0.29 0.38 d) picture average 9.50 30.66 1.09 4.87 0.56 0.73 6.28 2.36 0.25 16.24 26.68 0.13 0.29 0.38 86 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz 86 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz

a) Energo 1 year, magnification: 250× b) Energo 1 year, magnification: 500× a) Energo 1 year, magnification: 250× b) Energo 1 year, magnification: 500×

c) Energo 1 year, magnification: 500× d) Energo 1 year, magnification: 1,000× c) Energo 1 year, magnification: 500× d) Energo 1 year, magnification: 1,000×

Figure 4 Figure 4 SEM image of ashes of Energo 1 year willow SEM image of ashes of Energo 1 year willow

One of the major problems when burning a biomass, is that the melting point of the One of the major problems when burning a biomass, is that the melting point of the resulting ash is similar to the furnace temperature and the molten ash causes significant resulting ash is similar to the furnace temperature and the molten ash causes significant problems in the combustion chamber (heat insulation of heat exchanger surfaces). The problems in the combustion chamber (heat insulation of heat exchanger surfaces). The decrease of the melting point of the ash is mainly caused by the alkali metal and phosphorus decrease of the melting point of the ash is mainly caused by the alkali metal and phosphorus oxides contained therein. Although the K content is relatively high in the ashes of one- oxides contained therein. Although the K content is relatively high in the ashes of one- year-old willow, due to the high Ca content, this does not cause any major damage to the year-old willow, due to the high Ca content, this does not cause any major damage to the combustion chamber, because the softening temperature increases. combustion chamber, because the softening temperature increases.

We were inquired into the answer how the location of different particles were affected by We were inquired into the answer how the location of different particles were affected by the homogenization in unhomogenised ash, that is why the ashes of the two-year-old the homogenization in unhomogenised ash, that is why the ashes of the two-year-old samples were not homogenized. It can be seen that the CaO particles are grouped together samples were not homogenized. It can be seen that the CaO particles are grouped together in a row. The Ca content of the one- and two-year-old plants is also high, which can be in a row. The Ca content of the one- and two-year-old plants is also high, which can be explained by the fact that these plants are probably planted in calcic/lime soil. The avarage explained by the fact that these plants are probably planted in calcic/lime soil. The avarage compositions of the recordings and the composition of the selected points shown in Figure compositions of the recordings and the composition of the selected points shown in Figure 5 are shown in Table 4. 5 are shown in Table 4.

The Effect of Age on Combustion Properties of Energy Willows 87 The Effect of Age on Combustion Properties of Energy Willows 87

a) Energo 2 year, magnification: 250× b) Energo 2 year, magnification: 500× a) Energo 2 year, magnification: 250× b) Energo 2 year, magnification: 500×

c) Energo 2 year, magnification: 1,000× d) Energo 2 year, magnification: 500× c) Energo 2 year, magnification: 1,000× d) Energo 2 year, magnification: 500× Figure 5 Figure 5 SEM image of ashes of Energo 2 year willow SEM image of ashes of Energo 2 year willow

Table 4 Table 4 Semi-quantitative analysis of Energo 2 year willow Semi-quantitative analysis of Energo 2 year willow Ashes of Energo 2 Elements [% m/m] Ashes of Energo 2 Elements [% m/m] year willow (see Fig. year willow (see Fig. C O Na Mg Al Si P S Cl K Ca Ti Mn Fe C O Na Mg Al Si P S Cl K Ca Ti Mn Fe 5.) 5.) a) picture average 22.78 34.62 0.74 2.39 0.66 1.13 2.73 0.98 0.00 5.67 27.33 0.04 0.37 0.55 a) picture average 22.78 34.62 0.74 2.39 0.66 1.13 2.73 0.98 0.00 5.67 27.33 0.04 0.37 0.55 b) picture average 24.71 34.98 0.77 1.96 0.38 0.85 2.25 0.85 0.12 4.70 27.41 0.13 0.34 0.56 b) picture average 24.71 34.98 0.77 1.96 0.38 0.85 2.25 0.85 0.12 4.70 27.41 0.13 0.34 0.56 b) picture, point 1 34.36 37.53 0.82 3.55 0.31 0.32 2.60 0.83 0.00 4.17 14.98 0.00 0.13 0.40 b) picture, point 1 34.36 37.53 0.82 3.55 0.31 0.32 2.60 0.83 0.00 4.17 14.98 0.00 0.13 0.40 b) picture, point 2 9.76 38.68 0.86 0.94 0.70 0.75 0.97 0.87 0.47 1.78 43.52 0.27 0.18 0.26 b) picture, point 2 9.76 38.68 0.86 0.94 0.70 0.75 0.97 0.87 0.47 1.78 43.52 0.27 0.18 0.26 c) picture average 13.00 35.26 0.49 1.63 0.50 0.59 1.77 1.08 0.30 3.36 41.09 0.11 0.24 0.56 c) picture average 13.00 35.26 0.49 1.63 0.50 0.59 1.77 1.08 0.30 3.36 41.09 0.11 0.24 0.56 d) picture average 18.38 35.81 0.48 2.80 0.40 0.66 3.06 1.02 0.04 6.10 29.93 0.17 0.41 0.73 d) picture average 18.38 35.81 0.48 2.80 0.40 0.66 3.06 1.02 0.04 6.10 29.93 0.17 0.41 0.73 d) picture, point 1 7.53 37.76 0.88 1.58 0.62 0.61 1.48 0.90 0.23 1.87 46.28 0.00 0.15 0.10 d) picture, point 1 7.53 37.76 0.88 1.58 0.62 0.61 1.48 0.90 0.23 1.87 46.28 0.00 0.15 0.10 d) picture, point 2 7.82 30.48 0.78 0.95 0.77 0.78 0.95 1.46 0.65 2.06 51.81 0.52 0.50 0.48 d) picture, point 2 7.82 30.48 0.78 0.95 0.77 0.78 0.95 1.46 0.65 2.06 51.81 0.52 0.50 0.48 d) picture, point 3 6.69 39.29 1.16 6.26 0.27 0.59 9.42 2.02 0.13 14.55 18.91 0.11 0.13 0.45 d) picture, point 3 6.69 39.29 1.16 6.26 0.27 0.59 9.42 2.02 0.13 14.55 18.91 0.11 0.13 0.45

88 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz 88 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz

The ash of two-year-old sample has a higher carbon content, suggesting that the burning of The ash of two-year-old sample has a higher carbon content, suggesting that the burning of carbon in the samples was incomplete. Carbon content can be reduced by intensifying air/fuel carbon in the samples was incomplete. Carbon content can be reduced by intensifying air/fuel mixing or possibly by tertiary air intake. Due to the carbon content thus burnt, the amount of mixing or possibly by tertiary air intake. Due to the carbon content thus burnt, the amount of fly ash may be reduced in the flue gas. fly ash may be reduced in the flue gas. Compared to the ash of one year old samples, the sulfur, phosphorus, potassium, Compared to the ash of one year old samples, the sulfur, phosphorus, potassium, magnesium content and calcium content increase in the two years old samples. This can be magnesium content and calcium content increase in the two years old samples. This can be explained by the fact that in the first year of the plant, due to its stronger growth, it drains explained by the fact that in the first year of the plant, due to its stronger growth, it drains much more nutrients from the ground and supplies the nutrients needed to its younger parts. much more nutrients from the ground and supplies the nutrients needed to its younger parts. The results of the elemental composition of the ashes confirm the results of the softening The results of the elemental composition of the ashes confirm the results of the softening tests. tests.

2.4. Thermoanalytical examination 2.4. Thermoanalytical examination Figure 6 and 7 shows a derivatogram of one- and two-year-old willow samples. Figure 6 and 7 shows a derivatogram of one- and two-year-old willow samples.

Figure 6 Figure 6 Derivatogram of the one-year-old willow Derivatogram of the one-year-old willow

Figure 7 Figure 7 Derivatogram of the two-year-old willow Derivatogram of the two-year-old willow The Effect of Age on Combustion Properties of Energy Willows 89 The Effect of Age on Combustion Properties of Energy Willows 89

Table 5 shows the parameters of thermal analysis of the one- and two-year-old samples. Table 5 shows the parameters of thermal analysis of the one- and two-year-old samples. Table 5 Table 5 Parameters of thermal analysis investigation Parameters of thermal analysis investigation Parameters One-year-old Two-year-old Parameters One-year-old Two-year-old Starting temperature [°C] 30 40 Starting temperature [°C] 30 40 Ending temperature [°C] 1,000 800 Ending temperature [°C] 1,000 800 Heating speed [°C/min] 8 10 Heating speed [°C/min] 8 10 Test time [sec] 122 77.5 Test time [sec] 122 77.5 Sample weight [g] 101.4 54.6 Sample weight [g] 101.4 54.6

Table 6 shows the temperature and weight change of the characteristic points that can be read Table 6 shows the temperature and weight change of the characteristic points that can be read from the derivatogram. from the derivatogram. Table 6 Table 6 Typical temperature and weight change points for the derivatogram Typical temperature and weight change points for the derivatogram Typical One-year-old Two-year-old Typical One-year-old Two-year-old point T [°C] TG [%] T [°C] TG [%] point T [°C] TG [%] T [°C] TG [%] 1 98.3 –2.75 105.1 –3.02 1 98.3 –2.75 105.1 –3.02 2 194.2 –6.28 195.7 –6.52 2 194.2 –6.28 195.7 –6.52 3 292.4 –19 285.1 –19.74 3 292.4 –19 285.1 –19.74 4 310.2 –26.37 301.6 –27.95 4 310.2 –26.37 301.6 –27.95 5 334.2 –39.1 325.5 –44.62 5 334.2 –39.1 325.5 –44.62 6 403.0 –62.0 373.9 –63.71 6 403.0 –62.0 373.9 –63.71 7 727.8 –96.16 587.6 –96.99 7 727.8 –96.16 587.6 –96.99 8 736.3 –96.55 599.2 –98.33 8 736.3 –96.55 599.2 –98.33 9 955.2 –97.12 762.7 –99.4 9 955.2 –97.12 762.7 –99.4

Based on the derivatogram of the one- and two-year-old Energo willows, the following can Based on the derivatogram of the one- and two-year-old Energo willows, the following can be established: be established: • drying process of Energo willlows begins at ambient temperature and continues at • drying process of Energo willlows begins at ambient temperature and continues at an accelerating pace up to 98.3 °C in case of one-year-old, and 105 °C in case of an accelerating pace up to 98.3 °C in case of one-year-old, and 105 °C in case of two-year-old; two-year-old; • at temperatures ranging from 95 to 110 °C the moisture is the most intense of leaving • at temperatures ranging from 95 to 110 °C the moisture is the most intense of leaving the samples; the samples; • the drying of the tested samples at 194.2 °C (in case of one-year-old) and 195.7 °C • the drying of the tested samples at 194.2 °C (in case of one-year-old) and 195.7 °C (in case of two-year-old) it was completely completed; (in case of two-year-old) it was completely completed; • the leaving of the volatiles at a temperature between 195 and 200 °C and are • the leaving of the volatiles at a temperature between 195 and 200 °C and are accelerating at 334.2 °C (in case of one-year-old) and at 325 °C (in case of two- accelerating at 334.2 °C (in case of one-year-old) and at 325 °C (in case of two- year-old); year-old); • at temperatures ranging from 300 to 350 °C the leaving of the volatiles are the most • at temperatures ranging from 300 to 350 °C the leaving of the volatiles are the most intensive, and it ends at 403 °C (in case of one-year-old) and at 373 °C (in case of intensive, and it ends at 403 °C (in case of one-year-old) and at 373 °C (in case of two-year-old); two-year-old); • above 955 °C (in case of one-year-old) and 762 °C (in case of two-year-old) the • above 955 °C (in case of one-year-old) and 762 °C (in case of two-year-old) the weight loss the heat development and the combustion have been completed. weight loss the heat development and the combustion have been completed. 90 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz 90 Dóra Mentes–Csaba Póliska–Tamásné Szemmelveisz

Based on this, it is possible to say that both samples has similar temperature of the Based on this, it is possible to say that both samples has similar temperature of the completion of drying and starting temperature of the secession of the volatiles. Due to the completion of drying and starting temperature of the secession of the volatiles. Due to the differently selected parameters of the tests, temperature range of intensive combustion of the differently selected parameters of the tests, temperature range of intensive combustion of the two-year Energo was lower and the combustion was completed at a lower temperature. two-year Energo was lower and the combustion was completed at a lower temperature. From the results provided by the derivativogram, the approximate structural composition From the results provided by the derivativogram, the approximate structural composition of the energy willow (moisture, volatile, fixed carbon and ash content) can be calculated, as of the energy willow (moisture, volatile, fixed carbon and ash content) can be calculated, as shown in Table 7. shown in Table 7. Table 7 Table 7 Calculated composition as the results of the thermoanalytical measurements Calculated composition as the results of the thermoanalytical measurements

Name of the Moisture Volatile Fixed carbon Ash Name of the Moisture Volatile Fixed carbon Ash substance [% m/m] substance [% m/m] One-year-old Energo 6.28 55.72 34.55 3.45 One-year-old Energo 6.28 55.72 34.55 3.45 Two-year-old Two-year-old 6.52 57.19 34.62 1.67 6.52 57.19 34.62 1.67 Energo Energo

By increasing age, hygroscopic moisture and fixed carbon content do not change By increasing age, hygroscopic moisture and fixed carbon content do not change significantly. Differences can only be measured in the volatile and ash content. significantly. Differences can only be measured in the volatile and ash content.

CONCLUSION CONCLUSION Based on the combustion tests carried out on one- and two-year-old energy willow, it can be Based on the combustion tests carried out on one- and two-year-old energy willow, it can be stated that: stated that: • Increasing the age of the plant reduces the nitrogen content and increases the oxygen • Increasing the age of the plant reduces the nitrogen content and increases the oxygen content. content. • The calorific value of one-year-old willow is greater than the two-year-old. This • The calorific value of one-year-old willow is greater than the two-year-old. This result is the same as that available in the literature. result is the same as that available in the literature. • In the ashes of plants planted in presumably calcareous soil the Ca ratio and the ash • In the ashes of plants planted in presumably calcareous soil the Ca ratio and the ash softening temperature is high, therefore it hasn’t to be afraid of damage of the softening temperature is high, therefore it hasn’t to be afraid of damage of the combustion chamber. In the ash of two-years-old sample the Ca ratio is higher than combustion chamber. In the ash of two-years-old sample the Ca ratio is higher than in one-year-old. in one-year-old. • Increasing the age of the willows reduces the sulfur, phosphorus, potassium, and • Increasing the age of the willows reduces the sulfur, phosphorus, potassium, and magnesium content of the ash. This can be explained that biomass supplies nutrients magnesium content of the ash. This can be explained that biomass supplies nutrients to tissue parts that are still growing, in the older twigs it has less nutrients. to tissue parts that are still growing, in the older twigs it has less nutrients. • Due to the differently selected parameters of the tests, temperature range of • Due to the differently selected parameters of the tests, temperature range of intensive combustion of the two-year Energo was lower and the combustion was intensive combustion of the two-year Energo was lower and the combustion was completed at a lower temperature. completed at a lower temperature.

AKNOWLEDGEMENT AKNOWLEDGEMENT Hereby we express our special thanks to Tamás Koós for the ultimate analysis, thermal analysis and Hereby we express our special thanks to Tamás Koós for the ultimate analysis, thermal analysis and softening test, to Árpád Kovács and Dániel Koncz-Horváth for the scanning electron microscope softening test, to Árpád Kovács and Dániel Koncz-Horváth for the scanning electron microscope measurements. measurements. The research supported by the ÚNKP-17-2-I.-ME/16 New National Excellence Program of the Ministry The research supported by the ÚNKP-17-2-I.-ME/16 New National Excellence Program of the Ministry of Human Capacities. of Human Capacities.

The Effect of Age on Combustion Properties of Energy Willows 91 The Effect of Age on Combustion Properties of Energy Willows 91

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Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 92–97. Materials Science and Engineering, Volume 43, No. 1 (2018) pp. 92–97.

APPLICATION OF DIISOCYANATE ADDITIVE APPLICATION OF DIISOCYANATE ADDITIVE IN RIGID PVC/WOOD FLOUR COMPOSITE IN RIGID PVC/WOOD FLOUR COMPOSITE

KRISZTINA ROMÁN1–TAMÁS J. SZABÓ2 –KÁLMÁN MAROSSY 3 KRISZTINA ROMÁN1–TAMÁS J. SZABÓ2 –KÁLMÁN MAROSSY 3

In this paper, we are dealing with the preparation of various PVC/Wood flour/MDI composites. Using In this paper, we are dealing with the preparation of various PVC/Wood flour/MDI composites. Using additional additives to further develop Wood/PVC (WPVC) composites. For the tests, high purity MDI additional additives to further develop Wood/PVC (WPVC) composites. For the tests, high purity MDI (methylene diphenyl diisocyanate) was used. This additional agent was used in order to improve the (methylene diphenyl diisocyanate) was used. This additional agent was used in order to improve the adhesion between PVC and wood. The agent was used for surface treatment of the wood. The wood was adhesion between PVC and wood. The agent was used for surface treatment of the wood. The wood was treated with 1%, 2% and 5% by weight MDI. A number of tests were performed on the samples. From the treated with 1%, 2% and 5% by weight MDI. A number of tests were performed on the samples. From the measurement results, the modifying effects of the MDI can be observed. In some measurements, the measurement results, the modifying effects of the MDI can be observed. In some measurements, the properties of the samples change, but only slightly. The mixture containing of 5% by weight MDI, showed properties of the samples change, but only slightly. The mixture containing of 5% by weight MDI, showed greatly decreased thermal stability, but the tensile properties have increased. Based on the results, some greatly decreased thermal stability, but the tensile properties have increased. Based on the results, some properties of the specimens can be improved by increasing the amount of MDI. properties of the specimens can be improved by increasing the amount of MDI. Keywords: PVC, composite, mechanical properties Keywords: PVC, composite, mechanical properties

INTRODUCTION INTRODUCTION Products made from polyvinyl chloride (PVC) can be found in many areas in the world. Most Products made from polyvinyl chloride (PVC) can be found in many areas in the world. Most of these, we can commonly find it in the industry area, where various products of PVC of these, we can commonly find it in the industry area, where various products of PVC appear, such as drainage pipes, window/door profiles or floor covers [1]. Because of the appear, such as drainage pipes, window/door profiles or floor covers [1]. Because of the growing demand for special applications the need for product with special properties [2]. In growing demand for special applications the need for product with special properties [2]. In order to satisfy demand for improvements, it is necessary to improve present materials or order to satisfy demand for improvements, it is necessary to improve present materials or products, in order to get new materials with better properties. The properties of PVC can be products, in order to get new materials with better properties. The properties of PVC can be improved by mixing it with additives. PVC is a difficult to break down biologically material; improved by mixing it with additives. PVC is a difficult to break down biologically material; therefore it is preferred to be combined with natural materials. By mixing the two materials, therefore it is preferred to be combined with natural materials. By mixing the two materials, the product becomes more biodegradable and also more resistant mechanically. the product becomes more biodegradable and also more resistant mechanically. Beside to the wood fiber/flour the wood and plastic composites may be also made of Beside to the wood fiber/flour the wood and plastic composites may be also made of thermoplastic or thermoset polymers. Processing techniques for thermoplastics had been thermoplastic or thermoset polymers. Processing techniques for thermoplastics had been known since the early 1900s. The wood additives are dispersed in the plastic melt, and then known since the early 1900s. The wood additives are dispersed in the plastic melt, and then the mixtures are processed. The application of this technology has been going on since the the mixtures are processed. The application of this technology has been going on since the 1980s and has since expended [1]. The natural flour or fiber can work as a strengthening 1980s and has since expended [1]. The natural flour or fiber can work as a strengthening phase in the polymer matrix, where it gives some positive properties compared to the original phase in the polymer matrix, where it gives some positive properties compared to the original PVC [3]. These advantages are the reduced price and excellent mechanical properties and PVC [3]. These advantages are the reduced price and excellent mechanical properties and fire safety properties compared to wooden materials. Thus, the other advantages of the wood- fire safety properties compared to wooden materials. Thus, the other advantages of the wood- PVC combination are reduction of the flammability of the wood, and also reducing the PVC combination are reduction of the flammability of the wood, and also reducing the amount of toxic materials compounds from the burning of PVC. Variety of processing amount of toxic materials compounds from the burning of PVC. Variety of processing methods can be used to produce this wood-reinforced polymer composites, such as injection methods can be used to produce this wood-reinforced polymer composites, such as injection

1 Institute of Ceramics and Polymer Engineering, University of Miskolc 1 Institute of Ceramics and Polymer Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 2 Institute of Ceramics and Polymer Engineering, University of Miskolc 2 Institute of Ceramics and Polymer Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 3 Institute of Ceramics and Polymer Engineering, University of Miskolc 3 Institute of Ceramics and Polymer Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected]

Application of Diisocyanate Additive in Rigid PVC/Wood Flour Composite 93 Application of Diisocyanate Additive in Rigid PVC/Wood Flour Composite 93 molding, extrusion or pressure molding [4]. However, the disadvantages of the WPVC molding, extrusion or pressure molding [4]. However, the disadvantages of the WPVC materials are the change in weather ability. The worst of all of them are: degradation due to materials are the change in weather ability. The worst of all of them are: degradation due to the high temperature or moisture absorption, UV radiation [5]. So it is necessary to use the high temperature or moisture absorption, UV radiation [5]. So it is necessary to use different types of additives in the mixtures. These additives are stabilizers, antioxidants, different types of additives in the mixtures. These additives are stabilizers, antioxidants, biocides and other additives which increase the lifetime of the product [6]. The problem with biocides and other additives which increase the lifetime of the product [6]. The problem with the mixing of thermoplastics and natural additives is the weak adhesion between them, which the mixing of thermoplastics and natural additives is the weak adhesion between them, which is the results of a low chemical affinity between the cellulose and the “hydrophobic” plastic is the results of a low chemical affinity between the cellulose and the “hydrophobic” plastic [7]. The only way to increase the adhesion if we are using coupling agents between the [7]. The only way to increase the adhesion if we are using coupling agents between the additive and the polymer. In reality, it is very difficult to find the ideal coupling agent, which additive and the polymer. In reality, it is very difficult to find the ideal coupling agent, which achieves the necessary requirements. In case of this research, the isocyanates proved to be achieves the necessary requirements. In case of this research, the isocyanates proved to be reliable. The possibility of forming primary bonds – such as covalent bond’s between reliable. The possibility of forming primary bonds – such as covalent bond’s between cellulose and isocyanate – and forming secondary bonds between the isocyanate and PVC is cellulose and isocyanate – and forming secondary bonds between the isocyanate and PVC is present. The mechanical properties are improved by the wood flour, because it reinforced the present. The mechanical properties are improved by the wood flour, because it reinforced the polymer matrix. Generally, the efficiency of the coupling agents also depends on the method polymer matrix. Generally, the efficiency of the coupling agents also depends on the method of application, the method of surface treatment and the chemical structure [8]. of application, the method of surface treatment and the chemical structure [8]. In order to improve the material strength on the interface between the wood flour and PVC, In order to improve the material strength on the interface between the wood flour and PVC, we used additional additives in our research. In case of PVC, usually not necessary, but also we used additional additives in our research. In case of PVC, usually not necessary, but also was useful to use an extra agent to increase the connection. Therefore, the surface of natural was useful to use an extra agent to increase the connection. Therefore, the surface of natural filler was treated with MDI. We experimented with pure MDI, because it can be advantage filler was treated with MDI. We experimented with pure MDI, because it can be advantage of MDI that it can be chemically bonded to the free-OH groups of cellulose and lignin as of MDI that it can be chemically bonded to the free-OH groups of cellulose and lignin as well. The tension and mobility of MDI is very low, so is does not escape from the composites. well. The tension and mobility of MDI is very low, so is does not escape from the composites. Five types of measurements were carried out: Five types of measurements were carried out: ‒ Density ‒ Density ‒ Hardness test (Shore D) ‒ Hardness test (Shore D) ‒ Tensile test (100 mm/min) ‒ Tensile test (100 mm/min) ‒ Impact test (Charpy method) ‒ Impact test (Charpy method) ‒ Thermal Stability test (Stabilimetr method) ‒ Thermal Stability test (Stabilimetr method)

1. MATERIALS 1. MATERIALS The base mixtures with the required additive were: suspension PVC powder (Ongrovil S- The base mixtures with the required additive were: suspension PVC powder (Ongrovil S- 5258), Ca–Zn based stabilizer, paraffin based internal and glycerin ester type external 5258), Ca–Zn based stabilizer, paraffin based internal and glycerin ester type external lubricants, CaCO3 filler, acryl based processing aids and beech wood flour. To create a triple lubricants, CaCO3 filler, acryl based processing aids and beech wood flour. To create a triple system, pure methyl diphenyl diisocyanate was used. Table 1 shows the additive’s quantity system, pure methyl diphenyl diisocyanate was used. Table 1 shows the additive’s quantity in phr (per hundred resin). in phr (per hundred resin). Table 1 Table 1 Formulations of the PVC/Wood/MDI composites Formulations of the PVC/Wood/MDI composites Wood Wood Processig Processig PVC Stabilizers Lubricants Filler flour – PVC Stabilizers Lubricants Filler flour – aids aids MDI MDI 100 2.4 2 7 10 20 100 2.4 2 7 10 20

1.1. Sample preparation 1.1. Sample preparation First and foremost, we were carrying out the surface treatment of the wood flour. The MDI First and foremost, we were carrying out the surface treatment of the wood flour. The MDI was applied 1, 2 and 5% by weight to the wood’s surface for better miscibility and adhesion was applied 1, 2 and 5% by weight to the wood’s surface for better miscibility and adhesion with the PVC. The mixtures were hot mill rolled at 170 °C for until fully homogeneous and with the PVC. The mixtures were hot mill rolled at 170 °C for until fully homogeneous and were pressed to two different thicknesses at 175 °C. For the 4 mm thickness sheets, 5 minute were pressed to two different thicknesses at 175 °C. For the 4 mm thickness sheets, 5 minute 94 Krisztina Román–Tamás J. Szabó–Kálmán Marossy 94 Krisztina Román–Tamás J. Szabó–Kálmán Marossy at 20 bar and 5 minute at 300 bar pressures were used. While, for the 1 mm thickness at 20 bar and 5 minute at 300 bar pressures were used. While, for the 1 mm thickness specimens, 2.5 minute at 20 bar and 2.5 minute at 300 bar pressures were used. From the specimens, 2.5 minute at 20 bar and 2.5 minute at 300 bar pressures were used. From the prepared sheets, standard sized specimens were stamped using a pneumatic punching prepared sheets, standard sized specimens were stamped using a pneumatic punching equipment. equipment.

2. MEASUREMENT METHODS 2. MEASUREMENT METHODS 2.1. Density and hardness tests 2.1. Density and hardness tests Based on principle of Archimedes, the density values were determined by water immersion Based on principle of Archimedes, the density values were determined by water immersion measurement with a Mettler-Toledo digital analytical scale. measurement with a Mettler-Toledo digital analytical scale. The hardness tests were carried out using a Zwick/Roell Ho.43150 type digital Shore D The hardness tests were carried out using a Zwick/Roell Ho.43150 type digital Shore D testing equipment. The Shore D test tools are usually used to measure harder plastics and testing equipment. The Shore D test tools are usually used to measure harder plastics and elastomers, so it is well suitable for measuring the PVC composite samples. The tests were elastomers, so it is well suitable for measuring the PVC composite samples. The tests were carried out according to ISO 868. On each specimens of four mm thickness 20 parallel carried out according to ISO 868. On each specimens of four mm thickness 20 parallel measurements were made to determine the mean values and standard deviation. measurements were made to determine the mean values and standard deviation.

2.2. Tensile and impact tests 2.2. Tensile and impact tests The tensile tests were carried out using an INSTRON 5566 universal material tester The tensile tests were carried out using an INSTRON 5566 universal material tester according to ASTM D638-10 standard. During the tests, the stress-elongation behavior of the according to ASTM D638-10 standard. During the tests, the stress-elongation behavior of the samples can be determined. The tests were carried out at room temperature (23 ± 1), 50% samples can be determined. The tests were carried out at room temperature (23 ± 1), 50% humidity and with a cross-head speed of 100 mm/min. humidity and with a cross-head speed of 100 mm/min. Impact resistance of the materials can be determined by the impact tests. The impact tests Impact resistance of the materials can be determined by the impact tests. The impact tests were carried out according to the Charpy method (EN ISO 179) using a CEAST 6545 were carried out according to the Charpy method (EN ISO 179) using a CEAST 6545 instrumented pendulum equipment. The tests were done with a 2J hammer. instrumented pendulum equipment. The tests were done with a 2J hammer.

2.3. Thermal stability tests 2.3. Thermal stability tests The thermal stability can be determined using a Stabilometer. The device is used to examine The thermal stability can be determined using a Stabilometer. The device is used to examine the heat stability of PVC, PVC copolymers, blends and films, as function of time. The test the heat stability of PVC, PVC copolymers, blends and films, as function of time. The test can be used to determine the time, at which pre-determined color changes occur within the can be used to determine the time, at which pre-determined color changes occur within the materials at 190 °C. The tests were carried out on a Stabilimetr WC45 measuring equipment. materials at 190 °C. The tests were carried out on a Stabilimetr WC45 measuring equipment. The material thickness was 0.4 mm. The material thickness was 0.4 mm.

3. RESULTS 3. RESULTS 3.1. Density and hardness tests 3.1. Density and hardness tests During the tests, the density values of various composites can be determined. The composites During the tests, the density values of various composites can be determined. The composites of MDI may have a more compact structure, which could mean that the MDI is connected of MDI may have a more compact structure, which could mean that the MDI is connected both to the wood and the PVC better. both to the wood and the PVC better. Table 2 Table 2 Result of density tests of the PVC/Wood and PVC/Wood/MDI composites Result of density tests of the PVC/Wood and PVC/Wood/MDI composites Sample Density (g/cm3) Sample Density (g/cm3) PVC/Wood 1.38 ± 0.001 PVC/Wood 1.38 ± 0.001 PVC/Wood/MDI (1%) 1.43 ± 0.005 PVC/Wood/MDI (1%) 1.43 ± 0.005 PVC/Wood/MDI (2%) 1.43 ± 0,001 PVC/Wood/MDI (2%) 1.43 ± 0,001 PVC/Wood/MDI (5%) 1.42 ± 0.003 PVC/Wood/MDI (5%) 1.42 ± 0.003 Application of Diisocyanate Additive in Rigid PVC/Wood Flour Composite 95 Application of Diisocyanate Additive in Rigid PVC/Wood Flour Composite 95

However, the results show differences between the treated and untreated samples, but only However, the results show differences between the treated and untreated samples, but only slight differences treated samples. The amount of applied MDI does only affect the density slight differences treated samples. The amount of applied MDI does only affect the density slightly. slightly. Table 3 Table 3 Results of the hardness and deviation values of the specimens Results of the hardness and deviation values of the specimens Sample Shore D Sample Shore D PVC/Wood 80.76 ± 0.35 PVC/Wood 80.76 ± 0.35 PVC/Wood/MDI (1%) 80.13 ± 0.45 PVC/Wood/MDI (1%) 80.13 ± 0.45 PVC/Wood/MDI (2%) 81.01 ± 0.36 PVC/Wood/MDI (2%) 81.01 ± 0.36 PVC/Wood/MDI (5%) 81.19 ± 0.79 PVC/Wood/MDI (5%) 81.19 ± 0.79

The results of the hardness tests show no significant differences. In case of MDI composite The results of the hardness tests show no significant differences. In case of MDI composite the MDI did not cause material softening. If we are taking notice of the deviation values they the MDI did not cause material softening. If we are taking notice of the deviation values they are very close to each other. are very close to each other.

3.2. Tensile and impact tests 3.2. Tensile and impact tests The modifying effect of MDI is visible in Table 4. In case of 5% MDI mixtures, significant The modifying effect of MDI is visible in Table 4. In case of 5% MDI mixtures, significant increases in the strength values were observed. Figure 1 shows the elongation-stress curves, increases in the strength values were observed. Figure 1 shows the elongation-stress curves, where it can be seen that the deformations were almost the same, the tensile strength where it can be seen that the deformations were almost the same, the tensile strength increased by adding increased amounts of additive. For all blends, the tensile test shows increased by adding increased amounts of additive. For all blends, the tensile test shows significant improvement in mechanical properties. significant improvement in mechanical properties.

Figure 1 Figure 1 Stress-strain curves of PVC/Wood and PVC/Wood/MDI composites Stress-strain curves of PVC/Wood and PVC/Wood/MDI composites 96 Krisztina Román–Tamás J. Szabó–Kálmán Marossy 96 Krisztina Román–Tamás J. Szabó–Kálmán Marossy

Table 4 Table 4 Result of the tensile tests at room temperature Result of the tensile tests at room temperature Sample Tensile strength (MPa) Sample Tensile strength (MPa) PVC/Wood 42.05 ± 0.97 PVC/Wood 42.05 ± 0.97 PVC/Wood/MDI (1%) 39.33 ± 0.59 PVC/Wood/MDI (1%) 39.33 ± 0.59 PVC/Wood/MDI (2%) 39.01 ± 0.92 PVC/Wood/MDI (2%) 39.01 ± 0.92 PVC/Wood/MDI (5%) 50.54 ± 1.02 PVC/Wood/MDI (5%) 50.54 ± 1.02

In the impact strengths considering the deviation values only slight changes were observed. In the impact strengths considering the deviation values only slight changes were observed. Accordingly, MDI seems to have no significant effect on the impact strength. Accordingly, MDI seems to have no significant effect on the impact strength.

Table 5 Table 5 Results of Charpy – impact tests Results of Charpy – impact tests Sample Impact strength (kJ/m2) Sample Impact strength (kJ/m2) PVC/Wood 2.50 ± 0.03 PVC/Wood 2.50 ± 0.03 PVC/Wood/MDI (1%) 2.32 ± 0.27 PVC/Wood/MDI (1%) 2.32 ± 0.27 PVC/Wood/MDI (2%) 2.44 ± 0.05 PVC/Wood/MDI (2%) 2.44 ± 0.05 PVC/Wood/MDI (5%) 2.35 ± 0.07 PVC/Wood/MDI (5%) 2.35 ± 0.07

3.3. Thermal stability tests 3.3. Thermal stability tests During the thermal stability tests, the samples were inserted into the measuring equipments During the thermal stability tests, the samples were inserted into the measuring equipments at 190 °C. During the evaluation the sample’s time scale was compared to each other. The at 190 °C. During the evaluation the sample’s time scale was compared to each other. The thermal stability values were that time, when predetermined color changes occurred to the thermal stability values were that time, when predetermined color changes occurred to the samples. The times are expressed in minutes. samples. The times are expressed in minutes.

Figure 2 Figure 2 Result of PVC/Wood and PVC/Wood/MDI thermal stability tests Result of PVC/Wood and PVC/Wood/MDI thermal stability tests

Figure 2 shows that the thermal stability of the 1% MDI composites (70 minutes) composite Figure 2 shows that the thermal stability of the 1% MDI composites (70 minutes) composite was becoming worse with increasing MDI content. Larger sensitivity was measured at 5% was becoming worse with increasing MDI content. Larger sensitivity was measured at 5% composites (35 minutes). Thus, increasing the MDI content the heat resistance of the material composites (35 minutes). Thus, increasing the MDI content the heat resistance of the material is reduced. This was probably caused by the reactive amide content of the urethane bond is reduced. This was probably caused by the reactive amide content of the urethane bond formed between the cellulose/lignin and the isocyanate which can promote the scission of the formed between the cellulose/lignin and the isocyanate which can promote the scission of the HCl, decreasing the thermal stability of PVC. HCl, decreasing the thermal stability of PVC.

Application of Diisocyanate Additive in Rigid PVC/Wood Flour Composite 97 Application of Diisocyanate Additive in Rigid PVC/Wood Flour Composite 97

SUMMARY SUMMARY In this research, four different composites were prepared and tested. Numbers of tests were In this research, four different composites were prepared and tested. Numbers of tests were carried out on the specimens to determine the properties of the developed new material carried out on the specimens to determine the properties of the developed new material structures. Based on the results of density tests, those composites which contained MDI were structures. Based on the results of density tests, those composites which contained MDI were more compact that the other. Further tests would be needed to understand the result of the more compact that the other. Further tests would be needed to understand the result of the impact tests. From the results, an apparent decrease in strength is observed, probable caused impact tests. From the results, an apparent decrease in strength is observed, probable caused by the MDI, because the MDI works as a hard segment in these composites, making them by the MDI, because the MDI works as a hard segment in these composites, making them more rigid/brittle. The results of the 5% by weight MDI containing mixture provided more rigid/brittle. The results of the 5% by weight MDI containing mixture provided excellent tensile strength. We will also investigate this further. Probably, due to the strong excellent tensile strength. We will also investigate this further. Probably, due to the strong interaction between the polymer matrix and the organic filler, large parts of the load were interaction between the polymer matrix and the organic filler, large parts of the load were taken over by the fibrous filler (wood flour). From the thermal stability tests, significant taken over by the fibrous filler (wood flour). From the thermal stability tests, significant deterioration was observed. If we increased the dose of MDI then the thermal resistance of deterioration was observed. If we increased the dose of MDI then the thermal resistance of the composite deteriorated. This was expected, because the nitrogen content of the the composite deteriorated. This was expected, because the nitrogen content of the compounds generally has a negative effect on the PVC is thermal stability. In a continuation compounds generally has a negative effect on the PVC is thermal stability. In a continuation of the research means and methods will be sought after and tested to mitigate the MDI’s of the research means and methods will be sought after and tested to mitigate the MDI’s detrimental effect on thermal stability without compromising the improved tensile behavior detrimental effect on thermal stability without compromising the improved tensile behavior but hopefully improve on the impact resistance. but hopefully improve on the impact resistance.

ACKNOWLEDGMENT ACKNOWLEDGMENT This research was supported by the European Union ant the Hungarian State, co-financed by the This research was supported by the European Union ant the Hungarian State, co-financed by the European Regional Development Fund in the framework of the GINOP – 2.3.4.-15-2016-00004 project, European Regional Development Fund in the framework of the GINOP – 2.3.4.-15-2016-00004 project, aimed to promote the cooperation between the higher education and the industry. aimed to promote the cooperation between the higher education and the industry.

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INFLUENCE OF CHAIN EXTENDER ON SOFT AND INFLUENCE OF CHAIN EXTENDER ON SOFT AND HARD SEGMENT OF POLYURETHANE ELASTOMERS HARD SEGMENT OF POLYURETHANE ELASTOMERS

PATCHARAPON SOMDEE1–TÍMEA LASSÚ-KUKNYÓ– PATCHARAPON SOMDEE1–TÍMEA LASSÚ-KUKNYÓ– CSABA KÓNYA–KÁLMÁN MAROSSY2 CSABA KÓNYA–KÁLMÁN MAROSSY2

The goal of this study is investigation of the effect of chain extender content consisting of flexible The goal of this study is investigation of the effect of chain extender content consisting of flexible polyurethane elastomers at 7 phr and rigid polyurethane elastomers at 34 phr on mechanical, thermal polyurethane elastomers at 7 phr and rigid polyurethane elastomers at 34 phr on mechanical, thermal and structural properties of polyurethane elastomers (PUR). Firstly, polypropylene glycol (PPG) was and structural properties of polyurethane elastomers (PUR). Firstly, polypropylene glycol (PPG) was solution mixed with chain extender, amine catalyst, air release additive and moisture scavenger. After solution mixed with chain extender, amine catalyst, air release additive and moisture scavenger. After that, the mixture was shear mixed with diphenylmethane-4,4’-diisocyanate (MDI). In this study, the that, the mixture was shear mixed with diphenylmethane-4,4’-diisocyanate (MDI). In this study, the chain extender is monoethylene glycol (EG). Mechanical properties of polyurethane elastomers were chain extender is monoethylene glycol (EG). Mechanical properties of polyurethane elastomers were tested by Shore A/D hardness and tensile test. Thermal properties and structure were investigated by tested by Shore A/D hardness and tensile test. Thermal properties and structure were investigated by differential scanning calorimetry (DSC) and thermally stimulated discharge (TSD) method. Density differential scanning calorimetry (DSC) and thermally stimulated discharge (TSD) method. Density was also measured in the study. Results show Shore A and D hardness increase with increasing EG was also measured in the study. Results show Shore A and D hardness increase with increasing EG content from 7 to 34 phr. Tensile strength increases when EG content is increased while elongation at content from 7 to 34 phr. Tensile strength increases when EG content is increased while elongation at break decreases at EG content of 34 phr. Density of PUR slightly increases when EG content is break decreases at EG content of 34 phr. Density of PUR slightly increases when EG content is increased. For structure characterization, DSC thermogram clearly observed a relaxation temperature increased. For structure characterization, DSC thermogram clearly observed a relaxation temperature of soft segment at EG content of 7 phr. Furthermore, TSD technique was used to investigate chain of soft segment at EG content of 7 phr. Furthermore, TSD technique was used to investigate chain relaxation of PUR as well. Results show the same soft segment glass transition temperatures for both relaxation of PUR as well. Results show the same soft segment glass transition temperatures for both EG content 7 and 34 phr. However, the glass transition temperature of soft segment measured by DSC EG content 7 and 34 phr. However, the glass transition temperature of soft segment measured by DSC is lower than that shown by the TSD technique. is lower than that shown by the TSD technique. Keywords: polyurethane elastomers, chain extender content, soft and hard segments Keywords: polyurethane elastomers, chain extender content, soft and hard segments

INTRODUCTION INTRODUCTION Chain extenders play an important role in the molecular structure of polyurethane elastomers. Chain extenders play an important role in the molecular structure of polyurethane elastomers. Polyurethane elastomers without a chain extender formed by directly reacting diisocyanate Polyurethane elastomers without a chain extender formed by directly reacting diisocyanate and polyol generally have very poor physical properties and often do not exhibit microphase and polyol generally have very poor physical properties and often do not exhibit microphase separation. Polyurethane elastomers are formed typically by three chemical constituents separation. Polyurethane elastomers are formed typically by three chemical constituents reacting together such as a diisocyanate, a long chain diol and a small molecule chain reacting together such as a diisocyanate, a long chain diol and a small molecule chain extender diol or a diamine. extender diol or a diamine. The hard segments are built from alternating diisocyanate and chain extender sequences The hard segments are built from alternating diisocyanate and chain extender sequences while the soft segments originate from the polyol [1]. The alternating of hard segment and while the soft segments originate from the polyol [1]. The alternating of hard segment and soft segment is shown in Figure 1. soft segment is shown in Figure 1.

1 Institute of Ceramics and Polymer Engineering, University of Miskolc 1 Institute of Ceramics and Polymer Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] 2 Institute of Ceramics and Polymer Engineering, University of Miskolc 2 Institute of Ceramics and Polymer Engineering, University of Miskolc H-3515 Miskolc-Egyetemváros, Hungary H-3515 Miskolc-Egyetemváros, Hungary [email protected] [email protected] Influence of Chain Extender on Soft and Hard Segment of Polyurethane Elastomers 99 Influence of Chain Extender on Soft and Hard Segment of Polyurethane Elastomers 99

Figure 1 Figure 1 PUR alternating hard segment (HS) and soft segment (SS) structure PUR alternating hard segment (HS) and soft segment (SS) structure

Chain extender may increase the hard segment length to allow hard segment segregation Chain extender may increase the hard segment length to allow hard segment segregation which results in good mechanical properties such as an increase in modulus and an increase which results in good mechanical properties such as an increase in modulus and an increase in the hard segment glass transition temperature of polyurethane [1]. Chain extender can be in the hard segment glass transition temperature of polyurethane [1]. Chain extender can be categorized into two classes, aromatic diols or diamines and the corresponding aliphatic diols categorized into two classes, aromatic diols or diamines and the corresponding aliphatic diols or diamines. In general, polyurethane elastomers (PUR) chains extended with an aliphatic or diamines. In general, polyurethane elastomers (PUR) chains extended with an aliphatic diol produce a softer material than do their aromatic chain extended counterparts. Also, diol produce a softer material than do their aromatic chain extended counterparts. Also, diamine chain extenders are much more reactive than diol chain extenders and give properties diamine chain extenders are much more reactive than diol chain extenders and give properties superior to those of similar polymers prepared with the equivalent diol chain extenders. This superior to those of similar polymers prepared with the equivalent diol chain extenders. This is due to the HS (urea linkage) which has a higher density of hydrogen bonding, which results is due to the HS (urea linkage) which has a higher density of hydrogen bonding, which results in a higher glass transition temperature and higher thermal stability. However, polyurethane in a higher glass transition temperature and higher thermal stability. However, polyurethane urea made from diamine chain extenders tend to be less soluble in common solvents and urea made from diamine chain extenders tend to be less soluble in common solvents and therefore they are more difficult to process. Moreover, another factor is electron therefore they are more difficult to process. Moreover, another factor is electron delocalization, i.e. the aromatic chain extenders have less reactivity than aliphatic chain delocalization, i.e. the aromatic chain extenders have less reactivity than aliphatic chain extenders, which can be favorable in reactions. Examples of diol chain extenders include extenders, which can be favorable in reactions. Examples of diol chain extenders include ethylene glycol, 1,6-hexanediol (HG), 1,4-butanediol (BDO, BD or BG), diethylene glycol ethylene glycol, 1,6-hexanediol (HG), 1,4-butanediol (BDO, BD or BG), diethylene glycol (DEG), diacetylene diols such as 2,4-hexadiyne-1,6-diol or 5,7-dodecadiyne-1,12-diol and (DEG), diacetylene diols such as 2,4-hexadiyne-1,6-diol or 5,7-dodecadiyne-1,12-diol and some aromatic diols, triazine diols or 4,4’-(ethane-1,2-diyl) bis (benzene thiohexanol) [1]. In some aromatic diols, triazine diols or 4,4’-(ethane-1,2-diyl) bis (benzene thiohexanol) [1]. In the case of ethylene glycol or 1,2-ethanediol glycol, it is produced from ethylene by the the case of ethylene glycol or 1,2-ethanediol glycol, it is produced from ethylene by the intermediate ethylene oxide. Ethylene oxide reacts with water to produce ethylene glycol. intermediate ethylene oxide. Ethylene oxide reacts with water to produce ethylene glycol. Modifying the ratio between the polyol and chain extender, and polyurethane elastomers Modifying the ratio between the polyol and chain extender, and polyurethane elastomers may result in a change from a hard to a rubbery elastomer. The effect of chain extender on may result in a change from a hard to a rubbery elastomer. The effect of chain extender on tensile properties of polyurethane microcellular elastomers used in reaction injection tensile properties of polyurethane microcellular elastomers used in reaction injection moulding (RIM) technology and multivariable linear regression analysis was studied by moulding (RIM) technology and multivariable linear regression analysis was studied by Korodi et al. [2]. It was found that the molded density has the greatest influence on the tensile Korodi et al. [2]. It was found that the molded density has the greatest influence on the tensile strength, so the tensile strength is increased by the ethylene glycol and rigid polyol content. strength, so the tensile strength is increased by the ethylene glycol and rigid polyol content. All the chain extenders studied had a negative influence on the elongation at break. Barikani All the chain extenders studied had a negative influence on the elongation at break. Barikani and Barmar [3] studied about effective structure parameters of thermoplastic polyurethane and Barmar [3] studied about effective structure parameters of thermoplastic polyurethane elastomers. The role of the hard segment chemical construction in physical and mechanical elastomers. The role of the hard segment chemical construction in physical and mechanical properties of the elastomers studied by changing the chain extenders. Dynamic mechanical properties of the elastomers studied by changing the chain extenders. Dynamic mechanical analysis studies for polyester and polyether elastomers show that an elastomer with larger analysis studies for polyester and polyether elastomers show that an elastomer with larger 100 Patcharapon Somdee–Tímea Lassú-Kuknyó–Csaba Kónya–Kálmán Marossy 100 Patcharapon Somdee–Tímea Lassú-Kuknyó–Csaba Kónya–Kálmán Marossy chain extender has a larger hard segment and better phase separation. By increasing the phase chain extender has a larger hard segment and better phase separation. By increasing the phase separation, good physical and mechanical properties were identified. separation, good physical and mechanical properties were identified. The effect of the ratio between the hard and soft segment content was investigated by The effect of the ratio between the hard and soft segment content was investigated by Prisacariu and Scortanu [4]. Moreover, the effect of varying the odd-even number of CH2 Prisacariu and Scortanu [4]. Moreover, the effect of varying the odd-even number of CH2 groups in regard to the chain extender was examined. The best mechanical behavior as groups in regard to the chain extender was examined. The best mechanical behavior as elastomers was revealed for polyurethane with CH2 even numbers on the chain extender elastomers was revealed for polyurethane with CH2 even numbers on the chain extender when the different parts of the PUs macromolecular chains can adopt extended linear forms. when the different parts of the PUs macromolecular chains can adopt extended linear forms. Two series of polyurethane elastomers were synthesized to investigate the effect of Two series of polyurethane elastomers were synthesized to investigate the effect of incorporation of various new chain extenders on the mechanical and thermal properties of incorporation of various new chain extenders on the mechanical and thermal properties of polyurethane elastomers. The 2,5-dimethyl-3 hexine-2,5-diol-based polyurethane displayed polyurethane elastomers. The 2,5-dimethyl-3 hexine-2,5-diol-based polyurethane displayed a relatively low glass transition temperature of –57 °C, tensile strength of 11 to 14 MPa and a relatively low glass transition temperature of –57 °C, tensile strength of 11 to 14 MPa and elongation at break of 600 to 700% [4]. Several works have studied the effect of chain elongation at break of 600 to 700% [4]. Several works have studied the effect of chain extender with different methods to improve the properties of polyurethane such as the effect extender with different methods to improve the properties of polyurethane such as the effect of the polyol and chain extender ratio or the hard and soft segment ratio. Some new work of the polyol and chain extender ratio or the hard and soft segment ratio. Some new work synthesized a new polyurethane based polyurethane ureas with different chain extender type synthesized a new polyurethane based polyurethane ureas with different chain extender type and investigated their properties [5]. The effect of different types of chain extenders and their and investigated their properties [5]. The effect of different types of chain extenders and their dosage on the degree of phase separation between hard and soft segments in polyurethane dosage on the degree of phase separation between hard and soft segments in polyurethane prepolymers was investigated [6]. prepolymers was investigated [6]. From previous study, some papers focus on a small difference in chain extender content From previous study, some papers focus on a small difference in chain extender content on properties of polyurethane elastomers. Therefore, the effect of a large difference in the on properties of polyurethane elastomers. Therefore, the effect of a large difference in the chain extender content was investigated for wide range of polyurethane elastomer chain extender content was investigated for wide range of polyurethane elastomer applications with a very soft polymer and a hard polymer in this study. Chain extender applications with a very soft polymer and a hard polymer in this study. Chain extender content of PUR was varied at 7 or 34 phr. Shore A and D hardness, tensile strength and content of PUR was varied at 7 or 34 phr. Shore A and D hardness, tensile strength and elongation at break were measured and evaluated. Furthermore, thermal properties and elongation at break were measured and evaluated. Furthermore, thermal properties and structure of PUR were characterized by DSC and TSD techniques. The density of PUR with structure of PUR were characterized by DSC and TSD techniques. The density of PUR with different EG content was measured. different EG content was measured.

1. MATERIALS AND METHODS 1. MATERIALS AND METHODS 1.1. Materials 1.1. Materials Monoethylene glycol is used as chain extender. The EG content was either 7 or 34 phr. Monoethylene glycol is used as chain extender. The EG content was either 7 or 34 phr. Diphenylmethane-4,4’-diisocyanate was used for isocyanate. ONGRONAT XP 1147 is an Diphenylmethane-4,4’-diisocyanate was used for isocyanate. ONGRONAT XP 1147 is an acidified MDI blend. An average molecular weight is 266 g/mol and its equivalent weight is acidified MDI blend. An average molecular weight is 266 g/mol and its equivalent weight is 127.33 g/mol. ALCUPOL D4011 is used for polyol blend. It is reactive polypropylene glycol 127.33 g/mol. ALCUPOL D4011 is used for polyol blend. It is reactive polypropylene glycol (PPG-4000) with ethylene oxide. Its molecular weight is 4,000 g/mol. Jeffcat TD33 is used (PPG-4000) with ethylene oxide. Its molecular weight is 4,000 g/mol. Jeffcat TD33 is used for catalyst, it is 33.3 wt.% solution of triethylene diamine in dipropylene glycol. The air for catalyst, it is 33.3 wt.% solution of triethylene diamine in dipropylene glycol. The air release additive trade name is BYK A500. The trade name of the moisture scavenger is release additive trade name is BYK A500. The trade name of the moisture scavenger is Finmasorb430. All ingredients of mixture A are listed in Table 1. Finmasorb430. All ingredients of mixture A are listed in Table 1.

1.2. Methods 1.2. Methods PPG polyol or soft segment, chain extender, catalyst, air release additive and moisture PPG polyol or soft segment, chain extender, catalyst, air release additive and moisture scavenger were prepared in mixture A. Mixture A was solution mixed with weight fraction scavenger were prepared in mixture A. Mixture A was solution mixed with weight fraction shown in Table 1. All ingredients were homogenized for 10 to 15 min at 35% of a shear shown in Table 1. All ingredients were homogenized for 10 to 15 min at 35% of a shear mixing machine that has 6,000 rpm capacity. After that, mixture A was shear mixed for 8 to mixing machine that has 6,000 rpm capacity. After that, mixture A was shear mixed for 8 to 12 sec at 1,000 rpm with MDI by shear mixing machine. Then, it was poured into a warm 12 sec at 1,000 rpm with MDI by shear mixing machine. Then, it was poured into a warm Influence of Chain Extender on Soft and Hard Segment of Polyurethane Elastomers 101 Influence of Chain Extender on Soft and Hard Segment of Polyurethane Elastomers 101 mold of 70 °C and left for 30 min in order to prepare polyurethane elastomer samples. The mold of 70 °C and left for 30 min in order to prepare polyurethane elastomer samples. The cured sample sheets were stored at least four days at room temperature before testing. cured sample sheets were stored at least four days at room temperature before testing. Mechanical properties were tested such as Shore A hardness for soft material and Shore D Mechanical properties were tested such as Shore A hardness for soft material and Shore D for hard material following ISO 868. Tensile properties were measured according to ISO 527 for hard material following ISO 868. Tensile properties were measured according to ISO 527 1A. Structure of polyurethane elastomers was characterized by DSC technique performed on 1A. Structure of polyurethane elastomers was characterized by DSC technique performed on METTER TOLEDO model DSC823e with heating rate of 10 °C/min from –100 to 250 °C. METTER TOLEDO model DSC823e with heating rate of 10 °C/min from –100 to 250 °C. Thermally stimulated discharge technique was used to examine the glass transition of Thermally stimulated discharge technique was used to examine the glass transition of polyurethane elastomers. PUR sheet of 1 mm thickness was cut by die cutting of 26 mm polyurethane elastomers. PUR sheet of 1 mm thickness was cut by die cutting of 26 mm diameter and thin gold electrode deposited by sputter coater. Polarizing field was 500 V/mm diameter and thin gold electrode deposited by sputter coater. Polarizing field was 500 V/mm and temperature in the range of –120 to 10°C. Heating and cooling rates were 5 °C/min. and temperature in the range of –120 to 10°C. Heating and cooling rates were 5 °C/min. Moreover, the density of polyurethane elastomers was measured by calculation of the Moreover, the density of polyurethane elastomers was measured by calculation of the difference in weight between dry and wet. difference in weight between dry and wet. Table 1 Table 1 Ingredients of mixture A Ingredients of mixture A

Description Trade Name Weight (phr*) Description Trade Name Weight (phr*) Polypropylene glycol copolymer (PPG) ALCUPOL D4011 100 Polypropylene glycol copolymer (PPG) ALCUPOL D4011 100 Monoethylene glycol EG 7 or 34 Monoethylene glycol EG 7 or 34 Amine catalyst Jeffcat TD33 0.3 Amine catalyst Jeffcat TD33 0.3 Air release additive BYKA500 0.3 Air release additive BYKA500 0.3 Moisture scavenger Finmasorb 430 10 Moisture scavenger Finmasorb 430 10 *phr is parts per hundred resin *phr is parts per hundred resin

2. RESULTS AND DISCUSSIONS 2. RESULTS AND DISCUSSIONS The chain extender content of 7 and 34 phr were used to prepare the experimental PUR that The chain extender content of 7 and 34 phr were used to prepare the experimental PUR that consist of flexible and other one for rigid PUR, respectively. Mechanical properties such as consist of flexible and other one for rigid PUR, respectively. Mechanical properties such as Shore A hardness, Shore D and tensile properties of both flexible and rigid polyurethane Shore A hardness, Shore D and tensile properties of both flexible and rigid polyurethane elastomers were tested. The variation of Shore A and D hardness values with different EG elastomers were tested. The variation of Shore A and D hardness values with different EG content are shown in Figure 2. Both Shore A and D hardness increase with increasing EG content are shown in Figure 2. Both Shore A and D hardness increase with increasing EG content from 7 to 34 phr. Shore A hardness increases from 55.2 to 96.3 while Shore D content from 7 to 34 phr. Shore A hardness increases from 55.2 to 96.3 while Shore D hardness increases from 13.6 to 58.8. Both Shore A and D hardness have higher effectiveness hardness increases from 13.6 to 58.8. Both Shore A and D hardness have higher effectiveness at 1.7 and 4.3 times, respectively, than when compared to EG content of 7 phr. This is due to at 1.7 and 4.3 times, respectively, than when compared to EG content of 7 phr. This is due to increasing the hard segment content, which will also increase the hydrogen bonding index. increasing the hard segment content, which will also increase the hydrogen bonding index. If hydrogen bond is formed only within the hard segment, it may enhance crystallization and If hydrogen bond is formed only within the hard segment, it may enhance crystallization and phase separation of the PUR structure [7]. phase separation of the PUR structure [7]. The tensile strength of polyurethanes is dependent on the resistance of the cross-linking The tensile strength of polyurethanes is dependent on the resistance of the cross-linking bonds being either covalent or hydrogen bonds in order to prevent the chains from slipping bonds being either covalent or hydrogen bonds in order to prevent the chains from slipping completely and the material yielding. The harder the material, the dense the cross-linking. completely and the material yielding. The harder the material, the dense the cross-linking. When operating below the ultimate tensile strength, the harder materials retain their elastic When operating below the ultimate tensile strength, the harder materials retain their elastic properties and do not behave like a thermoset. Under long term tension, polyurethanes will properties and do not behave like a thermoset. Under long term tension, polyurethanes will suffer from creep (strain relaxation). Fully post cured polyurethanes will lose both tensile and suffer from creep (strain relaxation). Fully post cured polyurethanes will lose both tensile and modulus properties when heated in the short term to temperatures above ambient and below modulus properties when heated in the short term to temperatures above ambient and below their breakdown points [8]. The tensile strength of PUR increases with changing EG content their breakdown points [8]. The tensile strength of PUR increases with changing EG content 102 Patcharapon Somdee–Tímea Lassú-Kuknyó–Csaba Kónya–Kálmán Marossy 102 Patcharapon Somdee–Tímea Lassú-Kuknyó–Csaba Kónya–Kálmán Marossy from 7 to 34 phr. Tensile strength increases from 4 to 24 N/mm2 when EG content is increased from 7 to 34 phr. Tensile strength increases from 4 to 24 N/mm2 when EG content is increased to 34 phr. It was enhanced around 6 times when compared to EG content of 7 phr. On the to 34 phr. It was enhanced around 6 times when compared to EG content of 7 phr. On the other hand, elongation at break decreases with increasing EG content as shown in Table 2. other hand, elongation at break decreases with increasing EG content as shown in Table 2. Result shows elongation at break was decreased from 255 to 28% with increasing EG content Result shows elongation at break was decreased from 255 to 28% with increasing EG content of 34 phr. of 34 phr.

Figure 2 Figure 2 Shore A and D hardness of polyurethane elastomers with EG content of 7 and 34 phr Shore A and D hardness of polyurethane elastomers with EG content of 7 and 34 phr

The influence of monoethylene glycol which is a chain extender in PUR leads to formation The influence of monoethylene glycol which is a chain extender in PUR leads to formation of phase separated hard segments and affects properties of PUR. Thus, the hard segment of phase separated hard segments and affects properties of PUR. Thus, the hard segment concentration leads to high phase separation and increasing tensile strength as well. This is concentration leads to high phase separation and increasing tensile strength as well. This is in accordance with the widely accepted idea that the hard segment domains act as a in accordance with the widely accepted idea that the hard segment domains act as a reinforcing particle in the soft segment matrix. The effect of chain extender on the density of reinforcing particle in the soft segment matrix. The effect of chain extender on the density of polyurethane elastomer is shown in Table 2. Results show the density increases when polyurethane elastomer is shown in Table 2. Results show the density increases when increasing the EG content. increasing the EG content. Table 2 Table 2 Tensile strength, elongation at break and density Tensile strength, elongation at break and density of polyurethane elastomers at EG content of 7 or 34 phr of polyurethane elastomers at EG content of 7 or 34 phr Tensile strength Elongation at break Density Tensile strength Elongation at break Density EG content (phr) EG content (phr) (N/mm2) (%) (g/cm3) (N/mm2) (%) (g/cm3) 7 4 ± 0.07 255 ± 9 1.084 ± 0.00 7 4 ± 0.07 255 ± 9 1.084 ± 0.00 34 24 ± 0.40 28 ± 7 1.184 ± 0.01 34 24 ± 0.40 28 ± 7 1.184 ± 0.01 Influence of Chain Extender on Soft and Hard Segment of Polyurethane Elastomers 103 Influence of Chain Extender on Soft and Hard Segment of Polyurethane Elastomers 103

DSC thermograms from the first heating scans of polyurethane elastomers at EG content of DSC thermograms from the first heating scans of polyurethane elastomers at EG content of 7 and 34 are shown in Figure 3. In the case of flexible PUR at EG content of 7 phr, a small 7 and 34 are shown in Figure 3. In the case of flexible PUR at EG content of 7 phr, a small transition is clearly observed at around –62 °C that is the glass transition temperature of the transition is clearly observed at around –62 °C that is the glass transition temperature of the soft segment in PUR. In contrast, the soft segment relaxation temperature at EG content of soft segment in PUR. In contrast, the soft segment relaxation temperature at EG content of 34 phr was not clearly observed. This is due to the cross-linking of the hard segment 34 phr was not clearly observed. This is due to the cross-linking of the hard segment obstructing the PPG polyol chain motion, so the transition temperature was not clearly obstructing the PPG polyol chain motion, so the transition temperature was not clearly exhibited when increasing EG content to 34 phr. The broader endotherms peak at EG content exhibited when increasing EG content to 34 phr. The broader endotherms peak at EG content of 7 phr a small degree of ordering in hard segment domains. In the case of EG content 34 of 7 phr a small degree of ordering in hard segment domains. In the case of EG content 34 phr, the endotherms peak is narrower than of the soft PUR, which may be due to it being phr, the endotherms peak is narrower than of the soft PUR, which may be due to it being highly hard segment cross-linked compared to EG content of 7 phr EG content. However, highly hard segment cross-linked compared to EG content of 7 phr EG content. However, hard segment glass transition temperature could not be observed in either flexible or rigid hard segment glass transition temperature could not be observed in either flexible or rigid PUR. This is probably due to it having a low fraction of amorphous phase. PUR. This is probably due to it having a low fraction of amorphous phase. The thermally stimulated discharge technique can confirm the glass transition The thermally stimulated discharge technique can confirm the glass transition temperature results of PUR, as shown in Figure 4. The curves of both flexible and rigid temperature results of PUR, as shown in Figure 4. The curves of both flexible and rigid polyurethane elastomer show the same glass transition temperature of the soft segment polyurethane elastomer show the same glass transition temperature of the soft segment around –65 °C. Furthermore, the intensity peak of rigid PUR can be related to a small around –65 °C. Furthermore, the intensity peak of rigid PUR can be related to a small relaxation in the DSC thermogram, which is difficult to evaluate, as shown in Figure 3(b). It relaxation in the DSC thermogram, which is difficult to evaluate, as shown in Figure 3(b). It can be indicated that this originates from the polyol and also can prove that the hard and soft can be indicated that this originates from the polyol and also can prove that the hard and soft segments in polyurethane elastomer are an incompatible mixture. segments in polyurethane elastomer are an incompatible mixture. Figure 5 shows the first derivative of flexible polyurethane elastomers at EG content of Figure 5 shows the first derivative of flexible polyurethane elastomers at EG content of 7 phr. The primary curve is the derivative with respect to temperature of the original DSC 7 phr. The primary curve is the derivative with respect to temperature of the original DSC curve and is generally computed electronically. The first derivative curve of a glass transition curve and is generally computed electronically. The first derivative curve of a glass transition gives a peak which area is proportional to the value of ΔCp. Peak temperature of the first gives a peak which area is proportional to the value of ΔCp. Peak temperature of the first derivative can be used as a measure of change in glass transition temperature. The first derivative can be used as a measure of change in glass transition temperature. The first derivative curve exhibited the lowest peak at –72 °C. This can indicate that the glass transition derivative curve exhibited the lowest peak at –72 °C. This can indicate that the glass transition temperature of the soft segment is around –72 °C. A small peak that drops to base line on the temperature of the soft segment is around –72 °C. A small peak that drops to base line on the first derivative exhibited crystallization temperature before relaxation of the soft segment in first derivative exhibited crystallization temperature before relaxation of the soft segment in polyurethane elastomer. polyurethane elastomer.

104 Patcharapon Somdee–Tímea Lassú-Kuknyó–Csaba Kónya–Kálmán Marossy 104 Patcharapon Somdee–Tímea Lassú-Kuknyó–Csaba Kónya–Kálmán Marossy

) )

1 1

- -

g g

W W

Heat flow ( Heat flow (

Temperature (°C) Temperature (°C)

(a) (a)

) )

1 1

- -

Heat flow (Wg Heat flow (Wg

Temperature (°C) Temperature (°C)

(b) (b) Figure 3 Figure 3 DSC thermograms of polyurethane elastomers at EG content of 7 (a) and 34 (b) phr DSC thermograms of polyurethane elastomers at EG content of 7 (a) and 34 (b) phr Influence of Chain Extender on Soft and Hard Segment of Polyurethane Elastomers 105 Influence of Chain Extender on Soft and Hard Segment of Polyurethane Elastomers 105

Depolarization(pA) current Depolarization(pA) current

Temperature (°C) Temperature (°C) Figure 4 Figure 4 TSD thermograms of polyurethane elastomers at EG content of 7 and 34 phr TSD thermograms of polyurethane elastomers at EG content of 7 and 34 phr

Figure 5 Figure 5 DSC curve of polyurethane elastomer at EG content of 7 phr (dashed line) DSC curve of polyurethane elastomer at EG content of 7 phr (dashed line) and it’s first derivative (solid line) and it’s first derivative (solid line)

106 Patcharapon Somdee–Tímea Lassú-Kuknyó–Csaba Kónya–Kálmán Marossy 106 Patcharapon Somdee–Tímea Lassú-Kuknyó–Csaba Kónya–Kálmán Marossy

CONCLUSIONS CONCLUSIONS Flexible and rigid polyurethane elastomers matrix were produced with varying chain Flexible and rigid polyurethane elastomers matrix were produced with varying chain extender content of 7 and 34 phr. In case of mechanical properties, Shore A and D hardness extender content of 7 and 34 phr. In case of mechanical properties, Shore A and D hardness increased when EG content was increased from 7 to 34 phr. It can be enhanced 1.7 and 4.3 increased when EG content was increased from 7 to 34 phr. It can be enhanced 1.7 and 4.3 times, respectively, when compared to the EG content of 7 phr. In the same way, tensile times, respectively, when compared to the EG content of 7 phr. In the same way, tensile strength increases around 6 times, from 4 and 24 N/mm2, showing that the higher EG content strength increases around 6 times, from 4 and 24 N/mm2, showing that the higher EG content of the chain extender has significantly affected the mechanical properties. These results of the chain extender has significantly affected the mechanical properties. These results indicate that higher chain extender content reacts more strongly with the MDI part and can indicate that higher chain extender content reacts more strongly with the MDI part and can become a longer hard segment in PUR structure. Moreover, the mechanical property results become a longer hard segment in PUR structure. Moreover, the mechanical property results are also related to increasing of density of PUR. Flexible polyurethane elastomers became are also related to increasing of density of PUR. Flexible polyurethane elastomers became rigid polyurethanes when chain extender content was increased up to 34 phr. Therefore, rigid polyurethanes when chain extender content was increased up to 34 phr. Therefore, elongation at break decreased from 255 to 28%. In the case of thermal and structural elongation at break decreased from 255 to 28%. In the case of thermal and structural properties, the glass transition temperature of soft segment in PUR was observed by DSC properties, the glass transition temperature of soft segment in PUR was observed by DSC and TSD techniques to be –62 °C and –65 °C, respectively. It was difficult to observe and TSD techniques to be –62 °C and –65 °C, respectively. It was difficult to observe transition temperatures from the DSC thermogram at EG content of 34 phr. This might be transition temperatures from the DSC thermogram at EG content of 34 phr. This might be due to the higher EG content affecting polyol chain motion in the PUR structure. Glass due to the higher EG content affecting polyol chain motion in the PUR structure. Glass transition temperature measured by the DSC method had higher values than when measured transition temperature measured by the DSC method had higher values than when measured by TSD, which may have been caused by different evaluation algorithms. However, the glass by TSD, which may have been caused by different evaluation algorithms. However, the glass transition temperature of the hard segment can be proved by the TSD method. transition temperature of the hard segment can be proved by the TSD method.

ACKNOWLEDGMENTS ACKNOWLEDGMENTS This research was supported by the European Union and Hungarian State, co-financed by the This research was supported by the European Union and Hungarian State, co-financed by the European Regional Development Fund in the framework of the GINOP-2.3.4-15-2016-00004 project, European Regional Development Fund in the framework of the GINOP-2.3.4-15-2016-00004 project, aimed to promote the cooperation between the higher education and the industry. The research was aimed to promote the cooperation between the higher education and the industry. The research was also supported by the Institute of Ceramics and Polymer Engineering, University of Miskolc and also supported by the Institute of Ceramics and Polymer Engineering, University of Miskolc and BorsodChem Zrt. Company. BorsodChem Zrt. Company.

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MODEL AIDED BIOFUEL DESIGN: A CASE STUDY OF C6H12O MODEL AIDED BIOFUEL DESIGN: A CASE STUDY OF C6H12O

YILEI XUE1, 2, 3–ZSÓFIA BORBÁLA RÓZSA2, 4–ANDREA GULJAS2, 3– YILEI XUE1, 2, 3–ZSÓFIA BORBÁLA RÓZSA2, 4–ANDREA GULJAS2, 3– BÉLA FISER2, 4, 5–ANITA RÁGYANSZKI2, 3, 4–JOHN JUSTINE VILLAR2, 6– BÉLA FISER2, 4, 5–ANITA RÁGYANSZKI2, 3, 4–JOHN JUSTINE VILLAR2, 6– BÉLA VISKOLCZ2, 4–IMRE G. CSIZMADIA2, 3–MILÁN SZŐRI2, 4 BÉLA VISKOLCZ2, 4–IMRE G. CSIZMADIA2, 3–MILÁN SZŐRI2, 4

The aim of this project is to find the most promising C6H12O molecular entities for use as a biofuel. To The aim of this project is to find the most promising C6H12O molecular entities for use as a biofuel. To design such structures in a heuristic manner, gas-phase thermodynamic properties of all singlet C6H12O design such structures in a heuristic manner, gas-phase thermodynamic properties of all singlet C6H12O isomers (211 species) were calculated using G3MP2B3 ab initio composite method. For each isomer, isomers (211 species) were calculated using G3MP2B3 ab initio composite method. For each isomer, the G3MP2B3 standard enthalpy of formation (Δf,298.15KH°calc), higher heating value (HHV), as well as the G3MP2B3 standard enthalpy of formation (Δf,298.15KH°calc), higher heating value (HHV), as well as relative molar Gibbs free energy (ΔG), standard molar entropy (S) was computed, and it was found that relative molar Gibbs free energy (ΔG), standard molar entropy (S) was computed, and it was found that the computed Δf,298.15KH°calc reproduced the corresponding literature values – available only in case of the computed Δf,298.15KH°calc reproduced the corresponding literature values – available only in case of 11 species – by average absolute deviation of 3.3 kJ/mol, so it can be assumed that this uncertainty can 11 species – by average absolute deviation of 3.3 kJ/mol, so it can be assumed that this uncertainty can be used for the recommended Δf,298.15KH° values for the remaining molecular entities as well. These C6H12O be used for the recommended Δf,298.15KH° values for the remaining molecular entities as well. These C6H12O isomers were structurally categorized into 13 subgroups according to their backbone features and functional isomers were structurally categorized into 13 subgroups according to their backbone features and functional groups. Amongst these structures, ethers have the highest HHV from which 3-ethyl tetrahydrofuran groups. Amongst these structures, ethers have the highest HHV from which 3-ethyl tetrahydrofuran (38.3 MJ/kg) is a potential biofuel component however production from lignocellulose biomass is not (38.3 MJ/kg) is a potential biofuel component however production from lignocellulose biomass is not yet reported and its other fuel properties has to be waited for characterization. When LD50 values were yet reported and its other fuel properties has to be waited for characterization. When LD50 values were available, health risks of these compounds were also analyzed. available, health risks of these compounds were also analyzed. Keywords: ab initio, thermodynamic properties, thermodynamic map Keywords: ab initio, thermodynamic properties, thermodynamic map

INTRODUCTION INTRODUCTION An ideal biofuel is environmentally friendly, easily storable, renewable, sustainable, and a An ideal biofuel is environmentally friendly, easily storable, renewable, sustainable, and a widely available chemical compound with high energy density, which can be generated from widely available chemical compound with high energy density, which can be generated from inexpensive and abundant sources. It is even better if the fuel is an important intermediate for inexpensive and abundant sources. It is even better if the fuel is an important intermediate for chemical industry at the same time, making the compound multifunctional. The first-generation chemical industry at the same time, making the compound multifunctional. The first-generation (1G) of biofuels are made from food crops and are currently the major sources of biofuels (1G) of biofuels are made from food crops and are currently the major sources of biofuels despite their low energy density and conflict with food supply [1]. Second-generation (2G) despite their low energy density and conflict with food supply [1]. Second-generation (2G) biofuels overcame the latter issue since these are produced from sustainable feedstock such as biofuels overcame the latter issue since these are produced from sustainable feedstock such as cellulose, but their production requires several physical and chemical processes [1]. However, cellulose, but their production requires several physical and chemical processes [1]. However, using algae as an energy source can keep the third-generation (3G) biofuel production relatively using algae as an energy source can keep the third-generation (3G) biofuel production relatively simple [2]. Further improvement – the fourth-generation (4G) technology – is a combination of simple [2]. Further improvement – the fourth-generation (4G) technology – is a combination of genomically synthesized microbes (synthetized to efficiently produce fuels) and genetically genomically synthesized microbes (synthetized to efficiently produce fuels) and genetically

1 Department of Physical and Environmental Sciences, University of Toronto Scarborough, Canada 1 Department of Physical and Environmental Sciences, University of Toronto Scarborough, Canada 2 Institute of Chemistry, University of Miskolc, Miskolc, Hungary 2 Institute of Chemistry, University of Miskolc, Miskolc, Hungary e-mail: [email protected] e-mail: [email protected] 3 Department of Chemistry, University of Toronto, Canada 3 Department of Chemistry, University of Toronto, Canada 4 Higher Education Industry Cooperation Centre, University of Miskolc, Miskolc, Hungary 4 Higher Education Industry Cooperation Centre, University of Miskolc, Miskolc, Hungary 5 Ferenc Rákóczi II. Transcarpathian Hungarian Institute, Beregszász, Transcarpathia, Ukraine 5 Ferenc Rákóczi II. Transcarpathian Hungarian Institute, Beregszász, Transcarpathia, Ukraine 6 Scientific Computing Laboratory, Department of Computer Science, University of the Philippines 6 Scientific Computing Laboratory, Department of Computer Science, University of the Philippines Diliman, Philippines Diliman, Philippines Model Aided Biofuel Design: A Case Study of C6H12O 109 Model Aided Biofuel Design: A Case Study of C6H12O 109 optimized feedstocks (designed to capture large amounts of carbon). This may render 4G optimized feedstocks (designed to capture large amounts of carbon). This may render 4G biofuels a carbon neutral source of fuel [3]. An optimum molecule for such biofuel can be biofuels a carbon neutral source of fuel [3]. An optimum molecule for such biofuel can be difficult to select even with retrosynthetic approach, although some empirical rules are difficult to select even with retrosynthetic approach, although some empirical rules are already available. For instance, it is known that increasing hydrogen content leads to lower already available. For instance, it is known that increasing hydrogen content leads to lower carbon dioxide footprint and higher oxygen content decreases smoke emission [4], although carbon dioxide footprint and higher oxygen content decreases smoke emission [4], although it also leads to smaller carbon and hydrogen content which in turn lowers the heating value it also leads to smaller carbon and hydrogen content which in turn lowers the heating value [5]. For example, one of the C6H12O isomers, 2,5-dimethyltetrahydrofuran (2,5-DMTHF), is [5]. For example, one of the C6H12O isomers, 2,5-dimethyltetrahydrofuran (2,5-DMTHF), is already recommended as a biofuel component [6]. It has a relatively high energy density already recommended as a biofuel component [6]. It has a relatively high energy density (LHV = 35.2 MJ/kg and HHV = 37.8 MJ/kg), low volatility (Tb = 101.5 °C), low viscosity (LHV = 35.2 MJ/kg and HHV = 37.8 MJ/kg), low volatility (Tb = 101.5 °C), low viscosity (0.8 mm2/s), and it is immiscible with water [7]. Furthermore, it can be manufactured by a (0.8 mm2/s), and it is immiscible with water [7]. Furthermore, it can be manufactured by a one-step transformation of biomass-derived carbohydrates and raw lignocellulose with one-step transformation of biomass-derived carbohydrates and raw lignocellulose with reasonable yields at mild conditions in water [8]. Therefore, a chemical formula, like C6H12O, reasonable yields at mild conditions in water [8]. Therefore, a chemical formula, like C6H12O, with high degree of saturation and moderate oxygen content is promising, but 2,5-DMTHF with high degree of saturation and moderate oxygen content is promising, but 2,5-DMTHF is probably not the optimum structure amongst C6H12O isomers. Other oxygenated is probably not the optimum structure amongst C6H12O isomers. Other oxygenated hydrocarbons including alcohol, methyl ester and cyclic ethers can also be generated from hydrocarbons including alcohol, methyl ester and cyclic ethers can also be generated from cellulosic feedstocks [4]. cellulosic feedstocks [4]. In this research, an effort has been made to find better candidates described by the same In this research, an effort has been made to find better candidates described by the same chemical formula as 2,5-DMTHF, using data collection and ab initio prediction of chemical formula as 2,5-DMTHF, using data collection and ab initio prediction of thermodynamic properties for all C6H12O isomers. thermodynamic properties for all C6H12O isomers.

COMPUTATIONAL METHODS COMPUTATIONAL METHODS The enumeration of organic molecules corresponding to a given stoichiometry can be The enumeration of organic molecules corresponding to a given stoichiometry can be deduced to graph theory, if nuclei and chemical bonds are considered as the nodes and the deduced to graph theory, if nuclei and chemical bonds are considered as the nodes and the edges of a graph [9]. A certain number of atoms with a limited amount of different valences edges of a graph [9]. A certain number of atoms with a limited amount of different valences define the number of constitutional isomers. In this work, all possible stochiometric isomers define the number of constitutional isomers. In this work, all possible stochiometric isomers of C6H12O were generated, allowing hydrogen, carbon and oxygen to form 1, 4 and 2 of C6H12O were generated, allowing hydrogen, carbon and oxygen to form 1, 4 and 2 chemical bonds, respectively. This low dimensional representation is extended into three chemical bonds, respectively. This low dimensional representation is extended into three dimensions by means of the atom-type-specific geometric parameter set obtained from the dimensions by means of the atom-type-specific geometric parameter set obtained from the simplified MM2 force field [10]. By using this procedure, a number of 211 three dimensional simplified MM2 force field [10]. By using this procedure, a number of 211 three dimensional molecular configurations were generated by Molgen 5.0 [11]. These structures served as molecular configurations were generated by Molgen 5.0 [11]. These structures served as initial structures in the search for local minima on the multidimensional potential energy initial structures in the search for local minima on the multidimensional potential energy surface for the species. surface for the species. All quantum chemical calculations in this work were carried out using G3MP2B3 All quantum chemical calculations in this work were carried out using G3MP2B3 composite methods [12] as implemented in Gaussian 09 program package [13]. As part of composite methods [12] as implemented in Gaussian 09 program package [13]. As part of this method, B3LYP/6-31G(d) level of theory was used for geometry optimizations and this method, B3LYP/6-31G(d) level of theory was used for geometry optimizations and vibrational frequency calculations. The maximum optimization step size was limited to 0.01 vibrational frequency calculations. The maximum optimization step size was limited to 0.01 Bohr or radians and the number of optimization steps were restricted to 300, while harmonic Bohr or radians and the number of optimization steps were restricted to 300, while harmonic wavenumbers were scaled by factor of 0.96 for calculating thermodynamic properties such wavenumbers were scaled by factor of 0.96 for calculating thermodynamic properties such as standard enthalpy of formation [Δf,298.15KH°calc(g)], relative standard molar Gibbs free as standard enthalpy of formation [Δf,298.15KH°calc(g)], relative standard molar Gibbs free energy (ΔrG°) and standard molar entropy (S°). Only structures with no imaginary harmonic energy (ΔrG°) and standard molar entropy (S°). Only structures with no imaginary harmonic frequencies were further analyzed (otherwise the structure would have been re-optimized frequencies were further analyzed (otherwise the structure would have been re-optimized until it became a real minimum). To obtain more accurate standard enthalpy of formation until it became a real minimum). To obtain more accurate standard enthalpy of formation [Δf,298.15KH°(g)] and relative Gibbs free energy (ΔrG°) at P = 1 atm and T = 298.15 K, further [Δf,298.15KH°(g)] and relative Gibbs free energy (ΔrG°) at P = 1 atm and T = 298.15 K, further 110 Xue–Rózsa– Guljas–Fiser–Rágyanszki–Villar–Viskolcz–Csizmadia–Szőri 110 Xue–Rózsa– Guljas–Fiser–Rágyanszki–Villar–Viskolcz–Csizmadia–Szőri single point calculations were carried out using QCISD(T)/6-31G(d) including MP2/6-31G(d) single point calculations were carried out using QCISD(T)/6-31G(d) including MP2/6-31G(d) and MP2/GTMP2 levels of theories according to the G3MP2B3 protocol. Standard enthalpy and MP2/GTMP2 levels of theories according to the G3MP2B3 protocol. Standard enthalpy of formation, Δf,298.15KH°(g), was obtained using the atomization scheme. When available, of formation, Δf,298.15KH°(g), was obtained using the atomization scheme. When available, calculated Δf,298.15KH°(g) values were compared with literature ones (Δf,298.15KH°lit(g)). calculated Δf,298.15KH°(g) values were compared with literature ones (Δf,298.15KH°lit(g)). Literature data was mostly collected from Ruscic’s active thermochemistry tables [14] and Literature data was mostly collected from Ruscic’s active thermochemistry tables [14] and Burcat’s thermochemistry database [15]. Burcat’s thermochemistry database [15]. Finally, the higher heating value (HHV, also known as gross calorific value or gross Finally, the higher heating value (HHV, also known as gross calorific value or gross energy) of each species was calculated either in MJ/kg or GJ/m3 (when mass density was energy) of each species was calculated either in MJ/kg or GJ/m3 (when mass density was available in the literature). HHV is defined as the amount of heat released once the 1 mol available in the literature). HHV is defined as the amount of heat released once the 1 mol species burned to CO2 and H2O and the gas phase products returned to a reference species burned to CO2 and H2O and the gas phase products returned to a reference temperature (298.15 K). When the lower heating value (LHV, also known as net calorific temperature (298.15 K). When the lower heating value (LHV, also known as net calorific value) is determined, gas-phase standard enthalpy of formation Δf,298.15KH°[H2O(g)] is value) is determined, gas-phase standard enthalpy of formation Δf,298.15KH°[H2O(g)] is replaced by liquid-phase standard enthalpy of formation Δf,298.15KH°[H2O(l)]. replaced by liquid-phase standard enthalpy of formation Δf,298.15KH°[H2O(l)].

RESULTS AND DISCUSSION RESULTS AND DISCUSSION

1.1. Validation of the standard enthalpy of formation computed using G3MP2B3 1.1. Validation of the standard enthalpy of formation computed using G3MP2B3 composite method composite method

To the best of our knowledge, only 11 C6H12O isomers has previously published standard To the best of our knowledge, only 11 C6H12O isomers has previously published standard enthalpy of formation values from the existing 211 isomers. Available data was compared enthalpy of formation values from the existing 211 isomers. Available data was compared with the computed G3MP2B3 results and absolute deviation (AD) is presenteid in Table 1. with the computed G3MP2B3 results and absolute deviation (AD) is presenteid in Table 1.

Table 1 Table 1 G3MP2B3 calculated [Δf,298.15KH°calc(g)] and literature values [Δf,298.15KH°lit(g)] of standard G3MP2B3 calculated [Δf,298.15KH°calc(g)] and literature values [Δf,298.15KH°lit(g)] of standard enthalpy of formation for the C6H12O isomers. Absolute deviation (AD) of the G3MP2B3 results from enthalpy of formation for the C6H12O isomers. Absolute deviation (AD) of the G3MP2B3 results from the literature are also presented the literature are also presented

Species Δf,298.15KH°calc(g) Δf,298.15KH°lit(g) Ref. AD Species Δf,298.15KH°calc(g) Δf,298.15KH°lit(g) Ref. AD (kJ/mol) (kJ/mol) (kJ/mol) (kJ/mol) (kJ/mol) (kJ/mol) Cyclohexanol –261.0 –293.1 [15] 32.1 Cyclohexanol –261.0 –293.1 [15] 32.1 Oxepane –220.5 –224.5 [15] 4.0 Oxepane –220.5 –224.5 [15] 4.0 2,5-DMTHF –262.1 –262.4 [15] 0.3 2,5-DMTHF –262.1 –262.4 [15] 0.3 Hexan-2-one –275.6 –279.80 ± 1.1 [14] 4.2 Hexan-2-one –275.6 –279.80 ± 1.1 [14] 4.2 3-Hexanone –273.0 –278.25 ± 0.89 [14] 5.25 3-Hexanone –273.0 –278.25 ± 0.89 [14] 5.25 3,3-Dimethyl-2-butanone –290.7 –290.67 ± 0.88 [14] 0.03 3,3-Dimethyl-2-butanone –290.7 –290.67 ± 0.88 [14] 0.03 4-Methyl-2-pentanone –286.0 –291.2 ± 1.4 [16] 5.2 4-Methyl-2-pentanone –286.0 –291.2 ± 1.4 [16] 5.2 3-Methyl-2-pentanone –279.5 –284.1 ± 1.3 [16] 4.6 3-Methyl-2-pentanone –279.5 –284.1 ± 1.3 [16] 4.6 2-Methyl-3-pentanone –283.1 –286.1 ± 0.9 [17] 3.0 2-Methyl-3-pentanone –283.1 –286.1 ± 0.9 [17] 3.0 1-(Vinyloxy) butane –173.0 –179.2 ± 1.2 [18] 6.2 1-(Vinyloxy) butane –173.0 –179.2 ± 1.2 [18] 6.2 1-Methylcyclopentan-1-ol –283.6 –284.3 ± 1.4 [19] 0.7 1-Methylcyclopentan-1-ol –283.6 –284.3 ± 1.4 [19] 0.7

Literature values for cyclohexanol, oxepane, and 2,5-DMTHF were obtained from Burcat’s Literature values for cyclohexanol, oxepane, and 2,5-DMTHF were obtained from Burcat’s Thermodynamic Table [15], which were calculated using G3B3 composite method (G3B3 is Thermodynamic Table [15], which were calculated using G3B3 composite method (G3B3 is Model Aided Biofuel Design: A Case Study of C6H12O 111 Model Aided Biofuel Design: A Case Study of C6H12O 111 technically quite similar to G3MP2B3). While the absolute deviations in the case of oxepane technically quite similar to G3MP2B3). While the absolute deviations in the case of oxepane and 2,5-DMTHF are within the uncertainty of these methods (approx. 8 kJ/mol according to and 2,5-DMTHF are within the uncertainty of these methods (approx. 8 kJ/mol according to [12]), the values for cyclohexanol deviated significantly. A possible reason for this deviation [12]), the values for cyclohexanol deviated significantly. A possible reason for this deviation can be that different cyclohexanol conformers were used for our calculations and the can be that different cyclohexanol conformers were used for our calculations and the literature data. The remaining eight literature values are from calorimetric measurements: literature data. The remaining eight literature values are from calorimetric measurements: rotating bomb calorimetry method was used for 1-(vinyloxy) butane, and static bomb rotating bomb calorimetry method was used for 1-(vinyloxy) butane, and static bomb calorimetry method was used for the rest seven isomers. The maximum deviation between calorimetry method was used for the rest seven isomers. The maximum deviation between the computed and measured results is 6.2 kJ/mol. For the case of 1-(vinyloxy) butane the the computed and measured results is 6.2 kJ/mol. For the case of 1-(vinyloxy) butane the standard enthalpy of formation for 3,3-dimethyl-2-butanone shows almost a perfect match standard enthalpy of formation for 3,3-dimethyl-2-butanone shows almost a perfect match (absolute deviation is 0.03 kJ/mol). For these C6H12O isomers, the computed enthalpies of (absolute deviation is 0.03 kJ/mol). For these C6H12O isomers, the computed enthalpies of formation reproduced the corresponding literature values by an average absolute deviation formation reproduced the corresponding literature values by an average absolute deviation of 3.3 kJ/mol. of 3.3 kJ/mol.

1.2. Analysis of the relationship between structure and thermodynamic properties 1.2. Analysis of the relationship between structure and thermodynamic properties

Backbones and functional groups of the obtained molecules had been investigated to Backbones and functional groups of the obtained molecules had been investigated to understand the role of structural features defining the maximum reversible work that may be understand the role of structural features defining the maximum reversible work that may be performed by the C6H12O isomers at standard isothermal-isobaric condition (ΔG). According performed by the C6H12O isomers at standard isothermal-isobaric condition (ΔG). According to backbone structure, C6H12O isomers were divided into two main groups: an acyclic to backbone structure, C6H12O isomers were divided into two main groups: an acyclic (indicated by unfilled symbols in Figure 1) and a cyclic group (indicated by filled symbols (indicated by unfilled symbols in Figure 1) and a cyclic group (indicated by filled symbols in Figure 1). in Figure 1).

Figure 1 Figure 1 Thermodynamic map of the C6H12O isomers based on their relative molar Gibbs free energy (ΔrG) Thermodynamic map of the C6H12O isomers based on their relative molar Gibbs free energy (ΔrG) and standard molar entropy (S) and standard molar entropy (S) 112 Xue–Rózsa– Guljas–Fiser–Rágyanszki–Villar–Viskolcz–Csizmadia–Szőri 112 Xue–Rózsa– Guljas–Fiser–Rágyanszki–Villar–Viskolcz–Csizmadia–Szőri

The two groups were further classified: acyclic isomers were classified by their functional The two groups were further classified: acyclic isomers were classified by their functional groups into four families: alcohols, ethers, aldehydes, and ketones; cyclic isomers into: groups into four families: alcohols, ethers, aldehydes, and ketones; cyclic isomers into: cyclopropane, oxirane, cyclobutane, oxetane, cyclopentane, tetrahydrofuran, tetrahydro- cyclopropane, oxirane, cyclobutane, oxetane, cyclopentane, tetrahydrofuran, tetrahydro- pyran family, and cyclohexanol and oxepane as separate groups. Their relative molar Gibbs pyran family, and cyclohexanol and oxepane as separate groups. Their relative molar Gibbs free energy (ΔrG°) and entropy contents (S°) can be mapped out as shown in Figure 1. free energy (ΔrG°) and entropy contents (S°) can be mapped out as shown in Figure 1. Figure 1 shows that acyclic structures have a higher entropy content than cyclic structures. Figure 1 shows that acyclic structures have a higher entropy content than cyclic structures. Five- and six-membered ring structures such as oxepane and tetrahydrofurans have an Five- and six-membered ring structures such as oxepane and tetrahydrofurans have an extremely low entropy content compared to other C6H12O isomers. The higher the relative extremely low entropy content compared to other C6H12O isomers. The higher the relative Gibbs free energy and molar entropy, the smaller the ring size. It is also interesting to note Gibbs free energy and molar entropy, the smaller the ring size. It is also interesting to note that the Gibbs free energy content of the alkyl ethers is comparable to the molecules having that the Gibbs free energy content of the alkyl ethers is comparable to the molecules having strong ring-strain such as cyclopropanes, oxiranes, and oxetane. The Gibbs free energy strong ring-strain such as cyclopropanes, oxiranes, and oxetane. The Gibbs free energy content of the ketones is somewhat lower than ethers, while that of aldehydes is about the content of the ketones is somewhat lower than ethers, while that of aldehydes is about the average of the ketones. average of the ketones.

1.3. Higher heating values (HHV) as a function of the molecular structure motif 1.3. Higher heating values (HHV) as a function of the molecular structure motif

Similar to the case of the molar Gibbs free energy content, the cyclopropane family has the Similar to the case of the molar Gibbs free energy content, the cyclopropane family has the highest HHV value with a range between 38.7 MJ/kg and 39.4 MJ/kg as seen in Figure 2. highest HHV value with a range between 38.7 MJ/kg and 39.4 MJ/kg as seen in Figure 2. Again, oxirane, oxetane, and acyclic ether families are the second highest subgroups of the Again, oxirane, oxetane, and acyclic ether families are the second highest subgroups of the average HHV with 38.9 MJ/kg (significantly above that of 2,5-DMTHF). From each average HHV with 38.9 MJ/kg (significantly above that of 2,5-DMTHF). From each molecular family, an isomer with the highest HHV was selected as representative and listed molecular family, an isomer with the highest HHV was selected as representative and listed in the Table 2. in the Table 2.

Figure 2 Figure 2

Calculated HHV values grouped by molecule families of the C6H12O isomers Calculated HHV values grouped by molecule families of the C6H12O isomers

Model Aided Biofuel Design: A Case Study of C6H12O 113 Model Aided Biofuel Design: A Case Study of C6H12O 113

Table 2 Table 2 C6H12O isomers with highest HHV values from the 13 molecular families (classified by functional C6H12O isomers with highest HHV values from the 13 molecular families (classified by functional group). HHV are obtained from G3MP2B3 standard enthalpy of formation. Density (ρ), melting (Tm), group). HHV are obtained from G3MP2B3 standard enthalpy of formation. Density (ρ), melting (Tm), boiling (Tb), flash point (Tflash), and median lethal dose, LD50 were collected from Ref. 19 and 20. The boiling (Tb), flash point (Tflash), and median lethal dose, LD50 were collected from Ref. 19 and 20. The abbreviation n.a. stands for ‘not available’ abbreviation n.a. stands for ‘not available’

ρ HHV Tm Tb Tflash LD50 ρ HHV Tm Tb Tflash LD50 Family Species MJ/kg Family Species MJ/kg g/cm3 °C mg/kg g/cm3 °C mg/kg (GJ/m3) (GJ/m3) 38.8 38.8 Alcohol 5-hexen-1-ol 0.850 <–20 128 24.0 n.a. Alcohol 5-hexen-1-ol 0.850 <–20 128 24.0 n.a. (33.0) (33.0) 39.2 39.2 Ether 5-methoxypent-1-ene 0.792 –112 89.9 6.90 n.a. Ether 5-methoxypent-1-ene 0.792 –112 89.9 6.90 n.a. (31.0) (31.0) 38.3 38.3 Aldehyde n-hexanal 0.814 –49.0 131 32 4,890 Aldehyde n-hexanal 0.814 –49.0 131 32 4,890 (31.2) (31.2) 38.0 38.0 Ketone hexan-3-one 0.822 –55.2 121 35.0 2,901 Ketone hexan-3-one 0.822 –55.2 121 35.0 2,901 (31.2) (31.2) 2-methoxyethyl 39.4 2-methoxyethyl 39.4 Cyclopropane 0.910 –70.2 113 21.9 n.a. Cyclopropane 0.910 –70.2 113 21.9 n.a. cyclopropane (35.9) cyclopropane (35.9) Oxirane 2-butyloxirane n.a. 39.2 –72 117.1 ± 8.0 21.8 ± 21.9 n.a. Oxirane 2-butyloxirane n.a. 39.2 –72 117.1 ± 8.0 21.8 ± 21.9 n.a. (methoxymethyl)cyclo- (methoxymethyl)cyclo- Cyclobutane n.a. 39.3 –80 97 n.a. n.a. Cyclobutane n.a. 39.3 –80 97 n.a. n.a. butane butane Oxetane 3-propyloxetane n.a. 39.2 –75 117.1 ± 8.0 21.8 ± 21.9 n.a. Oxetane 3-propyloxetane n.a. 39.2 –75 117.1 ± 8.0 21.8 ± 21.9 n.a. cyclopentyl methyl ether 38.5 cyclopentyl methyl ether 38.5 Cyclopentane 0.863 –63.3 110 16.8 200 Cyclopentane 0.863 –63.3 110 16.8 200 (CPME) (33.2) (CPME) (33.2) 3-ethyl tetrahydrofuran 38.4 3-ethyl tetrahydrofuran 38.4 Tetrahydrofuran 0.890 –63.8 113 14.8 n.a. Tetrahydrofuran 0.890 –63.8 113 14.8 n.a. (3-ETHF) (34.2) (3-ETHF) (34.2) 38.1 38.1 Cyclohexanol cyclohexanol 0.948 23.0 161 62.6 1,400 Cyclohexanol cyclohexanol 0.948 23.0 161 62.6 1,400 (36.1) (36.1) 3-methyltetrahydro-2H- 3-methyltetrahydro-2H- Tetrahydropyran n.a. 38.2 –82.3 110 79.8 ± 15.9 n.a. Tetrahydropyran n.a. 38.2 –82.3 110 79.8 ± 15.9 n.a. pyran pyran 38.5 38.5 Oxepane oxepane 0.871 –44.6 119 21.9 n.a. Oxepane oxepane 0.871 –44.6 119 21.9 n.a. (33.5) (33.5)

The highest HHV belongs to 2-methoxyethyl cyclopropane with a value of 39.4 MJ/kg, The highest HHV belongs to 2-methoxyethyl cyclopropane with a value of 39.4 MJ/kg, which is relatively close to that of the fossil-based diesel (44.8 MJ/kg). Usually the energy which is relatively close to that of the fossil-based diesel (44.8 MJ/kg). Usually the energy density of a biofuel is significantly lower than the fossil counterparts (see HHV = 22.7 MJ/kg density of a biofuel is significantly lower than the fossil counterparts (see HHV = 22.7 MJ/kg for ethanol). The situation is even better if one compares the higher heating values per unit for ethanol). The situation is even better if one compares the higher heating values per unit volume for 2-methoxyethyl cyclopropane (35.9 GJ/m3) and diesel (39 GJ/m3). Although the volume for 2-methoxyethyl cyclopropane (35.9 GJ/m3) and diesel (39 GJ/m3). Although the HHV of cyclohexanol in MJ/kg is not outstanding (38.1 MJ/kg) amongst the C6H12O isomers, HHV of cyclohexanol in MJ/kg is not outstanding (38.1 MJ/kg) amongst the C6H12O isomers, its HHV in GJ/m3 is one of the highest in this study, since it is solid in ambient conditions. its HHV in GJ/m3 is one of the highest in this study, since it is solid in ambient conditions. Kumar et al. [20] investigated cyclohexanol as a fuel additive and found that it increases Kumar et al. [20] investigated cyclohexanol as a fuel additive and found that it increases ignition delay and heat release rates during the premixed combustion phase of diesel engine. ignition delay and heat release rates during the premixed combustion phase of diesel engine. From an emissions standpoint, the increasing cyclohexanol content reduces smoke opacity From an emissions standpoint, the increasing cyclohexanol content reduces smoke opacity 114 Xue–Rózsa– Guljas–Fiser–Rágyanszki–Villar–Viskolcz–Csizmadia–Szőri 114 Xue–Rózsa– Guljas–Fiser–Rágyanszki–Villar–Viskolcz–Csizmadia–Szőri

(up to 32.3%) but increases NOx significantly. It should also be mentioned that its toxicity is (up to 32.3%) but increases NOx significantly. It should also be mentioned that its toxicity is moderate as indicated by median lethal dose in Table 2 [LD50(cyclohexanol) = 1400 mg/kg moderate as indicated by median lethal dose in Table 2 [LD50(cyclohexanol) = 1400 mg/kg oral for rats]. Therefore, it can be a potential liquid fuel additive. The 3-ethyl tetrahydrofuran oral for rats]. Therefore, it can be a potential liquid fuel additive. The 3-ethyl tetrahydrofuran (3-ETHF) is the next largest HHV (38.4 MJ/kg and 34.2 GJ/m3), however it is just slightly (3-ETHF) is the next largest HHV (38.4 MJ/kg and 34.2 GJ/m3), however it is just slightly denser in energy than 2-ethyl tetrahydrofuran (2-ETHF, 38.3 MJ/kg). 2-ETHF can be denser in energy than 2-ethyl tetrahydrofuran (2-ETHF, 38.3 MJ/kg). 2-ETHF can be prepared from lignocellulose sources in a two-step pathway via the reduction of 2-acetylfuran prepared from lignocellulose sources in a two-step pathway via the reduction of 2-acetylfuran where the yield of the first and second step are 99% and maximum 80%, respectively [23], where the yield of the first and second step are 99% and maximum 80%, respectively [23], while such an established synthetic route is not yet reported for 3-ETHF. There is also no while such an established synthetic route is not yet reported for 3-ETHF. There is also no reported health risk of 3-ETHF yet. Beside toxicity, several other properties must also be reported health risk of 3-ETHF yet. Beside toxicity, several other properties must also be considered, for instance, the melting point (Tm) and boiling point (Tb) are essential to ensure considered, for instance, the melting point (Tm) and boiling point (Tb) are essential to ensure the fuels can be stored safety in liquid phase: Tm < –20 °C, 60 °C < Tb < 120 °C for spark- the fuels can be stored safety in liquid phase: Tm < –20 °C, 60 °C < Tb < 120 °C for spark- ignition (SI) engine and 60 °C < Tb < 250 °C for compression-ignition (CI) engine [7]. ignition (SI) engine and 60 °C < Tb < 250 °C for compression-ignition (CI) engine [7]. For the species shown in Table 2, Tm seems to not be a serious constrain. However, for For the species shown in Table 2, Tm seems to not be a serious constrain. However, for 5-hexen-1-ol, n-hexanal, hexan-3-one, and cyclohexanol, the boiling point is reached over 5-hexen-1-ol, n-hexanal, hexan-3-one, and cyclohexanol, the boiling point is reached over the limit of 120 °C used for SI engine. Moreover, flash point (Tflash) is also crucial to the fuel the limit of 120 °C used for SI engine. Moreover, flash point (Tflash) is also crucial to the fuel storage [24] and to avoid unwanted fuel ignition, the flash point must be between 52 °C and storage [24] and to avoid unwanted fuel ignition, the flash point must be between 52 °C and 96 °C for CI engine, while a low Tflash is desired for SI engine (and high autoignition 96 °C for CI engine, while a low Tflash is desired for SI engine (and high autoignition temperature). Species in Table 2 are out of the range for the Tflash of the CI engine, except temperature). Species in Table 2 are out of the range for the Tflash of the CI engine, except cyclohexanol and 3-methyltetrahydro-2H-pyran, therefore their potential use is limited to SI cyclohexanol and 3-methyltetrahydro-2H-pyran, therefore their potential use is limited to SI engines. Based on their LD50 value these species are moderately toxic. engines. Based on their LD50 value these species are moderately toxic.

CONCLUSION CONCLUSION

In this work, we intended to design a better C6H12O biofuel component than 2,5-DMTHF. In this work, we intended to design a better C6H12O biofuel component than 2,5-DMTHF. To achieve this, G3MP2B3 standard enthalpy of formation (Δf,298.15KH°calc), HHV, relative To achieve this, G3MP2B3 standard enthalpy of formation (Δf,298.15KH°calc), HHV, relative Gibbs free energy and entropy values were computed for all the possible C6H12O isomers. Gibbs free energy and entropy values were computed for all the possible C6H12O isomers. The computed G3MP2B3 enthalpies of formation reproduced the available literature values The computed G3MP2B3 enthalpies of formation reproduced the available literature values within an average absolute deviation of 3.3 kJ/mol demonstrating the reliability of G3MP2B3 within an average absolute deviation of 3.3 kJ/mol demonstrating the reliability of G3MP2B3 methodology. Amongst C6H12O structures, ethers have the highest HHV values from which methodology. Amongst C6H12O structures, ethers have the highest HHV values from which 3-ethyl tetrahydrofuran (3-ETHF) can be a promising structure for a biofuel component for 3-ethyl tetrahydrofuran (3-ETHF) can be a promising structure for a biofuel component for an SI engine, and it can be produced from lignocellulose biomass. Cyclohexanol was found an SI engine, and it can be produced from lignocellulose biomass. Cyclohexanol was found to be a potential biofuel additive as it has high energy density. Health risks of these molecules to be a potential biofuel additive as it has high energy density. Health risks of these molecules were also analyzed, and they were found to be moderately toxic. were also analyzed, and they were found to be moderately toxic.

ACKNOWLEDGEMENT ACKNOWLEDGEMENT

We acknowledge KIFÜ for awarding us access to resource based in Hungary at Szeged. Authors also We acknowledge KIFÜ for awarding us access to resource based in Hungary at Szeged. Authors also thanked Máté Labádi and Dávid Vincze for the administration of the Herkules computing cluster at thanked Máté Labádi and Dávid Vincze for the administration of the Herkules computing cluster at University of Miskolc also used in this work. This research was supported by the European Union and University of Miskolc also used in this work. This research was supported by the European Union and the Hungarian State, co-financed by the European Regional Development Fund in the framework of the Hungarian State, co-financed by the European Regional Development Fund in the framework of the GINOP-2.3.4-15-2016-00004 project, aimed to promote the cooperation between the higher the GINOP-2.3.4-15-2016-00004 project, aimed to promote the cooperation between the higher education and the industry. Milán Szőri is grateful for the financial support by the János Bolyai education and the industry. Milán Szőri is grateful for the financial support by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences (BO/00113/15/7), and the New National Research Scholarship of the Hungarian Academy of Sciences (BO/00113/15/7), and the New National Excellence Program of the Ministry of Human Capacities (ÚNKP-17-4-III-ME/26). Excellence Program of the Ministry of Human Capacities (ÚNKP-17-4-III-ME/26). Model Aided Biofuel Design: A Case Study of C6H12O 115 Model Aided Biofuel Design: A Case Study of C6H12O 115

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Secreteriat of the Vice-Rector for Research and International Relations, Secreteriat of the Vice-Rector for Research and International Relations, University of Miskolc, University of Miskolc, Responsible for the Publication: Prof. Dr. Tamás Kékesi Responsible for the Publication: Prof. Dr. Tamás Kékesi Published by the Miskolc University Press under leadership of Attila Szendi Published by the Miskolc University Press under leadership of Attila Szendi Responsible for duplication: Works manager: Erzsébet Pásztor Responsible for duplication: Works manager: Erzsébet Pásztor Number of copies printed: 200 Number of copies printed: 200 Put the Press in 2018 Put the Press in 2018 Number of permission: TNRT–2018–398–ME Number of permission: TNRT–2018–398–ME