Mullite Preparation from Kaolin Residue 21 03

Mullite Preparation from Kaolin Residue

M.I.Brasileiro1;D.H.S.Oliveira2;H.L.Lira3;L.N.L.Santana3;G. A.Neves3; A.P.Novaes4 J.M. Sasak5 1Universidade Federal de Campina Grande, UFCG/DEQ – PB, Departamento de Engenharia Química - Aprígio Veloso, 820 – CEP 58109-970 – Campina Grande, PB, Brasil. 2UFCG/DEMa/PIBIC/CNPq – Departamento de Engenharia de Materiais, PB, Brasil. 3UFCG/DEMa - Departamento de Engenharia de Materiais, PB, Brasil. 4SENAI – CTCmat/Criciúma – SC, Brasil. 5UFC – Universidade Federal do Ceará, CE, Brasil.

Keywords: kaolin waste; alumina; ball-clay; mullite; sintering.

Abstract: In the process of kaolin improvement to types of residue are generated and dispose in the environment. The first residue, about 70%wt, generated from the washing of the kaolin and the second generated residue from the improvement in sieve 200 mesh (0.074mm), of the remaining of the washed kaolin 30%. These residues can present excellent qualities to be used as raw materials rich in kaolinite. Kaolinite when is submitted to heat give two stable phases: mullite and crystobalite. The properties of mullite, such as, low thermal expansion, low dielectric constant and high mechanical resistance, make this material as a good candidate to be applied in electronic products and in structural high temperature uses. In this work, compositions with residue from kaolin, alumina and ball-clay were studied to obtain mullite. The compositions were established starting from proportion between silica and alumina to obtain mullite (2SiO2.3Al2O3). The samples were made by pressing processing with 27 MPa and sintering at temperatures of 1350 and 1500°C, with heating rate of 10°C/min. Through the results from chemical analysis of the formulated masses, it can be verified that the proportions of the oxides were close to the stoichiometric of the mullite and that the sintering, at studied temperatures, give the formation of mullite, and confirmed by the DRX analysis. The preliminary results showed that the compositions with low alumina content and submitted to a high temperatures, presented the best results.

Introduction

Mullite is a unique thermodynamically stable phase in the binary system Al2O3-SiO2 [1] and due to its excellent properties, such as, creep resistance at high temperature, chemical stability, low dielectric coefficient and low thermal expansion has called attention from several researchers [2,3]. As a mineral, mullite is rare in the nature [4] and the reserves are not sufficient to supply the crescent new applications. This is the reason for several researchers looking for process to obtain mullite from Al2O3-SiO2 or from some minerals that contain Al2O3 and SiO2 in their compositions [1]. An alternative material is study through calcination of a mix of kaolin residue, alumina and ball-clay, in an appropriate proportion of the oxides, taking in account the amount of SiO2 and Al2O3 to obtain mullite. In the improvement of primary kaolin two types of residue are disposed in the environment. The first one, with 70%wt, are generated during the washing of the raw kaolin and the second, with 30%wt, are produced during the sieve process in a mesh 200 (0.074mm). The aim of this study is to obtain mullite from the residue produced by kaolin industry, alumina and ball-clay and to characterize by physical and mechanical properties of the produced mullite.

Materials and Method

Materials: In this work it was used a residue from primary kaolin industry supplied by Caulisa Industria S/A, a clay provided by Armil Minerios Ltda. and calcined alumina S4G, supplied by Alcan. Treatment and characterization of the raw materials: The residue and ball-clay were dried at 110ºC for 24 hours, until constant weight and passed in a sieve 200 mesh to submitted to chemical analysis and X-ray diffraction, using a Siemens/Brucker-AXS, with CuKα radiation. Formulation and characterization of the masses: The masses formulations were set up taking in account the silica and alumina content of the raw materials. The compositions were submitted to a sieve 100mesh (0.150mm) and characterized by XRD analysis and particle size by laser. Processing and characterization of the specimens: The masses were mixed with ethylic alcohol and dry at room temperature. After dry the lumps were crushed and passed through a sieve with 100 mesh. Powder compacts were formed by uniaxially pressing at 27 MPa. The final dimension of green compacts was 6.0x2.0x0.5cm3. The compacts were then sintered in an electrical oven at various temperatures from 1350oC to 1500oC for 1 h in air. The heating rate was 10oC/min. After sintering the specimens were submitted to measurement of the following properties: porosity, linear shrinkage, water absorption, apparent density and flexural rupture strength. The flexural strength of specimens was determined by the three-point bending technique, at a loading rate of 0.5 mm/min. The result is the average of five specimens.

Results and Discussion

The Table 1 present the chemical composition of the raw materials. From Table 1 it can be observed that the residue contain basically silica (57.11%) and alumina (40.67%), also ball- clay, with 66.14% of silica and 32.00% of alumina. According to Chen at al [5], the reaction, 2SiO2 + Al2O3 + 2H2O + 2 Al2O3 Æ 3 Al2O3 +2SiO2 + 2 H2O, is observed during the firing of kaolin+alumina. By this reaction it can assume that SiO2 from kaolin can react completely with alumina to produce mullite and in the case of the residue it is necessary an excess of alumina to reach with all the silica.

Table 1 – Chemical composition of the raw materials. Raw materials % SiO2 % Al2O3 % Fe2O3 % Na2O % K2O Kaolin residue 57.11 40.67 0.04 0.53 1.65 Ball- clay 66.14 32.00 1.85 - - Alumina 0.04 99.4 0.04 0.37 0.23

The Table 2 presents the compositions studied in this work. The Table 3 presents the results for particle size distribution of the powders for each composition. From of the Table 3, it can observed that particle size distribution is very similar for the compositions I and II. The compositions III and IV present particle size lower than for the compositions I and II, this is due to the ball-clay with a high content of particle size lower than 2µm. Table 2 – Compositions of the specimens (% wt) Compositions Kaolin Residue Ball clay Alumina I 74.12 - 25.88 II 66.38 - 33.62 III 69.00 4.00 27.00 IV 67.00 7.00 26.00

Table 3 – Particle size (µm) for different composition 10% of 50% of 90% of 100% of Composition particles particles particles particles below below below below I 1.74 16.60 42.78 71.00 II 1.74 14.74 41.17 71.00 III 1.07 7.42 36.18 90.00 IV 1.26 8.44 36.72 71.00

Table 4 present the chemical compositions of the formulated masses. It can be observed a high content of silica and alumina that is excellent to obtain mullite.

Table 4 – Chemical composition (%) of the formulated pastes Specimens SiO2 Al2O3 Fe2O3 Na2O K2O TiO2 L.O.*

Composition I 39.25 49.72 0.36 0.26 3.27 0.06 6.92 Composition II 34.80 55.22 0.32 0.21 2.94 0.05 6.32 Composition III 38.91 50.36 0.42 0.24 3.13 0.10 6.69 Composition IV 40.91 47.97 0.42 0.23 3.25 0.12 6.94 *L.O.- Loss of ignition

Figures 1, 2, 3, and 4 present the XDR patterns of the compositions (I, II, III e IV) fired at different temperatures.

Composition II M - Mullite Composition I M - Mullite C - Cristoballite 5000 A - Alumina A - Alumina C - Cristoballite 4500 Q - Quartz M Q - Quartz M 4000 M M M M A M 3500 M A M A A M M A M M M M A A 1500°C M M MM A 3000 M M M A M 1500°C MM M M M M A A M M A 2500 M A M MA A M M M A MA C M M M M M M A 1450°C M M MM 2000 1450°C M M M M A A A M A A M M A 1500 A M M A M M M M M 1400°C C M M M M M M M C M A M 1400°C M M M MM M 1000 M A Q A M C M A A A AM A M M 500 M QM M MM A A M M M C M 1350°C M MM M 1350°C M M M MM M 0 0 102030405060 0 102030405060 20 degrees 20 degrees

Fig.1: The DRX patterns of the composition Fig.2: The DRX patterns of the composition I for different temperature. II for different temperature. Composition III Composition IV M - Mullite 5500 M - Mullite 5500 C - Cristoballite C - Cristoballite 5000 5000 A - Alumina 5000 A - Alumina M Q - Quartz Q - Quartz 4500 4500 M A M M 4000 M 4000 AM M M M MA A 3500 A A 3500 M M M M M M MA 1500°C M MM M 1500°C A M M MM 3000 M 3000 A A M M A A M M M 2500 A M A 2500 M M M M A M A 1450°C M M M M M M M C M M M M 2000 A 2000 1450°C M M M MAM M A A M C M M M M A 1500 1400°C M M MM M 1500 A A M A C M M M 1400°C M M M M M M M 1000 M A A A 1000 M A A A A M Q M M M M Q M M M A 500 C 500 C M M M M M 1350°C MM M M M MM M 1350°C M M 0 0 0 102030405060 0 102030405060 20 degrees 20 degrees

Fig.3: The DRX patterns of the composition Fig.4: The DRX patterns of the composition III for different temperature. IV for different temperature

From the results of phase analysis the mullite formation begins as the sintering temperature is above 1350oC and indicates that the compositions sintered at temperature of 1350oC are composed of: mullite, cristobalite, quartz and alumina. With increase of temperature it can be observed an increase of the mullite phase and vanishing of cristobalite and alumina. According to Ebadzadeh et al [2], the amount of silica in the vitreous phase can react with alumina to produce mullite [5]. According to Liu et al [6] mullite produced at 1200oC is called as primary mullite and above 1300oC secondary mullite is formed. An increase in temperature to 1500oC it can be observed the formation of mullite as unique crystalline phase. Tables 5, 6, 7 and 8 show the amounts of the silica, alumina and mullite as crystalline phases present for each composition and sintering temperature.

Table 5 – The amount of the crystalline Table 6 – The amount of the crystalline phases for the composition I. phases for the composition II. Temperature SiO2 Al2O3 Mullite Temperature SiO2 Al2O3 Mullite 1350 °C 4.9 46.3 48.8 1350 °C 4.9 54.8 40.3 1400 °C 4.5 41.8 53.7 1400 °C 3.1 50.2 56.7 1450 °C 2.1 36.2 61.7 1450 °C 2.5 46.4 52.7 1500 °C 0.9 16.1 83.0 1500 °C 0.9 26.5 71.0

Table 7 – The amount of the crystalline Table 8 – The amount of the crystalline phases for the composition III. phases for the composition IV. Temperature SiO2 Al2O3 Mullite Temperature SiO2 Al2O3 Mullite 1350 °C 5.4 45.6 49.0 1350 °C 6.4 48.1 45.5 1400 °C 5.7 43.1 51.3 1400 °C 3.7 46.1 50.2 1450 °C 3.7 33.3 63.0 1450 °C 3.5 34.7 61.8 1500 °C - 16.7 83.3 1500 °C 1.0 17.2 81.8

It can be observed that in all composition that the amount of mullite phase increase rapidly with sintering temperature from 1350oC to 1500oC. According to Chen et al [5] the amount of mullite increases quickly and the reduction of alumina occurs instantaneously in the range of 1300oC to 1500oC. In this range of temperature secondary mullite is produced by dissolution of alumina combined with silica and precipitation of mullite grain. The composition II present amount of mullite inferior compared to the others and this is due to the small content of silica from raw materials that is not enough to reach with residual alumina to form mullite and this affect the physical and mechanical properties of the specimens. On the other hand, the compositions with greater amount of silica (I, III and IV) present high content of mullite and also better physical and mechanical properties, as can be seen in Table 9.

Table 9 – Physical properties of the specimens Composition Temperature WA* (%) LS* (%) AP* (%) AD* (g/cm3) I 7.2 ± 1.37 5.73±0.74 16.57±2.85 2.31±0.24 II 8.98±1.29 5.11±0.66 20.36±2.36 2.28±0.06 1350 °C III 6.91±1.07 5.81±0.46 15.90±2.08 2.31±0.06 IV 6.03±0.78 6.01±0.54 14.23±1.63 2.33±0.04 Composition WA (%) LS (%) AP (%) AD (g/cm3) I 4.58±0.94 6.59±0.11 10.97±2.10 2.40±0.07 II 1400 °C 6.43±0.81 5.96±0.1 15.13±1.88 2.35±0.01 III 4.79±0.73 6.44±0.07 11.37±1.73 2.37±0.01 IV 4.34±0.53 6.26±0.62 10.35±1.28 2.38±0.01 Composition WA (%) LS (%) AP (%) AD (g/cm3) I 3.75±0.49 6.46±0.29 8.92±1.2 2.38±0.02 II 1450 °C 5.58±0.49 6.12±1.20 13.11±1.20 2.35±0.01 III 3.82±0.5 6.02±0.23 9.07±1.23 2.37±0.02 IV 3.69±0.34 6.0±0.23 8.73±0.86 2.36±0.03 Composition WA (%) LS (%) AP (%) AD (g/cm3) I 3.29±0.14 5.68±0.39 7.61±0.33 2.32±0.05 II 1500 °C 4.94±0.25 5.09±0.49 11.26±0.7 2.28±0.06 III 3.41±0.21 5.40±0.92 7.87±0.58 2.30±0.04 IV 3.20±0.40 5.22±0.58 7.37±1.0 2.29±0.04 *WA – Water Absorption; *LS – Linear Shrinkage; *AP – Apparent Porosity; *AD – Apparent Density.

The apparent density does not show significant difference in relation to the compositions and sintering temperature. According to Chen et al [5] the densification in this range of temperature (1300oC-1500oC) is relatively low and suggests the formation of secondary mullite produced from the reaction between vitreous phase and alumina. The composition IV present best results in terms of physical and mechanical properties and this is due to the presence of ball-clay to produce a good plasticity in the paste and give an excellent green density of the specimens. The increase in the sintering temperature give an increase of the amount of mullite and confer an improve of the properties. Figure 5 show the mechanical behavior of the specimens and the compositions I, III and IV present superior properties when compared with composition II. According to Ebadzadeh [2] the factors that affect the mechanical resistance is the high porosity and the big size of the mullite grain. Also the reduction of mechanical resistance can be attributed to the transformation of Fe2O3 (hematite) to Fe3O4(magnetite) with release of oxygen that form pore and act as defect in the sintered specimens.

Composição 1 Composição 2 65 Composição 3 Composição 4 60

50 Pa)

45 PF (M M 40

30 1300 1350 1400 1450 1500 1550 Temperature (°C)

Fig.5: Mechanical behavior for different compositions versus sintering temperatures.

Conclusions

The study of the kaolin residue, ball-clay and alumina to obtain mullite can give the following conclusions: 1. The raw materials (kaolin residue, ball-call and alumina) show content of SiO2 and Al2O3 suitable to produce mullite. 2. Mullite is produced with success after sintering reaction between kaolin residue, alumina and ball-clay. 3. The proof bodies made with the composition II, which presented small silica content, resulted in low properties physical-mechanics to the others for all of the temperatures; 4. The increase in the sintering temperature favored an improvement in the properties of the studied compositions; 5. The composition IV, with larger tenor of clay ball-clay, presented the best results, for this to have provided a better compacting and consequently the improvement of the properties.

Acknowledgement

The authors gratefully acknowledge financial support provided by CNPq.

References

[1] Monteiro, R.R.; Sabioni, A.C.S.; da Costa, G.M.,Revista cerâmica 50 (2004) pp.318-323. [2] Ebadzadeh, T., Materials Science and Engineering A355 (2003), pp. 56-61. [3] Rachida, E.Q.; Sophie, G.; Bernard, D.; Azzeddine, S.;Lahcen, R.; Redouane, M., J. Am. Ceram. Soc. 25 (2005) pp.73-80. [4] Goski, D.G.; Caley, W.F., Canadian Metallurgical Quartely 38, 2(1999) pp.119. [5] Chen, C. Y.,Tuan, W. H.,Lan, W.H., Journal of the European Ceramic Society 20 (2000). [6] Liu, K.C., Thomas, G., J. Am. Ceram. Soc. 77 (6) (1994) p.1545-1552.