Raman Analysis and Experimental Investigation of Nichrome and Aluminium Nitride Microtubular Coil Heaters: a 2D Approach

Int. J. Mech. Eng. & Rob. Res. 2013 G Sureshkannan and M Velliangiri, 2013

RAMAN ANALYSIS AND EXPERIMENTAL INVESTIGATION OF NICHROME AND ALUMINIUM NITRIDE MICROTUBULAR COIL HEATERS: A 2D APPROACH

G Sureshkannan1* and M Velliangiri1

*Corresponding Author: G Sureshkannan,  [email protected]

Raman spectroscopy is a spectroscopic technique based on inelastic scattering of monochromatic light, usually from a laser source. Surface-Enhanced Raman Scattering (SERS) combines modern laser spectroscopy with the exciting optical properties of metallic structures, resulting in strongly increased Raman signals when molecules are attached to micrometer- sized structures. Micro tubular coil heaters have been widely investigated because of their extensive applications in Microsystems. These are presently manufactured by using Nichrome, a commercial alloy suitable for all types of macro/micro tubular heaters, but can be used for relatively low temperature applications. This paper aims in determining a micro tubular coil heater material suitable for high temperature applications. The material characterization was performed using Raman spectrometer and the geometric optimization for the micro tubular coil heater was performed by using COMSOL Multiphysics software. The characteristic dimensions of the micro tubular coil heater are varied and the results are discussed and compared to each other. The result of temperature distribution of 2-Dimensional thermal analysis is applied to thermal stress analysis, enabling analysis of the time dependent thermal stress of Nichrome and Aluminium Nitride micro tubular coil heaters.

Keywords: Raman spectroscopy, Micro tubular coil heaters, Thermal stress, Temperature distribution, Rupture point, Comsol analysis

INTRODUCTION source. Inelastic scattering means that the Raman spectroscopy is a spectroscopic frequency of photons in monochromatic light technique based on inelastic scattering of changes upon interaction with a sample. monochromatic light, usually from a laser Photons of the laser light are absorbed by the

1 Coimbatore Institute of Technology, Coimbatore 641014, India.

265 Int. J. Mech. Eng. & Rob. Res. 2013 G Sureshkannan and M Velliangiri, 2013 sample and then reemitted. Frequency of the metallic properties is restricted by prohibitive reemitted photons is shifted up or down in selection rules, low penetration depth of the comparison with original monochromatic incident light, etc. frequency, which is called the Raman Effect. COMSOL Multiphysics is a finite element This shift provides information about analysis and solver software package for vibrational, rotational and other low frequency various physics and engineering applications, transitions in molecules. Raman spectroscopy especially coupled phenomena, or can be used to study solid, liquid and gaseous multiphysics. It is suitable software package samples. A Raman microscope consists of a for small scale electro thermal analysis since standard optical microscope, an excitation a separate MEMS module is present in it. laser, a monochromator and a sensitive COMSOL provides better solution accuracy detector. The correct selection of the laser and consistency. COMSOL has a separate wavelength is an important consideration for MEMS module which represents coupled Raman spectroscopy. With modern Raman processes in microelectromechanical and instruments, often several laser wavelengths microfluidic devices. may be employed to obtain the best detection limit of the Raman signal with sensitivity. For MICRO TUBULAR COIL example, many samples, especially organic HEATERS OVERVIEW or biological, will be quite fluorescent in nature. The first micro tubular heaters have been Exciting these samples with a laser in the designed for plastics injection molding industry green (532 nm) light may promote this where hot runner system is used and represent fluorescence, and this fluorescence the best solution to heat nozzles with very small background may suppress any underlying diameters requiring specific power and very Raman spectrum to such an extent that it is no high temperatures. Micro tubular coil heaters longer detectable. In this case, the use of a are made as rectangular, square and circular laser in the red (633 nm) or near infrared (NIR) sections, with or without built-in thermocouple. (785 nm) region may provide a solution. With Micro tubular heaters are swaged and the lower photon energy, a red or NIR laser compacted with magnesium oxide and a helical or straight resistance element. The main may not promote the electronic transition and features of these heaters are 3600 heated so the Raman scatter may be far easier to area, readily confirms to surface, fast response detect. The cross-section for fluorescence is and quick heat transfer, helical coil design for 10-16 cm2 per molecule, but for Raman superior performance, good resistance to scattering, the value is between 10-31 cm2 per corrosion and it can easily be coupled with J molecule (Jimenez-Sandoval, 2000; Thorley or K type thermocouple. It also provides the et al., 2006; Misra et al., 2007; Gaft and Nagi, best combination of physical strength, high 2008; and Alison and Bernhard, 2009). emissivity and good thermal conductivity to There has been a little work on the Raman heat hot runner bushing/nozzles mainly for multi spectroscopy studies on nitride based alloys. cavity hot runner PET perform moulds and thin Because Raman scattering of materials with wall container moulds.

266 Int. J. Mech. Eng. & Rob. Res. 2013 G Sureshkannan and M Velliangiri, 2013

CHARACTERIZATION AND The disadvantage of micro tubular coil EXPERIMENTAL heater and all types of heaters is the change INVESTIGATION of resistance with the change in dimensions. The resistance increases with the increase in Identification of Candidate Material length and it decreases with increase in cross sectional area, i.e., diameter. Table 2 shows Presently the micro tubular coil heater wires are the increase in resistance with its temperature manufactured using Nickel-Chrome alloys, of the nichrome heater wire. which are resistant to high temperatures. 80/ 20 Nickel-Chrome alloys containing long life Table 2: Change of Resistance with additions which make it eminently suitable for Temperature of Nichrome Heater Wire applications such as nichrome resistance wire, °C 20 95 208 316 427 537 689 subject to, frequent switching and wide % Increase in temperature fluctuations. Nicrome80:20 is a Resistance 0 0.8 2.1 3.4 4.7 6.3 5.8 non-magnetic alloy which consists of 79% It is evident from the table that the nickel, 19% chromium, 0.8% Iron, 0.5% resistance of the heater material increases with Silicon, 0.4% Carbon and 0.3% Manganese its temperature. Because of the increase in by weight, and is widely used in heating resistivity with the reduction in cross sectional elements because of its relatively high area, its operating temperature is limited to resistivity. A relatively low temperature 750 °C, which is very low for most of the heating coefficient of resistance with a high resistivity applications. makes it suitable for control resistors. Nichrome wire has two key virtues, firstly it is almost 100% In order to use micro tubular coil heaters efficient in converting electrical energy into heat, more than 750 °C, we select Aluminium Nitride and secondly provided the temperature is not (AlN) as the material for heating element for too high it will not oxidize in air (Table 1). which the melting point is 2200 °C, which is almost 1.5 times the melting point of Nichrome. Table 1 Physical Properties of Nichrome An attempt was already made with Titanium and AlN Nitride for micro tubular coil heater by us Material/Properties Nichrome AlN (Sureshkannan et al., 2012). Titanium Nitride Melting Point, ºC 1400 2200 has already been tried for heaters and micro Resistance at room heaters (de Moor et al., 1999; Creemer et al., temperature, ohm m 1.0  10–6 1.3  10–6 2008). The higher melting point of the AlN Thermal Conductivity, W/m ºC 11.3 120 material made us to select it as a candidate Density, kg/m3 8400 3260 material for high heat applications even though Modulus of elasticity, N/m2 2.2  1011 3.31  1011 its resistivity is relatively low. Even though AlN Thermal Expansion is tested for high temperature applications Coefficient, K–1 13.4  10–6 5.6  10–6 (Kazan et al., 2006; Trodahl et al., 2006; Operating temperature, ºC (As micro tubular heating Xiaojun et al., 2006; and Oliveira et al., 2001), element) 750 1450 it is not tried for micro tubular coil heaters.

267 Int. J. Mech. Eng. & Rob. Res. 2013 G Sureshkannan and M Velliangiri, 2013

Aluminum nitride has a hexagonal crystal Figure 2: Raman Spectra of Nichrome structure and is a covalent bonded material. at Different Temperatures The material is stable to very high temperatures in inert atmospheres. A layer of aluminum oxide forms which protects the material up to 1370 °C. Above this temperature bulk oxidation occurs. Aluminum nitride is stable in hydrogen and carbon dioxide atmospheres up to 980 °C.

Figure 1: Components of Micro Tubular Coil Heater

Figure 3: Raman Spectra of AlN at Different Temperatures

CHARACTERIZATION OF MATERIALS The Raman spectra of two materials are obtained using 785nm Raman spectrometer and these are shown in Figures 2 (Nichrome) and 3 (AlN). From the literature and these two spectra, it is evident that the AlN material has very high melting point and low thermal Expansion Coefficient. temperature ranges (Xiaojun et al., 2006) The ratio of the intensity of the Raman peaks which makes it suitable for high temperature in Figure 2 sharpens at higher temperatures. ranges and can be used for high temperature This shows that the crystal structure of microtubular heater applications. Also it has Nichrome gets changed at high temperature high modulus of elasticity which makes the ranges which makes it is not suitable for high material suitable for heavy load. temperature applications of microtubular heaters. The ratio of the intensity of the Raman EXPERIMENTAL peaks in Figure 3 changes little over the entire We made a micro tubular coil heater with AlN temperature range. This shows that the crystal as heating element without changing the structure of AlN remained stable at all the sheath material and insulation compound. The

268 Int. J. Mech. Eng. & Rob. Res. 2013 G Sureshkannan and M Velliangiri, 2013 external sheath is made in CrNi steel in which for small scale electro thermal analysis since inside a AlN resistive wire, uniformly a separate MEMS module is present in it distributed, is insulated in a high compressed Velmathi et al. (2010). The Electro-Thermal MgO compound The important parameters module of the COMSOL multiphysics tool has considered for manufacturing micro tubular coil been used for simulation to achieve the heaters are resistant wire material, sheath desired function of the micro tubular heater. material, insulation material, maximum sheath The Nichrome and AlN micro tubular coil temperature, and type of thermocouple. The heaters are modeled in four different sizes and AlN micro tubular coil heater is made in four simulation tests were carried out. The different sizes as like Nichrome micro tubular coil heater and tests were carried out. The test Figure 4: Temperature Distribution of Nichrome Micro Tubular Coil Heater system consists of a DC power source, (Diameter 0.5 mm) voltmeter, ammeter, variable resistor, micro tubular coil heater and J-type thermocouple. The power is applied by varying the current and voltage and the tests were carried out until the heater elements failed. The temperature and resistance for both the micro tubular coil heaters, at the point of rupture were obtained and the change of temperature and resistance with its diameter is calculated and shown in Table 3.

Table 3: Rupture Temperature of Nichrome and AlN

Size (Diameter of the Rupture Temperature in K Coil Wire Element) Figure 5: Temperature Distribution of AlN in mm Nichrome AlN Micro Tubular Coil Heater 0.5 751.13 1729.59 (Diameter 0.5 mm) 0.25 702.18 1687.06 0.125 665.29 1498.24 0.075 602.08 1310.05 SIMULATION OF TEMPERATURE DISTRIBUTION OF MICRO TUBULAR HEATERS The geometric optimization for the micro tubular heaters has been performed by simulating various geometries using COMSOL multiphysics. It is suitable software package

269 Int. J. Mech. Eng. & Rob. Res. 2013 G Sureshkannan and M Velliangiri, 2013 temperature of the micro tubular coil heaters From the Table 2, it is proved that the for various input parameters (current, voltage resistance of the heater material increases and wattage), including the point of rupture with its temperature and the resistivity of the were obtained and compared with the material increases with decrease in diameter. experimental results. And also from the Table 3, the maximum rupture temperature of the 0.075 mm SIMULATION OF THERMAL Nichrome heater is 602.089 K and AlN heater STRESS AND DEFLECTION is 1310.05. The experimental and simulated OF MICRO TUBULAR results for all the dimensions are presented HEATERS in the Figures 6-11, including the maximum Thermal stress is an important parameter operating temperatures. The rupture where heating is employed. The result of temperature of AlN micro tubular heater is temperature distribution of 2-Dimensional 2.17 times more than that of Nichrome. This thermal analysis is applied to thermal stress shows that AlN micro tubular heaters can be analysis, enabling analysis of the time used for high temperature applications. Due dependent thermal stress of Nichrome and to low resistivity of the AlN, the power applied Aluminium Nitride micro tubular coil heaters. to AlN heater is higher than that of Nichrome Figures 12 and 13 show the VonMises stress heater for the same dimension. But due to induced in Nichrome and Aluminium Nitride. the higher melting point and high operating temperature of AlN, it is suitable for high RESULTS AND DISCUSSION temperature applications which made the AlN It is evident from the Table 2 that the resistance a suitable candidate for micro tubular coil of the heater material increases with its heaters. temperature. Because of the increase in Figure 6: Current vs. Temperature resistivity with the reduction in cross sectional of 0.075 mm Diameter Nichrome Wire area, the operating temperature of Nichrome Element micro tubular coil element is limited to 602.89 K, which is very low for most of the heating applications. But the operating temperature of AlN micro tubular heating element is 1729.59 K for the diameter of 0.5 mm. The Table 3 shows the rupture temperature of both Nichrome and AlN micro tubular heating coils at various cross sections. From the Table 3 the rupture temperature of both micro tubular coil heaters decreased with decrease in its diameter since the resistance of the heater material increases with its decrease in diameter.

270 Int. J. Mech. Eng. & Rob. Res. 2013 G Sureshkannan and M Velliangiri, 2013

Figure 7: Current vs. Temperature Figure 10: Wattage vs. Temperature of 0.075 mm Diameter AlN Wire Element of 0.075 mm Diameter Nichrome Wire Element

Figure 8: Voltage vs. Temperature Figure 11: Wattage vs. Temperature of 0.075 mm Diameter Nichrome Wire of 0.075 mm Diameter AlN Wire Element Element

Figure 9: Voltage vs. Temperature The temperature distribution in a part may of 0.075 mm Diameter AlN Wire Element cause thermal stress effects i.e., stress caused by thermal expansion or contraction of the material. Thermal stress effects were simulated by coupling a steady state heat transfer analysis and a structural analysis. First a heat transfer analysis was performed to determine the temperature distribution and these temperature results were applied as load in a structural analysis to determine the stress and displacement caused by the temperature loads. Figures 12 and 13 show the thermal stress analysis of Nichrome and

271 Int. J. Mech. Eng. & Rob. Res. 2013 G Sureshkannan and M Velliangiri, 2013

AlN. From the Figures 12 and 13, it was Figure 14: Mechanical Deformation observed that the stress caused due to the of Nichrome thermal load is 4.53  104 N/m2 for Nichrome micro tubular heater and is 4.498  104 N/m2 for AlN micro tubular heater. This shows that the thermal stress is comparatively low for AlN micro tubular coil heater.

Figure 12: Thermal Stress Analysis of Nichrome

Figure 15: Mechanical Deformation of AlN

Figure 13: Thermal Stress Analysis of AlN

deformation caused by temperature load is comparatively less for the AlN micro tubular coil heater. From the Raman spectra of these two materials, it is observed that the structure of AlN is stable even at high temperatures Figures 14 and 15 are the result of structural (Xiaojun et al., 2006) and from the Comsol analysis with the temperature load as input analysis, it is found that the thermal stress and (Vanni and David, 2006) and these give the mechanical deformation are comparatively mechanical deformation of Nichrome and AlN less in AlN micro tubular heater which made micro coil heaters for a particular thermal load. AlN a suitable candidate material for high From these two figures it is found that the temperature applications.

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CONCLUSION with TiN Heaters”, J. Sensors and This paper describes the characterization, Actuators A 148: Physical, pp. 416-421. experimental investigation and analysis of 3. de Moor P, Witvrouw A, Simons V and de Aluminium Nitride (AlN) micro tubular coil Wolf I (1999), “The Fabrication and heater using Raman spectroscopy and Reliability Testing of Ti/TiN Heaters”, Proc. Comsol multiphysics. The material of SPIE, Vol. 3874, pp. 284-293, Santa characterization was performed using Raman Clara, CA, USA. spectrometer and the geometric optimization 4. Fischbach D B (2003), “Temperature for the micro tubular coil heater was performed Dependant of Raman Scattering by by simulating a wide range of possible Carbon Materials”, Journal of Carbon geometries using COMSOL multiphysics, a (Elsevier), pp. 365-369. commercial Finite Element Analysis (FEA) package. The characteristic dimensions of the 5. Gaft M and Nagi L (2008), Opt. Mater. micro tubular coil heater structures are varied (Amsterdam), Vol. 30, p. 1739. and the results are discussed and compared 6. Jimenez-Sandoval S (2000), “Micro- to each other. The temperature distribution of Raman Spectroscopy: A Powerful result of 2-dimensional thermal analysis is Technique for Material Research”, applied to thermal stress analysis Nichrome Microelectronics Journal, Vol. 31, and Aluminium Nitride micro tubular coil pp. 419-427. heaters and Aluminium Nitride coil heaters 7. Kazan M, Zgheib Ch, Moussaed E and provided satisfactory results over Nichrome Masri P (2006), “Temperature coil heaters. Dependence of Raman-Active Modes in ACKNOWLEDGEMENT AlN”, Diamond and Related Materials, pp. 1169-1174. The authors are thankful to All India Council for Technical Education (AICTE) and Ministry of 8. Misra A K, Sharma S K, Lucey P G, Lentz Human Resource and Development for funding R C F and Chio C H (2007), “Daytime this activity and setting up Center of Rapid Detection of Minerals and Organics Nanotechnology at Park College of from 50 and 100 m Distances Using a Engineering and Technology. Remote Raman System”, Proc. SPIE. 9. Oliveira C, Otani C, Maciel H S, Massi M, REFERENCES Noda L K and Temperini M L A (2001), 1. Alison J Hobro and Bernhard Lendl “Raman Active E2 Modes in Aluminum (2009), “Stand-Off Raman Spectroscopy”, Nitride Films”, Journal of Materials Trends in Analytical Chemistry, Vol. 28, Science: Materials in Electronics, Vol. 12, No. 11, pp. 1235-1242. Nos. 4-6, pp. 259-262. 2. Creemer J F, Briand D, Zandbergen H W, 10. Remédios C M R, Paraguassu W, Van der Vlist W, de Boer C R, de Rooij N Saraiva G D, Pereira D P, de Oliveira P F and Sarro P M (2008), “Microhotplates C, Freire P T C, Mendes-Filho J, Melo F

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E A and dos Santos A O (2010), 14. Vanni Lughi and David R Clarke (2006), “Temperature-Dependent Raman “Defect and Stress Characterization of Scattering of KDP: Mn (0.9% Weight of AlN Films by Raman Spectroscopy”, Mn) Crystal”, Journal of Raman Applied Physics Letters, Vol. 89. Spectroscopy, pp. 1318-1322. 15. Velmathi G, Ramshankar N and Mohan S 11. Sureshkannan G, Mohan Kumar G and (2010), “2D Simulations and Electro- Saravanan M P (2012), “Characterization Thermal Analysis of Micro-Heater and Experimental Investigation of TiN Designs Using COMSOL for Gas Sensor Applications”, Proceedings of the Micro Tubular Coil Heater Using Raman COMSOL Conference. Spectroscopy”, International Journal of Advanced Research in Technology, 16. Velmathi G, Ramshankar N and Mohan S Vol. 2, pp. 18-26. (2011), “Microheater Designs Using COMSOL for Gas Sensor Applications: 12. Thorley F C, Baldwim K J, Lee D C and 3D Simulations and Electro Thermal Batchelder D N (2006), Journal of Analysis”, Proceedings of the COMSOL Raman Spectroscopy, Vol. 37, p. 335. Conference. 13. Trodahl H J, Martin F, Muralt P and Setter 17. Xiaojun Li, Candong Zhou, Guochang N (2006), “Raman Spectroscopy of Jiang and Jinglin You (2006), “Raman Sputtered AlN Films: E-2(High) Biaxial Analysis of Aluminium Nitride at High Strain Dependence”, Applied Physics Temperature”, Journal of Materials Letters, Vol. 89. Characterization, Vol. 57, pp. 105-110.

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