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Temperature Measurements
Temperature Measurements Alexander S. Rogachev, Alexander S. Mukasyan
The most accurate method for measuring the sample temperature during combustion is the use of thermocouples. Because of the high temperatures developed in the combustion process, it is necessary to use the most refractory thermocouples made of tungstenrhenium alloys. The temperature in the combustion wave is often measured using tungsten-rhenium thermocouples WRe5/WRe20 with a diameter of d ¼ 100 μm, the thermal relaxation time of which is τ d2/4 a 4 105 s (a 0.65 cm2/s is the thermal diffusivity of tungsten). Thus such thermocouples allow not only accurately measure the temperature profiles of postcombustion and cooling stages but also grab some details of the reaction front. If more accurate measurements of the temperature profile of the combustion front are required, it is necessary to use micro-thermocouples with a thickness of about 10 μm or less [1,2], which should be protected by boron nitride coating. The procedure for the incorporation of the thin thermocouples into the samples is rather complex and time-consuming, because each thermocouple is used only once since usually it is destroyed in the burned sample. The accuracy of high-temperature thermocouple measurements in the SHS wave is about 10–50 degrees. Contactless methods for temperature measurement, e.g., with a pyrometer, are more productive [3,4], but the accuracy of the obtained data is typically lower than that for the thermocouples. This is primarily because of the uncertainty in the emissivity at different wavelengths. The combination of a photodetector with a microscope enables micro-pyrometric measurements to be taken within a region about 10 μm in size [5]. The most advanced method for measuring the temperature of SHS reactions is apparently thermovision. A thermovision camera registers the thermal radiation of the sample in the far-infrared (IR) range (2–5 μm) and shows the evolution of temperature distribution along the investigated surface. The recording rate for IR images is typically 30 frames per second. However, there are also high-speed IR cameras with a recording rate up to 15,000 frames per second, and they are also equipped with infrared lenses that improve the spatial resolution to tens of micrometers. However, these thermal imagers are still quite expensive and must be used in a reaction chamber with special high-cost windows (fluorite, NaCl, etc.). It is worth noting that all the preceding methods also work well in studies on synthesis in a thermal explosion mode [6,7].
374
Copyright © 2017 Elsevier Inc. All rights reserved.
Concise Encyclopedia of Self-Propagating High-Temperature Synthesis http://dx.doi.org/10.1016/B978-0-12-804173-4.00152-6
Temperature Measurements
REFERENCES [1] Zenin AA, Merzhanov AG, Nersisyan GA. Structure of heat-wave in some processes of self-propagating high temperature synthesis. Dokl Akad Nauk SSSR 1980;250(4):880–4. [2] Zenin AA, Merzhanov AG, Nersisian GA. Thermal wave structure in SHS processes (on the example of the boride synthesis). Combust Explos Shock Waves 1981;16(1):63–71. [3] Andreev VA, Maltsev VM, Seleznev VA. Combustion of Hf–B mixtures as studied by optical pyrometry. Combust Explos Shock Waves 1980;16(4):374–8. [4] Anselmi-Tamburini U, Maglia F, Spinolo G, Munir ZA. Use of two-color array pyrometry for characterization of combustion synthesis waves. J Mater Res 2000;15(2):572–80. [5] Garkol DA, Gulyaev PYu, Yevstigneev VV, Mukhachev AB. A new high-speed brightness pyrometry method to investigate self-propagating high-temperature synthesis. Combust Explos Shock Waves 1994;30(1):72–6. [6] Rogachev AS, Mukasyan AS, Varma A. Volume combustion modes in heterogeneous reaction systems. J Mater Synth Process 2002;10(1):31–6. [7] Rogachev AS, Mukasyan AS. Combustion for material synthesis. Boca Raton, London, New York: CRC Press Taylor & Francis Group; 2015. 397 p.
375
The most accurate method for measuring the sample temperature during combustion is the use of thermocouples. Because of the high temperatures developed in the combustion process, it is necessary to use the most refractory thermocouples made of tungstenrhenium alloys. The temperature in the combustion wave is often measured using tungsten-rhenium thermocouples WRe5/WRe20 with a diameter of d ¼ 100 μm, the thermal relaxation time of which is τ d2/4 a 4 105 s (a 0.65 cm2/s is the thermal diffusivity of tungsten). Thus such thermocouples allow not only accurately measure the temperature profiles of postcombustion and cooling stages but also grab some details of the reaction front. If more accurate measurements of the temperature profile of the combustion front are required, it is necessary to use micro-thermocouples with a thickness of about 10 μm or less [1,2], which should be protected by boron nitride coating. The procedure for the incorporation of the thin thermocouples into the samples is rather complex and time-consuming, because each thermocouple is used only once since usually it is destroyed in the burned sample. The accuracy of high-temperature thermocouple measurements in the SHS wave is about 10–50 degrees. Contactless methods for temperature measurement, e.g., with a pyrometer, are more productive [3,4], but the accuracy of the obtained data is typically lower than that for the thermocouples. This is primarily because of the uncertainty in the emissivity at different wavelengths. The combination of a photodetector with a microscope enables micro-pyrometric measurements to be taken within a region about 10 μm in size [5]. The most advanced method for measuring the temperature of SHS reactions is apparently thermovision. A thermovision camera registers the thermal radiation of the sample in the far-infrared (IR) range (2–5 μm) and shows the evolution of temperature distribution along the investigated surface. The recording rate for IR images is typically 30 frames per second. However, there are also high-speed IR cameras with a recording rate up to 15,000 frames per second, and they are also equipped with infrared lenses that improve the spatial resolution to tens of micrometers. However, these thermal imagers are still quite expensive and must be used in a reaction chamber with special high-cost windows (fluorite, NaCl, etc.). It is worth noting that all the preceding methods also work well in studies on synthesis in a thermal explosion mode [6,7].
374
Copyright © 2017 Elsevier Inc. All rights reserved.
Concise Encyclopedia of Self-Propagating High-Temperature Synthesis http://dx.doi.org/10.1016/B978-0-12-804173-4.00152-6
Temperature Measurements
REFERENCES [1] Zenin AA, Merzhanov AG, Nersisyan GA. Structure of heat-wave in some processes of self-propagating high temperature synthesis. Dokl Akad Nauk SSSR 1980;250(4):880–4. [2] Zenin AA, Merzhanov AG, Nersisian GA. Thermal wave structure in SHS processes (on the example of the boride synthesis). Combust Explos Shock Waves 1981;16(1):63–71. [3] Andreev VA, Maltsev VM, Seleznev VA. Combustion of Hf–B mixtures as studied by optical pyrometry. Combust Explos Shock Waves 1980;16(4):374–8. [4] Anselmi-Tamburini U, Maglia F, Spinolo G, Munir ZA. Use of two-color array pyrometry for characterization of combustion synthesis waves. J Mater Res 2000;15(2):572–80. [5] Garkol DA, Gulyaev PYu, Yevstigneev VV, Mukhachev AB. A new high-speed brightness pyrometry method to investigate self-propagating high-temperature synthesis. Combust Explos Shock Waves 1994;30(1):72–6. [6] Rogachev AS, Mukasyan AS, Varma A. Volume combustion modes in heterogeneous reaction systems. J Mater Synth Process 2002;10(1):31–6. [7] Rogachev AS, Mukasyan AS. Combustion for material synthesis. Boca Raton, London, New York: CRC Press Taylor & Francis Group; 2015. 397 p.
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