Experimental Studies On Thermal Conductivities Of Thermal Function Materials Based On Harmonic Detection Method

With the rapid development of modern science and technology, thermal management problems are involved in many fields, such as micro-electro-mechanical system (MEMS), aerospace, and so on. Proper thermal management materials are benefit to effectively take away heat generated by operation process, which is very important for the normal operation of the system. Carbon nano-tube (CNT) array, silicon carbide (SiC) Crystal, function ceramic materials and many other thermal function materials are usually used in thermal management system. It is not clear about thermal properties of thermal function materials, which is a great challenge for the application of thermal management materials. To improve the existing measurement methods and explore new thermal property measurement methods have great significance to study thermal properties of thermal function materials.This dissertation adopts the combined method including theory analysis and experiment to research thermal conductivities of thermal function materials. There are two major aspects. One is that harmonic detection method (3-omega method) is extended to study thermal conductivities of anisotropic materials. There, a new structure of micro heater/detector is designed, and it can be used for getting thermal conductivities of anisotropic material sample with three different directions. The other is to establish3-omega experiment system for high temperature. Then thermal conductivities of function ceramic materials with different temperature are studied, and thermal conductivity mechanism of function ceramic materials is analyzed.A new structure of micro heater/detector is designed based on3-omega experimental principle, through which thermal conductivities of anisotropic material with three different directions can be obtained. According to the law of heat wave generated by different width micro heater/detector heat the substrate, measurement principle on getting thermal conductivities of anisotropic material with three different directions at the same time is established. This new structure of micro heater/detector is calibrated using sapphire standard sample. Thermal conductivity of sapphire obtaining from this micro heater/detector is approach to thermal conductivity of sapphire given in literature, and the error is less than5%. It is first realized that thermal conductivities of anisotropic material with three different directions are obtained at the same time.Thermal conductivities of anisotropic SiC crystal (4H-SiC,6H-SiC) with three different directions are researched using this micro heater/detector structure. The desired maximum frequency range is derived. The accuracy of frequency range used in this experiment is verified. We improve the structure of micro heater/detector mentioned above, considering the problems that may occur in the experiment, for example, the wire bond the four pads and micro heater/detector is easy to disconnect. Thermal conductivities of sapphire and thermal oxidation of silicon dioxide films are measured by the improved the structure of micro heater/detector and the former micro heater/detector, respectively. Both results are close. It indicates that improved the structure of micro heater/detector can be used to study thermal conductivities of anisotropic materials.Then, thermal conductivities of CNT array with three different directions are measured by improved the structure of micro heater/detector. And corresponding to the three layer model is established and the mechanism of heat conduction is analyzed. In this experiment, the growth direction of carbon nano-tube is parallel to the substrate plane, which is very rare.It is very difficult to get material thermal properties in several hundred even above1000℃, because of inherent connection of3-omega method. High temperature experimental measurement system of3-omega method is built successfully in this dissertation. It includes that designing the structure of high temperature furnace for3-omega method, the structure of sample holder, and proper connection structure using in high temperature.Thermal conductivities of aluminum nitride (AlN) ceramic in different temperature (300K～1100K) are measured using the high temperature experimental measurement system. AlN ceramic are obtained by dry pressing method and casting method, respectively. Thermal conductivities of AlN ceramic reduce with the rise of temperature. And the results are compared with literature values. Thermal properties of germinate glass ceramic are researched from room temperature to750K, and heat conduction mechanism of germinate glass ceramic is analyzed theoretically. Three germinate glass ceramic samples have the same components, but the holding temperature are different. Thermal conductivities of germinate glass ceramic increase with the rise of holding temperature.