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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Material Thermal Properties Analysis of Sapphire and Silicon Nitride Using Cryogenic Cycling




Abstract

Accurate thermal expansion data of materials at low temperatures are important in material selection and thermal design of engineered systems. The importance of low thermal expansion materials is manifested in their widespread use in electronic devices, heat-engine components, aircraft materials and aerospace applications. Thermal expansion mismatch causes serious problems in operating device reliability due to stresses imposed on the joint materials undergoing temperature changes. This study investigates the effects of cryogenic temperatures on the thermal expansion, electrical resistivity and hardness for two ceramic substrates of Silicon Nitride (Si3N4) and alpha-Alumina/Sapphire (α-Al2O3). A continuous flow cryostat system is implemented to provide a successive cooling environment from 298 to 4K. Copper (Cu) is used as a reference material within this analysis for a comparative study of the theoretical models. The temperature coefficient of resistance, αt, was calculated for Cu between 25°C and -210°C with values of 0.0039 and 0.042, respectively. This calculation validated the theoretical electrical resistivity model that was used to calculate the resistivity of the sample materials. The results indicate that our continuous flow cryostat system and corresponding measurement methods will be a precise modus for measuring the thermal properties for these substrates, which will be compared with predictive theoretical data from existing literature.

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