Thermal conductivity measurements of semi-crystalline silica using a modified comparative method.

摘要

New semi-crystalline silica glasses were developed for use as a crucible material for gallium arsenide crystal growth. It was necessary that the thermal conductivity of the new materials be obtained for proper mathematical modeling of heat flow in crystal growth experiments.;Several established thermal conductivity methods were evaluated and a modified comparative method was selected. A furnace based on the comparative method was designed and constructed; a computerized control program was written to control the power input to each of the furnace elements, record data, and provide a user interface for the furnace. This furnace was tested, tuned and thermal conductivity measurements for the semi-crystalline silica were made over the desired temperature range. The accuracy of the measurements was increased by making a secondary comparison; specifically, the locations of the test and reference materials in the furnace were interchanged and the results averaged. At the temperature of crystal growth in gallium arsenide, the semi-crystalline silica glass was found to have a thermal conductivity that was approximately 16 percent lower than clear fused silica. Analysis of furnace performance resulted in recommendations for further design modifications to improve the accuracy of the thermal conductivity furnace.