Accurate determination of specific heat at high temperatures using the flash diffusivity method

Abstract

The flash diffusivity method can be extended, very simply, to measuring simultaneously thermal diffusivity and specific heat and thus obtaining the thermal conductivity directly. This was accomplished by determining the amount of heat absorbed by a sample with a well-known specific heat and then using this to determine the specific heat of any other sample. The key to using this technique was to have identically reproducible surfaces on the standard and the unknowns. This was achieved earlier by sputtering the surfaces of the samples with a thin layer of graphite. However, the accuracy in determining the specific heat was within ±10% and there was considerable scatter in the data. Several improvements in the technique have been made which have improved the accuracy to ±3% and increased the precision. The most important of these changes has been the introduction of a method enabling the samples to be placed in exactly the same position in front of the light source. Also, the control of the thickness and the application of the graphite coating have turned out to be very important. A comparison of specific heats obtained with this improved technique and with results obtained using other techniques has been made for two materials.