Development and test of a method for the simultaneous measurement of heat capacity and thermal diffusivity by laser-flash technique at very high temperatures: application to uranium dioxide

The "classical" laser-flash method is today the most used technique to measure the thermal diffusivity of a wide range of materials. This work describes the development of a new technique, based on the laser-flash method, which measures simultaneously on the same sample with an absolute method the thermal diffusivity and the specific heat, and its application to a number of high melting-point refractory materials. In this work, a new data processing procedure, which takes radiative and conductive heat losses into consideration, is introduced, and the thermal diffusivity, a, and specific heat, cp are determined by fitting the entire experimental transient temperature curve. The thermal conductivity is then calculated from the measured a and cp values via the relationship = apcP, where p is the density of the material. For the calculation the measured room temperature values of p corrected to the temperature of interest via literature data on thermal expansion are used. The new technique is applied to measure the specific heat, thermal diffusivity of POCO AXM 5Q graphite, zirconium dioxide and uranium dioxide (materials of scientific and technological interest) at very high temperatures (above 1800K) from which thermal conductivity values can be calculated. The values obtained, having a precision of ~2% in the case of the thermal diffusivity, and ~7% for the specific heat and the thermal conductivity, are discussed and compared with literature data. The results obtained for uranium dioxide are used for a critical analysis of the physical mechanisms underlying the heat transport in this material