Method for Obtaining Thermal Conductivity From Modified Laser Flash Measurement

Abstract

Laser flash method is commonly used to measure the thermal diffusivity of solids. In the original thermal analysis, adiabatic boundary conditions were used and the time for sample rear surface temperature to reach 50% of maximum value was used to calculate the thermal diffusivity. Later other boundary conditions were included in the analysis to compensate for the heat loss. The laser flash method can be modified to determine the thermal conductivity by comparing the temperature rise of the sample with a standard sample, both of which are coated to ensure identical surface emissivity. In our previous studies of applying the laser flash method to semiconductor melts, we have shown that it is possible to obtain thermal conductivity, specific heat capacity and thermal diffusivity from the experimental data. In these studies, the melt sample was sealed in a specially-designed fused silica cell. The heat transfer between melt sample and the fused silica cell allows the thermal conductivity to be included in the analysis. Therefore, the temperature response of the melt sample was controlled not only by the thermal diffusivity and conductivity of sample, but also by the thermal properties of fused silica cell. Using a computational fitting process, we obtained both thermal diffusivity and thermal conductivity of the sample. In this paper, an analytic solution for the transient heat transfer inside the sample and fused silica cell was developed. The influence of fused silica cell was included and the heat transfer to fused silica cell had a significant effect on the time-temperature response of the sample. Therefore, the rear surface temperature of the sample, described by an analytical solution, could be used to obtain both thermal diffusivity and thermal conductivity of the sample with known properties of the fused silica cell. The results indicated that this method was applicable for a wide range of sample and cell properties. The original solution for laser flash method became an extreme case in the current theory