Experimental verification to obtain inherent thermal diffusivity by laser flash method

M. Akoshima1, B. Hay2, M. Neda1 and M. Grelard2

1National Metrology Institute of Japan (NMIJ), AIST, Japan
2Laboratoire National de Métrologie et d’Essais (LNE), France

Keywords: inherent thermophysical properties
property: thermal diffusivity
material: ceramics, metals

Thermophysical properties of material are important in the fields of thermal management, thermal design, heat utilization and energy issue. There are needs to obtain high reliable values of thermophysical properties. Thermal conductivity of solids is often calculated from thermal diffusivity measured by the laser flash method, specific heat capacity measured by the differential scanning calorimetry and density. The laser flash method is one of the most popular methods to measure thermal diffusivity of solids above room temperature. Since the laser flash method is very convenient as a practical method to measure thermal diffusivity non-contacting in short time. On the other hands, this method is used as the standard measurement method because it is simple theory according to one dimensional heat diffusion phenomena and it can be analytically evaluate the uncertainty. However, the ideal one-dimensional heat-diffusion phenomenon is hard to be realized and it is pointed out that the results depend on some measurement conditions. It is often difficult to obtain reliable thermal diffusivity. It is known that thermal diffusivity measured by laser flash method depends on measurement conditions; for example, pulse heating energy and specimen thickness. A procedure to obtain inherent thermal diffusivity value proposed by National Metrology Institute of Japan (NMIJ). Here, “Inherent” means unique for the material and independent of measurement conditions. The first, apparent thermal diffusivity measured changing pulse heating energy at stable temperature. Then the extrapolating value in the plot of amplitude of output signal dependence of apparent thermal diffusivity is determined as inherent thermal diffusivity. In order to verify and exam applicability of the procedure for inherent thermal diffusivity measurement, we have measured thermal diffusivity of some materials (metal, ceramics) using laser flash method with the extrapolating procedure. NMIJ and Laboratoire National de Metrologie et dessais (LNE) have laser flash thermal diffusivity measurement system that is traceable to SI units, respectively. The thermal diffusivity measured by NMIJ and LNE shows good agreement although we used different measurement systems and different analysis method of temperature rise curve. We carried out experimental verification on the procedure using the measured results. We also discussed some problems and consider solutions for laser flash thermal diffusivity measurement.

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