Thermal Diffusivity Measurements of Refractory Metals as Candidate Reference Materials by the Laser Flash Method

A working group for standardization has organized to establish the Japanese Industrial Standard (JIS) for thermal diffusivity measurements of metals in the temperature range of 300–1700 K by the laser flash method. As candidate reference materials with high purity, high-temperature stability, and easy-to-get on a commercial basis, tantalum, niobium, and molybdenum have been selected. Thermal diffusivity values of the specimens, cut out of these materials, have been measured independently by members of the working group. Comparisons of results have been performed for different high-temperature stabilities, repeatabilities, and manufacturers, as well as by different members. Comparisons show that the measured values agree within 10% for different specimens by different institutions, and no systematic differences have been observed for materials from different manufacturers. The measured results for molybdenum specimens agree well with the recommended values of thermophysical properties of matter from the TPRC data series, and the high-temperature stability is found to be the best. The results for tantalum and niobium, however, show significant differences with those of the TPRC data series in the high-temperature range, and some further study on the stability of these materials is needed for recommending these values. As a result, molybdenum can be recommended as a reference material for practical use of the laser flash method.