The development of a thermal diffusivity reference material using alumina

Polycrystalline alumina developed by the Japan Fine Ceramics Center (JFCC) has been studied as a candidate thermal diffusivity reference material. It was experimentally confirmed that the alumina developed by the JFCC is homogeneous and stable enough to be used as a reference material. The thermal diffusivities of two specimens of different thicknesses (2 and 3 mm) were measured by the laser flash method with high accuracy in the temperature range from room temperature to 1000 K. From the results obtained by measurements, the reference equation of thermal diffusivity in the alumina was determined. The uncertainty of the equation consists of the uncertainties associated with material inhomogeneity of 1.61% and the measurement of 2.29%. Then the combined standard uncertainty is 2.80% (1σ) and the expanded uncertainty is derived as 5.60% with the coverage factor of `2' (2σ). Moreover, we developed a new measurement system for practical use of the laser flash method with a high accuracy technique. In the new system, the uncertainty of the measurement was evaluated by using specimens with the existing reference equation. The difference from the thermal diffusivity value measured by using the new system to the reference value is within ±2.3%, which is equal to the uncertainty of measurement obtained by using the system in the National Research Laboratory of Metrology.