TEMPERATURE-DEPENDENCE OF THERMAL-DIFFUSIVITY MEASURED BY PHOTOTHERMAL RADIOMETRY

Thermal diffusivity is generally measured by impulse or modulated flux methods; the temperature distribution inside the sample is measured by thermocouples. The nonintrusive photothermal techniques do not induce geometrical or thermal changes inside the sample; an indirect procedure gives the temperature variations on the sample surface. Photothermal radiometry, based on the measurement of the radiative flux emitted by the sample, is all the more accurate as the temperature is elevated. We have used this method to measure thermal diffusivities of thin and opaque solid samples at temperatures above 400 K. The temperature field is calculated by using a standard model accounting for the emitted radiative flux. The experimental apparatus is briefly described and experimental results for selected materials (nickel, stainless steel) and cast-iron samples are presented. The influence of the material structure on the thermal diffusivity is discussed.