THERMAL-DIFFUSIVITY OF PLASMA SPRAYED ALUMINA COATINGS

It is demonstrated in the paper, that the determination of the parameter thermal diffusivity of plasma sprayed coatings from refractory oxides (type ZrO2, Al2O3) must involve the usually neglected partial contribution of photon mechanism of heat transfer by the coating. The influence of the partial transparency of the coating for impinging radiation on the values of thermal diffusivity determined by the flash method is discussed. Definitions are given of the intrinsic thermal diffusivity, which is a material constant, and effective thermal diffusivity, which depends, above all, on the coating thickness and impinging radiation wavelength. The relation between the mechanism of heat transfer by the coating and the value of thermal diffusivity was tested experimentally on two types of alumina coatings, namely A 99 and A 96.