Experimental measurements of the phonic diffusivity of semitransparent materials up to 800 K

Abstract

A new flash equipment has been developed which enables the true thermal diffusivity of semitransparent materials to be measured in the temperature range from 300 to 800 K. A theoretical study of the coupled conduction-radiation mechanism of transient heat transfer that occurs in a plate sample during a flash experiment has proved that, with the heat pulse method, it is possible to experimentally determine the diffusivity of phonic origin, that is the diffusivity defined with the true conductivity of Fourier's law. The originality of this method over others is due to the fact that any calculations of the radiative contribution to heat transfer are unnecessary: The phonic diffusivity (conductivity) is directly extracted from the measured parameter in an identification process for opaque materials. Experimental results on various semitransparent materials are presented and discussed in relation with data available in the literature. For vitreous silica it is shown that the temperature dependence of the phonic conductivity is not linear, but similar to the variation of the specific heat content.