Thermal diffusivity of compacted coal powders

The pulse method was used to measure the thermal diffusivities of a polygranular nuclear-grade graphite and of several standard coals of the CERCHAR-SBN minibank, in the range 20-500 degrees C. Below 300 degrees C, the diffusivities of the coals decrease with increasing temperature (from 0.11 +/- 0.02 mm(2) s(-1) to 0.07 +/- 0.02 mm(2) s(-1), depending on the material), a reversible change mainly due to the increase of specific heat. Beyond that, an irreversible increase of diffusivity occurs, probably due to annealing (aromatization) of the carbon skeleton. When coupled with Modulated Emission Spectroscopy, the knowledge of diffusivities allows the determination of absolute values of infra-red absortivities, which are of current interest in astrophysics.