Thermal diffusivity at incandescent temperatures by a modulated electron beam technique

Apparatus is described for the determination of the thermal diffusivity by Cowan's method of a thin slab of material heated to incandescence by an electron beam. The electron beam is amplitude modulated to vary sinusoidally with time and the phase difference between the resulting temperature fluctuations of the two faces of the slab yields the thermal diffusivity of the sample. Results obtained for the thermal diffusivity and hence the thermal conductivity of platinum, tantalum, molybdenum and tungsten are given. The Lorenz functions of all four metals were found to be constant over the temperature ranges studied. Thermal conductivity values determined for three types of graphite, indium oxide, uranium dioxide, a U-49 at.%C alloy and boron nitride are also given. Results obtained with the apparatus to date cover a range of thermal conductivities of from 0.02 to 1.1 w cm -1 degK -1 within various temperature ranges between 1200 and 3000°K.