THERMAL-DIFFUSIVITY OF SILICA GLASS AT PRESSURES UP TO 9-GPA

The thermal diffusivity of silica glass was measured at pressures up t o 9 GPa and temperatures up to 1200 K. The measurements involve adopti ng the Angstrom method to a cylindrical geometry in a uniaxial split-s phere apparatus. This method can be used to determine thermal diffusiv ity in samples with dominant conductive heat transfer. The thermal dif fusivity of silica glass has a negative first pressure derivative but a positive second pressure derivative. Although the elastic moduli hav e minima near 3 GPa, the thermal diffusivity does not has minimum up t o 9 GPa, which cannot be explained by the model of Kittel (1949). The negative pressure derivative of thermal diffusivity is a feature proba bly unique in silica glass, and its magnitude should decrease with the addition of Na2O.