Compressions of Si, MgO, and ZrSiO4 to 8 GPa as measured with a WC-anvil x-ray apparatus and epoxy pressure medium

The compressions of silicon, magnesium oxide, and zircon have been measured to 8 GPa with a tungsten-carbide opposed-anvil x-ray apparatus using a boron-epoxy gasket and epoxy as a pressure-transmitting medium. For silicon and magnesium oxide, the bulk modulus and its pressure derivative were obtained by fitting a second-degree polynominal to the x-ray data. For zircon, the bulk modulus was determined by fitting an equation of the form (ΔV/V0) = −(P/B0). The values of the bulk modulus and its pressure derivative are B0=99.4±8 GPa, B′0=3.2±1 for silicon; B0=166±10 GPa, B′0=2.5±1 for magnesium oxide; B0=222±20 GPa for zircon. In all the cases, the present values of B0 are in good agreement with those obtained from ultrasonic measurements. On the basis of these results it is suggested that the use of epoxy as a pressure-transmitting medium can greatly reduce the uniaxial stress component and improve the sample-pressure distribution in the study of materials possessing large shear strength.