Kelly Woody and Baosheng Li
SUNY Stony Brook
kelsters99@yahoo.com
NSLS-X17B1 (MAP)
We measured P and S wave velocities and equation of state of MgO to conditions of 10.5 GPa and 1000°C using simultaneous ultrasonic interferometry and in-situ X-ray diffraction techniques with a DIA-type multi-anvil high pressure apparatus (SAM85) installed at the superconducting wiggler beamline at the National Synchrotron Light Source (NSLS, X17B1). The polycrystalline specimen was hot-pressed using a 1000-ton uniaxial-split-sphere apparatus (USCA-1000) at a pressure of approximately 8GPa and 1400°C. The bulk density of the sample, 3.566 g/cm3, is within 99.5% of the X-ray density. Acoustic measurements at ambient pressure and temperature yield values for Vp and Vs of 9.78+0.008 and 6.00+0.005 km/s, respectively. The calculated values of the elastic moduli, Ks and Gs of 166.8+4 and 128.6+3 GPa, respectively, agree with previously published data within 1%. A third-order Birch-Murnaghan equation of state fit to the unit cell volumes at high pressure and room temperature yields a value for KT that is within 1% of previously published data. X-ray imaging system allows us to monitor the length of the MgO specimen during the experiment at each P-T condition. Although the sample underwent plastic deformation at temperatures above 800°C as indicated by imaging data, acoustic velocities at high pressures and high temperatures were determined precisely using sample lengths obtained from X-ray images. By combining acoustic and unit cell volume data, the elastic moduli as well as their pressure dependence determined by fitting velocity data to Eulerian Finite Strain equations without using a secondary pressure standard. Sample pressures calculated from these results are compared with these obtained using NaCl during the experiment.