Sound velocity measurements on metals and Earth-forming materials at high pressure and temperature

Laboratory-based sound velocity measurements at high pressure and temperature are essential to the understanding of the elastic response of materials at extreme conditions. In this study, we introduce our simultaneous equation of state and sound velocity measurements on metals (W) and Earth-forming minerals (lawsonite). We use a Kawai-type (T25) large volume multi-anvil apparatus installed at beamline 13-ID-D of GSECARS/APS to generate high pressures. The apparatus compresses eight WC cubes, each with a corner truncated to a pre-specified edge length, forming an octahedral cavity, within which a MgO-MgAl₂O₄ octahedral pressure transmitting medium was compressed. The sample was located within a graphite sleeve heater inside the octahedron, with a buffer rod to connect the sample to one of the WC cubic anvils, to which a piezoelectric acoustic transducer was attached to generate and receive acoustic signals. Round-trip acoustic travel times through the sample were measured using the pulse-echo overlap method of ultrasonic interferometry. By using a dual-mode piezoelectric transducer (resonance frequency of 50 MHz and 30 MHz for P and S waves, respectively), P and S wave travel times were obtained simultaneously with an accuracy of ~0.1%. In the experiments conducted in conjunction with synchrotron X-ray radiation, the sample length was determined from X-ray radiographic imaging whereas the unit cell volumes (hence density) of the sample were obtained by energy-dispersive X-ray diffraction. By fitting the sound velocity and density data to the 3^rd-order finite strain equations, we determined the bulk and shear moduli as well as their respective pressure and temperature derivatives. At this meeting, new results for tungsten and lawsonite up to 10.5 GPa and 1073 K will be presented.