Rhenium, an in situ pressure calibrant for internally heated diamond anvil cells

The rheologic, chemical, thermal, and electrical properties of rhenium make it an excellent choice for containing and heating samples to very high pressures and temperatures in diamond anvil cells (DACs). In many experimental configurations, e.g., the internally heated diamond anvil cell (IHDAC), the rhenium parts are at or close to the pressure and temperature conditions of the sample. Because the pressure and temperature of the rhenium container are close to those of the specimen, rhenium offers an attractive means for determining pressure at high temperatures in x-ray diffraction experiments without the requirement of adding an additional material to the intricate and cluttered sample assembly. For this reason, we set out to determine an equation of state (EOS) of rhenium. We combine the isothermal equation of state of rhenium at ambient temperature with volume data collected at randomly distributed, simultaneous high pressure-temperature conditions. A linear dependence of thermal pressure on temperature at constant volume has been assumed. Data were collected using synchrotron radiation x-ray diffraction in con unction with an IHDAC equipped with a rhenium internal resistive heater developed recently at the Cornell High Energy Synchrotron Source. The consistency over a large P-T range between our EOS and shock EOS within the experimental uncertainty suggests that the thermal pressure is measurable using the method proposed in the article, and that the rhenium can be used as a convenient pressure calibrant although the accuracy of it depends on many factors including the reliability of the pressure scale at high temperature. (C) 2004 American Institute of Physics.