Noninvasive pressure and temperature estimation in large-volume apparatus by equation-of-state cross-calibration

The utility of internal calibration of large-volume cell high-pressure (p) and high-temperature (T) conditions by a noninvasive equation of state (EOS) cross-calibration method is assessed. This involved the introduction of simultaneously measured unit-cell volumes, measured by in-situ x-ray diffraction in Paris-Edinburgh large-volume apparatus, for gold and NaCl into their EOS to obtain a simplified solution set for p and T run conditions. These have been gauged from K-type thermocouple measurements and the EOS of hBN to establish an estimate of the combined errors involved in this method. It was found that the total error (in combined p, T and three EOS calculations) results in apparent p miscalculation of 0.2 GPa and with a mean error in T of 13%. This technique alone is valuable in high p and T experimentation above similar to 5 GPa where no reliable pressure correction exists for thermocouples and in situations where the use of a thermocouple is not advisable, for example, where thermocouple materials are sample-reactive. Combined with furnace power -p-T curves, this method offers a viable alternative to invasive measurement.