Melting of gold, silver, and copper-proposal for a new high-pressure calibration scale

The melting temperatures of gold, silver, and copper as a function of pressure have been determined to 65 kb by differential thermal analysis. The precision of the results is high. Replicate determinations at a given pressure agree within ±2°. After application of appropriate corrections for the effect of pressure on the emf of thermocouples, the melting curves are linear with the isothermal volume of the melting solid to within the precision of the measurement. Good agreement exists between shock-wave data, ultrasonic data, and static measurements on the relationship between P and V for these metals. Thus by extrapolation of the linear melting relationship, it is possible to construct a melting curve for these three metals to 200 or more kb. We propose the melting curve of gold as a primary standard of pressure measurement for work at high temperatures and pressures in the region 100–200 kb over the temperature interval 1600–2000°C.