The melting curve of gold, silver, and copper to 60‐Kbar pressure: A reinvestigation

Abstract

The melting curves of gold, silver, and copper were redetermined by differential thermal analysis to 60‐kbar pressure. The experiments were carried out with an end‐loaded piston‐cylinder high‐pressure apparatus using a recently developed low‐friction cell. Significant improvements in the precision of the temperature determination above 40 kbar were obtained. We observed a slight lowering of the melting temperature of copper when graphite capsules were used, which is consistent with our past experience and indicates some alloying of the copper and carbon. The following parabolic functions (Tm = a3 + [a2(P − a1)]½ 10 8a2) were fitted to the raw data, and the data corrected for the influence of pressure on the emf of the thermocouples (in parenthesis): gold, Tm = −2439.28 + [0.262850×10−4(P + 322.668)]½ × 2628.50 (Tm = −1773.88 + [0.309303×10−4(P + 249.167)]½ × 3093.03); silver, Tm = −261.759 + [0.661750×10−4 (P + 99.085)]½ × 6617.50 (Tm = −194.145 + [0.668583 × 10−4(P + 89.347)]½ × 6685.83); and copper, Tm = 129.171 + [0.134011×10−3(P + 122.305)]½ × 134.011 (Tm = 199.265 + [0.135218×10−3(P + 105.960)]½ × 135.218). The precision of the pressure measurements at the 90% confidence level is 0.3±0.5 kbar. The precision in the temperature is ±5°C. A revision of a previously made suggestion for a high‐pressure calibration scale based on the melting temperatures of pure elements is proposed.