Equilibrium study of the Cu-O-SiO₂ system at various oxygen partial pressures

Phase relationships of the Cu-O-SiO₂ system in various boundary conditions (metallic copper saturation, under oxygen partial pressures of 0.01 atm and 0.21 atm) have been experimentally determined by the equilibration/quenching/EPMA technique up to 1773 K. No ternary compounds were observed. An isopleth (Cu₂O-SiO₂) was used to represent the liquidus in equilibrium with air (P_O2 = 0.21 atm). One simple eutectic reaction with two primary phases (copper oxide and SiO₂) was found. The eutectic point was determined to be 1336 ± 2 K and 0.23 ± 0.01 mol fraction of SiO₂. Equilibrium at copper saturation was achieved in an inert atmosphere of purified argon gas (P_O2 ≈ 10^-5 atm) within the temperature range from 1453 K to the critical point of Cu-O system (1620 K). Above 1620 K, experiments were conducted in a N₂ atmosphere containing 1% O₂ by volume (P_O2 = 0.01 atm). The copper-saturated results were presented on ternary Cu-O-SiO₂ phase diagrams, and the eutectic point was found to be 1456 ± 2 K and 0.08 ± 0.01 mol fraction of SiO₂, 0.60 ± 0.01 mol fraction of Cu. The experimental results have been compared with previous studies and the phase diagrams calculated by MTDATA 5.10 software and its Mtox 8.1 database. The agreement within the temperature range of 1333-1623 K is good. Phase equilibria in the temperature range from T = (1673-1773) K with SiO₂ as the primary phase has been studied systematically for the first time.