Phase Equilibria of the Bismuth Oxide‐Copper Oxide System in Oxygen at 1 atm

Phase equilibria of the Bi 2 O 3 –CuO system have been determined from 700° to 1040°C in oxygen at 1 atm pressure. Bi 2 O 3 is stable in the Bi‐rich portions of the system and undergoes a phase transition from α‐Bi 2 O 3 to δ‐Bi 2 O 3 at 730°C. Bi 2 CuO 4 is the only binary compound found to be stable; it melts incongruently to CuO + liquid at 849°C. CuO is the stable copper oxide at temperatures below 1040°C. The liquidus is composed of three segments. The Bi 2 O 3 + liquid segment intersects the Bi 2 CuO 4 + liquid segment at a eutectic at 784°C with 92% Bi 2 O 3 . The Bi 2 CuO 4 + liquid segment and the CuO + liquid segment meet at a peritectic at 849°C at 66% Bi 2 O 3 . Superliquidus liquids with Bi:Cu = 2 were formed at 950°C at values of oxygen fugacity between 0.05 and 1. Glasses quenched from these liquids were analyzed for Cu + and total Cu. All contained both Cu + and Cu 2+ . The value of Cu 2+ /Cu + increases as the oxygen fugacity increases but, even in pure oxygen, more than half the copper in the glasses is monovalent. The variation in Cu + :Cu 2+ in liquids with Bi:Cu = 4 at an oxygen fugacity of 1 is analyzed as a function of temperature. At the lowest temperatures (<900°C), the copper is almost all divalent; at >∼1100°C, most of the copper is univalent. There is more univalent copper relative to divalent in liquids at lower oxygen fugacity and higher temperature. The value of Bi:Cu in the glass also affects the ratio of Cu + to Cu 2+ . At T < ∼900°C (and f o2 = 1), copper in liquids with Bi:Cu = 4 is dominantly divalent, whereas copper in liquids with Bi:Cu = 2 is composed of subequal amounts of Cu 2+ and Cu + . The system Bi 2 O 3 –CuO is a pseudobinary as at least some liquids in the system are actually in the Bi 2 O 3 –Cu 2 O–CuO system.