PHASE-EQUILIBRIA OF THE BISMUTH OXIDE COPPER-OXIDE SYSTEM IN OXYGEN AT 1-ATM

Phase equilibria of the Bi2O3-CuO system have been determined from 700 degrees to 1040 degrees C in oxygen at 1 atm pressure. Bi2O3 is stable in the Bi-rich portions of the system and undergoes a phase transition from alpha-Bi2O3 to delta-Bi2O3 at 730 degrees C. Bi2CuO4 is the only binary compound found to be stable; it melts incongruently to CuO + liquid at 849 degrees C. CuO is the stable copper oxide at temperatures below 1040 degrees C. The liquidus is composed of three segments. The Bi2O3 + liquid segment intersects the Bi2CuO4 + liquid segment at a eutectic at 784 degrees C with 92% Bi2O3. The Bi2CuO4 + liquid segment and the CuO + liquid segment meet at a peritectic at 849 degrees C at 66% Bi2O3. Superliquidus liquids with Bi:Cu = 2 were formed at 950 degrees 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 Cu2+. The value of Cu2+/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+:Cu2+ in liquids with Bi:Cu = 4 at an oxygen fugacity of 1 is analyzed as a function of temperature. At the lowest temperatures (<900 degrees C), the copper is almost all divalent; at > approximate to 1100 degrees 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 Cu2+. At T < approximate to 900 degrees C (and F-O2 = 1), copper in liquids with Bi:Cu = 2 is composed of subequal amounts of Cu2+ and Cu+. The system Bi2O3-CuO is a pseudobinary as at least some liquids in the system are actually in the Bi2O3-Cu2O-CuO system.