PHASE EQUILIBRIA IN SYSTEM COBALT OXIDE/COPPER OXIDE IN AIR

A phase diagram is proposed for the system cobalt oxide/copper oxide showing the phases which are stable in air at temperatures between 600 and 1200°C. From X-ray analyses of quenched samples and from high-temperature X-ray analyses the occurrence of the following phases was established: a cubic spinel phase CuxCo3-xO4 () ≤ x ≤ 0·3), a cubic rock-salt phase CuyCo1-yO (0 ≤ y ≤ 0·39), a phase CuyCo1-yO (0·63 ≤ y ≤ 0·68) with a specific structure, a liquid phase, the phase Cu2O and the phase CuO. The oxygen content of most of the quenched samples consisting of a single phase was slightly higher than that given by the above formulae. The position of the phase boundaries and the phase transitions was further investigated by differential thermal analyses and by microscopic observations on quebched samples as well as on samples at high temperatures. The isomorphism of the compound Cu2CoO3 (y = 2 3) and the mineral güggenite, Cu2MgO3, is discussed. © 1968.