CUPRIC OXIDE-MOLYBDENUM OXIDE PHASE DIAGRAM IN AIR AND IN OXYGEN

Phase diagrams of the CuO‐MoO3 system were determined in oxygen, in air, and under oxygen pressure. The first two diagrams are quite similar, with temperatures up to 40° higher occurring in oxygen than in air. Stable compounds obtained by low‐temperature sintering were CuMoO4 and CUZMoO5, which melted incongruently at 835° and 880° in oxygen and at 812° and 840°C in air, respectively. The MoO3‐CuMoO4 eutectic occurs near 30 molyo CuO at 705° in oxygen and at 700° C in air. Above temperatures as low as 865° in oxygen and 840° C in air, oxygen is lost with the production of cuprous compounds. This phenomenon probably accounts for all of the inconsistencies in previous phase diagrams. The dominant cuprous compound in the central region at high temperatures is Cu6Mo4O15, melting congruently at 880° and 895°C in air and oxygen, respectively. On cooling in oxygen‐containing atmospheres, this compound changes to cupric Cu3Mo2O9. Unit cell dimensions and an indexed powder pattern are presented for this compound. Experiments under an oxygen pressure of 2 to 3 atm indicate that the cupric compounds in the simple CuO‐MoO4, system without reduction are CuMoO4, Cu3Mo2O9, and Cu2MoO5, melting incongruently at 850°, 910°, and 940°C, respectively. In all atmospheres Cu3Mo2O9 is metastable with respect to CuMoO4 and Cu2MoO5 below the incongruent melting point of CuMoO4. Copyright © 1969, Wiley Blackwell. All rights reserved