Phase studies in the chromium-manganese-titanium oxide system at different oxygen partial pressures

The phase diagram of the quasi-ternary oxide system Cr-Mn-Ti has been investigated at 1000°C in air and in an Ar-4 vol.% H2 atmosphere (PO2 ≈ 10−21 bar). All samples have been water-quenched and investigated by X-ray diffraction. The results can be summarized as follows. Phase relationships in air: • — The spinel Mn(MnxCr1−x)2O4, with a cubic structure for 0<-x<0·39 and tetragonal for 0·39<-x<0·87, dissolves up to 16% of the spinel phase Mn2TiO4. • — The solubility of manganese oxide in Cr2O3 is negligible (≈ 1·6 at.%). • — In the system Cr2O3-TiO2 only the continuous region of the Andersson phase exists. Cr2Ti3O9 is metastable under these conditions. Heat treatments under p02 ≈ 10−21: • — The monoclinic phase CrTi2O5 was observed in the Cr-Ti oxide system. • — Cr2O3 dissolves 18 at.% Ti as oxide, and Ti4O7 12 at.% Cr2O3. • — The spinels MnCr2O4 and Mn2TiO4 form a complete series of solid solutions and up to 24% Cr3+ ions can be replaced by Ti3+ ions.