Activity–Composition Relations in MnCr2O4–CoCr2O4 Solid Solutions and Stabilities of MnCr2O4 and CoCr2O4 at 1300°C
Phase equilibria in the system MnO–CoO–Cr2O3 were investigated at 1300°C under controlled oxygen partial pressures by using the gas equilibration technique. The CoO activities in various phase assemblages of the system were measured by determining the partial pressures of oxygen in the gas phase for coexistence with metallic cobalt. The activity data revealed that at 1300°C, MnO–CoO and MnCr2O4–CoCr2O4 solid solutions exhibit mild positive departures from ideal behavior. The activities in the stoichiometric spinel solutions were found to be in good agreement with those predicted from a model based on cation distribution equilibria. The standard free energy of formation of the compound CoCr2O4 from its oxide components at 1300°C was determined as −37 636 J/mol, while that for MnCr2O4 was found as −44 316 J/mol.
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Document Type: Research Article
Affiliations: Metallurgical and Materials Engineering Department, Middle East Technical University, Ankara, Turkey
Publication date: 2005-09-01