DIAGRAMS E-R-M(KOH) FOR COBALT AT 25-125 DEGREES-C AND AT TOTAL PRESSURE OF 1-30 BAR

Diagrams E-r-m(KOH) for cobalt were calculated in the range of molalit y m(KOH) = 2-18 mol kg(-1), temperature t = 25-125 degrees C and total pressure P = 1-30 bar (0.1-3.0 MPa) on the basis of recent reliable d ata for individual reaction components. The water activity a(H2O), the equilibrium pressure of the water vapour P-H2O in or above the KOH so lutions was considered. The results displayed differences from the ori ginal E-pH diagram for cobalt after Pourbaix. The direct oxidation of Co3O4 to CoO2 without any intermediate stage of Co(III) oxo compounds was found to be thermodynamically more favourable. Consideration of th e reduced water activity in concentrated KOH solutions led to the find ing that solid Co(OH)(2) can be dehydrated to CoO at elevated temperat ures in contact with KOH solutions. With rising temperature, dehydrati on can occur at lower KOH molality. CoO2, not known in a pure form, wa s assumed to exist as a pure substance in mixtures with other solid Co oxo compounds in lower states of oxidation.