Spinel deoxidation equilibrium in the cobalt-manganese-aluminum-oxygen system: Experiment and modeling

The concentration and chemical potential of O in molten Co-Mn alloys equilibrated with (Co, Mn)$Al_2O_4$ spinel solid solns. and $\alpha-Al_2O_3$ were detected at 1873 K as a function of Mn concentration Compostion of the equilibrim spinel phase was detected by using electron probe microanal. The effect of Mn on the activity coefficient of O in liquid Co was derived. The deoxidation equilibrium was computed by using data on the activity coefficient of O and Mn in liquit Co, Gibbs energies of formation of pure spinels, and published interaction parameters. The activity-compn. relation for the spinel solid soln. was derived from a cation distribution model. The computations were in agreement with exptl. data only when the activity coefficient of Mn was taken as 0.22, rather than 0.154 suggested in the literature