Phase relations between Al₂O₃-Cr₂O₃ and FeAl₂O₄-FeCr₂O₄ solid solutions at 1823 K

Tie-lines between the corundum and spinel solid solutions have been determined experimentally at 1823 K. Next, activities of FeCr₂O₄ and FeAl₂O₄ in the spinel solid solution were determined by combining the tie-line data with literature values for the activities of Cr₂O₃ and Al₂O₃ in the corundum phase. Activities and the Gibbs energy of mixing for the spinel solid solution were also obtained from a model based on cation distribution between nonequivalent crystallographic sites in the oxide lattice. The difference between the Gibbs energy of mixing obtained experimentally and from the model has been attributed to a strain enthalpy term which is relatively unchanged in magnitude from the reported at 1373 K. The integral enthalpy of mixing obtained from experimental data at 1373 and 1823 K using the second law is compared with the model result