Thermodynamic properties of NiCr2O4-NiFe2O4 spinel solid solution

The tie lines delineating ion-exchange equilibria between NiFe2O4-NiCr2O4 s pinel solid solution and Fe2O3-Cr2O3 corundum solid solution were determine d at 900, 1000, and 1200 degrees C by electron microprobe and energy disper sive X-ray analysis of oxide phases, using the flux growth technique. Activ ities of the spinel components were calculated from the tie lines, assuming Temkin's ideal mixing in the corundum solid solution. The spinel phase cou ld be expressed by a regular solution with negative deviations from idealit y. The Gibbs free energies of mixing for spinel solid solution were discuss ed in terms of the cation distribution model, based on site preference ener gies and assuming random mixing on both tetrahedral and octahedral sites.