Thermodynamic Properties of Fe3O4‐FeAl2O4 Spinel Solid Solutions

The Gibbs energy of mixing for the system Fe3O 4 ‐FeAl 2 O 4 was determined at 1573 K using a gas‐metal‐oxide equilibration technique. Oxide solid solution samples were equilibrated with Pt foils under controlled CO+CO 2 gas streams. The equilibrium iron concentration in the foil was determined by chemical analysis. The cation distribution between tetrahedral and octahedral sites in the spinel crystal can be calculated from site‐preference energies and used as an alternate method of determining some thermodynamic properties, including the Gibbs energy of mixing. The solvus occurring at low temperatures in the system Fe 3 C 4 ‐FeAl 2 C 4 was used to derive the effect of lattice distortion due to cation size difference on the enthalpy of mixing and to obtain a better approximation to the measured thermodynamic quantities.