Electrochemical determination of the Gibbs energy of formation of MgAl2O4

The standard Gibbs energy of formation of the spinel MgAl2O4 from component oxides, MgO and alpha-Al2O3, has been determined in the temperature range 900 to 1250 K using a solid-state cell incorporating single-crystal CaF2 as the solid electrolyte. The cell can be represented as [GRAPHICS] The standard Gibbs energy of formation from binary oxides, computed from the reversible emf, can be represented by the expression Delta G(f,ox)degrees = -23600 - 5.91T (+/-150) J/mol The "second-law" enthalpy of formation of MgAl2O4 obtained in this study is in good agreement with high-temperature solution calorimetric studies reported in the literature.