Electrochemical Determination of the Gibbs Energy of Formation of $MgAl_2O_4 $

The standard Gibbs energy of formation of the spinel $MgAl_2O_4$ from component oxides, MgO and alpha-$Al_2O_3$, has been determined in the temperature range 900 to 1250 K using a solid-state cell incorporating single-crystal $CaF_2$ as the solid electrolyte. The cell can be represented as--$Pt,O_2,MgO+MgF_2|CaF_2|MgF_2+MgAl_2O_4+alpha-Al_2O_3,O_2,Pt$--The standard Gibbs energy of formation from binary oxides, computed from the reversible emf, can be represented by the expression--capdelta $G^o_{f,ox}$ = -23600 - 5.91 $\tau$ (±150) J/mol--The ``second-law'' enthalpy of formation of $MgAl_2O_4$ obtained in this study is in good agreement with high-temperature solution calorimetric studies reported in the literature