Electrochemical Determination of the Gibbs Energy of Formation of MgAl 2 O 4

The standard Gibbs energy of formation of the spinel MgAl 2 O 4 from component oxides, MgO and α‐Al 2 O 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 2 O 4 +α‐Al 2 O 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 ° f,ox =−23600 − 5.91 T (±150) J/mol—The ‘second‐law’ enthalpy of formation of MgAl 2 O 4 obtained in this study is in good agreement with high‐temperature solution calorimetric studies reported in the literature.