Determination of the thermodynamic properties of 'xMgO + (1 - x)MnO' (s,sln) from a solid-electrolyte galvanic cell in the temperature range 1163 to 1318 K

Abstract

The thermodynamic activities of MgO in the NaCl-type solid solutions which can exist in "xMgO + (1 - x)MnO' have been determined in the temperature range 1163 to 1318 K from a solid-state galvanic cell incorporating MgF₂ as the solid electrolyte. The activities of MnO have been calculated by a graphical Gibbs-Duhem integration method. The activities of both the components exhibit positive deviations from ideality over the entire composition range. The excess molar enthalpies are found to be positive. Further, "xMgO + (1 - x)MnO' does not conform to regular-solution behaviour. The origin of the excess thermodynamic properties is discussed in relation to the cationic size disparity and the crystal-field effects.