Thermodynamics of copper-manganese and copper-iron spinel solid solutions

High-temperature oxide melt solution calorimetry has been performed to investigate the energetics of spinel solid solutions in the Mn₃O₄-CuMn₂O₄ and Fe₃O₄-CuFe₂O₄ systems. The spinel solid solutions were synthesized by a ceramic route and calcined at appropriate temperatures to obtain single phase samples. The drop solution enthalpies of the solid solutions in the Mn₃O₄-CuMn₂O₄ system are the same within experimental error as the enthalpies of drop solution of mechanical mixtures of the end-members, indicating a zero heat of mixing, i.e., ideal mixing in terms of enthalpy. In Fe₃O₄-CuFe₂O₄, the drop solution enthalpy of the solid solutions shows a positive deviation from those of the mechanical mixture of the end-members, suggesting negative mixing enthalpy. The formation enthalpies of the spinel solid solutions from their constituent oxides plus oxygen and from the elements were also determined.