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 Mn 3 O 4 ‐CuMn 2 O 4 and Fe 3 O 4 ‐CuFe 2 O 4 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 Mn 3 O 4 ‐CuMn 2 O 4 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 Fe 3 O 4 ‐CuFe 2 O 4 , 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.