Thermodynamics of CuAlO ₂ and CuAl ₂ O ₄ and Phase Equilibria in the System Cu ₂ O‐CuO‐Al ₂ O ₃

Abstract

The standard Gibbs free energies of formation of CuAlO 2 and CuAl 2 O 4 were determined in the range 700° to 1100°C, using emf measurements on the galvanic cells (1) Pt,CuO +] Cu 2 O/CaO‐ZrO 2 /O 2 ,Pt; (2) Pt,Cu +] CuAlO 2 +] Al 2 O 3 /CaO‐ZrO 2 / Cu +] Cu 2 O,Pt; and (3) Pt,CuAl 2 O 4 +] CuAlO 2 +]Al 2 O 3 /CaO‐ZrO 2 /O 2 ,Pt. The results are compared with published information on the stability of these compounds. The entropy of transformation of CuO from tenorite to the rock‐salt structure is evaluated from the present results and from earlier studies on the entropy of formation of spinels from oxides of the rock‐salt and corundum structures. The temperatures corresponding to 3‐phase equilibria in the system Cu 2 O‐CuO‐Al 2 O 3 at specified O 2 pressures calculated from the present results are discussed in reference to available phase diagrams.