Thermodynamic analysis of aluminate formation at Fe/Al2O3 and Cu/Al2O3 interfaces

Subsolidus ternary phase relationships in the systems Fe Al O and Cu Al O are reviewed in order to provide a basis for thermodynamic analysis of aluminate formation at Fe/α-Al 2 O 3 and Cu/α-Al 2 O 3 interfaces. Expressions for the critical oxygen activity in the Fe-rich and Cu-rich solid solutions necessary to stabilize the equilibrium aluminate phases (FeAl 2 O 4 and CuAlO 2 , respectively) in the presence of α-Al 2 O 3 are derived using data available in the literature. As in previous work in the Ni α Al 2 O 3 system, aluminate formation by solid state reaction of Fe and Cu with α-Al 2 O 3 was calculated to require a threshold concentration of oxygen in the metal, which is of the order of 1/5 the solubility limit. The sults are presented in stability diagrams and compared with previous results on the Ni/α-Al 2 O 3 system in terms of the free energies of formation of the aluminates and the relative free energes of solution of oxygen in the metals. The results are also compared with available experimental observations on Fe/α-Al 2 O 3 and Cu/α-Al 2 O 3 interfaces.