A method for the estimation of the enthalpy of formation of mixed oxides in Al2O3-Ln2O3 systems

A new method is proposed for the estimation of the enthalpy of formation (Δ_oxH) of various Al₂O₃-Ln₂O₃ mixed oxides from the constituent binary oxides. Our method is based on Pauling's concept of electronegativity and, in particular, on the relation between the enthalpy of formation of a binary oxide and the difference between the electronegativities of the oxide-forming element and oxygen. This relation is extended to mixed oxides with a simple formula given for the calculation of Δ_oxH. The parameters of this equation were fitted using published experimental values of Δ_oxH derived from high-temperature oxide melt solution calorimetry. Using our proposed method, we obtained a standard deviation (σ) of 4.87 kJ mol⁻¹ for this data set. Taking into account regularities within the lanthanide series, we then estimated the Δ_oxH values for Al₂O₃-Ln₂O₃ mixed oxides. The values estimated using our method were compared with those obtained by Aronson's and Zhuang's empirical methods, both of which give significantly poorer results.