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 (ΔoxH) 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 ΔoxH. The parameters of this equation were fitted using published experimental values of ΔoxH 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 ΔoxH 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.

Enthalpy of formation of Ln–Al–O oxides from the constituent binary ones.Figure optionsDownload as PowerPoint slide