Determination of the standard free energies of formation of Ce 2O 2S and Y 2O 2S at high temperatures

Abstract

The formation of rare earth oxysulphides is of importance in the rare earth treatment of iron and steel and the desulphurization of gaseous fuels with rare earth oxides. Phase stability diagrams governing the formation of cerium oxide, oxysulphide and sulphides in these processes are constructed from the limited thermochemical and experimental thermodynamic data available in the literature. In this paper the results of a galvanic cell technique using a calcia-stabilized zirconia solid electrolyte are reported, from which the standard free energies of formation of Ce 2O 2S and Y 2O 2S are calculated: ΔG f o ( Ce 2 O 2 S) = −354300 ± 3000 cal mol − at 1068 K and Δ f o ( Y 2 O 2 S) = −340100 ± 3000 cal mol −1 at 1072 K.