STANDARD FREE-ENERGIES OF FORMATION OF RARE-EARTH SESQUISULFIDES

Rare earth sulphides are precipitated as inclusions in steel during the desulphurization of steel with rare earth elements. However, thermodynamic data on the rare earth sulphides are limited in content. An e. m. f. (electromotive force) technique is used for the measurement of the Gibbs' energy changes involved in the conversion of the rare earth oxysulphides to the corresponding sesquisulphides in the temperature range 870 to 1120 K. The changes in the standard free energy, enthalpy and entropy associated with the conversion of the rare earth oxysulphide to the sesquisulphide all show a smooth variation with rare earth atomic number.