Thermal decomposition of the rare earth sulfates of cerium(III), cerium(IV), lanthanum(III) and samarium(III)

Surface and bulk chemical and elemental composition of the rare earth sulfates of cerium(III), cerium(IV), lanthanum(III) and samarium(III) were characterized during various stages of thermal decomposition. Decomposition was conducted under both vacuum and atmospheric conditions. In situ analysis was conducted on samples decomposed in vacuum. As identified by X-ray diffraction, the bulk decomposition of all the rare earth sulfate samples to their corresponding oxide, in atmosphere, proceeded via the formation of an oxysulfate. For the exception of cerium(III) sulfate, similar results were obtained in thermogravimetric analysis. The thermal decomposition profile, as determined by X-ray microanalysis was similar to that observed in thermogravimetric analysis and X-ray diffraction. Elemental maps revealed no observable concentration gradients of sulfur. Surface composition was not necessarily representative of the bulk composition. Thermal decomposition of sulfates to an oxide initiated at a lower temperature in vacuum than that observed at atmospheric pressure.