Thermal decomposition features of calcium and rare-earth oxalates

Thermal decomposition of Ln(2)(C2O4)(3) center dot 9H(2)O concentrate (Ln = La, Ce, Pr, Nd) in the presence of CaC2O4 center dot H2O was studied by X-ray diffraction, thermogravimetry, and chemical analysis. Annealing at temperatures above 374A degrees C in the absence of calcium oxalate gives rise to the solid solution of CeO2-based rare-earth oxides. Calcite CaCO3 is formed in the presence of calcium oxalate at annealing temperatures above 442A degrees C, which impedes the formation of lanthanide oxide solid solution and favors crystallization of oxides as individual La2O3, CeO2, Pr6O11, and Nd2O3 phases. An increase in temperature above 736A degrees C is accompanied by decomposition of calcium carbonate to give rise to an individual CaO phase and an individual phase of CeO2-based lanthanide oxide solid solution.