Thermal Stability of Cerium Selenite and Solubility of the System Ce₂O₃–SeO₂–H₂O at 100°C

Abstract

The solubility of the three-component system Ce 2 O 3 -SeO 2 -H 2 O was studied at 100 • C. By the Schreinemakers' method, the relevant solubility isotherm was drawn. In the studied system, Ce 2 O 3 -SeO 2 -H 2 O in the concentration range 1.52-15.25 mass% of SeO 2 in the liquid phase was formed anhydrous cerium(III) selenite Ce 2 (SeO 3 ) 3 , and in concentration range 15.25-61.35 mass% of SeO 2 -cerium(III)hydrogen selenite Ce(SeO 3 )(HSeO 3 ), respectively. The obtained phases in the systems were characterized by chemical, X-ray diffraction, and thermogravimetric analysis. The thermal stability and kinetics of decomposition of Ce 2 (SeO 3 ) 3 was studied under non-isothermal heating on a derivatograph. Several mathematical models were used to describe the processed as well as eight different calculation methods. The values of the kinetic parameters strongly depend on the kind of g(α) function, whereas the used calculation procedures have not an influence. On this basis, the values of process activation energy E, pre-exponential factor A in the Arrhenius equation, change of entropy S = , enthalpy H = , and Gibbs free energy G = for the formation of activated complex by the reagent were calculated.