On the Chemical Stability of CeIV(PO4)(HPO4)0.5(H2O)0.5 in Alkaline Media

Reaction of cerium(IV) orthophosphate-hydrogen orthophosphate Ce(PO4)(HPO4)(0.5)(H2O)(0.5) with aqueous solution of sodium hydroxide has been analyzed. It has been shown that the keeping of compound Ce(PO4)(HPO4)(0.5)(H2O)(0.5) in strongly alkaline solution at ambient temperature for 3 days leads to complete degradation of its structure to form X-ray amorphous phase with monazite admixture. According to IR spectroscopy, the reaction of Ce(PO4)(HPO4)(0.5)(H2O)(0.5) with NaOH over first day leads to deprotonation of hydrogen phosphate group and formation of Ce-O-Ce bonds. In alkaline medium, Ce(PO4)(HPO4)(0.5)(H2O)(0.5) phase shows no cation-exchange properties toward sodium ions. Thermal treatment of the products of alkaline hydrolysis of cerium(IV) orthophosphate-hydrogen orthophosphate allows preparation of composite material consisted of well crystallized CeO2 and CePO4 particles, the content of CeO2 in the resultant material may vary from 55 to 92 mol % depending on synthesis conditions.