Rare earth phosphate powders RePO4 center dot nH(2)O (Re = La, Ce or Y) II. Thermal behavior

摘要

The thermal behavior, thermostructural and morphological changes, of rare earth phosphate powders RePO4 (.) nH,0 (Re La, Ce or Y) was investigated up to 1500degreesC using high temperature X-ray diffraction, FT-infrared and Raman spectroscopies and thermogravimetry coupled with differential thermal analysis. The hydration water of the compounds was zeolitic (for Re = La or Ce) or coordinated (for Re = Y) and was associated with a divariant or a monovariant equilibrium of dehydration, respectively. The high temperature anhydrous monoclinic phase LaPO4 or CePO4 formed irreversibly at about 750degreesC after the total dehydration of the hexagonal hydrated structure while the dehydration of the monoclinic YPO4 (.) 2H(2)O phase began from about 190degreesC with its simultaneous decomposition into tetragonal YPO4. A polytrioxophosphate secondary minor phase Re(PO3)(3) resulting from adsorbed H3PO4 was formed at 950degreesC and decomposed at 1350degreesC. The particle morphology did not change with the temperature but grain coalescence occurred below 1000degreesC. (C) 2003 Elsevier Inc. All rights reserved.