Rare earth phosphate powders RePO4 • nH2O (Re= La, Ce or Y) -: Part I.: Synthesis and characterization

Rare earth phosphate powders (Re = La, Cc or Y) were synthesized from an aqueous precipitation method. The effect of temperature, pH, ripening time and Re/P mole ratio of the initial reagents was investigated. Elementary analysis, surface area and bulk density measurements, FT-infrared spectroscopy, X-ray diffraction and SEM observations were performed to characterize the precipitates. All the powders of hydrated form (La, Cc or Y)PO4 (.) nH(2)O were single phase. They exhibited a Re/P mole ratio smaller than I due to residual H3PO4 adsorbed at their surface. A unit formula could be written as RePO4 (.) nH(2)O (.) (H3PO4)(x) with n approximate to 0.5 (for Re = La or Cc) or n = 2 (for Re = Y) and x < 0.1. High-temperature thermogravimetry was necessary to detect these residuals and insure the purity of the powders. The precipitation of lanthanum or cerium phosphates was slow, resulting in powders with a high specific surface. The precipitation of yttrium phosphate was faster and significant crystal growth occurred during the ripening, which resulted in a whisker-like morphology and a very low specific surface. (C) 2003 Elsevier Inc. All rights reserved.