High-Surface-Area Nanocrystalline Cerium Phosphate through Aqueous Sol−Gel Route

Abstract

Rare earth phosphates have recently been investigated as a potential ceramic material in view of their high-temperature phase stability, high melting point, low thermal conductivity, optical, fluorescence, and catalytic properties, and layered structural features. The present work describes a method for synthesizing nanocrystalline cerium phosphate starting from cerium nitrate and orthophosphoric acid by sol−gel process involving controlled precipitation followed by electrostatic stabilization (peptization) using nitric acid and deagglomeration of sol particles using ultrasonication. Average particle size of cerium phosphate in the precursor sol is 50 nm. Dehydroxylation of the precursor gel was studied by thermal analysis and FTIR spectrum. The transformation of low-temperature rhabdophane phase to hexagonal and further to monoclinic monazite type at 800 °C is evidenced from the XRD pattern. Cerium phosphate had crystallite size of 10 nm and excellent thermal phase stability up to 1700 °C as observed from XRD data. Specific surface area of 98 m2/g was obtained for precursor gel calcined at 400 °C. The nanosize cerium phosphate has been sintered at 1300 °C to ∼99% density with an average grain size of 1 μm as observed from SEM micrographs.