Preparation and compaction of synthetic monazite powders

Analogs of the mineral monazite, a mixed lanthanide orthophosphate (LnPO4), are potentially important primary containment forms for the isolation of actinide nuclear wastes. A method of preparing orthophosphate powders by precipitation in molten urea has been developed. This process was used to produce orthophosphate powders of all of the naturally occurring lanthanides in the first half of the transition series. The particle size is readily controlled in the urea precipitation process and a series of cerium orthophosphate powders with varying particle size were prepared and employed in a study of the systematics of compaction by hot pressing for this system. Consolidation via hot pressing at 11000C of CePO4 powders with a suitably small particle size has resulted in bodies with 97.2% of the theoretical density. Examination of Gd3+-doped precipitated CePO4 powders using electron paramagnetic resonance techniques has shown that this impurity occupies the same sites in the urea precipitated material and in flux-grown single crystals. (Auth.)