PVA aided microwave synthesis: a novel route for the production of nanocrystalline thoria powder

A new method is reported for the preparation of nanocrystalline thoria powder that yields pellets of high density. The powder is prepared by denitration of an aqueous solution of thorium nitrate and polyvinyl alcohol (PVA) using microwave heating. The powder was characterized for its surface area and crystallite size by both X-ray line broadening and transmission electron microscopy. The reactivity of the powder was estimated by determining the density of the compacts prepared from these powders and sintered at 1573 K in air. For the sake of comparison, powders obtained by direct denitration were also characterized as above. The X-ray crystallite size for the calcined powders obtained by both routes is found to be ∝10 nm and found to be in agreement with the crystallite size obtained by conventional transmission electron microscopy. The density of pellets prepared from the powder produced by denitration in the presence of PVA was 92-93% of the theoretical density and that obtained with direct denitrated powder was ∝85% of theoretical density. (orig.)