Electron Microscopic and Electron Diffraction Studies on Hydrous Thorium Oxide

Abstract

Hydrous thorium oxide has been prepared by the addition of ammonium hydroxide to solutions of thorium chloride (Series A) and thorium nitrate (Series B), followed by dialysis for varying periods of time at room temperature; and by hydrolysis at 100° of thorium chloride solution (Series C) and thorium nitrate solution (Series D), followed by dialysis at 100° for varying periods of time. Samples from Series A and B were found by electron diffraction to be essentially amorphous, the diffraction pattern consisting of a few broad bands, in agreement with earlier work. Primary particles in the range 8–20 Å were observed on electron micrographs, the size increasing slowly with time of dialysis and aging, Samples from Series C and D likewise were found to be essentially amorphous at first, but the electron diffraction patterns became sharper and became identical with that from normal cubic ThO2 after several hours of hydrolysis and aging at 100°. Electron micrographs show a growth in crystal size to 200–400 Å as the hydrolysis and aging proceeds. A very small percentage of plate-like particles have been detected by both electron microscopy and electron diffraction in samples for Series C (hydrolysis of thorium chloride at 100°). The number of such plate-like particles increases but slightly with prolonged aging. The plates exhibit a hexagonal crossgrating single crystal type of electron diffraction pattern. They have not been detected in samples prepared from the nitrate. Because of the infrequent occurrence of the plates, attempts to secure such plates isolated from the bulk of the small crystals of hydrous thorium oxide were unsuccessful. Their chemical composition is not known. Future work will involve hydrolysis in a high pressure bomb, with the view of producing the plate-like material in larger amounts, and with the view of eliminating the possibility that the plates result from a recurring impurity.