| Abstrakt: |
An electron microscopic and electron diffraction examination has been made of freshly precipitated and aged hydrous thoria gels prepared by (a) slow precipitation at room temperature by diffusion of CO gas into thorium nitrate solution, (b) rapid precipitaticn by the addition of ammonium hydroxide, (c) slow hydrolysis of ThCl at 80–90°, and (d) slow hydrolysis of ThCl at 180° in sealed glass tubes. Hydrous thoria gels are essentially “amorphous”, but age under water at room temperature in several months, and at 100 ° in a few days, to form anhydrous, cubic ThO. Hydrolysis of ThCl solutions at 80° or 180° yields thin transparent sheets or plate-like aggregates 400–4000 Å in thickness. These present a “shiny” or glittering appearance in suspension, and dried samples of overlapping plates exhibit interference colors. The sheets often form on the walls of the glass container, which may exert a catalytic effect. In the electron microscope the transparent sheets are found to be “secondary” aggregates composed of disc-like “ primary ” aggregates about 5OO–1000 Å in diameter, which in turn are composed of crystallites of ThO 20–30 Å in diameter. The primary crystallites were identified by their electron and x-ray diffraction patterns. The transparent thoria sheets are porous in the sense that they contain (a) small interstices between the primary crystallites and (b) larger interstices between the “ primary aggregates ”. The structure of the thoria sheets in similar to that of previously reported transparent alumina films, except that the ThO crystallites in the former are random, whereas the γ-AIOOH crystals in the latter are oriented. The transparent plates roll into scrolls in aqueous suspension, and their relation to rolls or scrolls of Halloysite clay, alumina (bayerite), and Nd(OH) is discussed. Continued aging of the thoria sheets in sealed glass tubes at 180° for periods as long as 5–6 weeks Results in a reaction with the glass, producing micron sized crystals of tetragonal ThSiO. [ABSTRACT FROM PUBLISHER] |
