Search

High-area thorium oxide, outgassed at 200°C, is covered by surface hydroxyl groups and strongly bound water molecules. Gravimetric sorption studies show that onto this hydration layer, a monolayer of water can be physically adsorbed. This physisorbed water slowly becomes more firmly bound, apparently as water of hydration of the surface hydroxyl. For one type of thorium oxide, the conversion proceeds more rapidly at relative pressures above 0.5, and adsorption-desorption cycling to 1.0 p/p 0 profoundly changes the nature of the surface to permit a discrete second step in the adsorption isotherm. The second step appears to be associated with restructuring processes. Nuclear magnetic resonance (n.m.r.) data for surface water point not only to a sluggish approach to an equilibrium state but also to the development of special structure in the multilayer region.

As part of a search for conducting refractory oxides which can be heated directly from room temperature to temperatures in excess of 2,000° C by induced radio-frequency currents without the need for pre-heating arrangements, a study has been made of the behaviour of hot-pressed thorium dioxide doped with various amounts of tantalum pentoxide. These systems possess no apparent advantages in oxidizing atmospheres, but do exhibit striking properties when prepared in reducing conditions and operated in a neutral atmosphere.