Structure and surface properties of dual oxide gels in the system beryllium oxide-indium oxide
Adams, Charles Rex
Doctor of Philosophy thesis
The phenomenon of mutual protective action in dual systems of hydrous oxides has been studied extensively at The Rice Institute. A variety of systems has been studied and in many of these systems each oxide prevents or retards the crystallization of the other. The degree of mutual protection varies from system to system and also depends upon the temperature level at which the dual gels have been heated. The system BeO-In2O 3 was first studied in 1947 by Watt by x-ray diffraction techniques. Marked mutual protection was observed in this system in two composition zones. Only the diffraction pattern of cubic In2O3 was observed for any sample containing In2O3, agreeing with the observations of Ensslin and Valentiner. Extensive sorption-desorption studies have been made by the author on the system BeO-In2O3, heat-treated for 2 hours at 500°. From these studies surface areas, specific adsorptive capacities, differential and integral heats of adsorption, and pore size distributions were obtained. Enhanced adsorptive capacities, surface areas, and differential and integral heats of adsorption were observed in the same composition zones which had previously shown protection against crystallization. It is noted that there are two major regions of increased surface area and adsorptive capacity, at a region corresponding to 40--60% BeO and at a region corresponding to 90% BeO. The enhanced surface area and adsorptive capacity has been explained on the basis of mutual protection against crystallization, utilizing the concept of adsorption of one oxide on the other in the solid state. The differential and integral heats of adsorption as a function of composition at various values of the relative pressurer show two maxima exist, one between 30% BeO and 60% BeO, the other between 80% BeO and 90% BeO. These are essentially the same composition ranges in which there is mutual protection against crystallization and an increase in surface area and adsorptive capacity. If these zones correspond to smaller crystal size, and it will be shown that this is the case, the increase in heat of adsorption may be explained on the basis of increase of heterogeneity of the surface, due to a larger predominance of cracks, crevices, sharp edges and the like for an assembly of smaller crystals. The purpose of the present investigation is an attempt to elucidate the structure of these gels, especially in the zones of mutual protection.