On the relative importance of the bulk and surface of a dielectric in radiation-catalytic processes

Abstract

The contribution from bulk and surface to radiation-catalytic conversion of methanol was studied for a set of samples of two dielectrics: silica gel and aluminum oxide. It was found that the extent of methanol conversion for the same amount adsorbed and for the same dose of energy taken up depends neither on the specific surface, nor on its coverage or sizes of the adsorbent globules, but is a function only of the relationship between the amount of adsorbed substance and the number of excess charge carriers formed in the bulk of the solid. The diffusion of charge carriers under the action of ionizing radiation does not interfere with the radiation-catalytic process and adsorbed molecules act only as effective surface traps (holes) for charge carriers. This conclusion is consistent with the concept that practically all excess charge carriers formed in the bulk of the dielectric take part in the radiation chemical process occurring on its surface.