COMPARISON OF SURFACE STATES OF QUARTZ CRISTOBALITE AND SILICIC ACID

The surface states of silica in the forms quartz, cristobalite, and silicic acid were studied by investigating the kinetics of para‐ortho hydrogen conversion and of hydrogen‐deuterium equilibration from 93° to 773°K. The products of conversion were analyzed by microthermal conductivity, and those of equilibration by mass spectrometry. The results are discussed in terms of the reaction mechanisms. The active sites for low‐temperature conversion are thought to be stable free radicals produced by the thermal removal of hydroxyl groups from the surfaces. Reactivity at high temperatures depends on thermal activation procedure and time. The order of reactivity for equilibration at all temperatures is: quartz > cristobalite > silicic acid. For conversion at low temperatures the order is: quartz > cristobalite > silicic acid; at high temperatures, cristobalite > quartz > silicic acid. Copyright © 1968, Wiley Blackwell. All rights reserved