EFFECT OF VARIOUS CATALYSTS ON CONVERSION OF QUARTZ TO CRISTOBALITE AND TRlDYMlTE AT HIGH TEMPERATURES

The action of a considerable number of pure oxides, fluorides, chlorides, borates, phosphates, carbonates, and other compounds and of certain mixtures, as well as the effect of several minerals in promoting or accelerating the inversion of quartz to cristobalite and tridymite at temperatures between 1000 and 1500°C. has been studied. Alkali oxides are found to be superior to all other substances, and they are effective in amounts of less than 0.1%. Acid oxides, such as BIOs or Plot., seem to have little or no value as catalysts for this inversion. Possible mechanisms for the inversion process are presented, and some applications of controlled inversion in the heat treatment of ceramic bodies are mentioned. A few data are also given on the temperature of the “low-high’ change in cristobalite.