TRANSFORMATION OF TRIDYMITE TO CRISTOBALITE BELOW 1470-DEGREES-C IN SILICA REFRACTORIES

The cause and mechanism of this tridymite-to-cristobalite transformation below 1470 degree C was studied. The transformation temperature of tridymite to cristobalite decreased on addition of Al//2O//3. The apparent activation energy of the tridymite-to-cristobalite transformation was found to be 787 kJ mol** minus **1 above 1470 degree C and 176 kJ mol** minus **1 below 1470 degree C with Al//2O//3 by measuring the transformation rate. It was also observed that the tridymite included CaO; however, CaO and Al//2O//3 were located on the outside of the cristobalite which was produced below 1470 degree C. Therefore, it is supposed that the liquid phase was produced by the penetration of Al//2O//3, and impurities in the tridymite crystal diffused outside and then silica was precipitated as cristobalite.