Abstract

The formation of cristobalite and tridymite compounds is described in the system SiO2-V2O5-M2CO3 (M = Na, K). Syntheses were performed with various vanadium concentrations at annealing temperatures between room temperature and 1000°C. Crystallization of cristobalite occurs at much lower temperatures (about 800°C) in the presence of vanadium than observed in the pure silica system, which remains amorphous in this temperature range. With increasing amounts of vanadium, the crystallization of NaVO3 or K3V5O14 is observed along with the formation of cristobalite and tridymite. XRD, IR, and NMR indicate that cristobalite is formed by catalytic processes in the presence of vanadium without measurable V-substitution in its structure. Variations in the thermal behavior of cristobalite are attributed to different states of crystallinity.

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