Formation conditions of metastable α-cristobalite from amorphous silica with and without V₂O₅ flux

Abstract

We investigated the synthesis conditions of metastable α-cristobalite using amorphous silica (silica-gel) with and without V₂O₅ as a flux. Secondary electron microprobe observations for synthesized samples with flux revealed the formation of faceted α-cristobalite crystals (2-19 µm), whereas those synthesized without flux did not exhibit a clear facet. Powder X-ray diffraction analysis showed that the addition of flux lowered the formation temperature of metastable α-cristobalite to 1000 °C, which contrasts with the fact that the crystallization occurred at 1200 °C in the case without flux. These observations demonstrate that the V₂O₅ flux alone promotes crystallization by lowering the activation energy of the crystallization process of metastable cristobalite as well as other kinds of flux materials.