α-Crystobalite Preparation via Supercritical Carbon Dioxide Drying of Opal Matrices Synthesized by Sol-Gel Method

—This article describes the method for preparation of opal matrices by the sol–gel method, their drying in supercritical carbon dioxide, and the preparation of α-cristobalite with high temperature annealing. The conditions for the preparation of synthetic opal matrices and the concentration of reagents for this process are described. A supercritical operation mode of the drying of silica xerogel to produce porous matrices is proposed. The transition of SiO 2 from an amorphous to a crystalline state by supercritical drying and annealing is shown. All processes were controlled by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction.