Effect of Temperature on Annealing Products of Synthesized Opal Matrices

Resumo

In this paper, we describe the synthesis of opal matrices by the sol-gel method and the α-cristobalite production from them by high-temperature annealing. Both the conditions for preparing synthetic opal matrices by the hydrolysis of tetraethoxysilane in a binary ethanol-water solvent using an ammonia solution as a catalyst and the reagent concentrations for this process are described in detail. The silica particles were prepared by multistage growth to the required size at addition of tetraethoxysilane to the reaction mixture. A temperature regime for drying the siliceous xerogel with the production of porous matrices for further use and annealing to obtain high-purity α-cristobalite is proposed. Structural adjustments, such as an increase in the matrix density, their hardening, and a temperature-dependent change in the matrix porosity, are described. Open-pore matrices consisting of amorphous silicon dioxide are prepared by annealing up to 1100°C. The prepared matrices can later be used for their impregnation with various compositions to obtain various types of sensors, composite materials, and inverted matrices. The transition of a silica xerogel from an amorphous state to a crystalline state with the formation of low-temperature α-cristobalite with an α-tridymite admixture by drying and annealing at 1300°C is shown. Further annealing at 1650°C leads to the formation of a transparent nonporous sample of α-cristobalite. All processes were performed under the control of scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analysis.