ИСТИНА

The authors developed a way of silica producing allowing to lower the content of water and other volatile impurities in it and also practically completely to eliminate a porosity. The way is based on thermo-hydro stress with use of surface-active substances. The glassformic silica was formed. At the fusion of this product in the vacuum furnace and in a hydrogen-oxygen flame the transparent glass without bubbles was received. The researches were carried out on silicas received by two ways: ammoniac hydrolysis of tetraethylorthosilicate (I) and water hydrolysis of silicon tetrachloride (II). Silica samples were exposed to high-temperature processing in different mediums for a variation of their properties. The content of water and others volatile impurities was determined by mass spectrometric method. Besides, the quantitative analysis of the kinetics of volatile impurity evaporation at different temperatures was investigated as well as the energetic and kinetic characteristics of water evaporation from silica were calculated. For definition of water state in silica structure the methods NMR1Í of the wide lines and NMR29Si of the high resolution were used. Structural - morphological characteristics of silica samples were studied with the help of raster electronic microscopy and by adsorption method. High-temperature warming up of silica samples I and II in air up to 1200 C reduces the content of water, chlorine and organic impurities more than in 10 times. However, after such processing the level of the content of structural water in samples remains rather high: 0.5 and 0.3% accordingly for samples I and II at 0.25 and 0.1 cm3/g porosity. The stayed water represents SiOH-groups in a silica matrix. The diffusion in particle bulk and evaporation of water formed from OH-groups energetically and sterically are complicated.