Onset Temperatures and Kinetics of Quartz Glass Crystallization
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TAL GROWTH
First Russian Crystallographic Congress
Onset Temperatures and Kinetics of Quartz Glass Crystallization A. I. Nepomnyashchikh*, A. A. Shalaev, T. Yu. Sizova, A. S. Paklin, A. N. Sapozhnikov, and L. A. Pavlova Vinogradov Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk, 664033 Russia *e-mail: [email protected] Received May 15, 2017
Abstract—A complex analysis of the crystallization of quartz glass from quartzites of the Bural-Sardyk deposit (the Eastern Sayan) has been performed. A mineralogical and petrographic characterization of the quartzites of this deposit is presented, and techniques of quartz grit preparation and quartz glass formation are described. Quartz glass samples prepared from grits of two types have been thermally tested, and crystallization onset temperatures and character of their crystallization were determined for them. DOI: 10.1134/S1063774518020153
INTRODUCTION The stability of quartz glass to crystallization is one of its most important characteristics, which determines the functioning of quartz glass products at high temperatures upon rapid heating. These parameters must be taken into account when designing, e.g., ceramic radio-transparent coverings of antenna fairings of high-speed aircrafts [1], optical fiber claddings [2], and microelectronic devices. Analysis of the quartz glass crystallization is also important for determining the general regularities of glass–crystal phase transitions. The tendency of glasses to crystallization is determined by their chemical composition and external parameters (such as temperature and pressure). Glass crystallization is facilitated by the presence of interfaces, regions of contact with refractory materials, gas bubbles in the glass mass, foreign solid inclusions, etc. On the whole, glass crystallization occurs in two stages: formation of crystallization centers (nuclei) and crystal growth thereon [3–5]. The crystallization centers are microparticles with an ordered composition and structure, having an interface with the environment. Glass crystallization may have either surface or bulk character. Generally, bulk crystallization follows the surface one. Quartz glass is generally stable to crystallization at temperatures below 1000°C, and crystallization temperatures range from 1000 to 1650°C. Cristobalite is released in the entire temperature range of quartz glass crystallization. However, the presence of alkali metal oxide impurities in quartz glass may induce formation
of tridymite crystals. The presence of alkali metal oxides and aluminum impurities may significantly increase the quartz glass crystallization rate. The purpose of this study was to analyze the quartz glass obtained from high-purity quartzite species from the Bural-Sardyk deposit (the Eastern Sayan) [6]. During the analysis, we compared glasses obtained from chemically enriched quartz concentrates of two types, one of which was subjected to initial calcination at 1550°C for 6 h, while the other was not. EXPERIMENTAL Rock crystal and vein var
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