Natural silica quartz

Silica, Si02, is a hard, rigid network solid that is insoluble in water. It occurs naturally as quartz and as sand, which consists of small fragments of quartz, usually colored golden brown by iron oxide impurities. Some precious and semiprecious stones are impure silica (Fig. 14.36). Flint is silica colored black by carbon impurities. 

Silica occurs widely in Nature as quartz, often in large transparent crystals of characteristic shape but also in the translucent agglomerations of microscopic crystals known as chalcedony, which includes cherts and flint. Other natural crystalline varieties of Si02 include tridymite and cristobalite (opal is a semiprecious stone that consists of microcrystalline, hydrous cristobalite). All forms of silica involve three-dimensional networks of corner-linked Si04 tetrahedra. 

Six different silica modifications were used vitreous silica, quartz, cristobalite, tridymite, coesite, and stishovite. Two of these—cristobalite and tridymite—were prepared from fine amorphous silica powder by tempering samples at 950°C. with 1% of a mineralizer (K2CO3 and KH2P04, respectively). Vitreous silica was obtained from fused rock crystals. All other samples were natural minerals pure specimens of Brazilian rock crystal were used as quartz coesite and stishovite were obtained as fine powders by isolation from Coconino sandstone of the Barringer Meteor Crater in Arizona (4). 

Silica, or Si02, occurs in nature as quartz, cristobalite, or tidymite. 

High Purity Quartz Type 31/90, Type P, Starsil Spherical Silica - natural silica of different sizes and purity... 

Now let s apply what we have learned from the biqrcle example to a calculation that deals with a chemical reaction. Electronic grade (EG) silicon used in the electronics industry is a purified form of metallurgical grade silicon, which is made from the reaction of silica, Si02, with carbon in the form of coke at 2000 °C. (Silica is found in nature as quartz or quartz sand.)... 

SILICA - Silicon dioxide (Si02), a mineral found naturally as quartz or in complex combination with other elements such as silicates. 

Vitreous silica is produced from either melting of natural quartz crystals natural silica or fused quartz) or from vapor phase reaction of oxygen with SiCb synthetic silica). The archaic term fused quartz should be used with care, since those unaware of the jargon of the industry frequently misunderstand this term and believe that the glass is actually a crystalline material. 

Definition Does not occur freely in nature found as silica (quartz, sand) or as silicate (feldspar, kaolinite) 27.6% of earth s emst Ertpirical Si... 

Temperatures above 1800°C would be required to contain a fiber forming silica melt in a bushing. A requirement like this would by far exceed the practical capability of most precious metal and/or other practical alloy materials. As a result, pure silica glass fibers are downdrawn from solid silica preform rods (Figure 14). Gas flame or electrical furnaces soften the ends of the quartz rods, and thereby facilitate the formation of continuous silica fibers. Preforms made from natural silica contain 99.99% Si02 and impurities include 20-50 ppm Al, <5 ppm OH", and <4 ppm Na. Preforms made by oxidation of SiCl4 in a plasma flame [60] afford even purer silica fibers (<1 ppm Al, <0.1 ppm OH, <1 ppm Na, and <50 ppm Cl). 

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