Vitreous silica properties

Noncrystalline Silicas. The noncrystalline forms of silica iaclude bulk vitreous silica and a variety of other amorphous types, which are of substantial commercial importance (see SiLiCA, AMORPHOUS SILICA SiLiCA, VITREOUS SILICA). A review discussiag the occurrence, synthesis, properties, and apphcations of the various forms of silica adsorbents is available (71). 

Conner has recently extended the longitudinal stress loading investigations of vitreous silica to shear loading, and shown that within the accepted elastic range the materials deformation properties are strongly influenced by shear [88C02]. 

Gulaev, V. M. The Strength and Deformation Properties of Vitreous Silica , Glass Ceramics, 30 No. 6, 279 (1973)... 

Intrinsically conducting polymers, 13 540 Intrinsic bioremediation, 3 767 defined, 3 759t Intrinsic detectors, 22 180 Intrinsic fiber-optic sensors, 11 148 Intrinsic magnetic properties, of M-type ferrites, 11 67-68 Intrinsic photoconductors, 19 138 Intrinsic rate expressions, 21 341 Intrinsic semiconductors, 22 235-236 energy gap at room temperature, 5 596t Intrinsic strength, of vitreous silica, 22 428 Intrinsic-type detectors, cooling, 19 136 Intrinsic viscosity (TV), of thermoplastics, 10 178... 

Property taxes, 9 533-534 Property-temperature relationships, of vitreous silica, 22 416-417 P-Propiolactone, polymerization of, 14 259 Propiolic acid, 5 34t Propionaldehyde... 

Vitreous Silica Vitreous sdica is a glass form of sdica composed of Si02. It may be transparent, translucent, or opaque. It has a number of abnormal and anomalous properties in thermal expansion, viscosity, bulk density, compressibility, and elasticity. These properties depend on thermal history and preparation method. Vitreous sdica exhibits high resistance to chemical attack. At ambient temperature, it is not attacked by any chemical except hydrofluoric acid. 

The properties of high quality vitreous silica that determine its uses include high chemical resistance, low coefficient of thermal expansion (5.5 x 10-7 /° C), high thermal shock resistance, high electrical resistivity, and high optical transmission, especially in the ultraviolet. Bulk vitreous silica is difficult to work because of the absence of network-modifying ions present in common glass formulations. An extensive review of the properties and structure of vitreous silica is available (72). 

The diversity of silica forms and their properties leads to a broad range of applications. Reviews on usage include those on crystalline and vitreous silicas (94), on silica sols (95), on silica gels and precipitated silicas (96), and on pyrogenic silicas, precipitated silicas, and silica gels (97). 

Vitreous silica has a wide range of commercial and scientific applications. Its unique combination of physical properties includes good chemical resistance, minimal thermal expansion, high refractoriness, and excellent optical transmission from the ultraviolet to the near-infrared. 

Although vitreous silica is a simple, single-component glass, its properties can vary significantly, depending on thermal history, the type and concentration of defects, and impurities. Vitreous silica can, however, be one of the purest commercially available glassy materials. In synthetic vitreous silicas, for example, total metal contamination is typically measured in the 50—100 ppb range. Even at such a low level of impurities, differences in properties, such as uv-transmission, are observed for various silicas. 

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