Silica 2-tridymite

Porous Lattices Strongly Bonded in All Three Dimensions. This group forms relatively rigid, nonswelling frameworks (Table III). The interstices in crystalline Ge and Si are small, and helium can diffuse in these crystals less readily than in the crystalline silicas tridymite and cristo-... 

Silica Silica Tridymite, cristobalite 1650 Glass tanks crowns... 

Pernis B Paronetto F (1962) Adjuvant effects of silica (tridymite) on antibody production. Proc Soc Exp Biol Med, 110 390-392. 

Quartz Silica Cristobalite Silica Tridymite Silica Oil of vitriol... 

Quartz Silica CristobaUte Silica Tridymite Silica... 

Silicon group Cristobalite Diatomite Novaculite Quartz Silica Tridymite... 

Further, because the primary mineral constituent in the mortar is quartz, the mortar is not volume-stable. The quartz in sihca mortar installed in an operating battery will slowly convert to the high-temperature forms of silica— tridymite and cristobalite—during normal battery operation. This conversion is accompanied by a significant increase in volume. This conversion happens first on the hotter flue side of the wall. This means that the mortar in the horizontal joints assumes a wedge shape thicker on the flue side and thinner on the oven side of the wall. 

Haccuria, M., 1953. Infrared spectra of amorphous silica, tridymite, cristobalite, quartz and vitreous silica. Bull. Soc. Chim. Beiges 62 428. 

Crystalline Silica. Sihca exists in a variety of polymorphic crystalline forms (23,41—43), in amorphous modifications, and as a Hquid. The Hterature on crystalline modifications is to some degree controversial. According to the conventional view of the polymorphism of siHca, there are three main forms at atmospheric pressure quart2, stable below about 870°C tridymite, stable from about 870—1470°C and cristobaHte, stable from about 1470°C to the melting point at about 1723°C. In all of these forms, the stmctures are based on SiO tetrahedra linked in such a way that every oxygen atom is shared between two siHcon atoms. The stmctures, however, are quite different in detail. In addition, there are other forms of siHca that are not stable at atmospheric pressure, including that of stishovite, in which the coordination number of siHcon is six rather than four. 

Respiratory fibrogens Fibrogenic dusts e.g. Free crystalline silica, (quartz, tridymite, cristobalite), asbestos (chrysotile, amosite, crocidolite etc.), talc. 

Silica, Crystalline (Respirable) Cristobalite Quartz Tridymite Tripoli... 

The dimensions of the unit in the basal plane closely approximate those for the similarly pseudohexagonal crystal hydrargillite, Al(OH)3, as well as of the hexagonal layers in two forms of silica, /3-tridymite and 0-cristo-balite. The monoclinic (pseudohexagonal) unit of structure of hydrargillite8 has a = 8.70 A, b = 5.09 A, c = 9.76 A, and 0 = 85°29, and contains 8A1(0H)3. The crystal is composed of layers of octahedra,... 

As a result of its unique chemical and physical properties, silica gel is probably the most important single substance involved in liquid chromatography today. Without silica gel, it is doubtful whether HPLC could have evolved at all. Silica gel is an amorphous, highly porous, partially hydrated form of silica which is a substance made from the two most abundant elements in the earth s crust, silicon and oxygen. Silica, from which silica gel is manufactured, occurs naturally, either in conjunction with metal oxides in the form of silicates, such as clay or shale, or as free silica in the form of quartz, cristobalite or tridymite crystals. Quartz is sometimes found clear and colorless, but more often in an opaque form, frequently colored... 

Tridymite Vitreous, colourless form of free silica. Formed when quartz is heated to 87U°C (I598°F). 

They made several assumptions about which minerals could precipitate from the fluid. The alkaline lakes tend to be supersaturated with respect to each of the silica polymorphs (quartz, tridymite, and so on) except amorphous silica, so they suppressed each of the other silica minerals. They assumed that... 

To keep our discussion simple for the moment, we suppress the silica polymorphs tridymite and chalcedony. In the calculation results (Fig. 26.1), the silica concentration gradually decreases from its initial value and, as in the previous calculation, approaches equilibrium with quartz after about half a year. 

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