Silica, silicon oxide

Silica Silicon oxide (Si02(s)), which can occur in crystalline form, e.g., quartz, or noncrystaUine form, e.g., opal. 

Sellaite, see Magnesium fluoride Senarmontite, see Antimony(III) oxide Siderite, see Iron(II) carbonate Siderotil, see Iron(II) sulfate 5-water Silica, see Silicon dioxide Silicotungstic acid, see Silicon oxide—tungsten oxide—water (1/12/26)... 

Anhydrous hydrogen fluoride and hydrofluoric acid react with substances containing silica and silicon oxide to form silicon tetrafluoridc and fluorosilic acid. SiF, a colorless gas at ambient temperature, is liighly toxic. An equilibrium mixture of SiF in the presence of moisture also contains hydrogen fluoride and hydrofluoric acid. 

The composition of the particles is related to that of the source rocks. Quartz sand [composed of silica (silicon dioxide)], which makes up the most common variety of silica sand, is derived from quartz rocks. Pure quartz is usually almost free of impurities and therefore almost colorless (white). The coloration of some silica sand is due to chemical impurities within the structure of the quartz. The common buff, brown, or gray, for example, is caused by small amounts of metallic oxides iron oxide makes the sand buff or brown, whereas manganese dioxide makes it gray. Other minerals that often also occur as sand are calcite, feldspar and obsidian Calcite (composed of calcium carbonate), is generally derived from weathered limestone or broken shells or coral feldspar is an igneous rock of complex composition, and obsidian is a natural glass derived from the lava erupting from volcanoes see Chapter 2. 

The dust of silicon oxide (silicate) can burn or explode and is very harmful if inhaled. Continued exposure to silica dust causes silicosis, a form of pneumonia. 

Anticaking agents commonly used include calcium carbonate, phosphate, silicate, and stearate cellulose (microcrystalline) kaolin magnesium carbonate, hydroxide, oxide, silicate, and stearate myristates palmitates phosphates silica (silicon dioxide) sodium ferrocyanide sodium silicoa-lummale and starches. 

These important results have stimulated many research workers in universities and industrial research laboratories in the world to investigate the particular state of aggregation and coordination that Tilv assumes when forced into framework positions of hydrophobic crystalline silicas. Researchers are also engaged in the search for other compounds containing titanium and silicon oxides with Tilv in the same coordination and environment, on the assumption that similar catalytic properties would be obtained. Relevant discoveries have been made, and additional valuable information has been obtained on this new class of materials and on their catalytic performance in many different reactions. 

Silica, see Silicon dioxide, 4833 Silicon dibromide sulfide, 0280 Silicon monosulfide, 4892 Silicon oxide, 4822 Silicon, 4903 Silicon tetraazide, 4785a... 

In Chapter 4 we learned that clay is made of minerals, including potassium, aluminum, and silicon oxides. Barium and other metal oxides, vermiculite, and mold controllers are often added to clay to enhance clay properties. If dry clay is mixed with water, large amounts of silica can be released into the air. 

Fluorosilicones can be compounded by the addition of mineral fillers and pigments. Fillers for such compounds are most commonly silicas (silicon dioxide), because they are compatible with the elastomeric silicon-oxygen backbone and thermally very stable. They range in surface areas from 0.54 to 400 m2/g and average particle size from 100 to 6 nm. Because of these properties, they offer a great deal of flexibility in reinforcement. Thus, cured compounds can have Durometer A hardness from 40 to 80. Other fillers commonly used in fluorosilicones are calcium carbonate, titanium dioxide, and zinc oxide. 

In various industrial applications, silica modification is used on thin layers of Si02, rather than on the powdered form. Monomolecular or thin layers of silicon oxide are thermally grown on Si-wafers for the production of high-tech materials. The surface chemistry of these layers is comparable to the powdered form, with the absence of a porous structure. 

While there appears to be some agreement between the observed and theoretical iron oxide solids settling velocities, the observed silicon oxide values appear to be several times greater than expected. This difference in behavior of the silicon oxide and iron oxide slurries cannot be accounted for by density effects. Since the ratio of the density of iron oxide and silica is 2.ll+, the predicted VgT for an iron oxide would be 3.8 times greater than for silica, Further work is needed to determine the critical characteristics of a solid that are important in governing its settling velocity. 

As described previously, flame s3mthesis reactions include the oxidation of silicon chloride to produce silica the oxidation of titanium chloride to produce titania and the oxidation of other metal chlorides (see Table 7.2 also). 

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