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silicon dioxide,

chemical compound, SiO2. It is insoluble in water, slightly soluble in alkalies, and soluble in dilute hydrofluoric acid. Pure silica is colorless to white. It occurs in several forms and is widely and abundantly distributed throughout the earth, both in the pure state and in silicatessilicate,
chemical compound containing silicon, oxygen, and one or more metals, e.g., aluminum, barium, beryllium, calcium, iron, magnesium, manganese, potassium, sodium, or zirconium. Silicates may be considered chemically as salts of the various silicic acids.
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, e.g., in quartz (agate, amethyst, chalcedony, flint, jasper, onyx, and rock crystal), opal, sand, sandstone, clay, granite, and many other rocks; in skeletal parts of various protists and animals, such as certain sarcodines (see SarcodinaSarcodina,
the largest phylum (11,500 living species and 33,000 fossil species) of protozoans). It comprises the amebas and related organisms; which are all solitary cells that move and capture food by means of pseudopods, flowing temporary extensions of the cell.
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), diatomsdiatom
, unicellular organism of the kingdom Protista, characterized by a silica shell of often intricate and beautiful sculpturing. Most diatoms exist singly, although some join to form colonies.
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, and spongessponge,
common name for members of the aquatic animal phylum Porifera, and for the dried, processed skeletons of certain species used to hold water. Over 4,500 living species are known; they are found throughout the world, especially in shallow temperate waters.
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, and in the stems and other tissue of higher plants. Silica has many important uses. It is used as a filler for paint and rubber; in making ordinary glassglass,
hard substance, usually brittle and transparent, composed chiefly of silicates and an alkali fused at high temperature. Composition and Properties of Glass
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; in ceramics; in construction; and in the preparation of other substances, e.g., silicon carbidesilicon carbide,
chemical compound, SiC, that forms extremely hard, dark, iridescent crystals that are insoluble in water and other common solvents. Widely used as an abrasive, it is marketed under such familiar trade names as Carborundum and Crystolon.
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. Fused quartz is pure amorphous silica; it is used in special chemical and optical apparatus. Because it has a low thermal coefficient of expansion, it withstands sudden changes in temperature and can be used in parts that are subjected to wide ranges of heat and cold. Unlike ordinary glass, it does not absorb infrared and ultraviolet light.



(silicon dioxide), SiO2, a compound of silicon and oxygen. In the form of the mineral quartz and other varieties, silica constitutes about 12 percent of the mass of the earth’s crust. It is widely used in the silicate industry, particularly in the production of glass (quartz glass and other types of glass), ceramics, abrasives, concrete structures, and silicate brick. Radio technology and ultrasonic devices are important areas of application of quartz crystals. (For a more detailed discussion of silica, seeQUARTZ.)


SiO2 Naturally occurring silicon dioxide; occurs in five crystalline polymorphs (quartz, tridymite, cristobalite, coesite, and stishovite), in cryptocrystalline form (as chalcedony), in amorphous and hydrated forms (as opal), and combined in silicates.

silica, silicon dioxide

A white or colorless substance, nearly insoluble in water and in all acids except hydrofluoric; extremely hard; fuses to a colorless amorphous glass.


the dioxide of silicon, occurring naturally as quartz, cristobalite, and tridymite. It is a refractory insoluble material used in the manufacture of glass, ceramics, and abrasives
References in periodicals archive ?
Demand for specialty silicas in North America and Western Europe is projected to advance at below average rates through 2020.
This move follows Evonik's expansion of its global silica production capacities.
Fischer explained the capacity addition in Chester was part of Evonik s initiative to increase world-wide capacities for precipitated silica by 30 percent since 2010.
China will drive growth in the region as it is by far the largest global consumer of specialty silica and will boast one of the world's fastest growth rates through 2016.
The NMR spectra of in situ alkylated silicas prepared from TEOS/VTOS and TEOS/ETOS are illustrated in Fig.
Syloid and Sylobloc pure, chemically inert, nontoxic synthetic amorphous silicas used in PVC, PE, PP, PVDC, EVA, and other polymers.
It can be applied on machine via metered size press to achieve inkjet print results close to those of silica.
11 Coatings & Inks Market for Specialty Silicas by Type 102
Demand for specific silica products is closely tied to the outlook for key end use industries.
The degradation behaviors below 300[degrees]C were similar for both unmodified and modified silicas, except that the latter showed earlier evaporation of water than the former due to the introduction of the hydrophobic MPS units.
However, competition from lower-cost silicas and other abrasive materials in wafer polishing may restrain further growth opportunities.
HDS, compared to conventional silicas, provides substantially better dispersibility in robber compounds due to its specific structure.