alumina


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alumina

(əlo͞o`mĭnə) or

aluminum oxide,

Al2O3, chemical compound with m.p. about 2,000°C; and sp. gr. about 4.0. It is insoluble in water and organic liquids and very slightly soluble in strong acids and alkalies. Alumina occurs in two crystalline forms. Alpha alumina is composed of colorless hexagonal crystals with the properties given above; gamma alumina is composed of minute colorless cubic crystals with sp. gr. about 3.6 that are transformed to the alpha form at high temperatures. Alumina powder is formed by crushing crystalline alumina; it is white when pure. Alumina is widely distributed in nature. Combined with silica and other minerals it occurs in clays, feldspars, and micas. It is the major component of bauxitebauxite
, mixture of hydrated aluminum oxides usually containing oxides of iron and silicon in varying quantities. A noncrystalline substance formerly thought to be a mineral, bauxite is claylike and earthy and ranges in color from white to deep brown or red according to the
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 and occurs in an almost pure form as corundumcorundum
, mineral, aluminum oxide, Al2O3. The clear varieties are used as gems and the opaque as abrasive materials. Corundum occurs in crystals of the hexagonal system and in masses. It is transparent to opaque and has a vitreous to adamantine luster.
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. Alumina is commercially important. A major use is in the production of aluminumaluminum
, called in British countries aluminium
, metallic chemical element; symbol Al; at. no. 13; at. wt. 26.98154; m.p. 660.37°C;; b.p. 2,467°C;; sp. gr. 2.6989 at 20°C;; valence +3.
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 metal. It is also used for abrasives; corundum and emery are widely used, as are artificially prepared alumina abrasives. Trade names for alumina abrasives include Alundum and Aloxite. Alumina is also used in ceramics, in pigments, and in the manufacture of chemicals. Clays containing alumina are used in porcelain, pottery, and bricks. Pure alumina is used in making crucibles and other refractory apparatus. Hydrated alumina is used in mordant dyeing to make lake pigments; it is also used in glassmaking, in cosmetics, and in medicine as an antacid.

alumina

[ə′lüm·ə·nə]
(inorganic chemistry)
Al2O3 The native form of aluminum oxide occurring as corundum or in hydrated forms, as a powder or crystalline substance.

alumina

The oxide of aluminum; an important constituent of the clays used in brick, tile, and refractories.
References in periodicals archive ?
Under the agreement, Vinacomin will supply EGA with up to 300,000 tonnes of alumina per year.
Eleven of the women are graduate trainees who will fill mechanical and process engineering roles in the new alumina refinery.
Some five million tonnes of bauxite ore will be imported each year from the Republic of Guinea to feed the Al Taweelah alumina refinery.
The mine has initial capacity to produce 4 million mt/y of bauxite, which is transported by rail to the alumina refinery.
The Commission had concerns that, following the transaction, Motim and other suppliers from outside the EEA would be unable to exercise sufficient competitive constraint on the merged entity to avoid price increases for white fused alumina.
SDK has been continuously transferring its industrial technology to produce chemical alumina built up over many years operation of its Yokohama Plant to the new plant in Indonesia.
Glinozium owns concessions for three alumina deposits with total raw reserves of 828m tonnes in the southeastern part of Kyrgyzstan.
8 million tonnes per annum (Mtpa) of alumina and 750,000 tonnes of aluminium, making the project the world's largest integrated bauxite to aluminium facility.
In the present study, the viscosity and dynamic cure of BECy monomer/alumina nanoparticle suspensions were studied to investigate the effect of adding alumina nano-particles to the BECy resin on the processing behavior.
The stronger financial profile of Alumina reflects its prudent financial management and increased dividend allocation from Alcoa World Alumina and Chemicals, which boosted its business in 2010 and is 40% owned by Alumina.
While SDK is currently producing 200,000 t/y of chemical alumina at Yokohama, the company has decided to terminate disposal of bauxite residue into the sea by the end of 2015 and withdrawfrom the chemical alumina production at Yokohama.
A continuous alumina fiber sheet with a basis weight was patented.