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 ?
High grade alumina crucibles, with negligible impurity, possess high resistance to chemical and heat, and can withstand inert and vacuum condition.
'The tight Western world alumina market conditions of 2018 have subsided in the first half of 2019 as curtailed supply came back on stream and new refineries ramped up.
Alumina has declared a final, fully franked dividend of 14.1 US cents per share.
Bauxite is the ore from which aluminium is derived and is refined into alumina, the feedstock for aluminium smelters.
Alumina is the feedstock for aluminium smelters and is refined from bauxite ore.
Caustic soda and bauxite are "the two most important raw materials" in the alumina refining process.
To achieve this advance, engineers devised new materials processing strategies to dissolve high concentrations of neodymium ions into alumina crystals.
In related news, UC RUSAL also announced the restart of the Friguia Alumina Refinery in Guinea.
Keywords: Cobalt, Alumina, Adsorption kinetics, Isotherms, Thermodynamics.
Abu Dhabi: Emirates Global Aluminium (EGA) received its first shipment of bauxite ore on Sunday as the largest industrial company in the UAE gets ready to commission the UAE's first alumina refinery next year.
Scientific research company THC BioMed Intl Ltd (CSE:THC) reported on Friday a commitment of up to USD12m with Alumina Partners (Ontario) Ltd in a private placement.
Past studies have shown that supplementary cementitious materials (SCMs) that contain alumina ([Al.sub.2][O.sub.3]) are more effective at mitigating ASR than SCMs purely rich in silica (Si[O.sub.2]), they say, citing their research on pure hydrated alumina, Al[(OH).sub.3] as a cement replacement to isolate its role in ASR mitigation.