aluminum oxide

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aluminum oxide:

see aluminaalumina
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.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Aluminum Oxide


alumina, A1203; a compound of aluminum with oxygen; a component of clays and a raw product for the production of aluminum. Colorless crystals with a melting point of 2,050°C and a boiling point above 3,000°C.

Aluminum oxide is known in two modifications, α and γ. Of these two, α-Al2O3 is found in nature in the form of the colorless mineral corundum. Crystals of α-Al2O3 which have been stained red or blue by the oxides of other metals are the precious stones ruby and sapphire. Corundum crystallizes in a hexagonal system with a density of 3,960 kg/m3. It is possible to obtain α-Al203 artificially by heating aluminum hydroxide or its salts above 900°C. In heating aluminum salts within the limits of 600–900°C, γ-Al2O3 is formed; it is a cubic modification which changes irreversibly into α-Al2O3 when heated above this temperature. Hydrated (hydrous) forms of Al2O3 of varying composition are also known. Among the aluminum hydroxides are hydrargillite (gibbsite) Al(OH)3, which is found in many bauxites, and the artificially produced unstable form of Al(OH)3, bayerite. There is also an incomplete aluminum hydroxide, AlOOH which exists in two modifications—α (diaspore) and γ (boehmite).

Aluminum oxide and its hydrated forms are insoluble in water and possess amphoteric properties; that is, they react with both acids and alkalies. In the air, natural corundum is chemically inert and nonhygroscopic. Aluminum oxide reacts intensively with alkalies at approximately 1,000°C, forming water-soluble aluminates of the base metals. It reacts more slowly with Si02 and acid slags, with the formation of aluminosilicates, and it decomposes in an alloy with KHSO4.

Bauxites, nephelites, kaolins, and other raw materials containing aluminum are used as the stock for obtaining aluminum oxide. Bauxites are always contaminated with iron oxides or silicic acid. In order to obtain pure aluminum oxide, the bauxites are processed by heating with CaO and Na2CO3 (the dry method) or with caustic soda in autoclaves (the Bayer process). In both methods the aluminum oxide in the form of aluminates is converted into a solution, which is then broken down by running it through carbon dioxide or adding prepared aluminum hydroxide. In the first case, the decomposition occurs according to the equation

2[Al(OH)4] + CO2→2Al(OH)3 + C032− + H20

Decomposition according to the second method is based on the fact that the aluminate solution obtained by autoclaving is metastable. The added aluminum hydroxide accelerates the decomposition of the aluminate:

[AL(OH)4]→Al(OH)3 + OH

The aluminum hydroxide obtained is roasted at 1,200°C and pure alumina is obtained as a result.

The basic use of aluminum oxide is in aluminum production. Corundum is widely used as an abrasive material (corundum wheels and emery), as well as for manufacturing ceramic cutting tools and extremely fire-resistant materials—in particular the “fused alumina” which is used for lining cement kilns. Bearing stones in precision mechanisms and jewelry are made from corundum monocrystals obtained by melting powdered aluminum oxide with the addition of chromium, iron, titanium, and vanadium oxides.

“Hairs” (filamentary crystals) of aluminum oxide are formed by the distillation of pure aluminum at 1,650°C in a hydrogen atmosphere containing water vapor. These “hairs” possess enormous strength, close to the theoretical. Sapphire “hairs” (α-Al2O3) 2–3 microns in diameter possess a strength of 16 henrys per square meter (H/m2), and those with a diameter of 10 microns have a strength of 11 H/m2. “Hairs” of larger diameter have a strength of 6.5–7 H/m2 (1 H/m2 = 100 kilogram forces per square meter). The introduction of these “hairs” into structural materials, even under the condition of a partial maintenance of their strength, makes it possible to obtain valuable materials for missile construction. Metals reinforced with such fibers have greater strength at high as well as low temperatures.

A specially prepared aluminum oxide, known as active aluminum oxide, is used in the form of a fine crystallic powder as an adsorbent and catalyst. Its adsorbent and catalytic properties depend to a great degree upon the quality and processing of the initial materials and upon the method of preparation. As an adsorbent, active aluminum oxide is widely used for chromatographic analysis of all types of organic and (more rarely) inorganic substances. Aluminum hydroxides are also used for producing all possible aluminum salts. Careful drying of gelatinous hydroxide produces alumogel; this is a porous, porcelain-like substance which is sometimes transparent. Alumogel is used in catalysis and serves as one of the most important industrial adsorbents.


Lainer, A. I. Proizvodstvo glinozema. Moscow, 1961.
Carroll-Porczynski, C. Materialy budushchego. Moscow, 1966. (Translated from English.)


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

aluminum oxide

[ə′lüm·ə·nəm ′äk‚sīd]
(inorganic chemistry)
Al2O3 A compound in the form of a white powder or colorless hexagonal crystals; melts at 2020°C; insoluble in water; used in aluminum production, paper, spark plugs, absorbing gases, light bulbs, artificial gems, and manufacture of abrasives, refractories, ceramics, and electrical insulators.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


The oxide of aluminum; an important constituent of the clays used in brick, tile, and refractories.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
References in periodicals archive ?
Lee, Effects of temperature and voltage mode on nanoporous anodic aluminum oxide films by one-step anodization, Thin Solid Films, 520, 1554 (2011).
Prepare a small bucket or dish with a bedding of aluminum oxide. Carefully place the frame onto the bed and gently pour more aluminum car-bide over the grip until it is completely covered in the material.
30% phosphoric acid, 10% phosphoric acid, and 30% aluminum oxide showed the highest value of tensile strength (14.5 MPa), elongation at break (12.5%), and tensile modulus (1.213 GPa).
FURNACE WALL CLEANING FLUXES: Wall cleaning fluxes are specifically designed for the softening and removal of excessive aluminum oxide build up that occurs on melting furnaces walls, especially along the melt line.
K., and Afzulpurkar, N.: "Anodic aluminum oxide (AAO) to AAO bonding and their application for fabrication of 3D microchannel" Nanoscience and Nanotechnology Letters.
In order to verify if the kinetics of these reactions is sufficient to guarantee the transformation of aluminum oxide into magnesium oxide, DSC measurements were carried out first on mixtures of pure magnesium and alumina and then on the mixtures of AZ91 or EL21 alloys with alumina.
Four factors were varied to develop the experimental design: wood species (two levels: maple and pine), abrasive (two levels: aluminum oxide and silicon carbide), belt speed (two levels: 2,000 and 2,600 feet per minute [fpm]), and interface pressure (four levels: 0.75, 1.00, 1.25, 1.50 psi).
Electrolytic reduction is the particularly energy-hungry step through which the aluminum and oxygen in aluminum oxide are separated.
The walls, floors and doors were scraped with metal implements to remove aluminum oxide buildup that occurs when molten aluminum contacts air.
Like other products in the Altro safety flooring product line, Altro Impressionist II has aluminum oxide and colored quartz throughout the thickness, with silicon carbide in the surface.
The synergistic coating combines the hardness of aluminum oxide ceramic with the properties of polymers, providing aluminum parts with new levels of hardness, wear and corrosion resistance, and permanent lubricity.
Rollprint is focusing a great deal of its resources to work with companies who prefer not to use PVDC to make the change to aluminum oxide (A1203)-coated laminates for products that require barrier properties.