Information AboutAlumina |
| CATEGORIES ABOUT ALUMINIUM OXIDE | |
| aluminium compounds | |
| oxides | |
| refractory materials | |
| inorganic compounds | |
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Aluminium oxide is an Amphoteric Oxide of Aluminium with the Chemical Formula 23. It is also commonly referred to as '''alumina''' in the Mining , Ceramic and Materials Science communities. PROPERTIES Aluminium oxide is a good thermal insulator and electrical Insulator . In its most commonly occurring crystalline form, called Corundum or α-aluminum oxide, its hardness makes it suitable for use as an Abrasive and as a component in Cutting Tools . Aluminium oxide is responsible for metallic aluminium's resistance to Weathering . Metallic aluminium is very reactive with atmospheric Oxygen , and a thin Passivation Layer of alumina quickly forms on any exposed aluminium surface. This layer protects the metal from further oxidation. The thickness and properties of this oxide layer can be enhanced using a process called Anodising . A number of Alloys , such as Aluminium Bronze s, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance. The alumina generated by anodising is typically Amorphous , but discharge assisted oxidation processes such as Plasma Electrolytic Oxidation result in a significant proportion of crystalline alumina in the coating, enhancing its Hardness . Aluminium oxide was taken off the United States Environmental Protection Agency 's chemicals lists in 1988 . Aluminum oxide is on EPA's TRI list if it is a fibrous form. NATURAL OCCURRENCE Corundum is the naturally occurring Crystalline form of aluminium oxide. Rubies and Sapphire s are gem-quality forms of corundum with their characteristic colors due to trace impurities in the corundum structure. CRYSTAL STRUCTURE The most common form of crystalline alumina, α-aluminum oxide, is known as Corundum and has a hexagonal close packed (HCP) lattice structure. INDUSTRIAL FABRICATION PROCESS Aluminium Oxide , also known as alumina, is the main component of Bauxite , the principal Ore of Aluminium . The largest Manufacturers in the world of alumina are Alcoa , Alcan and Rusal . Companies which specialise in the production of speciality aluminium oxides and aluminium hydroxides include Alcan and Almatis . The bauxite ore is made up of impure Al2O3, Fe2O3, and SiO2. These are then purified by the Bayer Process : Al2O3 + 3H2O + 2NaOH + heat → 2NaAl(OH)4 The Fe2O3 does not dissolve in the base. The SiO2 dissolves as silicate Si(OH)62-. Upon filtering, Fe2O3 is removed. When the Bayer liquor is cooled, Al(OH)3 precipitates. The silicate remains in solution. Then: 2Al(OH)3 + heat → Al2O3 + 3H2O The formed Al2O3 is alumina. In 1961, GE developed " Lucalox ", a transparent alumina used in Sodium Vapor Lamp s. In August 2004 , scientists in the United States working for 3M developed a technique for making an Alloy of aluminium oxide and Rare Earth Element s to produce a strong Glass called Transparent Alumina . As discussed above (in the "Properties" section), alumina can be grown as a coating on aluminium by Anodising or by Plasma Electrolytic Oxidation . USES Annual world production of alumina is approximately 65 million tonnes, over 90% of which is used in the manufacture of aluminium metal. Major uses for aluminium hydroxide include the manufacture of water treatment chemicals such as aluminium sulphate, Poly Aluminium Chloride and sodium aluminate. Large tonnages are also used in the manufacture of Zeolites , coating titania pigments and as a fire retardants/smoke suppressant. The major uses of speciality aluminium oxides are in refractories, ceramics, polishing and abrasive applications. Minor uses include use in toothpaste formulations, and as a medium for Chromatography . In this latter application alumina is available in the so-called Brockmann Type s neutral, basic ( PH 9.5) and acidic (pH 4.5 when in water). Aluminium oxide is also used in preparation of coating suspensions in Compact Fluorescent Lamp s. Al2O3 is also used in fluoride water filters. It is one of the few methods available to filter water soluble fluorides out of water. Aluminum oxide is also used as a material in Hip Replacements . Commercial uses Because of aluminium oxide's position on the Mohs Scale Of Mineral Hardness , (9), it is very widely used as an Abrasive as a significantly less expensive replacement for Industrial Diamond s. Many types of Sandpaper use aluminium oxide crystals. In addition, its low heat retention and specific heat makes it widely used in almost all grinding operations, particularly Cutoff tools. Aluminium oxide is used in certain CD / DVD cleaning kits. Alumina will Polish the media surface, leaving it clean and relatively Scratch -free. Alumina is also the Byproduct of Hydrogen generation for the purposes of fuel generation when water is added to Pellet s comprised of aluminum and Gallium . The other byproduct of the reaction is of course gallium. Most pre- Finish ed Wood Flooring now uses aluminum oxide as a hard protective Coating . SEE ALSO EXTERNAL LINKS |
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