What are the properties and usage of alumina?
Compounds of aluminum and oxygen are referred to as aluminum oxides (Al2O3), whereas compounds with hydroxyl groups are known as hydroxides. Alpha-Al2O3 (corundum) is the most well-known and significant form of the existing Al2O3 modifications . Besides, there are further aluminum oxides of different structures called transition aluminas. Corundum has a density of 3.98 g/cm³, a high hardness, a melting point of 2053 °C, and a high specific electrical resistance of approximately 1012 ohm·m (at 20 °C). It is chemically very stable and is almost insoluble in water, acids, and bases. The transition aluminum oxide gamma-Al2O3, in contrast, dissolves in strong acids and in bases. Due to its high surface activity, gamma-aluminum oxide is used as an adsorbent and catalyst material. In addition to oxides of aluminum, there are different hydroxides, e.g. aluminum hydroxides [Al (OH)3] such as bayerite and gibbsite and the so-called aluminum oxy-hydroxides [AlO(OH)] boehmite and diaspore. Gibbsite, boehmite, and diaspore are constituents of the technically important aluminum mineral bauxite.silicon carbide wholesale
Due to its high hardness, corundum is used as a bearing jewel in watches and as a grinding and polishing agent for precious stones, metals, and Silica wafers. Mixed with binders, especially with other oxides, corundum powder is used for manufacturing crucibles, dishes, sheath tubes, electrical insulators, artificial joints (artificial hip or knee joints), dental ceramics, burner tubes, catalyst carriers, wear protections, hard-facings, furnace linings, and metal forming and machining tools.
Corundum has a low toughness in spite of its hardness and brittleness. To obtain products with improved ductility or toughness, partially stabilized zirconium oxide or...
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