Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula Al2O3. It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium oxide. It is commonly called alumina and may also be called aloxide, aloxite, ALOX or alundum in various forms and applications and alumina is refined from bauxite. It occurs naturally in its crystalline polymorphic phase α-Al2O3 as the mineral corundum, varieties of which form the precious gemstones ruby and sapphire, which have an alumina content approaching 100%. Al2O3 is used as feedstock to produce aluminium metal, as an abrasive owing to its hardness, and as a refractory material owing to its high melting point.
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In this Dossier
Aluminum oxide in the context of Upper mantle
The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (at about 10 km (6.2 mi) under the oceans, and about 35 km (22 mi) under the continents) and ends at the top of the lower mantle, at about 670 km (420 mi). Temperatures range from around 900 K (627 °C; 1,160 °F) at the upper boundary with the crust to around 1,200 K (930 °C; 1,700 °F) at the boundary with the lower mantle. Upper mantle material that has come up onto the surface comprises about 55% olivine, 35% pyroxene, and 5–10% of calcium oxide and aluminum oxide minerals such as plagioclase, spinel, or garnet, depending on depth.
Aluminum oxide in the context of Diatomaceous earth
Diatomaceous earth (/ˌdaɪ.ətəˈmeɪʃəs/ DY-ə-tə-MAY-shəs), also known as diatomite (/daɪˈætəmaɪt/ dy-AT-ə-myte), celite, or kieselguhr, is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 mm to less than 1 μm, but typically 10 to 200 μm. Depending on the granularity, this powder can have an abrasive feel, similar to pumice powder, and has a low density as a result of its high porosity. The typical chemical composition of oven-dried diatomaceous earth is 80–90% silica, with 2–4% alumina (attributed mostly to clay minerals), and 0.5–2% iron oxide.
Diatomaceous earth consists of the fossilized remains of diatoms, a type of hard-shelled microalgae, that have accumulated over millions of years. It is used as a filtration aid, mild abrasive in products including metal polishes and toothpaste, mechanical insecticide, absorbent for liquids, matting agent for coatings, reinforcing filler in plastics and rubber, anti-block in plastic films, porous support for chemical catalysts, cat litter, activator in coagulation studies, a stabilizing component of dynamite, a thermal insulator, and a soil for potted plants and trees as in the art of bonsai. It is also used in gas chromatography packed columns made with glass or metal as stationary phase.
Aluminum oxide in the context of Razor strop
A razor strop or simply a strop (sometimes called a razor strap or strap) is a flexible strip of leather, canvas, denim fabric, balsa wood, or other soft material, used to straighten and polish the blade of a straight razor, a knife, or a woodworking tool such as a chisel. In many cases stropping re-aligns parts of the blade edge that have been bent out of alignment. In other cases, especially when an abrasive polishing compound is used, stropping may remove a small amount of metal (functionally equivalent to lapping). Stropping can also burnish (i.e., push metal around on) the blade.
The strop may be a hanging strop, a block (placed on a table, or in ones hand), or a hand-held paddle. Various abrasive compounds may be applied to the strop to aid in polishing the blade while stropping to obtain a mirror-like finish. Common abrasive compounds include diamonds, chromium(III) oxide, aluminum oxide, and iron(III) oxide.