aluminum oxide found in the natural environment in the form of a conventional alumina, its chemical formula - AL2O3.In view of this crystal with no colors at a temperature of 2044 ° C begin to melt, and when you reach the mark of 3530 ° C to boil.
in natural surroundings only stable modification of a substance is alumina having a density of 3.99 g / cm3.This is a very solid sample belonging to the ninth level of the table Mohs.The value of the refractive index is as follows: for the ordinary ray - 1,765 and 1,759 for the extraordinary.In natural surroundings alumina often contains various metal oxides, however, the mineral corundum may acquire various shades of its color.For example, these are sapphires, rubies and other precious stones.In this way the alumina may be derived and laboratory-chemical method.For this purpose, metastable form of A12O3 and decompose them thermally.Also, as a source of aluminum oxide laboratory method using aluminum hydroxide.
Standard version connection is tetragonicheskuyu lattice containing in its composition about 1-2% water.One can also obtain amorphous in structure alumina - alumina gel, which gelevidny solution of AL (OH) 3 is dewatered to obtain a porous material in a transparent mass.
Aluminium oxide is completely insoluble in water, but may well be dissolved in cryolite, heated to a high temperature.Amphoteric substance.Characteristic is the property of the synthesized aluminum oxide as the inverse temperature dependence of its formation and chemical activity.As artificial (i.e., obtained at a temperature of over 1200 ° C) and natural corundum in the usual medium exhibit almost completely full chemical inertness and lack of hygroscopicity.
alumina chemical properties of active exercise begins at temperatures around 1000 ° C, when it begins to rapidly interact with substances such as various alkali, alkaline carbonates.When this interaction formed aluminates.Over a slow connection it reacts with SiO2, as well as various types of acidic slags.As a result of these interactions are obtained aluminosilicates.
alumina gel and alumina which are prepared by calcination of aluminum hydroxides at any of at least 550 ° C, have a very high hygroscopicity, excellent react chemically active and react with acidic and alkaline solutions.
Typically, as a raw material for aluminum oxide are bauxite, alunite and nepheline.When the content of the substance in question are more than 6-7% production is the main way - by Bayer, and with a lower content of substances used method of sintering ore with lime or soda.The method involves the treatment of Bayer crushed rock in ball mills, bauxite then treated with alkaline solutions at a temperature of 225-250 ° C.The composition thus obtained is diluted with an aqueous sodium aluminate solution and filtered.During filtration, a slurry containing alumina, whose properties correspond to the standard, is decomposed in centrifuges.Such technology allows to obtain 50% yield of material.Furthermore, the use of this method makes it possible to keep the mother liquor for use in subsequent operations leaching of bauxite.
typically obtained by a synthetic aluminum oxide is used as an intermediate material for the production of pure aluminum.In industry, it is used as a raw material for the production of refractory materials, ceramic abrasive and cutting tools.Modern technology is actively used single crystals of aluminum oxide in the manufacture of watches, printed circuit boards, jewelery.