Aluminium oxide is the family of inorganic compounds Traditionally, inorganic compounds are considered to be of a mineral, not biological, origin. Complementarily, most organic compounds are traditionally viewed as being of biological origin. Over the past century, the precise classification of inorganic vs organic compounds has become less important to scientists, primarily because the majority of with the chemical formula A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound Al Aluminium (UK: /ˌæljʉˈmɪniəm/ AL-yew-MIN-ee-əm) or aluminum (US: /əˈluːmɨnəm/ ( listen) ə-LOO-mi-nəm) is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al and its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth'2O Oxygen (pronounced /ˈɒksɨdʒɨn/, OK-si-jin, from the Greek roots ὀξύς (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter), is the element with atomic number 8 and represented by the symbol O. It is a member of the chalcogen group on the periodic table, and is a highly3. It is an amphoteric oxide and is commonly referred to as alumina, corundum Corundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red, while all other colors are called sapphire as well as many other names, reflecting its widespread occurrence in nature and industry. Its most significant use is in the production of aluminium Aluminium (UK: /ˌæljʉˈmɪniəm/ AL-yew-MIN-ee-əm) or aluminum (US: /əˈluːmɨnəm/ ( listen) ə-LOO-mi-nəm) is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al and its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth' metal, although it is also used as an abrasive due to its hardness and as a refractory A refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 1,000 °F " material due to its high melting point.[3]
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Natural occurrence
Corundum Corundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red, while all other colors are called sapphire is the most common naturally occurring crystalline A crystal or crystalline solid is a solid material, whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography. The process of crystal formation via mechanisms of crystal growth is called form of aluminium oxide. Rubies A ruby is a pink to blood-red gemstone, a variety of the mineral corundum . The red color is caused mainly by the presence of the element chromium. Its name comes from ruber, Latin for red. Other varieties of gem-quality corundum are called sapphires. The ruby is considered one of the four precious stones, together with the sapphire, the emerald, and sapphires Sapphires are commonly worn as jewellery. Sapphires can be found naturally, by searching through certain sediments or rock formations, or they can be manufactured for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires , sapphires are used in some non-ornamental applications, including are gem-quality forms of corundum, which owe their characteristic colors to trace impurities. Rubies are given their characteristic deep red color and their laser Light Amplification by Stimulated Emission of Radiation is a mechanism for emitting electromagnetic radiation, typically light or visible light, via the process of stimulated emission. The emitted laser light is (usually) a spatially coherent, narrow low-divergence beam, that can be manipulated with lenses. In laser technology, "coherent qualities by traces of chromium Chromium is a chemical element which has the symbol Cr and atomic number 24, first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable. The name of the element is derived from the Greek word "chrōma" (χρώμα), meaning color,. Sapphires come in different colors given by various other impurities, such as iron and titanium.
Properties
Aluminum oxide in its powdered form.Aluminium oxide is an electrical insulator An insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate electrical conductors without passing current but has a relatively high thermal conductivity In physics, thermal conductivity, k, is the property of a material that indicates its ability to conduct heat. It appears primarily in Fourier's Law for heat conduction. Thermal conductivity is measured in watts per kelvin per metre . Multiplied by a temperature difference (in kelvins, K) and an area (in square metres, m2), and divided by a (30 Wm−1K−1[4]) for a ceramic material. In its most commonly occurring crystalline form, called corundum Corundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red, while all other colors are called sapphire or α-aluminium oxide, its hardness makes it suitable for use as an abrasive An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away. While finishing a material often means polishing it to gain a smooth, reflective surface it can also involve roughening as in satin, matte or beaded finishes and as a component in cutting tools Cutting is the separation of a physical object, or a portion of a physical object, into two portions, through the application of an acutely directed force. An implement commonly used for cutting is the knife or in medical cases the scalpel. However, any sufficiently sharp object is capable of cutting if it has a hardness sufficiently larger than.[3]
Aluminium oxide is responsible for resistance of metallic aluminium to weathering Weathering is the breaking down of Earth's rocks, soils and minerals through direct contact with the planet's atmosphere. Weathering occurs in situ, or "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, wind, and gravity. Metallic aluminium is very reactive with atmospheric oxygen Oxygen (pronounced /ˈɒksɨdʒɨn/, OK-si-jin, from the Greek roots ὀξύς (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter), is the element with atomic number 8 and represented by the symbol O. It is a member of the chalcogen group on the periodic table, and is a highly, and a thin passivation layer Passivation is the process of making a material "passive" in relation to another material prior to using the materials together. For example, prior to storing hydrogen peroxide in an aluminium container, the container can be passivated by rinsing it with a dilute solution of nitric acid and peroxide alternating with deionized water. The of alumina (4 nm thickness) forms in about 100 picoseconds on any exposed aluminium surface.[5] This layer protects the metal from further oxidation. The thickness and properties of this oxide layer can be enhanced using a process called anodising Anodizing, or anodising in British English, is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. The process is called "anodizing" because the part to be treated forms the anode electrode of an electrical circuit. Anodizing increases corrosion resistance and wear. A number of alloys An alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history. Alloys usually have different properties from those of the, such as aluminium bronzes Aluminium bronze is a type of bronze in which aluminium is the main alloying metal added to copper. A variety of aluminium bronzes of differing compositions have found industrial use, with most ranging from 5% to 11% aluminium by weight, the remaining mass being copper; other alloying agents such as iron, nickel, manganese, and silicon are also, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance. The alumina generated by anodising is typically amorphous An "amorphous solid" is a solid in which there is no long-range order of the positions of the atoms. . Most classes of solid materials can be found or prepared in an amorphous form. For instance, common window glass is an amorphous solid, many polymers (such as polystyrene) are amorphous, and even junkfoods such as cotton candy are, but discharge assisted oxidation processes such as plasma electrolytic oxidation result in a significant proportion of crystalline alumina in the coating, enhancing its hardness Hardness is the measure of how resistant solid matter is to various kinds of permanent shape change when a force is applied. Macroscopic hardness is generally characterized by strong intermolecular bonds, however the behavior of solid materials under force is complex, therefore there are different measurements of hardness: scratch hardness,.
Aluminium oxide was taken off the United States Environmental Protection Agency The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged to protect human health and the environment, by writing and enforcing regulations based on laws passed by Congress. The EPA was proposed by President Richard Nixon and began operation on December 2, 1970, when its establishment was passed's chemicals lists in 1988. Aluminium oxide is on EPA's TRI list if it is a fibrous form.[6]
Structure
The most common form of crystalline alumina is known as corundum Corundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red, while all other colors are called sapphire. The oxygen ions nearly form a hexagonal close-packed structure with aluminium ions filling two-thirds of the octahedral interstices. Each Al3+ center is octahedral In chemistry, octahedral molecular geometry describes the shape of compounds where in six atoms or groups of atoms or ligands are symmetrically arranged around a central atom, defining the vertices of an octahedron. The octahedron has eight faces, hence the prefix octa. The octahedron is one of the Platonic solids, although octahedral molecules. In terms of its crystallography Crystallography is the experimental science of determining the arrangement of atoms in solids. The word "crystallography" is derived from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write, corundum adopts a trigonal In crystallography, the trigonal crystal system is one of the seven crystal systems, and the rhombohedral lattice system is one of the seven lattice systems. They are often confused with each other: crystals in the rhombohedral lattice system are always in the trigonal crystal system, but some crystals such as quartz are in the trigonal crystal Bravais lattice with a space group of R-3c (number 167 in the International Tables). The primitive cell contains two formula units of aluminium oxide.
Alumina also exists in other phases, namely η-, χ-, γ-, δ- and θ-aluminas.[7] Each has a unique crystal structure and properties. The so-called β-alumina proved to be NaAl11O17.[8]
Production
Aluminium hydroxide In chemistry, hydroxide is the name for the diatomic anion OH−, consisting of covalently bonded oxygen and hydrogen atoms, usually derived from the dissociation of a base. It is one of the simplest and most pervasive diatomic ions known minerals are the main component of bauxite Bauxite is the most important aluminium ore. This form of rock consists mostly of the minerals gibbsite Al3, boehmite γ-AlO(OH), and diaspore α-AlO(OH), in a mixture with the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase TiO2. Bauxite was named after the village Les Baux in southern France, where, the principal ore An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element of aluminium Aluminium (UK: /ˌæljʉˈmɪniəm/ AL-yew-MIN-ee-əm) or aluminum (US: /əˈluːmɨnəm/ ( listen) ə-LOO-mi-nəm) is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al and its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth'. A mixture of the minerals comprise bauxite ore, including gibbsite Gibbsite, Al3, is one of the mineral forms of aluminium hydroxide. It is often designated as γ-Al(OH)3 (but sometimes as α-Al(OH)3 .). It is also sometimes called hydrargillite (or hydrargyllite) (Al(OH)3), boehmite (γ-AlO(OH)), and diaspore Diaspore is a native aluminium oxide hydroxide, α-AlO, crystallizing in the orthorhombic system and isomorphous with goethite and manganite. It occurs sometimes as flattened crystals, but usually as lamellar or scaly masses, the flattened surface being a direction of perfect cleavage on which the lustre is markedly pearly in character. It is (α-AlO(OH)), along with impurities of iron oxides Iron oxides are chemical compounds composed of iron and oxygen. Altogether, there are sixteen known iron oxides and oxyhydroxides and hydroxides, quartz and clay minerals Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets. Clay minerals are common weathering products and low temperature hydrothermal alteration products. Clay.[9] Bauxites are found in laterites Laterite is a surface formation in hot and wet tropical areas which is rich in iron and aluminium and develops by intensive and long lasting weathering of the underlying parent rock. Nearly all kinds of rocks can be deeply decomposed by the action of high rainfall and elevated temperatures. The percolating rain water causes dissolution of primary. Bauxite is purified by the Bayer process:
- Al2O3 + 3 H2O + 2 OH- → 2 Al(OH)4-
Except for SiO2, the other components of bauxite do not dissolve in base. Upon filtering the basic mixture, Fe2O3 is removed. When the Bayer liquor is cooled, Al(OH)3 precipitates, leaving the silicates in solution. The solid is then calcined (heated strongly) to give aluminium oxide:[3]
- 2 Al(OH)3 → Al2O3 + 3 H2O
The product alumina tends to be multi-phase, i.e., consisting of several phases of alumina rather than solely corundum.[7] The production process can therefore be optimized to produce a tailored product. The type of phases present affects, for example, the solubility and pore structure of the alumina product which, in turn, effects the cost of aluminium production and pollution control.[7]
Known as alundum (in fused form) or aloxite[10] in the mining Mining is the extraction of valuable minerals or other geological materials from the earth, usually from an ore body, vein or seam. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock salt and potash. Any material that cannot be grown through agricultural processes, or, ceramic A ceramic is an inorganic, non-metallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous . Because most common ceramics are crystalline, the definition of ceramic is often restricted to inorganic crystalline materials, as opposed to the non- and materials science Materials science is an interdisciplinary field involving the properties of matter and its applications to various areas of science and engineering. This science investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It includes elements of applied physics and chemistry communities, alumina finds wide use. Annual world production of alumina is approximately 45 million tonnes The tonne or metric ton (U.S.), often redundantly referred to as a metric tonne, is a unit of mass equal to 1,000 kg (2,205 lb) or approximately the mass of one cubic metre of water at four degrees Celsius. It is sometimes abbreviated as mt in the United States, but this conflicts with other SI symbols. The tonne is not a unit in the International, over 90% of which is used in the manufacture of aluminium metal.[3]. The major uses of specialty aluminium oxides are in refractories, ceramics, and polishing and abrasive applications. Large tonnages are also used in the manufacture of zeolites Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that had been adsorbed by the material. Based on this,, coating titania pigments, and as a fire retardant/smoke suppressant.
Applications
The great majority of alumina is consumed for the production of aluminium, usually by the Hall process.
As a filler
Being fairly chemically inert, relatively non-toxic, and white, alumina is a favored filler for plastics.
As a catalyst and catalyst support
Alumina catalyses a variety of reactions that are useful industrially. In its largest scale application, alumina is the catalyst in the Claus process The Claus process is the most significant gas desulfurizing process, recovering elemental sulfur from gaseous hydrogen sulfide. First patented in 1883 by the scientist Carl Friedrich Claus, the Claus process has become the industry standard for converting hydrogen sulfide waste gases into elemental sulfur in refineries. It is also useful for dehydration of alcohols In chemistry, an alcohol is any organic compound in which a hydroxyl functional group (-O to alkenes.
Alumina serves as a catalyst support for many industrial catalysts, such as those used in hydrodesulfurization Hydrodesulfurization is a catalytic chemical process widely used to remove sulfur (S) from natural gas and from refined petroleum products such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils. The purpose of removing the sulfur is to reduce the sulfur dioxide (SO2) emissions that result from using those fuels in automotive and some Ziegler-Natta polymerizations. Zeolites Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that had been adsorbed by the material. Based on this, are produced from alumina.
Gas purification and related absorption applications
Alumina is widely used to remove water from gas streams. Other major applications are below.[11]
As an abrasive
Aluminium oxide is used for its hardness and strength. It is widely used as a coarse or fine abrasive An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away. While finishing a material often means polishing it to gain a smooth, reflective surface it can also involve roughening as in satin, matte or beaded finishes, including as a much less expensive substitute for industrial diamond. Many types of sandpaper use aluminium oxide crystals. In addition, its low heat retention and low specific heat make it widely used in grinding operations, particularly cutoff tools. As the powdery abrasive mineral aloxite, it is a major component, along with silica, of the cue tip "chalk" used in billiards. Aluminium oxide powder is used in some CD/DVD polishing and scratch-repair kits. Its polishing qualities are also behind its use in toothpaste. Alumina can be grown as a coating on aluminium by anodising or by plasma electrolytic oxidation (see the "Properties" section, above). Both its strength and abrasive characteristics are due to aluminium oxide's great hardness (position 9 on the Mohs scale of mineral hardness). Most pre-finished wood flooring now uses aluminium oxide as a hard protective coating.
Alumina output in 2005Niche applications and research themes
In lighting, transparent alumina is used in some sodium vapor lamps.[12] Aluminium oxide is also used in preparation of coating suspensions in compact fluorescent lamps.
In chemistry laboratories, alumina is a medium for chromatography, available in basic (pH 9.5), acidic (pH 4.5 when in water) and neutral formulations.
Health and medical applications include it as a material in hip replacements.[3]
As well, it is used as a dosimeter for radiation protection and therapy applications for its optically stimulated luminescence properties.
Aluminium oxide is widely used in the fabrication of superconducting devices, particularly single electron transistors and superconducting quantum interference devices (SQUID), where it is used to form highly resistive quantum tunneling barriers.
See also
References
- ^ P. Patnaik (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 0070494398.
- ^ Roew, Raymond (2009). "Adipic Acid". Handbook of Pharmaceutical Excipients. pp. 11–12
- ^ a b c d e "Alumina (Aluminium Oxide) – The Different Types of Commercially Available Grades". The A to Z of Materials. http://www.azom.com/details.asp?ArticleID=1389. Retrieved 2007-10-27.
- ^ Material Properties Data: Alumina (Aluminum Oxide)
- ^ Campbell, Timothy; Kalia, Rajiv; Nakano, Aiichiro; Vashishta, Priya; Ogata, Shuji; Rodgers, Stephen (1999). "Dynamics of Oxidation of Aluminum Nanoclusters using Variable Charge Molecular-Dynamics Simulations on Parallel Computers". Physical Review Letters 82: 4866. doi:10.1103/PhysRevLett.82.4866. http://cacs.usc.edu/papers/Campbell-nAloxid-PRL99.pdf.
- ^ "EPCRA Section 313 Chemical List For Reporting Year 2006" (PDF). US EPA. http://www.epa.gov/tri/chemical/chemical%20lists/RY2006ChemicalList.pdf. Retrieved 2008-09-30.
- ^ a b c G. Paglia (2004). "Determination of the Structure of γ-Alumina using Empirical and First Principles Calculations Combined with Supporting Experiments" (free download). Curtin University of Technology, Perth. http://espace.library.curtin.edu.au/R?func=search-simple-go&ADJACENT=Y&REQUEST=adt-WCU20040621.123301. Retrieved 2009-05-05.
- ^ E. Wiberg and A. F. Holleman (2001). Inorganic Chemistry. Elsevier. ISBN 0123526515.
- ^ "Bauxite and Alumina Statistics and Information". USGS. http://minerals.usgs.gov/minerals/pubs/commodity/bauxite/. Retrieved 2009-05-05.
- ^ "Aloxite". ChemIndustry.com database. http://www.chemindustry.com/chemicals/14835.html. Retrieved 24 February 2007.
- ^ L. Keith Hudson, Chanakya Misra, Anthony J. Perrotta, Karl Wefers, F. S. Williams “Aluminum Oxide” in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a01_557.
- ^ "GE Innovation Timeline 1957-1970". http://www.ge.com/innovation/timeline/eras/science_and_research.html. Retrieved 2009-01-12.
External links
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Categories: Aluminium compounds | Oxides | Refractory materials | Inorganic compounds | Common oxide glass components | Sesquioxides
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Tue, 15 Jun 2010 20:55:27 GMT+00:00
The Moscow Times United Company RusAl said Tuesday that it had agreed on a strategic partnership with Guinea and will maintain bauxite and alumina output, a year after the ...
G. Prevot, A. Naitabdi, R. Bernard, and Y. Borensztein
Mon, 01 Feb 2010 05:00:00 GM
combined with low energy electron diffraction and Auger electron spectroscopy were performed to investigate the structure of a thin aluminum oxide film grown on Ni(111). Well-ordered . alumina. films were obtained after the depos. ...
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