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Aluminium oxide is a
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical bonds. A homonuclear molecule, m ...
of
aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
and
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
with the
chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and ...
23. It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium(III) oxide. It is commonly called alumina and may also be called aloxide, aloxite, or alundum depending on particular forms or applications. It occurs naturally in its crystalline polymorphic
phase Phase or phases may refer to: Science * State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter) In the physical sciences, a phase is a region of space (a thermodynamic system A thermodynamic system is a ...
α-Al2O3 as the
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

mineral
corundum Corundum is a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directio ...

corundum
, varieties of which form the precious
gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemic ...

gemstone
s
ruby A ruby is a pink to blood-red coloured gemstone A gemstone (also called a gem, fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewellery, jewelry or othe ...

ruby
and
sapphire Sapphire is a precious gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical c ...

sapphire
. Al2O3 is significant in its use to produce aluminium metal, 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 by friction. While finishing a material often means polishing it to gain a smooth, reflect ...
owing to its
hardness Hardness (antonym: softness) is a measure of the resistance to localized induced by either mechanical or . In general, different materials differ in their hardness; for example hard metals such as and are harder than soft metals such as and ...
, and as a
refractory A refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperature Temperature is a physical quantity that expresses hot and cold. ...
material owing to its high melting point.


Natural occurrence

Corundum Corundum is a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directio ...

Corundum
is the most common naturally occurring
crystalline A crystal or crystalline solid is a solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The molecules in a solid are closely packed together and contain the least amount of kinet ...
form of aluminium oxide.
Rubies A ruby is a pink-ish red to blood-red colored gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaki ...

Rubies
and
sapphire Sapphire is a precious gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical c ...

sapphire
s 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 A laser is a device that emits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visible light is usually defined as ...

laser
qualities by traces of
chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

chromium
. Sapphires come in different colors given by various other impurities, such as iron and titanium. An extremely rare, δ form, occurs as the mineral deltalumite.


Properties

Al2O3 is an
electrical insulator An electrical insulator is a material in which the electron does not flow freely or the atom of the insulator have tightly bound electrons whose internal electric charges do not flow freely; very little electric current will flow through it unde ...
but has a relatively high
thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

thermal conductivity
()Material Properties Data: Alumina (Aluminum Oxide)
. Makeitfrom.com. Retrieved on 2013-04-17.
for a ceramic material. Aluminium oxide is insoluble in water. In its most commonly occurring crystalline form, called
corundum Corundum is a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directio ...

corundum
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 by friction. While finishing a material often means polishing it to gain a smooth, reflect ...
and as a component in
cutting tools In the context of machining, a cutting tool or cutter is any tool that is used to remove some material from the work piece by means of shear deformation. Cutting may be accomplished by single-point or multipoint tools. Single-point tools are used i ...

cutting tools
. Aluminium oxide is responsible for the resistance of metallic aluminium to
weathering Weathering is the deterioration of rocks In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology ...
. Metallic aluminium is very reactive with atmospheric oxygen, and a thin passivation layer of aluminium oxide (4 nm thickness) forms on any exposed aluminium surface in a matter of hundreds of picoseconds. 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 An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts Elec ...
, such as
aluminium bronze Aluminium bronze is a type of bronze in which aluminium is the main alloying metal added to copper, in contrast to standard bronze (copper and tin) or brass (copper and zinc). A variety of aluminium bronzes of differing compositions have found in ...
s, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance. The aluminium oxide generated by anodising is typically
amorphous In condensed matter physics Condensed matter physics is the field of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science th ...

amorphous
, but discharge assisted oxidation processes such as
plasma electrolytic oxidation Plasma electrolytic oxidation (PEO), also known as electrolytic plasma oxidation (EPO) or microarc oxidation (MAO), is an electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical poten ...
result in a significant proportion of crystalline aluminium oxide in the coating, enhancing its
hardness Hardness (antonym: softness) is a measure of the resistance to localized induced by either mechanical or . In general, different materials differ in their hardness; for example hard metals such as and are harder than soft metals such as and ...
. Aluminium oxide was taken off the
United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an of the tasked with matters. President proposed the establishment of EPA on July 9, 1970; it began operation on December 2, 1970, after Nixon signed an . The was ratified by committee hearings ...
's chemicals lists in 1988. Aluminium oxide is on the EPA's
Toxics Release Inventory The Toxics Release Inventory (TRI) is a publicly available database containing information on toxic chemical releases and other waste management activities in the United States. Image:TRI-ME2006.jpg, TRI-ME, the TRI computer reporting program Summa ...
list if it is a fibrous form.


Amphoteric nature

Aluminium oxide is an
amphoteric In chemistry, an amphoteric compound is a molecule or ion that can react both as an acid An acid is a molecule or ion An ion () is a particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older ...

amphoteric
substance, meaning it can react with both
acids An acid is a molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical phenomena associated wi ...
and bases, such as
hydrofluoric acid Hydrofluoric acid is a Solution (chemistry), solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly Corrosive substance, corrosive. It is used to make most fluorine-containing compounds; examples include th ...
and
sodium hydroxide Sodium hydroxide, also known as lye A lye is a metal hydroxide traditionally obtained by leaching wood ashes, or a strong alkali In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chem ...

sodium hydroxide
, acting as an acid with a base and a base with an acid, neutralising the other and producing a salt. :Al2O3 + 6 HF → 2 AlF3 + 3 H2O :Al2O3 + 2 NaOH + 3 H2O → 2 NaAl(OH)4 (
sodium aluminate Sodium aluminate is an inorganic In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, be ...
)


Structure

The most common form of crystalline aluminium oxide is known as
corundum Corundum is a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directio ...

corundum
, which is the thermodynamically stable form. The oxygen ions form a nearly
hexagonal close-packed In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space that ...
structure with the aluminium ions filling two-thirds of the octahedral interstices. Each Al3+ center is
octahedral In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space ...
. In terms of its
crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek language, Greek words ''crystallon'' "cold drop, frozen drop" ...

crystallography
, corundum adopts a
trigonal A triangle is a polygon with three Edge (geometry), edges and three Vertex (geometry), vertices. It is one of the basic shapes in geometry. A triangle with vertices ''A'', ''B'', and ''C'' is denoted \triangle ABC. In Euclidean geometry, any ...
Bravais lattice In geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of Translation operator (quantum mechanics)#Discrete Translational Symmetry, discrete translation operations described in t ...
with a
space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unchan ...
of Rc (number 167 in the International Tables). The
primitive cell In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space that ...
contains two formula units of aluminium oxide. Aluminium oxide also exists in other metastable phases, including the cubic γ and η phases, the monoclinic θ phase, the hexagonal χ phase, the orthorhombic κ phase and the δ phase that can be tetragonal or orthorhombic. Each has a unique crystal structure and properties. Cubic γ-Al2O3 has important technical applications. The so-called β-Al2O3 proved to be NaAl11O17. Molten aluminium oxide near the melting temperature is roughly 2/3
tetrahedral In , a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular , is a composed of four , six straight , and four . The tetrahedron is the simplest of all the ordinary and the only one that has fewer than 5 faces. The t ...

tetrahedral
(i.e. 2/3 of the Al are surrounded by 4 oxygen neighbors), and 1/3 5-coordinated, with very little (<5%)
octahedral In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space ...

octahedral
Al-O present. Around 80% of the oxygen atoms are shared among three or more Al-O polyhedra, and the majority of inter-polyhedral connections are corner-sharing, with the remaining 10–20% being edge-sharing. The breakdown of octahedra upon melting is accompanied by a relatively large volume increase (~20%), the density of the liquid close to its melting point is 2.93 g/cm3. The structure of molten alumina is temperature dependent and the fraction of 5- and 6-fold aluminium increases during cooling (and supercooling), at the expense of tetrahedral AlO4 units, approaching the local structural arrangements found in amorphous alumina.


Production

Aluminium
hydroxide Hydroxide is a diatomic anion with chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical physics and general che ...
minerals are the main component of
bauxite Bauxite is a sedimentary rock Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation ( ...

bauxite
, the principal
ore ore – psilomelane Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous manganese Manganese is a chemical element Image:Simple Periodic Table Chart- ...

ore
of
aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
. A mixture of the minerals comprise bauxite ore, including
gibbsite Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer Polymorphism (materials science), polymorp ...

gibbsite
(Al(OH)3),
boehmite Boehmite or böhmite is an aluminium oxide hydroxide (γ-AlO(OH)) mineral, a component of the aluminium ore bauxite Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. ...
(γ-AlO(OH)), and
diaspore Diaspore , also known as diasporite, empholite, kayserite, or tanatarite, is an aluminium oxide hydroxide mineral, α-AlO(OH), crystallizing in the orthorhombicIn crystallography, the orthorhombic crystal system is one of the 7 crystal systems. ...

diaspore
(α-AlO(OH)), along with impurities of
iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, ...

iron oxide
s and hydroxides, quartz and
clay minerals Clay minerals are hydrous aluminium Aluminium (aluminum in American English, American and Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than thos ...
. Bauxites are found in
laterite Laterite is both a soil and a rock type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by int ...
s. Bauxite is purified by the
Bayer processThe Bayer process is the principal industrial means of refining bauxite Bauxite is a sedimentary rock Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic p ...
: : Al2O3 + H2O + NaOH → NaAl(OH)4 : Al(OH)3 + NaOH → NaAl(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. : NaAl(OH)4 → NaOH + Al(OH)3 The solid Al(OH)3
Gibbsite Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer Polymorphism (materials science), polymorp ...

Gibbsite
is then
calcined Calcination refers to heating a solid to high temperatures in absence of air or oxygen, generally for the purpose of removing impurities or volatile substances. However, calcination is also used to mean a thermal treatment process in the absence o ...
(heated to over 1100 °C) to give aluminium oxide: : 2 Al(OH)3 → Al2O3 + 3 H2O The product aluminium oxide tends to be multi-phase, i.e., consisting of several phases of aluminium oxide rather than solely
corundum Corundum is a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directio ...

corundum
. 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 aluminium oxide product which, in turn, affects the cost of aluminium production and pollution control.


Applications

Known as alpha alumina in
materials science The interdisciplinary Interdisciplinarity or interdisciplinary studies involves the combination of two or more academic discipline An academic discipline or academic field is a subdivision of knowledge that is Education, taught and resea ...
communities or alundum (in fused form) or aloxite in the
mining Mining is the extraction of valuable mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occu ...

mining
and
ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant Corrosion is a Erosion, natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, carbonate or sulfide. ...

ceramic
communities aluminium oxide finds wide use. Annual world production of aluminium oxide in 2015 was approximately 115 million
tonne The tonne ( or ; symbol: t) is a metric unit of mass equal to 1,000 kilogram The kilogram (also kilogramme) is the base unit of mass Mass is the physical quantity, quantity of ''matter'' in a physical body. It is also a meas ...
s, over 90% of which is used in the manufacture of aluminium metal. The major uses of speciality aluminium oxides are in refractories, ceramics, polishing and abrasive applications. Large tonnages of aluminium hydroxide, from which alumina is derived, are used in the manufacture of
zeolites Zeolites are microporous, aluminosilicate mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (g ...
, coating
titania Titania may refer to: Astronomy * Titania (moon) Titania (), also designated Uranus III, is the largest of the moons of Uranus and the List of natural satellites by diameter, eighth largest moon in the Solar System at a diameter of . Discovere ...
pigments, and as a fire retardant/smoke suppressant. Over 90% of the aluminium oxide, normally termed Smelter Grade Alumina (SGA), produced is consumed for the production of aluminium, usually by the
Hall–Héroult process The Hall–Héroult process is the major industrial process Industrial processes are procedures involving chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add ...
. The remainder, normally called speciality alumina is used in a wide variety of applications which reflect its inertness, temperature resistance and electrical resistance.


Fillers

Being fairly chemically inert and white, aluminium oxide is a favored filler for plastics. Aluminium oxide is a common ingredient in
sunscreen Sunscreen, also known as sunblock or suntan lotion, is a photoprotective topical A topical medication is a medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug use ...
and is sometimes also present in cosmetics such as blush, lipstick, and nail polish.


Glass

Many formulations of
glass Glass is a non- crystalline, often transparency and translucency, transparent amorphous solid, that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by ...

glass
have aluminium oxide as an ingredient. Aluminosilicate glass is a commonly used type of glass that often contains 5% to 10% alumina.


Catalysis

Aluminium oxide catalyses a variety of reactions that are useful industrially. In its largest scale application, aluminium oxide is the catalyst in the
Claus process The Claus process is the most significant gas desulfurizing process, recovering elemental sulfur Sulfur (in traditional laity, lay Commonwealth English: sulphur) is a chemical element with the Symbol (chemistry), symbol S and atomic nu ...
for converting hydrogen sulfide waste gases into elemental sulfur in refineries. It is also useful for dehydration of
alcohol In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term alcohol originally referred to the primary alcohol ethan ...

alcohol
s to alkenes. Aluminium oxide serves as a
catalyst support In chemistry, a catalyst support is the material, usually a solid with a high surface area, to which a catalyst that utilizes a low-temperature oxidation catalyst to convert carbon monoxide to less toxic carbon dioxide at room temperature. It c ...
for many industrial catalysts, such as those used in
hydrodesulfurization Hydrodesulfurization (HDS) is a catalytic chemical process widely used to remove sulfur Sulfur (in traditional laity, lay Commonwealth English: sulphur) is a chemical element with the Symbol (chemistry), symbol S and atomic number  ...
and some Ziegler–Natta polymerizations.


Gas purification

Aluminium oxide is widely used to remove water from gas streams.


Abrasive

Aluminium oxide is used for its hardness and strength. Its naturally occurring form,
Corundum Corundum is a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directio ...

Corundum
, is a 9 on the
Mohs scale of mineral hardness The Mohs scale of mineral hardness () is a qualitative ordinal scale Ordinal data is a categorical, statistical data type where the variables have natural, ordered categories and the distances between the categories are not known. These data e ...
(just below diamond). It is widely used 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 by friction. While finishing a material often means polishing it to gain a smooth, reflect ...
, including as a much less expensive substitute for
industrial diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. Wh ...
. Many types of
sandpaper upright=1.35, Sheets of sandpaper with different grit sizes (40 (coarse), 80, 150, 240, 600 (fine)). Sandpaper and glasspaper are names used for a type of coated abrasive A coated abrasive is an abrasive grain bonded to a flexible Substrate (m ...

sandpaper
use aluminium oxide crystals. In addition, its low heat retention and low
specific heat In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quant ...
make it widely used in grinding operations, particularly cutoff tools. As the powdery abrasive mineral aloxite, it is a major component, along with
silica Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any su ...

silica
, of the cue tip "chalk" used in
billiards Cue sports (sometimes written cuesports), also known as billiard sports, are a wide variety of generally played with a , which is used to strike s and thereby cause them to move around a -covered bounded by elastic bumpers known as . Histor ...
. Aluminium oxide powder is used in some /
DVD The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital electronics Digital electr ...

DVD
polishing Polishing is the process of creating a smooth and shiny surface by rubbing it or by applying a chemical treatment, leaving a clean surface with a significant specular reflection Reflections on still water are an example of specular reflectio ...
and scratch-repair kits. Its polishing qualities are also behind its use in toothpaste. It is also used in
microdermabrasion Dermabrasion is a type of surgical skin planing, typically performed in a professional medical setting by a dermatologist or plastic surgeon trained specifically in this procedure. Dermabrasion has been practiced for many years (before the advent o ...
, both in the machine process available through dermatologists and estheticians, and as a manual dermal abrasive used according to manufacturer directions.


Paint

Aluminium oxide flakes are used in paint for reflective decorative effects, such as in the automotive or cosmetic industries.


Composite fiber

Aluminium oxide has been used in a few experimental and commercial fiber materials for high-performance applications (e.g., Fiber FP, Nextel 610, Nextel 720). Alumina nanofibers in particular have become a research field of interest.


Body armor

Some body armors utilize alumina ceramic plates, usually in combination with aramid or UHMWPE backing to achieve effectiveness against most rifle threats. Alumina ceramic armor is readily available to most civilians in jurisdictions where it is legal, but is not considered military grade.


Abrasion protection

Aluminium oxide can be grown as a coating on aluminium by
anodizing s have an anodized aluminium surface that has been dyed; they are made in many colours. Anodizing is an electrolyte, electrolytic Passivation (chemistry), passivation process used to increase the thickness of the natural oxide layer on the surface ...
or by
plasma electrolytic oxidation Plasma electrolytic oxidation (PEO), also known as electrolytic plasma oxidation (EPO) or microarc oxidation (MAO), is an electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical poten ...
(see the "Properties" above). Both the
hardness Hardness (antonym: softness) is a measure of the resistance to localized induced by either mechanical or . In general, different materials differ in their hardness; for example hard metals such as and are harder than soft metals such as and ...
and abrasion-resistant characteristics of the coating originate from the high strength of aluminium oxide, yet the porous coating layer produced with conventional direct current anodizing procedures is within a 60-70 Rockwell hardness C range which is comparable only to hardened carbon steel alloys, but considerably inferior to the hardness of natural and synthetic corundum. Instead, with
plasma electrolytic oxidation Plasma electrolytic oxidation (PEO), also known as electrolytic plasma oxidation (EPO) or microarc oxidation (MAO), is an electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical poten ...
, the coating is porous only on the surface oxide layer while the lower oxide layers are much more compact than with standard DC anodizing procedures and present a higher crystallinity due to the oxide layers being remelted and densified to obtain α-Al2O3 clusters with much higher coating hardness values circa 2000 Vickers hardness. Alumina is used to manufacture tiles which are attached inside pulverized fuel lines and flue gas ducting on coal fired power stations to protect high wear areas. They are not suitable for areas with high impact forces as these tiles are brittle and susceptible to breakage.


Electrical insulation

Aluminium oxide is an electrical
insulator Insulator may refer to: * Insulator (electricity), a substance that resists electricity ** Pin insulator, a device that isolates a wire from a physical support such as a pin on a utility pole ** Strain insulator, a device that is designed to work i ...
used as a substrate (
silicon on sapphire Silicon on sapphire (SOS) is a hetero-epitaxial process for metal-oxide-semiconductor (MOS) integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electron ...
) for
integrated circuits An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuit 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of indiv ...

integrated circuits
but also as a tunnel barrier for the fabrication of
superconducting Superconductivity is a set of physical properties observed in certain materials where Electrical resistance and conductance, electrical resistance vanishes and magnetic field, magnetic flux fields are expelled from the material. Any material exh ...
devices such as s and superconducting quantum interference devices (
SQUID Squid are cephalopod A cephalopod is any member of the mollusca Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is ...

SQUID
s). For its application as an electrical insulator in integrated circuits, where the conformal growth of a thin film is a prerequisite and the preferred growth mode is
atomic layer deposition Atomic layer deposition (ALD) is a thin-film deposition A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometre, micrometers in thickness. The controlled synthesis of materials as thin films (a ...
, Al2O3 films can be prepared by the chemical exchange between trimethylaluminum (Al(CH3)3) and H2O: :2 Al(CH3)3 + 3 H2O → Al2O3 + 6 CH4 H2O in the above reaction can be replaced by
ozone Ozone (), or trioxygen, is an inorganic molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a cha ...

ozone
(O3) as the active oxidant and the following reaction then takes place: :2 Al(CH3)3 + O3 → Al2O3 + 3 C2H6 The Al2O3 films prepared using O3 show 10–100 times lower leakage current density compared with those prepared by H2O. Aluminium oxide, being a dielectric with relatively large
band gap In solid-state physics Solid-state physics is the study of rigid matter, or solids, through methods such as quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state ...

band gap
, is used as an insulating barrier in
capacitors A capacitor is a device that stores electric charge in an electric field An electric field (sometimes E-field) is the physical field that surrounds each electric charge Electric charge is the physical property of matter that causes it t ...
.


Other

In lighting, transparent aluminium oxide is used in some
sodium vapor lamp A sodium-vapor lamp is a gas-discharge lamp Gas-discharge lamps are a family of artificial light sources that generate light by sending an electric discharge through an ionization, ionized gas, a plasma (physics), plasma. Typically, such la ...
s. Aluminium oxide is also used in preparation of coating suspensions in s. In chemistry laboratories, aluminium oxide is a medium for
chromatography In chemical analysis, chromatography is a laboratory technique for the Separation process, separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it ...

chromatography
, available in
basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming language In computer science Computer science deals with the theoretical foundations of information, algorithms and the ar ...
(pH 9.5),
acid An acid is a or capable of donating a (hydrogen ion H+) (a ), or, alternatively, capable of forming a with an (a ). The first category of acids are the proton donors, or s. In the special case of , proton donors form the H3O+ and are ...
ic (pH 4.5 when in water) and neutral formulations. Health and medical applications include it as a material in
hip replacement Hip replacement is a surgical procedure in which the hip joint is replaced by a prosthetic implant, that is, a hip prosthesis. Hip replacement surgery can be performed as a total replacement or a hemi (half) replacement. Such joint replacement ...
s and
birth control pillsOral contraceptives, abbreviated OCPs, also known as birth control pills, are medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to medical diagnosis, diagnose, cure, t ...
. It is used as a
scintillator A scintillator is a material that exhibits scintillation, the property of luminescence Luminescence is spontaneous emission of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum ...

scintillator
and
dosimeterA radiation dosimeter is a device that measures dose uptake of external ionizing radiation. It is worn by the person being monitored when used as a personal dosimeter, and is a record of the radiation dose received. Modern electronic personal dosim ...

dosimeter
for radiation protection and therapy applications for its
optically stimulated luminescence In physics, optically stimulated luminescence (OSL) is a method for measuring doses from ionizing radiation Ionizing radiation (ionising radiation) consists of subatomic particles or electromagnetic waves that have sufficient energy to ionizatio ...
properties. Insulation for high-temperature furnaces is often manufactured from aluminium oxide. Sometimes the insulation has varying percentages of silica depending on the temperature rating of the material. The insulation can be made in blanket, board, brick and loose fiber forms for various application requirements. Small pieces of aluminium oxide are often used as in chemistry. It is also used to make
spark plug A spark plug (sometimes, in British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codification of ...

spark plug
insulator Insulator may refer to: * Insulator (electricity), a substance that resists electricity ** Pin insulator, a device that isolates a wire from a physical support such as a pin on a utility pole ** Strain insulator, a device that is designed to work i ...
s. Using a
plasma spray Thermal spraying techniques are coating processes in which melted (or heated) materials are sprayed onto a surface. The "feedstock" (coating precursor) is heated by electrical (plasma or arc) or chemical means (combustion flame). Thermal sprayin ...
process and mixed with
titania Titania may refer to: Astronomy * Titania (moon) Titania (), also designated Uranus III, is the largest of the moons of Uranus and the List of natural satellites by diameter, eighth largest moon in the Solar System at a diameter of . Discovere ...
, it is coated onto the braking surface of some
bicycle A bicycle, also called a bike or cycle, is a human-powered transport, human-powered or motorized bicycle, motor-powered, bicycle pedal, pedal-driven, single-track vehicle, having two bicycle wheel, wheels attached to a bicycle frame, frame, ...

bicycle
rims to provide abrasion and wear resistance. Most ceramic eyes on fishing rods are circular rings made from aluminium oxide. In its finest powdered (white) form, called Diamantine, aluminium oxide is used as a superior polishing abrasive in watchmaking and clockmaking.


See also

* Aluminium oxide nanoparticle * Bauxite tailings * Beta-alumina solid electrolyte, a fast ion conductor * Charged Aerosol Release Experiment (CARE) * List of alumina refineries * Micro-Pulling-Down * Transparent alumina


References


External links


CDC - NIOSH Pocket Guide to Chemical Hazards
{{DEFAULTSORT:Aluminium Oxide Acid catalysts Abrasives Aluminium compounds Amphoteric compounds Biomaterials Oxides Refractory materials Sesquioxides