Aluminium Oxynitride
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Aluminium oxynitride (marketed under the name ALON by Surmet Corporation) is a transparent ceramic composed of
aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
,
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
and
nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
. Aluminium oxynitride is optically transparent (≥80% for 2 mm thickness) in the near-ultraviolet, visible, and mid-wave-
infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
regions of the electromagnetic spectrum. It is four times as hard as
fused silica Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses, such as soda-lime glass, lead glass, or borosil ...
glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...
, 85% as hard as
sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, cobalt, lead, chromium, vanadium, magnesium, boron, and silicon. The name ''sapphire ...
, and nearly 115% as hard as magnesium aluminate spinel. It can be fabricated into transparent windows, plates, domes, rods, tubes, and other forms using conventional ceramic powder processing techniques. Aluminium oxynitride is the hardest polycrystalline transparent ceramic available commercially.Mohan Ramisetty ''et al.'
Transparent Polycrystalline Spinels Protect and Defend
American Ceramic Society Bulletin, vol.92, 2, 20–24 (2013)
Because of its relatively low weight, distinctive optical and mechanical properties, and resistance to oxidation or radiation, it shows promise for applications such as bulletproof, blast-resistant, and optoelectronic windows. Aluminium oxynitride-based armor has been shown to stop multiple armor-piercing projectiles of up to .50 BMG.


Properties

Aluminium oxynitride is resistant to various acids, bases, and water.


Mechanical

Aluminium oxynitride has the following mechanical properties: *
Compressive strength In mechanics, compressive strength (or compression strength) is the capacity of a material or Structural system, structure to withstand Structural load, loads tending to reduce size (Compression (physics), compression). It is opposed to ''tensil ...
2.68 GPa *
Flexural strength Flexural strength, also known as modulus of rupture, or bend strength, or transverse rupture strength is a material property, defined as the Stress (mechanics), stress in a material just before it Yield (engineering), yields in a flexure test. T ...
0.38–0.7 GPa *
Fracture toughness In materials science, fracture toughness is the critical stress intensity factor of a sharp Fracture, crack where propagation of the crack suddenly becomes rapid and unlimited. It is a material property that quantifies its ability to resist crac ...
2.0 MPa·m1/2 * Knoop hardness 1800 kg/mm2 (0.2 kg load) *
Poisson ratio In materials science and solid mechanics, Poisson's ratio (symbol: (Nu (letter), nu)) is a measure of the Poisson effect, the Deformation (engineering), deformation (expansion or contraction) of a material in directions perpendicular to the spec ...
0.24 *
Shear modulus In materials science, shear modulus or modulus of rigidity, denoted by ''G'', or sometimes ''S'' or ''μ'', is a measure of the Elasticity (physics), elastic shear stiffness of a material and is defined as the ratio of shear stress to the shear s ...
135 GPa *
Young's modulus Young's modulus (or the Young modulus) is a mechanical property of solid materials that measures the tensile or compressive stiffness when the force is applied lengthwise. It is the modulus of elasticity for tension or axial compression. Youn ...
334 GPa


Thermal and optical

Aluminium oxynitride has the following thermal and optical properties: *
Specific heat In thermodynamics, the specific heat capacity (symbol ) of a substance is the amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. It is also referred to as massic heat ...
0.781 J/(g·K) *
Thermal conductivity The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low ...
12.3 W/(m·K) * Thermal expansion coefficient ~4.7/K * Transparency range 200–5000 nm


Applications

Aluminium oxynitride is used for infrared-optical windows, with greater than 80% transparency for 2 mm thickness at wavelengths below about 4 micrometers, dropping to near zero at about 6 micrometers. It has also been demonstrated as an interface passivation layer in some
semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...
-related applications. Aluminium oxynitride has less than half the weight and thickness of glass-based transparent armor. Aluminium oxynitride armor of thickness is capable of stopping .50 BMG armor-piercing rounds, which can penetrate of traditional glass laminate. In 2005, the
United States Air Force The United States Air Force (USAF) is the Air force, air service branch of the United States Department of Defense. It is one of the six United States Armed Forces and one of the eight uniformed services of the United States. Tracing its ori ...
began testing aluminium-oxynitride-based armor.


Manufacture

Aluminium oxynitride can be fabricated as windows, plates, domes, rods, tubes and other forms using conventional ceramic powder processing techniques. Its composition can vary slightly: the aluminium content from about 30% to 36%, which has been reported to affect the bulk and shear moduli by only 1–2%. The fabricated greenware is subjected to heat treatment (densification) at elevated temperatures followed by grinding and
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 (still limited by the index of refraction of the material accordi ...
to transparency. It can withstand temperatures of about in inert atmospheres. The grinding and polishing substantially improves the
impact resistance In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.Recent Advances in ALON Optical Ceramic
Surmet


Patents

Patents related to aluminium oxynitride include: * Aluminium oxynitride having improved optical characteristics and method of manufacture TM Hartnett, RL Gentilman , 1984 * Process for producing polycrystalline cubic aluminium oxynitride JW McCauley , 1980 * Transparent aluminium oxynitride and method of manufacture RL Gentilman, EA Maguire , 1985; , 1988 * Transparent aluminium oxynitride-based ceramic article JP Mathers , 1993


See also

*
Aluminium nitride Aluminium nitride ( Al N) is a solid nitride of aluminium. It has a high thermal conductivity of up to 321 W/(m·K) and is an electrical insulator. Its wurtzite phase (w-AlN) has a band gap of ~6 eV at room temperature and has a potent ...
*
Corundum Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium, and chromium. It is a rock (geology), rock-forming mineral. It is a naturally transparency and translucency, transparent material, but ...
* Transparent ceramics * Transparent aluminum (material in ''
Star Trek ''Star Trek'' is an American science fiction media franchise created by Gene Roddenberry, which began with the Star Trek: The Original Series, series of the same name and became a worldwide Popular culture, pop-culture Cultural influence of ...
'') * Gorilla Glass


References


External links


Processing of Optically Transparent Aluminum Oxynitride

"Solubility Limits of La and Y in Aluminum Oxynitride (AlON) at 1870°C"
Lior Miller and Wayne D. Kaplan. Department of Materials Engineering, Technion, Haifa, Israel, 2006.
''The Influence of Sintering Additives on the Microstructure and Properties of ALON''.
Yechezkel Ashuach. Master's Thesis, Technion – Israel Institute of Technology, 2003. {{Authority control Aluminium compounds Ceramic materials Nitrides Oxides Transparent materials Mixed anion compounds