Aluminium oxynitride (marketed under the name ALON by Surmet Corporation) is a
transparent ceramic
Many ceramic materials, both glassy and crystalline, have found use as optically transparent materials in various forms from bulk solid-state components to high surface area forms such as thin films, coatings, and fibers. Such devices have found ...
composed of
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
,
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
and
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
. ALON is optically transparent (≥ 80%) in the
near-ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
, visible, and midwave-
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
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 in which other ingredients are added which ch ...
glass
Glass is a non-crystalline, often 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 rapid cooling (quenching) of ...
, 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, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sapphir ...
spinel
Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals.
Properties
S ...
structure, it can be fabricated to transparent windows, plates, domes, rods, tubes, and other forms using conventional ceramic powder processing techniques.
ALON 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
Bulletproofing is the process of making an object capable of stopping a bullet or similar high velocity projectiles (e.g. shrapnel). The term bullet resistance is often preferred because few, if any, practical materials provide complete protecti ...
, blast-resistant, and optoelectronic windows. ALON-based armor has been shown to stop multiple armor-piercing projectiles of up to .50 BMG.
ALON is commercially available in sizes as large as monolithic windows.
Properties
ALON is resistant to damage from various acids, bases, and water.
Mechanical
Aluminum oxynitride has the following mechanical properties:
*
Young's modulus
Young's modulus E, the Young modulus, or the modulus of elasticity in tension or compression (i.e., negative tension), is a mechanical property that measures the tensile or compressive stiffness of a solid material when the force is applied leng ...
334 GPa
*
Shear modulus
In materials science, shear modulus or modulus of rigidity, denoted by ''G'', or sometimes ''S'' or ''μ'', is a measure of the elastic shear stiffness of a material and is defined as the ratio of shear stress to the shear strain:
:G \ \stackre ...
135 GPa
*
Poisson ratio
In materials science and solid mechanics, Poisson's ratio \nu ( nu) is a measure of the Poisson effect, the deformation (expansion or contraction) of a material in directions perpendicular to the specific direction of loading. The value of Poi ...
0.24
*
Knoop hardness
The Knoop hardness test is a microhardness test – a test for mechanical hardness used particularly for very brittle materials or thin sheets, where only a small indentation may be made for testing purposes. A pyramidal diamond point is pressed i ...
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 in a material just before it yields in a flexure test. The transverse bending test is most frequ ...
0.38–0.7 GPa
*
Compressive strength
In mechanics, compressive strength or compression strength is the capacity of a material or structure to withstand loads tending to reduce size (as opposed to tensile strength which withstands loads tending to elongate). In other words, compre ...
2.68 GPa
Thermal and optical
Aluminum oxynitride has the following thermal and optical properties:
*
Specific heat
In thermodynamics, the specific heat capacity (symbol ) of a substance is the heat capacity of a sample of the substance divided by the mass of the sample, also sometimes referred to as massic heat capacity. Informally, it is the amount of heat t ...
0.781 J/(g·°C)
*
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 ...
12.3 W/(m·°C)
*
Thermal expansion coefficient
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.
Temperature is a monotonic function of the average molecular kinetic ...
~4.7/°C
* Transparency range 200–5000 nm
Applications
ALON is used for infrared-optical windows, with greater than 80% transparency at wavelengths below about 4 micrometers, dropping to near zero at about 6 micrometers.Lee M. Goldman, Rich Twedt, Sreeram Balasubramanian, and Suri Sastri (2011). "ALON Optical Ceramic Transparencies for Sensor and Armor Applications," ''Proc. of SPIE, Vol. 8016'', 801608-12 abstract /ref> As such, it has applications as a sensor component, specialty IR domes, and windows for laser communications. It has also been demonstrated as an interface passivation layer in some
semiconductor
A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
-related applications.
ALON has less than half the weight and thickness of glass-based transparent armor. thick ALON armor 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 service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Signal ...
began testing ALON, "to shield troops".
Manufacture
ALON 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
Grind is the cross-sectional shape of a blade.
Grind, grinds, or grinding may also refer to:
Grinding action
* Grinding (abrasive cutting), a method of crafting
* Grinding (dance), suggestive club dancing
* Grinding (video gaming), repetitive and ...
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 accordin ...
to transparency. It can withstand temperatures of about in inert atmospheres. The grinding and polishing substantially improves the
Corundum
Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the pres ...
*
Transparent ceramics
Many ceramic materials, both glassy and crystalline, have found use as optically transparent materials in various forms from bulk solid-state components to high surface area forms such as thin films, coatings, and fibers. Such devices have found ...