Aluminium oxynitride (marketed under the name ALON by Surmet Corporation^[3]) is a transparent ceramic composed of aluminium, oxygen and nitrogen. Aluminium oxynitride is optically transparent (≥ 80%) in the near-ultraviolet, visible, and mid-wave-infrared regions of the electromagnetic spectrum. It is four times as hard as fused silica glass, 85% as hard as 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.^{[citation needed]}

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Aluminium oxynitride

Spinel structure of ALON
Names
Systematic IUPAC name Aluminium oxynitride
Identifiers
CAS Number	12633-97-5 Y
Abbreviations	ALON
Properties
Chemical formula	(AlN)x·(Al2O3)1−x, 0.30 ≤ x ≤ 0.37
Appearance	White or transparent solid
Density	3.691–3.696 g/cm3[1]
Melting point	~2150 °C[1]
Solubility in water	insoluble
Refractive index (nD)	1.79[2]
Structure
Crystal structure	cubic spinel
Lattice constant	a = 794.6 pm[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

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Aluminium oxynitride is the hardest polycrystalline transparent ceramic available commercially.^[2] 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.^[4] Aluminium oxynitride-based armor has been shown to stop multiple armor-piercing projectiles of up to .50 BMG.^[5]

Aluminium oxynitride is resistant to various acids, bases, and water.^[6]

Aluminium oxynitride 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.^[8] It has also been demonstrated as an interface passivation layer in some semiconductor-related applications.^[9]

Aluminium oxynitride has less than half the weight and thickness of glass-based transparent armor.^[10] Aluminium oxynitride armor of 1.6-inch (41 mm; 4.1 cm) thickness is capable of stopping .50 BMG armor-piercing rounds, which can penetrate 3.7 inches (94 mm; 9.4 cm) of traditional glass laminate.^[8][11]

In 2005, the United States Air Force began testing aluminium oxynitride-based armor.^[12]

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%.^[13] The fabricated greenware is subjected to heat treatment (densification) at elevated temperatures followed by grinding and polishing to transparency. It can withstand temperatures of about 2,100 °C (2,370 K) in inert atmospheres. The grinding and polishing substantially improves the impact resistance and other mechanical properties of armor.^[7]

Patents related to aluminium oxynitride include:

• Aluminium oxynitride having improved optical characteristics and method of manufacture TM Hartnett, RL Gentilman U.S. patent 4,481,300, 1984
• Process for producing polycrystalline cubic aluminium oxynitride JW McCauley U.S. patent 4,241,000, 1980
• Transparent aluminium oxynitride and method of manufacture RL Gentilman, EA Maguire U.S. patent 4,520,116, 1985; U.S. patent 4,720,362, 1988
• Transparent aluminium oxynitride-based ceramic article JP Mathers U.S. patent 5,231,062, 1993

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• Corundum
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