Aluminium oxynitride
Transparent ceramic material
From Wikipedia, the free encyclopedia
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% for 2 mm thickness) in the near-ultraviolet, visible, and mid-wave-infrared regions of the electromagnetic spectrum. It is four times as hard as fused silica glass, the same hardness of 9 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]
Spinel structure of ALON | |
| Names | |
|---|---|
| Systematic IUPAC name
Aluminium oxynitride | |
| Identifiers | |
3D model (JSmol) |
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| Abbreviations | ALON |
CompTox Dashboard (EPA) |
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| Properties | |
| (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] |
| insoluble | |
Refractive index (nD) |
1.79[2] |
| Structure | |
| cubic spinel | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Aluminium oxynitride is the hardest polycrystalline transparent ceramic available commercially.[2][needs update] 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.[1] Aluminium oxynitride–based armor has been shown to stop multiple armor-piercing projectiles of up to .50 BMG.[4]
Properties
Aluminium oxynitride is resistant to various acids, bases, and water.[5]
Mechanical
Aluminium oxynitride has the following mechanical properties:[2]
- Compressive strength 2.68 GPa
- Flexural strength 0.38–0.7 GPa
- Fracture toughness 2.0 MPa·m1⁄2
- Knoop hardness 1800 kg/mm2 (0.2 kg load)
- Poisson ratio 0.24
- Shear modulus 135 GPa
- Young's modulus 334 GPa
Thermal and optical
Aluminium oxynitride has the following thermal and optical properties:[6]
- Specific heat 0.781 J/(g·K)
- Thermal conductivity 12.3 W/(m·K)
- Thermal expansion coefficient ~4.7×10−6/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.[7] It has also been demonstrated as an interface passivation layer in some semiconductor-related applications.[8]
Aluminium oxynitride has less than half the weight and thickness of glass-based transparent armor.[9] Aluminium oxynitride armor of 1.6-inch (41 mm) thickness is capable of stopping .50 BMG armor-piercing rounds, which can penetrate 3.7 inches (94 mm) of traditional glass laminate.[7][10]
In 2005, the United States Air Force began testing aluminium-oxynitride-based armor.[11]
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%.[12] 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.[6]
Patents
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