Aluminium oxynitride

Aluminium oxynitride (marketed under the name ALON by Surmet Corporation[3]) is a transparent ceramic composed of aluminium, oxygen and nitrogen. ALON is optically transparent (≥ 80%) in the near-ultraviolet, visible, and midwave-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. Since it has a cubic spinel structure, it can be fabricated to transparent windows, plates, domes, rods, tubes, and other forms using conventional ceramic powder processing techniques.[citation needed]

Aluminium oxynitride
Spinel structure of ALON
Systematic IUPAC name
Aluminium oxynitride
Abbreviations ALON
0.30 ≤ x ≤ 0.37
Appearance White or transparent solid
Density 3.691–3.696 g/cm3[1]
Melting point ~2150 °C[1]
cubic spinel
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).
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ALON 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] ALON-based armor has been shown to stop multiple armor-piercing projectiles of up to .50 BMG cal.[5]

ALON is commercially available in sizes as large as 18-by-35-inch (460 mm × 890 mm; 46 cm × 89 cm) monolithic windows.[6]


ALON is resistant to damage from various acids, bases, and water.[7]


Aluminum oxynitride has the following mechanical properties:[2]

Thermal and opticalEdit

Aluminum oxynitride has the following thermal and optical properties:[8]


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.[9] As such, it has applications as a sensor component, specialty IR domes, and windows for laser communications.[9] It has also been demonstrated as an interface passivation layer in some semiconductor-related applications.[10]

ALON has less than half the weight and thickness of glass-based transparent armor.[11] 1.6-inch (41 mm; 4.1 cm) thick ALON armor is capable of stopping .50 BMG armor-piercing rounds, which can penetrate 3.7 inches (94 mm; 9.4 cm) of traditional glass laminate.[9][12]

In 2005, the United States Air Force began testing ALON, "to shield troops".[13]


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%.[14] 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.[8]


Patents related to aluminum oxynitride include:

In popular cultureEdit

"Transparent aluminum" became a popular term after its use in the film Star Trek IV: The Voyage Home (1986).[15][16]

See alsoEdit


  1. ^ a b "ALON Optical Ceramic. Technical data" (PDF). Surmet Corporation. 2003. Archived from the original (PDF) on 2013-06-12. Retrieved 2009-01-09.
  2. ^ a b c d Mohan Ramisetty et al. Transparent Polycrystalline Spinels Protect and Defend, American Ceramic Society Bulletin, vol.92, 2, 20–24 (2013)
  3. ^ Richard L. Gentilman et al. Transparent aluminum oxynitride and method of manufacture U.S. Patent 4,520,116 Issue date: May 28, 1985
  4. ^ "Domes & Infrared Optics". Surmet.
  5. ^ Ramisetty, Mohan; Sastri, Suri A.; Goldman, Lee (Aug 2013). "Transparent Ceramics Find Wide Use in Optics". Photonics Spectra.
  6. ^ "Surmet Achieves Major Milestone on its ALON Window Scale-up Program". PRWeb. May 28, 2013.
  7. ^ Corbin, N (1989). "Aluminum oxynitride spinel: A review". Journal of the European Ceramic Society. 5 (3): 143–154. doi:10.1016/0955-2219(89)90030-7.
  8. ^ a b Joseph M. Wahl et al. Recent Advances in ALON Optical Ceramic, Surmet
  9. ^ a b c 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
  10. ^ Zhu, Ming; Tung, Chih-Hang; Yeo, Yee-Chia (2006). "Aluminum oxynitride interfacial passivation layer for high-permittivity gate dielectric stack on gallium arsenide". Applied Physics Letters. 89 (20): 202903. Bibcode:2006ApPhL..89t2903Z. doi:10.1063/1.2388246. Retrieved 2022-02-11.
  11. ^ Security News (2015-06-03). Optically Clear Aluminium Provides Bulletproof Protection. TSS, 3 June 2015. Retrieved on 2015-07-10 from
  12. ^ Surmet's ALON Transparent Armor .50 Caliber Test
  13. ^ Schogol, Jeff (October 30, 2005). "Air Force testing lighter, transparent ALON armor". Stars and Stripes. Retrieved 2020-06-25.
  14. ^ Graham, Earl K.; Munly, W.C.; McCauley, James W.; Corbin, Norman D. (1988). "Elastic properties of polycrystalline aluminum oxynitride spinel and their dependence on pressure, temperature and composition". Journal of the American Ceramic Society. 71 (10): 807–812. doi:10.1111/j.1151-2916.1988.tb07527.x.
  15. ^ Harve Bennett, Nicholas Meyer, Steve Meerson, & Peter Krikes (1986). "Screenplay for Star Trek IV: The Voyage Home". Retrieved 2020-02-22.{{cite web}}: CS1 maint: multiple names: authors list (link)
  16. ^ Harve Bennett, Nicholas Meyer, Steve Meerson, & Peter Krikes (1986). "Screenplay for Star Trek IV: The Voyage Home". Retrieved 2020-02-22.{{cite web}}: CS1 maint: multiple names: authors list (link)

External linksEdit