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]
Properties
Aluminium oxynitride is resistant to various acids, bases, and water.[6]
Mechanical
Aluminium oxynitride has the following mechanical properties:[2]
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]
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
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
^4520116, Richard L. Gentilman, Edward A. Maguire, Leonard E. Dolhert, "Transparent aluminum oxynitride and method of manufacture", published May 28, 1985, assigned to Surmet Corp
^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.