Aluminium oxynitride
Encyclopedia
Aluminium oxynitride or AlON is a transparent polycrystalline ceramic
with cubic spinel crystal structure composed of aluminium
, oxygen
and nitrogen
. It is currently marketed under the name ALON by Surmet Corporation. ALON is optically transparent (≥80%) in the near ultra violet, visible and near infrared regions of the electromagnetic spectrum. It is 4 times harder than fused silica glass
, 85% as hard as sapphire
and nearly 15% harder than magnesium aluminate spinel
. The material is stable up to 1200 °C (2,192 °F). It can be fabricated to transparent windows, plates, domes, rods, tubes and other forms using conventional ceramic powder processing techniques. Because of its relatively light weight, optical and mechanical properties, and its resistance to damage due to oxidation or radiation, it shows promise for use as infrared, high temperature and ballistic and blast resistant windows. Manufacturing methods continue to be refined. At US$10–$15 per square inch the cost is currently (2005) higher than that of other ballistic resistant window materials.
Thermal and optical
In a 1989 review, Corbin summarized research showing that ALON appears to be radiation resistant and resistant to damage from various acids, bases and water.
(IR) related applications such as Recce
sensor windows, specialty IR domes with different shapes such as hemispherical, hyper-hemispherical and tangent ogive domes, transparent armor, windows for laser communications, and in some semi-conductor related applications When formed and polished as a window, the material currently (2005) costs about US$10 to US$15 per square inch (~ US$20,000/m2).
ceramic material which can be fabricated to windows, plates, domes, rods, tubes and other forms using conventional ceramic
powder processing techniques. It is made primarily of aluminum, oxygen, and nitrogen, and can vary slightly in its components (such as varying the aluminum 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
and polishing
to transparency
. It remains transparent until about 2100 °C. The grinding and polishing substantially improves the impact resistance and other mechanical properties of armor. Densities of 85% of the theoretical can be achieved. It is 85% as hard as sapphire and 15% harder than magnesium aluminate spinel. ALON is four times harder than fused silica glass, thus making it useful in a wide range of armor applications.
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
with cubic spinel crystal structure composed of aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
. It is currently marketed under the name ALON by Surmet Corporation. ALON is optically transparent (≥80%) in the near ultra violet, visible and near infrared regions of the electromagnetic spectrum. It is 4 times harder than fused silica glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
, 85% as hard as sapphire
Sapphire
Sapphire is a gemstone variety of the mineral corundum, an aluminium oxide , when it is a color other than red or dark pink; in which case the gem would instead be called a ruby, considered to be a different gemstone. Trace amounts of other elements such as iron, titanium, or chromium can give...
and nearly 15% harder than magnesium aluminate spinel
Spinel
Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4. Balas ruby is an old name for a rose-tinted variety.-Spinel group:...
. The material is stable up to 1200 °C (2,192 °F). It can be fabricated to transparent windows, plates, domes, rods, tubes and other forms using conventional ceramic powder processing techniques. Because of its relatively light weight, optical and mechanical properties, and its resistance to damage due to oxidation or radiation, it shows promise for use as infrared, high temperature and ballistic and blast resistant windows. Manufacturing methods continue to be refined. At US$10–$15 per square inch the cost is currently (2005) higher than that of other ballistic resistant window materials.
Properties
Mechanical- Young modulus 334 GPa
- Shear modulus 135 GPa
- Poisson ratio 0.24
- Knoop hardness 1800 kg/mm2 (0.2 kg load)
- Fracture toughnessFracture toughnessIn materials science, fracture toughness is a property which describes the ability of a material containing a crack to resist fracture, and is one of the most important properties of any material for virtually all design applications. The fracture toughness of a material is determined from the...
2.0 MPa·m1/2 - Flexural strengthFlexural strengthFlexural strength, also known as modulus of rupture, bend strength, or fracture strength, a mechanical parameter for brittle material, is defined as a material's ability to resist deformation under load...
0.38–0.7 GPa - Compressive strengthCompressive strengthCompressive strength is the capacity of a material or structure to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Concrete can be made to have high compressive strength, e.g...
2.68 GPa
Thermal and optical
- Specific heat 0.781 J/(g·°C)
- Thermal conductivityThermal conductivityIn physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
12.3 W/(m·°C) - Thermal expansion coefficient ~4.7/°C
- Transparency range 200–5000 nm
In a 1989 review, Corbin summarized research showing that ALON appears to be radiation resistant and resistant to damage from various acids, bases and water.
Applications
ALON is used in various defense and InfraredInfrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
(IR) related applications such as Recce
Recce
Recce may refer to:* Reconnaissance, military scouting* SEAL Recon Rifle, a rifle used by US Navy SEALs also called the Recce Rifle* Recce , a pre-shoot reconnaissance of a film location...
sensor windows, specialty IR domes with different shapes such as hemispherical, hyper-hemispherical and tangent ogive domes, transparent armor, windows for laser communications, and in some semi-conductor related applications When formed and polished as a window, the material currently (2005) costs about US$10 to US$15 per square inch (~ US$20,000/m2).
Manufacture
ALON is a polycrystallinePolycrystalline
Polycrystalline materials are solids that are composed of many crystallites of varying size and orientation. The variation in direction can be random or directed, possibly due to growth and processing conditions. Fiber texture is an example of the latter.Almost all common metals, and many ceramics...
ceramic material which can be fabricated to windows, plates, domes, rods, tubes and other forms using conventional ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
powder processing techniques. It is made primarily of aluminum, oxygen, and nitrogen, and can vary slightly in its components (such as varying the aluminum 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
Grinding (abrasive cutting)
Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.A wide variety of machines are used for grinding:* Hand-cranked knife-sharpening stones * Handheld power tools such as angle grinders and die grinders...
and polishing
Polishing
Polishing is the process of creating a smooth and shiny surface by rubbing it or using a chemical action, leaving a surface with a significant specular reflection In some materials polishing is also able to reduce diffuse reflection to...
to transparency
Transparency and translucency
In the field of optics, transparency is the physical property of allowing light to pass through a material; translucency only allows light to pass through diffusely. The opposite property is opacity...
. It remains transparent until about 2100 °C. The grinding and polishing substantially improves the impact resistance and other mechanical properties of armor. Densities of 85% of the theoretical can be achieved. It is 85% as hard as sapphire and 15% harder than magnesium aluminate spinel. ALON is four times harder than fused silica glass, thus making it useful in a wide range of armor applications.
Patents
- Process for producing polycrystalline cubic aluminum oxynitride JW McCauley , 1980
- Aluminum oxynitride having improved optical characteristics and method of manufacture TM Hartnett, RL Gentilman , 1984
- Transparent aluminum oxynitride and method of manufacture RL Gentilman, EA Maguire , 1985
- Transparent aluminum oxynitride and method of manufacture RL Gentilman, EA Maguire , 1988
- Transparent aluminum oxynitride-based ceramic article JP Mathers , 1993
External links
- The Influence of Sintering Additives on the Microstructure and Properties of ALON. Yechezkel Ashuach. Master's Thesis, Technion – Israel Institute of Technology, 2003
- Solubility Limits of La and Y in Aluminum Oxynitride (AlON) at 1870°C Lior Miller and Wayne D. Kaplan. Department of Materials Engineering, Technion, Haifa, Israel, 2006