Making a transparent metal - ALON

ALON, also known as transparent aluminium armour is a ceramic alloy made of aluminum oxynitride, a combination of aluminum, oxygen and nitrogen. 

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ALON is both lighter (about 0.5x) and stronger (> 2x) than the traditional bullet-proof glass; it is resistant to scratches, radiation, various acids and bases.

According to Surmet Corporation, the sole producer of ALON globally, the properties of ALON are as follows:

• Structure: Cubic-spinel
• Density: 3.691 - 3.696 g/cm³
• Refractive index: 1.79
• Form: Polycrystalline
• Melting Point: 2150°C
• Young's Modulus: 323 GPa
• Knoop Hardness: 1850 kg/mm2 (0.2 kg load)
• Fracture Toughness: 2.0 - 2.9 MPa.m½
• Flexure Strength: 380 - 700 MPa
• Thermal Conductivity: 13 W/mK

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Like every other ceramic, ALON starts as a powder which is then molded by heating and baking at high temperature. During this process, the powder liquefies and then quickly cools forming a solid crystalline structure. Additional polishing strengthens the aluminium alloy and also makes it very clear.

ALON is highly applicable as bulletproof glass of automobiles and warships, aerospace.

**References:** 1. https://science.howstuffworks.com/transparent-aluminum-armor3.htm 2. http://www.surmet.com/technology/alon-optical-ceramics/ 3. https://en.m.wikipedia.org/wiki/Aluminium_oxynitride