Transparent aluminium

[edit] Introduction

Transparent Aluminium (Aluminum in US) or more specifically Aluminum Oxynitride, is an advanced polycrystalline ceramic with a cubic spinel crystal structure. In its raw form it is a powder that is then set under heat and pressure. It is made up of a mix of Aluminium, Oxygen and Nitrogen, so the chemical chemical structure is Al2 O27 N5, hence it is known commercially as commercially known as ALON® (image credits).

To some extent it came to be known as transparent aluminium because this fictional material was included in the American futuristic film Star Treck IV the Voyage Home, the film and series have fictionally portrayed futuristic technologies, some of which have become reality. Credit: Wonder World

The material was first investigated during the 1960s−1970s, with the first Al2 O3–AlN equilibrium phase diagram completed and the material processed. This produced a translucent aluminium oxynitride spinel ceramic (McCauley, 1978; McCauley and Corbin, 1979; McCauley et al., 2009; Yamaguchi and Yanagida, 1959). Over time this material has been slightly adapted to produce the Al2 O27 N5 ALON® material now manufactured.

Since then it was been widely used as a transparent ceramic in many applications, including transparent armour. ALON is used for infrared-optical windows, as it has 80% transparency at wave lengths below about 4 micrometers, dropping to near zero at about 6 micrometers. It is used in sensor parts, infrared domes, and windows for lasers. The material is half as heavy as glass and can be half as thick and capable of stopping armoury that traditional laminate glass cannot.

As it can be manufactured using conventional ceramic powder processing techniques and can be fabricated as windows, plates, domes, rods, tubes and other forms. Once set after heat and pressure are applied to the powder the surfaces need to be ground and polished to achieve transparency.

[edit] Physical and mechanical characteristics of Aluminum Oxynitride or ALON®

• Density (g/cc) 3.68 - 3.69
• Flexural Strength (MPa) : 350 – 640*
• Hardness (kg/mm2, Knoop, 200g) : 1,850 (9 Moh’s scale)
• Elastic/Young’s Modulus (GPa) : 320
• Fracture Toughness (MPa – m1/2) : 2.0 – 2.9
• Compressive Strength (GPa) : 2.7

[edit] Optical characteristics of Aluminum Oxynitride or ALON®

• Transmission range (>80%) : ~0.22 – 4.5 micron
• Typical Haze <3%
• Typical Clarity >95%
• Typical RI inhomogeneity : 5ppm over 11-inch dia aperture

[edit] Thermal characteristics of Aluminum Oxynitride or ALON®

• Melting Point (0C) : 2,150
• Thermal Conductivity (W/mK) : ~13
• Coefficient of Thermal Expansion (x10-6) : 7.50 (30-900oC)
• Specific Heat (cal/g-oC) : 0.22
• Max. Usable Temperature (inert atm.) 1,900oC

[edit] Electrical characteristics of Aluminum Oxynitride or ALON®

• Volume resistivity$ (ohm-cm) : >1014
• Dielectric Constant : f (GHz) - 35-45 k - 9.19 / f (GHz) - 55-60 k - 9.18 / f (GHz) - 90-110 k - 9.17
• Loss Tangent ( tan d , x10-5) : f (GHz) - 35-45 tan d - 31 / f (GHz) - 55-60 tan d - 361 / f (GHz) - 90-110 tan d - 96
• Dielectric Strength (kV/mm) : ~23

For further information and specifications visit the America Ceramic Society or the ALON product site page on Surmet.

[edit] Related articles on Designing Buildings

• Acrylic.
• Aluminium.
• Composites.
• Glass.
• Glazing.
• Optical properties.
• Plexiglas.
• Transparent.
• Transparent insulation.
• Types of materials.
• Types of metal.