By Kari Williamson
ALON – aluminium oxynitride – is a synthetic ceramic which combines mechanical, physical, electrical, chemical and optical properties. It is transparent from the ultra-violet (UV) Mid-Wave Infrared (MWIR), and because it is transparent in its polycrystalline form, it can be produced using conventional powder processing techniques in large sizes and complex geometries.
The aluminium oxynitride powder forms green bodies, which through heat treatment become fully dense optical blanks that are fabricated into optical components.
In collaboration with Thomas Jefferson National Laboratory in Newport, VA, USA, Surment's ALON Optical Ceramic will be evaluated as a High Power RF window material to replace the current ‘opaque’ alumina window.
ALON’s properties such as thermal conductivity, thermal expansion coefficient and dielectric properties will be measured down to liquid helium temperatures, extending the current database for ALON Optical Ceramic from -150°C to temperatures as low as 2°K. In addition to low loss tangent and high strength, ALON Windows are also transparent allowing the inside of the superconducting cavities to be viewed during testing and operation, Surmet says.
An important aspect of this project involves combining ALON Windows with metallic ‘retaining’ structures, with hermetic seals which must operate down to cryogenic temperatures. This will require the development of new ‘brazing’ processes, since those used for conventional oxide ceramics like alumina, are strictly not applicable to ALON.
