Scientists from the National Research Nuclear University (MEPhI), Moscow, Russia, have developed a technology to produce compacts from aluminium oxynitride (Al23O27N5), or ‘transparent aluminium’, reports Phys.org. The method incorporates the use of spark-plasma sintering in a process based on the modified method of hot pressing.
In this case, electric current is passed directly through the mould and pressing billet. Researchers at the Institute of nuclear physics and engineering (INPhE) MEPhI reported that rapid heating is achieved by the pulsed current, resulting in an extremely short work-cycle time.
According to a paper published by MEPhl’s researchers, spark-plasma sintering was conducted in a LABOX machine model 625 (produced by Sinter Land, Japan). The sintering procedure used was standard, using a graphite matrix with an additional layer of graphite paper between the matrix and the powder filling, and between the graphite punches and the powder to prevent the latter and the equipment from sintering.
The primary use for transparent aluminium is currently the development of high strength armour and protective structures used by the armed forces and police, as the penetrative power of small arms and small-caliber artillery continues to increase. Currently, sapphire is often used to create materials for military armour. However, its use may be cost-prohibitive for some military organisations. According to MEPhl’s scientists, transparent polycrystalline ceramics provide a promising solution to the need for increased protection against ammunition and artillery, including ceramics based on aluminium oxynitride.
The use of transparent materials for armour is becoming more important as military organisations increase their dependence on UV, visible and infrared optical sensors. Different sensors ‘see’ different wavelengths of light: For example, infrared is important for heat-seeking capabilities, while UV imaging can be used to detect threats not seen in the visible spectrum.
In addition to its strength, transparent aluminium can can withstand temperatures of up to 2100°C. This means that transparent aluminium-based armouring may also be used to produce windows and domes for spacecraft, which encounter high temperatures and gravitational forces as they exit and enter Earth’s atmosphere.