Specialists from the National Research Nuclear University MEPhI and multi-institutional collaborators have developed a technology to produce compacts from aluminum oxynitride (ALON). They've published their results in IOP Conference Series: Materials Science and Engineering.
To obtain "transparent aluminum," researchers at the Institute of nuclear physics and engineering (INPhE) MEPhI applied the method of spark-plasma sintering. This is a new sintering process based on the modified method of hot pressing. In this case, electric current is passed directly through the mold and pressing billet, but not through an external heater. Very rapid heating is achieved by pulsed current for an extremely short work-cycle time.
"Among all present ceramics of medium density, aluminum oxynitride has a significantly high strength, comparable to that of YAG ((yttrium aluminum garnet) and cubic zirconia (stabilized zirconium oxide). Its toughness, which is the most important characteristic for armor protection, surpasses those of all transparent materials including quartz glass, fused quartz, spinel and leucosapphire," explains one of the authors of the publication, postgraduate student of INPhE Nikita Rubinkovskii.
Fans of Star Trek will recall that in the fourth movie, The Voyage Home, a material called "transparent aluminum" plays an important role in the story. Such materials have already been created and successfully used. It's four times stronger than aluminosilicate glass, and more scratch resistant. In addition, this material can withstand temperatures up to 2100 degree Celsius.
Currently, the penetrating power of small arms and small-caliber artillery forces the developers of protection equipment to improve the performance of armor materials and protective structures. This is especially true of transparent armor materials. Transparent polycrystalline ceramics is the most promising in this respect, in particular, ceramics based on aluminum oxynitride. It is possible to obtain transparent products of complex shape using the ceramics technology processes of molding and sintering.
The developers also claim that ALON can be used in several military and commercial applications, e.g., windows and domes for spacecraft and outer transparent armor.
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N A Rubinkovskiy et al. Consolidation of Transparent ALON by Spark Plasma Sintering Methods, IOP Conference Series: Materials Science and Engineering (2017). DOI: 10.1088/1757-899X/218/1/012015