Scientists perfect material that looks like glass, acts like armor, molds like plastic
NRL researchers develop inexpensive process for sintering magnesium aluminate powder into transparent spinel sheets.
“The advantage [of spinel] is it’s so much tougher, stronger, harder than glass,” he says. “For weight-sensitive platforms—UAVs [unmanned autonomous vehicles], head-mounted face shields—it’s a game-changing technology.” Spinel could also be used, he adds, to make consumer electronics, like smart phones, with screens that may chip but don’t crack or shatter when dropped.
According to Sanghera, the ceramic material’s dense polycrystalline structure deflects and dissipates impact energy, whereas a crack in glass goes all the way through. Also, unlike glass, spinel transmits infrared light. Currently, the military is considering using spinel as transparent and light-weight armor for vehicles and face shields, in place of bullet-proof glass, as well as to protect visible- and infrared-wavelength cameras on planes and in other harsh-environment applications.
Past attempts to produce transparent spinel required melting magnesium aluminate in a crucible at 2000C, an expensive and ultimately impracticable process due to introduced impurities. NRL new method sinters the powered in a vacuum press at relatively low-temperatures. In addition, the team also refined the purity of the chemicals used to ensure that the sheets are uniformally clear and free of air bubbles.
Beyond flat sheets, sintering also allows for the production of curved forms, depending on the shape of the press. And, like a gem stone, the material can also be ground and polished to remove any surface irregularity introduced by the press.
To date, NRL researchers say they have made eight-inches diameter pieces but, with the new process, sheet size is limited only by the size of the press. “Ultimately, we’re going to hand it over to industry, so it has to be a scalable process,” says Sanghera. “We licensed the technology to a company who was able then to scale that up to much larger plates, about 30-inches wide.”