Bulletproof transparent material for unbreakable smartphones

US Navy researchers, including one of Indian-origin, have developed a bulletproof transparent material that may allow for glass windows that are tough like armour or smartphone screens that don't break when dropped.
The US Naval Research Laboratory (NRL) has been researching a special ceramic called spinel over the last 10 years.
"Spinel is actually a mineral, it's magnesium aluminate," said Dr Jas Sanghera, who leads the research.
"The advantage is it's so much tougher, stronger, harder than glass. It provides better protection in more hostile environments - so it can withstand sand and rain erosion," Sanghera said.
As a more durable material, a thinner layer of spinel can give better performance than glass.

"For weight-sensitive platforms-UAVs [unmanned autonomous vehicles], head-mounted face shields - it's a game-changing technology," Sanghera said.

NRL has invented a new way of making transparent spinel, using a hot press, called sintering. It's a low-temperature process, and the size of the pieces is limited only by the size of the press.
In the lab, Sanghera made pieces eight inches in diameter.
"Then we licensed the technology to a company who was able then to scale that up to much larger plates, about 30-inches wide," he said.
The sintering method also allows NRL to make optics in a number of shapes, "conformal with the surface of an airplane or UAV wing," depending on the shape of the press.

In addition to being tougher, stronger, harder, Sanghera said spinel has "unique optical properties; not only can you see through it, but it allows infrared light to go through it."
That means the military, for imaging systems, can use spinel as the window because it allows the infrared light to come through.
The spinel NRL makes is a polycrystalline material, or a lot of crystal particles all pressed together.
Whereas with glass, a crack that forms on the surface will go all the way through, spinel might chip but it won't crack, Sanghera said.
The spinel has a lot of applications, said Sanghera.

He mentioned watches and consumer electronics, like the smartphone, as examples.
The military in particular may want to use spinel as transparent armour for vehicles and face shields.
The military's also interested in using spinel to better protect visible and infrared cameras on planes and other platforms.
Glass doesn't transmit infrared, so today's optics are made of exotic materials that are very soft and fragile, and have multiple layers to compensate for colour distortions.