CrazyNeutrino said:
Transparent magnesium aluminate
Researchers finding applications for tough spinel ceramic
Imagine a glass window that’s tough like armor, a camera lens that doesn’t get scratched in a sand storm, or a smart phone that doesn’t break when dropped. Except it’s not glass, it’s a special ceramic called spinel {spin-ELL} that the U.S. Naval Research Laboratory (NRL) has been researching over the last 10 years.
“Spinel is actually a mineral, it’s magnesium aluminate,” says 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.”
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Reading more closely, I now understand the problem and the effort required to solve it. Just about any mineral can be made from melt, artificial diamonds for example are difficult but possible.
But whereas sintering at low temperatures is much easier, I’ve never before heard of getting a clear mineral by sintering. It always comes out opaque or at best cloudy. This team has cracked the problem of getting a transparent window of spinel out of sintered powder, and that’s a big breakthrough.
On price, corundum from melt is available at $50-100 US per kilogram. That’s a spectacularly low price for a transparent gemstone with Mohs hardness 9, but it’s not the right shape or size for window glass.
Uncut cubic zirconia has Mohs hardness 8 (harder than spinel) and is available at $8-60 US per kilogram. Again not usually the right size or shape for window glass.
Some minerals other than spinel, including sapphire and diamond, are suitable as transmission of IR radiation.