[Suicide Junkie]

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(from slashdot)This isn't transparent aluminum; this is a transparent aluminum oxide. That is just not the same thing as aluminum anymore then water is Hydrogen gas, or table salt is the same thing as Sodium metal or Chlorine gas (both very harmful chemicals, sodium can explode when it comes in contact with water, and Chlorine can kill you in a few breaths, yet we eat salt all the time)

And secondly we have known about aluminum based compounds for a long time, in fact, longer then we have known about Aluminum or even about elements in general. Alum, the compound from which aluminum gets it's name (and which we extract aluminum from) has been known to man for ages and is, in fact, transparent.

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Bottom line is that alumina (Al2O3) and aluminum (Al) are totally different materials, so naturally they have different properties such as hardness, stiffness, transparency, etc. Alumina is what sapphires and rubies are made of. Pure alumina is clear, but the addition of color centers like chromium ions results in the color of gemstone rubies and sapphires. A search for sapphire conformal optics [google.com] will show you that making windows out of sapphire for military applications is nothing new. Just about the only thing that might be new is how they make the sapphire, but the article does not provide any details about that. Yes, sapphire is cool stuff, but it's not some magical new material.

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