Re: transparent aluminum

From: Mike Lorrey (
Date: Mon Feb 25 2002 - 10:11:47 MST

Doug Jones wrote:
> justin corwin wrote:
> >
> > This small item details the apparent manufacture of small quantities
> > of "tranparent aluminum"
> >
> >
> >
> > it's listed as a weapon's technology, but i have to wonder, is this kind
> > of thing useful as a spacecraft material? and baking extremely finegrained
> > aluminum into transparency kind of implies this can be done to other
> > metals. titanium windows, anyone?
> I get really exasperated with sloppy terminology and incompetent
> reporting. It's transLUCENT aluminA, not transparent aluminum, dammit.
> It's simply sintered aluminum oxide with particles significantly less
> than 500 nm, so that it scatters visible wavelengths poorly. If you
> want it actually transparent, hell, just use crystalline alumina- better
> known as sapphire. 'Taint cheap, though. The sintered material is
> probably tougher than sapphire, but still very brittle. Glass makes
> lousy armor.

On the contrary, ceramic materials are the new thing in body armor as
well as in heavy military equipment. There was an interesting show on
Discovery a week or so ago about an armored vest which sandwiches a 1/4"
plate of sintered ceramic between a couple thin sheets of kevlar.
Effective against AP rifle rounds, even.

> Metals are inherently opaque precisely because they are electrically
> conductive- once you get more than a few skin depths of material, the EM
> field gets attenuated away to nothing. Transparent aluminum or any
> other metal is physically impossible. It ain't often that I can state
> something with such confidence.

The only way to have your cake and eat it with transparent metals is to
honeycomb it with transparent crystals.

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