Topic: Transparent aluminum (Read 1574 times)

Stormbringer · « **on:** August 23, 2004, 10:47:16 am »

http://physicsweb.org/article/news/8/8/9

And actually aluminum is capable of a grain size that would make light photons ignore it. get the grain size smaller than the wave length of visible light, and walla! trransparent aluminum. But if you remember the movie, scoty's formula looked like a complex molecule. So this article is closer to what he showed on "computer."

Gambler · « **Reply #1 on:** August 23, 2004, 10:51:29 am »

Once again the geeks step towards making science fiction into science fact.

Ravok · « **Reply #2 on:** August 23, 2004, 11:06:48 am »

And people make fun of us, for dreaming?

Thanks again Storm!!!

Good to hear from you again.

I have really missed your Science posts.

Stormbringer · « **Reply #3 on:** August 23, 2004, 11:24:01 am »

No problem I don't post here as much because I cannot get used to the look and feel of it.

That and the hostile and arrogant tones of a handful people I know to be full of crap but completely insistent that thier worthless and harmful political views are correct. You won't see much of me until after november.

Ravok · « **Reply #4 on:** August 23, 2004, 11:53:42 am »

I know who you are refering to. Its beginning to wear on me as well.

And to be honest i really can't wait untill November. All of this political BS is making me numb.

Death_Merchant · « **Reply #5 on:** August 23, 2004, 12:56:12 pm »

Hate to rain on the geek parade guys......

This is a type of nanocrystalline alumina (ie. Al2O3), not aluminum.

Big difference: One is a ceramic, the other a metal

Edit: More info than you want follows

Nanophase Al IS an active research area, but not for transparency. Nanophase Al (grain < 100nm, while typical Al has grains > µm) has shown higher specific strength. In metals, grain boundaries typically act as dislocation barriers. This leads to strengthening of the Al -> small grains = more boundaries = more stiffening.

To the naked eye, it looks exactly like regular aluminum.

Lono · « **Reply #6 on:** August 23, 2004, 10:35:39 pm »

Ahhhhhhh !!!!!!!! MOLES!!!!!!

Ahh ackk AKKKKK!!!!!!

Very cool article however...

Mentat Jon · « **Reply #7 on:** August 23, 2004, 10:45:51 pm »

Funny I guess Gene was right again, he was just a few hundred years off, we already have commuitcators ( cellphones)

all we need now is transwarp drive

E_Look · « **Reply #8 on:** August 23, 2004, 11:10:54 pm »

Quote

Nanophase Al IS an active research area, but not for transparency. Nanophase Al (grain < 100nm, while typical Al has grains > µm) has shown higher specific strength. In metals, grain boundaries typically act as dislocation barriers. This leads to strengthening of the Al -> small grains = more boundaries = more stiffening.

I wonder if it begins to exhibit quantum confinement effects. THAT would be cool... ah, at least to me!

Stormbringer · « **Reply #9 on:** August 24, 2004, 12:57:20 am »

Quote from: E_Look on August 23, 2004, 11:10:54 pm

Quote
Nanophase Al IS an active research area, but not for transparency. Nanophase Al (grain < 100nm, while typical Al has grains > µm) has shown higher specific strength. In metals, grain boundaries typically act as dislocation barriers. This leads to strengthening of the Al -> small grains = more boundaries = more stiffening.

I wonder if it begins to exhibit quantum confinement effects. THAT would be cool... ah, at least to me!

well if you remember I posted a year or so ago that scientist had concluded the grainsize of aluminum could be made small enough to allow transparency. It was just a matter of gettingthen uniformly that small so thatthe grains could not absorb visible wave lengths.
I knew that this was not alumium metal but I thought it was a ceramic that contained the metal. If you remember Scotty displayed a complex molecule on the computer when showing the factory chief the transparent aluminun. Which means trek TA is not a metal either.

Death_Merchant · « **Reply #10 on:** August 24, 2004, 01:04:56 pm »

Gents...
You're making me feel as curmudgeonly as my avatar....
but this needs to be said: In the interest of good science...

Star Trek is fiction.
Transparent Aluminum is fiction. The "complex molecule formula" was created by a graphics artist.
and the Mac Plus shown in the movie could NEVER do what Scotty showed.
Heck, my G5 now can't.....
type...type...type...voila! A complete description of the atomic arrangement of a new material + spinning graphics! LOL

BTW: I loved the entire scene. Even if it scientifically is ludicrous...

Talking about grain size relative to transparency is not entirely accurate.
Think more along the lines of photon interaction with the electrons of a material:

Possibilities:
1) An electron absorbs the energy of the photon and sends it back out the way it came in (reflection)
2) An electron absorbs the energy of the photon and transforms it (usually into heat)
3) An electron absorbs the energy of the photon and stores it (fluorescence or phosphorescence)
4) An electron cannot absorb the energy of the photon, ie the photon continues on its path (transmitted)

Sub-atomic interaction is a relatively minor factor.
More important is the ordering of atoms.
Gases are mostly transparent due to the dispersed and random nature of the atoms positions.
Same (but less so) for liquids.
Solids are highly ordered (think of a stack of tightly packed ping-pong balls). Metals are predominately crystalline.

Aluminum, for example, is a cubic structure (actually face centered cubic)

A Grain = a region with the same crystallographic orientation.
Even if the grain size were reduced to ~ one unit cell as shown above: It would still be opaque to visible light.

There are amorphous metals (now only made in small quantities, usually by rapid spray forming),
but they also are opaque.

In the image below is a simply representation of a crystalline metal (if Al, each dot is a unit cell of ~ 4 atoms)

Now this is an amorphous metal:

As you can see, light cannot pass without interacting. The only way to make it transparent is to make it very, very thin.

Silica (window) glass has a similar amorphous structure, but it's much more widely spaced.
Al alloys simply don't like being that widely spaced.

Whatever Scotty is going on about...it ain't an Al alloy. It can't be.

Let's just say "transparent Aluminum" is a trademark name (like Kleenex, lol) and leave it at that...

Just plain old Punisher · « **Reply #11 on:** August 24, 2004, 05:17:01 pm »

How do we know he didn't invent the thing?

E_Look · « **Reply #12 on:** August 24, 2004, 10:10:30 pm »

Hey Death Merchant,

I think we all knew that more or less; I was just wondering if, say like gold, or some of the compound semiconductors that if a crystallite was shrunken down enough, would it be a quantum dot! I mean... that'd be great, as cheap as aluminum is... and relatively nontoxic unlike other QD materials that are currently played with.

But since you broached the subject (and you're the physicist), what prevents a non-direct gap crystal from emitting light? Never mind the textbook explanation... I mean, if it takes a photon PLUS a phonon to provide enough energy to make the excitonic transition, what mechanism(s) exists in the lattice that would prevent a "reverse" process, that is, emission of a photon plus some phonon that would be propagated through the lattice? In other words, why is the recombination process in a indirect gap material nonoptical? Why does the energy get dispersed through other means?

P.S., Stormbringer- I truly apologize for the hijack.

Stormbringer · « **Reply #13 on:** August 24, 2004, 11:23:50 pm »

You mean....(gasp!) Trek ain't real?!

Ravok · « **Reply #14 on:** August 24, 2004, 11:27:27 pm »

Blasphemer!!!!! He is not of the body!!! We must call the law givers!!!

Just plain old Punisher · « **Reply #15 on:** August 25, 2004, 07:36:18 pm »

::gets out the blender::

I think for this case we'll use the "ice crusher" setting.

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