Transparent aluminum -- this time for real? Well, not quite.

[Christopher]

It seems like every couple of months for the past few years, there's been a news item crowing "Transparent aluminum has been invented!" and it's really been about a tough transparent ceramic/glass made of alumina, aka aluminum oxide, aka corundum or emery, which isn't aluminum any more than water is hydrogen (and is the main component of rubies and sapphires, so its transparency isn't really surprising). So when I saw the TrekToday news item over on the right of the page, my initial reaction was, "Oh, not this again!"

But it turns out that this time, scientists really have made aluminum, the metal, transparent using an x-ray laser to turn it into an exotic state of matter by knocking electrons out of its atoms. Of course, it's not quite the "transparent aluminum" seen in Trek; it was only transparent to extreme ultraviolet radiation (which isn't transparent at all by the normal definition), and it only stayed that way for 40 femtoseconds (40 quadrillionths of a second). So while the other stuff was transparent but wasn't actually aluminum, this is really aluminum but isn't really transparent in any practical sense. Still, it's interesting, and the technique for altering the electron shells of materials to alter their properties could have all sorts of potential if scientists can find more practical uses for it than marginally approximating something mentioned in a sci-fi movie. (I wonder if there was any scientific reason for choosing aluminum, or if they just went with it so they could get the headline. You can always get more media attention for a scientific breakthrough if you can pretend it resembles something from Star Trek or another sci-fi franchise, because reporters don't understand or care much about science for its own sake.)

http://www.sciencedaily.com/releases/2009/07/090727130814.htm

(EDIT: It just occurred to me that maybe this should be in Science and Technology instead. Maybe the mods should move it?)

 

[CuttingEdge100]

This should probably be under science and technology...

 

[Gepard]

You know, I saw the title of this thread without seeing who posted it, and my first thought was, "great, another thread that'll drive Christopher batshit."

 

[Technobuilder]

^Hehe. I thought the same thing when I noticed the link to the article on the front page and decided to track down the inevitable thread.

 

[Patrickivan]

Let's just keep in mind that what they're calling this material, is based on what it was, and not what it became. And there's nothing wrong with that. From reading it, they don't hide the fact that this is a new material. "Transparent aluminium" would no doubt be the product name if it ever achieved marketable fruition.

There are a few people here that are quite vocal on the subject of "transparent aluminium". I can't wait!

 

[Christopher]

It's still aluminum, it's just aluminum that had its electron-shell properties briefly altered in a way that rendered it transparent to far UV radiation. It's a new state of matter, not a new material. States of matter are things like solid, liquid, gas, and plasma. Solid aluminum and molten aluminum are both still aluminum, just in different states.

And as the article says, the significance of this is not in the specific material itself, but in the technique used to create it and the ramifications it has to our understanding of science. By studying such extreme states of matter, we can learn new things about the behavior of matter in extreme planetary or stellar conditions, perhaps gain insights into the way stellar fusion works and come closer to harnessing fusion power as a practical energy source. This is about a scientific principle, not a single material. Unfortunately, the news media are idiots when it comes to science, and care more about "Gee, that sounds coincidentally like something somebody made up for a sci-fi show!" than they care about "Gee, that's a broad scientific principle that could enhance our understanding of the universe!"

 

[Patrickivan]

^ I suppose I misuderstood when I read:

"knocked out’ a core electron from every aluminium atom in a sample without disrupting the metal’s crystalline structure."

I interpreted that as the atomic structure being altered with the removal of those atoms. (That doesn't happen when you melt aluminium, does it?). But hey, I'm no science guy, I'm just a layman.

 

[Christopher]

Electrons have nothing to do with the atomic structure that defines an element's identity. It's the number of protons in the nucleus that defines an element, and the number of neutrons that defines an isotope of the element. Electrons occupy various energy levels or "shells" around the nucleus (generally misrepresented in science classes as "orbits" around the nucleus like planets around a star). The electrons in the outermost shell, the valence electrons, are the ones that determine an atom's bonding behavior (the way it forms compounds and crystals) as well as its optical, thermal, and conductive properties -- the way it interacts with light, heat, electricity, and magnetism. The reason some materials are opaque and others are transparent is because of the way their valence electrons interact with light, either absorbing and scattering it or transmitting it. The core electrons are those residing in the inner shells, the ones that don't contribute materially to the element's behavior.

When the scientist in the article says, "In certain respects, the way it reacts is as though we had changed every aluminium atom into silicon," he means that the outermost electron shells of the aluminum atoms were changed to behave like those in silicon, which is the next element up on the periodic table. Now, aluminum (element 13) normally has 2 electrons in the base level, 8 in the second level, and 3 in the outer level, while silicon (element 14) has 2, 8, and 4. If one of the 10 core electrons was excited into jumping up to the valence level, then you'd have aluminum atoms with 1, 8, and 4 electrons in the first three shells. That would mean that the outermost shell would have the same number of electrons as a normal silicon atom, and so you'd get optical properties analogous to those of silicon. That's an unstable configuration, like taking a book from the bottom of a stack and sticking it on top, so naturally it promptly collapsed back into the standard 2:8:3 configuration. That's what makes it a novel state of matter -- the fact that the gap was down at the bottom of the "stack" instead of up in the valence level. Normally if you excite or ionize an atom, it's the valence electrons that get bumped up to higher shells or kicked out altogether.

 

[jefferiestubes8]

This should probably be under science and technology...

I posted it yesterday here:
The science of "Star Trek"
http://www.trekbbs.com/showpost.php?p=3239828&postcount=29

 

[Christopher]

It turns out this stuff is a lot more interesting than the "transparent aluminum" description suggests. It's basically an example of this:

http://en.wikipedia.org/wiki/Warm_dense_matter

And calling it "warm dense matter" is an understatement. We're talking something that's halfway between solid and plasma, as dense as a solid but with temperatures of tens of thousands of degrees, way above the temperature that would normally turn just about anything into vapor. This is stuff you'd find in ultra-hot, ultra-dense conditions like the middle of a star or a nuclear explosion. Calling it "transparent aluminum" is just nonsense. It sounds so sedate and inert compared to what it really is.

Or actually, looking over the abstract to the paper, the transparent phase comes between the initial x-ray irradiation and the aluminum's transition to "the warm dense matter regime." So first it becomes transparent (to UV) for a fraction of an eyeblink, then it becomes something really interesting.

 

[DEWLine]

Transparent to extreme UV, no matter how briefly, does not strike me as particularly useful. Transparent to visible light, whilst shielding against UV, however?

That would be a preferred end-goal of the research in progress, yes?

(And perhaps from there to similarly-treated steel alloys?)

 

[Patrickivan]

Electrons have nothing to do with the atomic structure that defines an element's identity. It's the number of protons in the nucleus that defines an element, and the number of neutrons that defines an isotope of the element. Electrons occupy various energy levels or "shells" around the nucleus (generally misrepresented in science classes as "orbits" around the nucleus like planets around a star). The electrons in the outermost shell, the valence electrons, are the ones that determine an atom's bonding behavior (the way it forms compounds and crystals) as well as its optical, thermal, and conductive properties -- the way it interacts with light, heat, electricity, and magnetism. The reason some materials are opaque and others are transparent is because of the way their valence electrons interact with light, either absorbing and scattering it or transmitting it. The core electrons are those residing in the inner shells, the ones that don't contribute materially to the element's behavior.

When the scientist in the article says, "In certain respects, the way it reacts is as though we had changed every aluminium atom into silicon," he means that the outermost electron shells of the aluminum atoms were changed to behave like those in silicon, which is the next element up on the periodic table. Now, aluminum (element 13) normally has 2 electrons in the base level, 8 in the second level, and 3 in the outer level, while silicon (element 14) has 2, 8, and 4. If one of the 10 core electrons was excited into jumping up to the valence level, then you'd have aluminum atoms with 1, 8, and 4 electrons in the first three shells. That would mean that the outermost shell would have the same number of electrons as a normal silicon atom, and so you'd get optical properties analogous to those of silicon. That's an unstable configuration, like taking a book from the bottom of a stack and sticking it on top, so naturally it promptly collapsed back into the standard 2:8:3 configuration. That's what makes it a novel state of matter -- the fact that the gap was down at the bottom of the "stack" instead of up in the valence level. Normally if you excite or ionize an atom, it's the valence electrons that get bumped up to higher shells or kicked out altogether.

If I'm understanding, it's like a +/- charged electron? Nothing like the removal of an enitre atom, say like spliting up a water molecule in to 2 more basic elements...

It's been 13 years since my college chemistry class, and my brain just does not retain things I don't use. Or much of anything anymore.

Damnit.

 

[Christopher]

Transparent to extreme UV, no matter how briefly, does not strike me as particularly useful. Transparent to visible light, whilst shielding against UV, however?

That would be a preferred end-goal of the research in progress, yes?

(And perhaps from there to similarly-treated steel alloys?)

Look, just forget about the "transparent aluminum" hype. It's misleading. This isn't about making aluminum into a clear building material like in Star Trek. This is about the discovery of a new exotic phase of matter found in conditions of extreme temperature and density such as one would find in the core of a star or a nuclear fusion reaction. It's a transitional state that only exists for a split-second in conditions that would kill you almost as quickly. It's an esoteric discovery that might provide new insights into planetary and stellar physics, nuclear reactions, things like that. It might conceivably give us information that could help us achieve practical fusion reactors. It's got absolutely nothing whatsoever to do with building materials. As usual, the media are misrepresenting this news.

If I'm understanding, it's like a +/- charged electron? Nothing like the removal of an enitre atom, say like spliting up a water molecule in to 2 more basic elements...

All electrons are negatively charged. Their positively charged antiparticles are called positrons.

This is about removing electrons from their shells around the aluminum atoms. For a split-second, the electron shells are in an artificially excited state where one of the core electrons is bumped up to the valence level. Then the electrons apparently get knocked out of the atoms altogether, and the solid becomes analogous to a plasma, made up of ionized atoms and with a temperature of tens of thousands of degrees. By all rights, it should fly apart, because the positive charges of the atoms should repel each other, but because of the extreme pressure it's under, it maintains the density and structure of a solid.