Is transparent aluminum even remotely possible?

[Ficer67]

In the movie, Star Trek IV - The Voyage Home, Mr. Scott trades the formula for transparent aluminum for a quantity of plastic. That’s great for the movie. But is transparent aluminum even remotely possible?

Thanks

Ficer67

[running_coach]

Kinda.

[Ficer67]

I guess that answers my question. I don’t know why I did not find that in Wikipedia…

Thanks Running Coach

[Captain_Amazing]

There are transparent aluminum compounds, like Aluminium oxynitride, marketed as ALON, which is a ceramic that’s being considered as armor, because it’s bullet resistant and lighter than bullet resistant glass. It’s also more expensive to make though, which is why it’s not yet in common use.

Still, if you want to see a piece get shot, and how it compares to traditional bullet resistant glass, check here:

Surmet's ALON® Transparent Armor 50 Caliber Test

[cochrane]

From Wikipedia:

Pure transparent aluminum was created as a new state of matter by a team of scientists in 2009. A laser pulse removed an electron from every atom without disrupting the crystalline structure.[3] However, the transparent state lasted for only 40 femtoseconds, until electrons returned to the material.

[eltro102]

Aluminium Oxide makes transparent crystal

[eltro102]

(more commonly known as sapphires)

[picunurse]

Glass is just transparent sand… Well, special sand (Modern day glass is 75% silica (SiO2) which comes from quartz in sand, plus 13% sodium oxide (Na2O) and 10.5% calcium oxide (CaO). Other minor additives include 1.3% aluminum oxide (Al2O3), 0.3% potassium oxide (K2O), 0.2% sulfur trioxide (SO3), 0.2% magnesium oxide (MgO), 0.04% iron(III) oxide (Fe2O3), and 0.01% titanium oxide (TiO2).

[njtt]

Calling aluminium oxynitride (or aluminium oxide) “transparent aluminium” is a bit like calling water “drinkable oxygen”.

[Learjeff]

Well frankly, we wouldn’t even want transparent pure elemental aluminum. Aluminum isn’t very strong structurally unless alloyed. Yet we still often call things made of aluminum alloys “aluminum”, albeit, inaccurately.

[TriPolar]

I have noticed that you can see through aluminized mylar. I assumed that was because the aluminum coating had enough holes in it too allow a very dimmed view through it when held close to the eyes. But I’ll ask anyway, is it possible that a thin enough layer of aluminum allows light to pass through?

I’ll note that any aluminum exposed to the oxygen has a passivating layer of aluminum oxide on it, so to be transparent under normal circumstances that oxide would have to be transparent also.

[running_coach]

@Learjeff

Well frankly, we wouldn’t even want transparent pure elemental aluminum. Aluminum isn’t very strong structurally unless alloyed. Yet we still often call things made of aluminum alloys “aluminum”, albeit, inaccurately.

And Derek Zoolander will have a new look; “Clear Steel”.

[jz78817]

@TriPolar

I have noticed that you can see through aluminized mylar. I assumed that was because the aluminum coating had enough holes in it too allow a very dimmed view through it when held close to the eyes. But I’ll ask anyway, is it possible that a thin enough layer of aluminum allows light to pass through?

sure. the shiny part of a CD is a thin vapor-deposited coating of aluminum. light passes through it.

[CalMeacham]

I did an article on transparent metal for Optics and Photonics News some years ago. Very thin metals, like gold and silver, will actually transmit visible light, but we’;re talking about thicknesses like that of gold leaf.

Alkali Metals (Lithium, sodium, potassium, cesium) are actually transparent in the ultraviolet, but for the heavier ones it edges up into the edge of the visible. Of course, they’re also highly reactive, so you’d want them sandwiched between quartz plates or something.

In both these cases, there’s no weird or special circumstances needed. You’re not looking through vapor or plasma or anything, but through bulk metal (albeit not a lot of bulk).

I’d also point out an article that appeared in Skeptical Inquirer several years ago where someone interpreted a story from Classical Rome about someone who had a malleable optical material as referring to aluminum. Although how someone in the classical world got a bulk sample of aluminum, or how they thought the aluminum was transparent is beyond me.

In Hugo Gernsbach’s Adventures of Ralph 124C41+, Ralph (the fictional character, not the Doper) uses high frequency radio waves to see through solid metal. Gernsbach based his assertion on something he found in another technical magazine, but I haven’t been able to obtain a copy of that issue. Whatever it was, he obviously misinterpreted it, or else it was an enthusiastic and not very accurate report, because we don’t have anything like that now.

[Learjeff]

So, what makes glass or water transparent?

It’s not surprising to me that some materials reflect photons (some scattering them, others not), and others absorb them. Or, more accurately materials reflect some frequencies and absorb others. But what property makes it so it can pass right through?

I suppose the question applies to gases, too, assuming it’s not the low density that makes them transparent.

(Thanks!)

[njtt]

@Learjeff

Well frankly, we wouldn’t even want transparent pure elemental aluminum. Aluminum isn’t very strong structurally unless alloyed. Yet we still often call things made of aluminum alloys “aluminum”, albeit, inaccurately.

Alloys are very different things from compounds. Aluminium oxynitride is not an alloy of aluminium, any more than water is an alloy, or mixture, of oxygen and hydrogen.

[Learjeff]

Ah well, should have wiki’d first:

@wiki

At the electronic level, absorption in the ultraviolet and visible (UV-Vis) portions of the spectrum depends on whether the electron orbitals are spaced (or “quantized”) such that they can absorb a quantum of light (or photon) of a specific frequency, and does not violate selection rules. For example, in most glasses, electrons have no available energy levels above them in range of that associated with visible light, or if they do, they violate selection rules, meaning there is no appreciable absorption in pure (undoped) glasses, making them ideal transparent materials for windows in buildings.
At the atomic or molecular level, physical absorption in the infrared portion of the spectrum depends on the frequencies of atomic or molecular vibrations or chemical bonds, and on selection rules. Nitrogen and oxygen are not greenhouse gases because there is no absorption because there is no molecular dipole moment.

I think I get the idea: as long as the light doesn’t match the filtration allowed by the orbitals et al, it passes right through. If it matches, various things can happen (absorption, re-radiation, etc.)

Feel free to elucidate. Based on that oversimplification, it’s just a matter of whether Al’s electrons can be coaxed into orbits with specific characteristics.

Are there substances that are opaque unless combined in a mixture or alloy? Can alloys affect electron orbits?

[Learjeff]

@njtt

Alloys are very different things from compounds. Aluminium oxynitride is not an alloy of aluminium, any more than water is an alloy, or mixture, of oxygen and hydrogen.

Yes, I know. I should have said “for example”. But I bet we have compounds that get simplified in common language to the principle element too. Can’t think of any examples, so maybe I’m just plain wrong.

[Learjeff]

Thinking out loud: metals have crystalline structure. Alloys have different crystalline structure than pure metals. Degrees of motion are a function of crystalline structure, and thus can affect transparency. Correct? But there’s still the selection rules at the electronic level …

so much to learn, so little time!

[Bert_Nobbins]

@jz78817

sure. the shiny part of a CD is a thin vapor-deposited coating of aluminum. light passes through it.

Completely untrue. The aluminium layer is there to reflect the laser light back to the photosensor. You do realise the data is on the TOP side of a CD?