What’s The Deal With Transparent Aluminum?

It looks like a tube made of glass but it’s actually aluminum. Well, aluminum with an asterisk beside it — this is not elemental aluminum but rather a material made using it.

We got onto the buzz about “transparent aluminum” as a result of a Tweet from whence the image above came. This Tweet was posted by [Jo Pitesky], a Science Systems Engineer at the Jet Propulsion Lab in Pasadena. [Jo] reported that at a recent JPL technology open house she had the chance to handle a tube of material that looks for all the world like a section of glass tubing, but was billed as transparent aluminum. [Jo] tweeted this because it was an interesting artifact that few people get to play with and she’s right, this is fascinating!

The the material itself is intriguing, and I immediately had practical questions like what is this stuff? What is it good for? How is it made? And is it really aluminum rendered transparent by some science fiction process?

Can Aluminum Be Transparent?

As with many things in life, the answer to that question is, “It depends.” In this case, it depends on how you define aluminum. Or more precisely, it depends on what your expectations are for a material that purports to be aluminum. Regular old aluminum is an abundant metal with all the expected properties of metals — electrically and thermally conductive, ductile, malleable, and lustrous. You can melt it and cast it into useful shapes, beat it flat into a foil to wrap a sandwich, or crush an empty can made from it against your forehead, if you’re so inclined.

ALON blocks after polishing. Source: Surmet Corp

If you’re expecting transparent aluminum to have all of those properties, you’ll be disappointed. Although she doesn’t identify the material specifically, the material [Jo] got to handle was most likley not a metal at all, but a ceramic called aluminum oxynitride, composed of equal parts aluminum, oxygen, and nitrogen and known by the chemical formula AlON.

Aluminum oxynitride ceramics have been around since the 1980s, so it’s not new stuff by any means. Coincidentally, AlON development was underway more or less at the same time that Star Trek IV: The Voyage Home was being produced; it was from the now classic scene from that film were Scotty uses a mouse as a microphone in an attempt to trade the formula for “transparent aluminum” for sheets of plexiglass that AlON and similar transparent ceramics get their colloquial name.

What’s It Good For?

Despite clearly not being a metal — and not a glass either; glasses are amorphous solids, while ceramics are crystalline — AlON and the other transparent ceramics that have been developed since have some amazing properties. AlON, marketed as the uncreatively named ALON by its manufacturer, Surmet Corporation, is produced by sintering. Powdered ingredients are poured into a mold, compacted under tremendous pressure, and cooked at high temperatures for days. The resulting translucent material is ground and polished to transparency before use.

Aside from being optically clear, ALON is also immensely tough. Tests show that a laminated pane of ALON 1.6″ thick can stop a 50 caliber rifle round, something even 3.7″ of traditional “bullet-proof” glass can’t do. ALON also has better optical properties than regular glass in the infrared wavelengths; where most glasses absorbs IR, ALON is essentially transparent to it. That makes ALON a great choice for the windows on heat seeking missiles and other IR applications.

On the downside, ALON is expensive — in the armored glass market, it’s about 5 times the price of traditional laminated glass. But it has so many benefits, not least of which is superior scratch resistance, that for some applications it’s the material of choice. Chances are good that increased demand for the material will drive costs down, and it may not be long before Gorilla Glass is replaced by transparent aluminum smartphone screens that might actually damage the pavement when you drop your phone.

So, sorry Scotty — there’s no such thing as transparent aluminum metal. But the stuff we’re calling transparent aluminum is just as fascinating and just as sci-fi as it sounds. Isn’t material science cool? If you have other interesting materials like AlON that we should dig into, let us know about it in the comments below.

[image Source: Screen Rant, Memory Alpha]

139 thoughts on “What’s The Deal With Transparent Aluminum?

  1. That seems like it would make very fine fireplace/wood stove glass if it allows so much IR passthrough. You would get much better radiant heat I think. Am I correct in assuming that the oxynitride means that the aluminium atoms are no longer exposed in a way to be reactive to oxygen? IOW this stuff won’t oxidize? That was my first question when I saw the words “transparent aluminium”, which seems to be something of a misnomer, because aluminium normally oxidizes very rapidly, and nobody would want a window that tarnished quickly.

    1. One of the benefits of using standard (borosilicate) glass *is* that it absorbs IR light. The absorption at a given wavelength is equivalent to the black body emission at that wavelength (Kirchhoff’s law) – as the glass gets hot, it emits tons of IR. The longer wavelengths of IR are more effective in warming the surrounding area than the vis/nir/mwir that would escape with ALON or other IR transparent substrates.

      1. How does that work in more layman’s terms? A fire emits a broad spectrum of IR. All of it gets converted to heat at the surface of the room, regardless of if it gets re-emitted at lower frequencies or not, correct?

      2. That’s a common myth. You should not run a fireplace with the doors closed in most cases. It is less efficient (heat) and also risky for the doors.

        The doors are strictly there to manage the fire at the end of burning when you’re not around. When the fire burns out, but you’re sleeping, you can’t close the damper – that would allow a clear path to the sky from inside. So you close the doors instead.

        They also block embers from a dying fire from sparking into the room when you aren’t around to monitor it.

        This link covers it very well.

        1. Probably worth mentioning that some fireplaces are absolutely designed to run with their doors closed and sealed. The reburners/secondary combustion burners/fire box type fireplaces you commonly find all over the place are totally designed to run with their doors shut. Airflow around the box is tightly controlled and allows you to throttle the burn rate. They all (as far as I’m aware) have borosilicate glass though. ‘Open’ fireplaces definitely want their doors open. Tempered glass will definitely go bang if it gets too hot. They’re also typically less efficient than fireboxes – and harder to get permits for (don’t think you can in NZ urban areas anymore).
          If you have a fireplace and aren’t sure – read the manual.
          Fireboxes with open doors can get pretty exciting pretty quick if you let them :-)

        2. In good old eco-fascist Germany (and meanwhile most of the EU), open fireplaces are now illegal … has something to do with polar bears or some other BS. Nah, seriously: all our fireplaces are now supposed to have (glass) doors. When done correctly, the wood burns cleaner. However, it is now very hard to distinguish a fireplace from a TV and we are chopping down trees “to save the climate” faster than our forests can reproduce biomass from the CO2 in the air…

          1. That does sound pretty bad. Maybe Hackaday could do an article on the current most successful and efficient ways countries are combating Global Warming?

          2. Simply Nonsense even in 2022 open fireplaces are still allowed in germany. What the need is a separate chimney. A dust filter might be necessary if the micro dust level is to high.

    2. Good point with the IR passthrough. This would also make it a great material for a lightbulb-style nuclear reactor, assuming UV is also fairly transparent and it has a high enough melting point. Ceramics are pretty good about that.

      I guess the material they billed for it in the fifties or so was quartz. And the specific impulse and thrust vs. mass wasn’t so great either. Gas core fission is hard. I wonder if this stuff would outdo quartz?

      1. Yes, al2o3, aluminum oxide when made as a single crystal is sapphire and when .05% chromium is added to it, it becomes ruby. In alumina’s polycrystaline form, it is white and not transparent at all. All measure 9 on the Moh’s scale of relative hardness.

    1. So how does aluminium go from a metal to an insulator. You increase the bandgap.
      Interestingly that’s also why things are transparent. Very difficult for metals to be transparent beause photons of light have to have the right energy to not be ‘caught’ by the conductivity=bandgap.
      Here’s an excellent-ish video.
      Would make a great hackaday article on this. Yay quantum mechanics.

      1. Actually that’s just the half of the answer in optically homogeneous cases. Why glass powder is not transparent? And the answer is the scattering. And in most cases that’s the answer why a material is not transparent.

  2. So what’s new here?
    Ruby’s are from Aluminium oxide and they have been made synthetically for 80 years or so.
    The “characteristic” red color of rubies is because of chrome inclusions and “clean” rubies (als called “sapphires” can be perfectly transparant.

    And for stuff like this you need a bit of a better definition of what “transparent” is.
    Some time ago I saw an IR cam shot of a sewing machine, and the weirdest part was that the black timing belt was almost completely transparant to the IR camera. The strengthening cords in the timing belt were clearly visible through the black rubber / polyurethane / whatever it was made of.

    1. ALON can be pressed and sintered – which is easier for fabrication than Sapphire (which is generally how the optics industry refers to Al2O3). Sapphire needs to be grown with a crystal puller. Unfortunately, the sintering process leaves inclusions that have hampered precision optical applicaitons to date.

      In terms of transparency, it’s good out to about 5um, much like Al2O3.

      1. Corundum is a crystalline form of aluminium oxide (Al2 O3). Corundum has two primary gem varieties, ruby and sapphire depending on the impurities.
        So Rubys are made from Aluminium oxide.

          1. Michael was, inadvertently or not, was showing how proper grammar doesn’t automatically lead to clear communication. If you’re going to be pedantic, at least make sure people understand you.

          2. BNBN I thought of that just after I hit Post Comment. If only it was possible to modify a comment after posting it, people who make minor mistakes could correct them. Too bad our technology does not allow for such a miracle.

            KingCogi PhD “Ruby made ruby lasers with Ruby’s rubies.” :p

          3. Michael – Use your favorite word processor like a HaD posting pre-processor. Use it to check your spelling, reformatting, and sanity-checker. THEN do a CTRL-A, then CTRL-C, return to the HaD blank field, click in it and hit CTRL-V, and only then hit (POST COMMENT). Remember only 1 hyperlink per post to avoid moderation. Or just cripple your links with spaces. Have a Google window up to check your facts too. Use Google’s define:word function to avoid using wrong word to describe something. The HaD grammar-police will pounce on you. Think about using GRAMMARLY.Its free and I think it may do about 90% what I said above. Or not…

            IMO – Also remember some HaD authors are running WordPress word filters that act like the infamous NSA Echelon. If you notice your post is not going through at all and gets mysteriously lost, it is ostensibly because of a trigger-word, a banned web site (or domain), or whatever. It wont go into HaD moderation just into a private HaD hell…

          4. Ostracus: Good idea. I just downloaded Grammarly as a plugin and it is trying to do something. Ah! there it is! And the first gotcha was “You spelled our name, incorrectly moron!” (no just kidding)- wow, it’s working quite well. My postings now have superpowers. Maybe I’ll stop being a sematics-butcher now. Or maybe not. :-(

      1. This looked sooo cool, until I watched these vidoes on youtube, and found all the comments, and then video evidence, of these dishes _exploding_ when they do break…. noooope. Not in my house.

        1. But the rest of the time the bounce! which is hilarious for something made out of glass. Also the plates are nice and thin so they’re easy to handle and pack tightly.

          1. Well, that bounce likely causes a fracture of some kind. Many people report just putting hot food on the plat, just washing it, or picking them up and exploding. Not even dropping or hitting them on anything.

            The bounce is not worth glass in the eyes. Seriously, go watch the videos and read comments. People saying the glass pieces explode like popcorn, even after the plate breaks. They literally _explode_ when they break. And the build up of flaws and fissures can cause an catastrophic explosion without notice.

            The fact that HAD has so many people up in arms about exploding PVC pipes used for potato guns, this product should be added to the list.

          2. We had tempered glass glasses in the company restaurant, and a tiled floor. Regularly someone would drop a glass and the whole restaurant would go quiet as everyone counted the bounces, five or six bounces was common, before the almost inevitable “poof”. The rare non-shatterings got a cheer.

        2. I have used Corelle as everyday dishware for decades, only had a few break, and they broke into a few large pieces, nothing like an “explosion”.
          Were the ones that “exploded” subjected to thermal shock?

          1. I experienced both “large pieces” and “explosion” failures of Corelle.
            Not a lot of either, but both.
            I suspect that like crystal, a small scratch/chip becomes the key of any failure. Reflections/distortions/shock waves become non-linear at a defect.

          2. Following up to my comment.
            The Great Caruso” was often asked to shatter a crystal wine glass with his voice.
            He wore a large diamond on a ring, and would surreptitiously scratch the glass before singing to aid in its breaking.

          3. Same here. I use Corelle every day. A couple dishes have chips in them, and I’ve never seen the “exploding” that people are describing.

        1. Unfortunately, much Pyrex-branded kitchen ware isn’t even borosilicate glass.
          Corning Visions cookware is, like AlON, not a glass but a ceramic. It is translucent, if you like to watch your food cook, and will survive extreme temperature swings, but its low thermal conductivity makes it perform poorly at heating evenly.

          1. They switched to regular soda lime glass in the late 90’s early 00’s. Apparently they found a process that gives very similar performance without messing around with borosilicate glass. You lose some thermal shock resistance but you don’t need the 400C range that older vitrelle formulations had.

      2. Growing up my mother had Corelle dishes, and they broke at the drop of a dime it seemed. And when they did they turned into super thin “cat claw” shaped shards that went everywhere ( mostly in peoples feet ). I’d rather have ceramic that break into larger chunks myself than glass that’s supposed to bounce, but when it doesn’t it is weaponized.

        1. We also had Corelle dishes when I was a child. I only remember having two, or maybe three, break. Mostly in large manageable pieces, but also with some of the “cat’s claws” you describe. We were very careful to sweep up after, and they caused no further harm.
          As a parent and owner of regular glass and ceramic dishes, I see much more breakage and even more (per dish) tiny sharp pieces. Annoying, but still just requires careful cleanup.

          Pick your poison. My wife likes pretty dishes, so we have the ones that don’t bounce.

    1. The Australian Gov. research dept (CRISO) held an interview on some radio program I was listening to ooh about 30 years ago. They had invented a spray that is sprayed onto glass during the molding process that made it as hard as bullet proof glass (caliber unknown). They had a glass bottle similar to a plastic 2lt bottle, it was said to be lighter and we heard it bounce when it was thrown to the ground. They said it would replace plastics, was fully recyclable, basically the best thing since sliced bread, resulting in a major manufacturing boon for Australia. Unfortunately it didn’t happen and any inquiries that I made about this ….. nope ….. no-one remembers anything about it. I wonder if the German’s have hit on the same or similar idea?

      1. Sorry to beat a dead horse and revive the comment thread here, but maybe you’re from an alternate universe/timeline and due to the Mandela effect brought about during CERN’s large hadron collision testing you ended up being one of many people who were unfortunately incidentally transported to this universe/timeline from an alternate one where such a thing did happen 30 years ago in Australia. This effect has been reported repeatedly, causing large groups of people to have shared memories that don’t match up with other groups memories of historical events, and the effect has been largely attributed to CERNs hadron collider as the timing of such effects matches up quite closely with the timing of their experiments. The most famous of which being the one the effect is named after, where many people remember Nelson Mandela dying in prison and others clearly remembering him being released. It’s a very interesting phenomenon, one that has no reported cases before CERN began experimenting with the hadron collider, and which has happened repeatedly, parallel to each individual collision.

        1. The article is wrong, though:

          “Coincidentally, AlON development was underway more or less at the same time that Star Trek IV: The Voyage Home was being produced; it was from the now classic scene from that film were Scotty uses a mouse as a microphone in an attempt to trade the formula for “transparent aluminum” for sheets of plexiglass that AlON and similar transparent ceramics get their colloquial name.”

          Why would Scotty trade the formula of transparent aluminum for _plexiglass_? He specifically gave them the formula in exchange for panels made of said transparent aluminum.

          1. Haven’t watched it recently, eh? The Plexi manufacturer, Nichols, says it’s gonna take years to figure out “the dynamics of this matrix”, meaning a formula and molecular diagram isn’t enough to just go whipping the stuff up. The whole point was to get plexiglass, which was the technology available at the time. The panels they install are the 6″ thick plexi Nichols was talking about having in stock, not the 1″ thick aluminum Scotty was touting.

          2. Scott Petrovits – What gets me is that since reverse time travel is impossible, the way Gene Roddenberry portrayed it, why didn’t they just forget about bringing back 2 humpback whales to deal with the alien ship? There was no guarantee that the two would even mate after she might have miscarried the calf. So the Enterprise’s situational logistics were a bit illogical to me.

            They were “thinking outside the box” when they defeated the undefeated Borg, why couldn’t they think of a unconventional attack scenario like in that episode? Also, with all of the technology available in the 23rd century AD, why couldn’t they use an old WW2 (and today) trick? They could have “simulated” humpback whales with audio and B/G Laser underwater holographic signatures. They can do that now to fake out the enemy of the fake presence of an American submarine. Doing the reverse time travel thing was not logical as even if it weren’t impossible (which it clearly is), they may have changed the timeline causing something far worse than the alien highly destructive Cetacean-Probe returning. I understand the BORG had a crack at it previously but failed.

            I know Gene was really trying to deliver a environmental message embedded in the movie. I just wish it was better story-boarded by the screenwriters (even though it was a spectacular movie). Independence Day was far better. Repelling an ET attack may well be fatal to us as a species, so I do not look forward to such a hypothetical future battle. But at least we can do much better with strategically preparing mentally and physically for it.

            I like Penn and Teller’s method in the movie short THE INVISIBLE THREAD (1987) with infamous G. Gordon Liddy portraying a DoD general from the E-Ring (@Pentagon) – ask me for YouTube link. Teller actually repelled the attack with his impeccable logic (despite being a voluntary mute). NASA not so much… :-)

            P.S. tell the HaD Brits here to pronounce SCHOOL before we stubborn benighted Yanks say A-LOU-MIN-EE-UM :p

  3. It’s transparent Alumina not aluminum. A lot of people hear aluminum when when people are actually saying alumina. And then you have a lot of articles on the net who propagate this misunderstanding. Just like silica/silicon/silicone.

      1. Davy named it aluminum (alumium was a competing name) when he discovered* it (*Hans Oersted was first to isolate it). IUPAC retconned aluminium in 1990. When you discover it, you get to name it.

        I recognize the council has made a decision, but given it’s a stupid-ass decision, I’ve elected to ignore it.

        1. aluminium is less stupid than sodum (which I just made up). But Helum, call it wat u want, just make sure you provide a structural formula so the chemists among us can read the “short hand” version. Oh, and it is not Alumina (Aluminium oxide). And it is not transparent ali, any more than glass is transparent silicon.

          1. yes, the title is misleading. Transparent aluminium/aluminum would be very interesting, this is a lot less interesting, there are many transparent minerals.

  4. “Aside from being optically clear, ALON is also immensely tough. Tests show that a laminated pane of ALON 1.6″ thick can stop a 50 caliber rifle round, something even 3.7″ of traditional “bullet-proof” glass can’t do. ”

    Windows of the White House.

    1. Ostracus – “Windows of the White House.”

      Wouldn’t a lev-8 PC like LEXAN be cheaper (and ostensibly safer for POTUS)? And has anybody done any real backgrounding on Surmet Corporation (ALON) in Boston MA usa? This story disturbs me as I read somewhere that a Saudi scientist actually invented this stuff and then there’s this:http://russianconstruction.com/news-1/28294-russian-scientists-develop-transparent-aluminum-technology.html

      I’m just a paranoid tin-foil hat I guess right Marty? I can’t get that License to Kill (1989) Bond movie out of my head where Timothy Dalton plants a RC shape charge against some Lexan and metal armored window then tries to take out bad guy Sanchez with his special gadget rifle. youtu . be / b8yfMsNnCv8 (take out all spaces). Then I can’t get Olympus Has Fallen (2013) out too. And it’s much more topical! Don’t you think? youtu . be / 3rVA22f_T_w

  5. It makes as much sense to call this bulletproof glass “Transparent Aluminum” as it makes to call regular glass “Transparent Silicon”; ie… not much sense at all

  6. If you have other interesting materials like AlON that we should dig into, let us know about it in the comments below.

    You already covered polyamides so UHMWPE, Flash Bainite, Amorphous Metals, Carbon Carbon composites, PEEK, cubic boron nitride.

  7. “..makes ALON a great choice for the windows on heat seeking missiles..”

    There are too many people reading this site that will, after proper motivation and inspiration, try almost anything. Geez, stand by for a rash of home-made AIM-9s.

    1. Luckily for you, the cooled mid-wave IR detectors are fairly expensive and hard to get on the civilian market…also – for a DIY anti…something… rocket, you’d be better of with leaving as much of the guidance electronics you can out of the rocket, since they get destroyed once the rocket does it’s intended job :P
      Traditional “TV guidance” would be a good first choice ;-)

      anyway – a hard to scratch and durable window/front lens would probably be very welcome in the RC FPV crowd if they didn’t cost an arm and a leg…

  8. Apparently all the buildings in police procedurals where the cops use an IR camera have windows glazed with ALON (really thin so bullets will go through) or some other material that is transparent to both visible and IR light.
    If the windows had ordinary glass, they wouldn’t be able to see the shapes of people behind them with their fancy cameras.

    Still no explanation for how they see IR shapes of people through all kinds of wall and roof materials.

  9. I wonder if this will eventually find its way into automotive windshields on the “inexpensive” end of the spectrum rather than the armored end, at least then my transition lend glasses would dim while in the drivers seat

  10. Next up: knives made from air (oxynitride ceramic), liquid oxygen and hydrogen at room temperature (water), gaseous polymers (we just burnt them).
    C’mon, this is not a hack, It is not even news. It is clickbait.

  11. Actually, ALON is a real material.
    I did some preliminary calculations and it could be *the* ideal material for a fusion reactor because all its decay products are non reactive and don’t affect the fusion burn.
    Also handy for making actual light bulbs for harsh environments because they can be sealed at manufacture, with InGaN/AlP/etc vapor deposited on the back of the glass to make a nearly indestructible multilayer composite.

      1. Yes I recall the story, I searched again. The American Chemical Society brought back to -inum, while outside North America has been teached as -inium, as per IUPAC. Both is defined to be acceptable, no more right or wrong.

  12. Some errors in this article. Firstly, ALON is only 85% as hard as sapphire, which is a material actively in use for smartphone panels at a similar 5x price point. Secondly, the mineral aggregate that is combined with asphalt to create blacktop is composed of a variety of minerals including flint and basalt which are, again, harder than ALON.

  13. “So, sorry Scotty — there’s no such thing as transparent aluminum metal. ”

    Are you *sure* anyone said “transparent aluminum *metal*” on Star Trek, much less Scotty? This strikes me as a weird write-up that reads in “metal” when it might be you that is insisting on it having been said.

      1. JRDM – I think the OP was ad-libbing… It appears neither Scotty nor Bones said it at all. It would be nice to hear Scotty say the YANK pronunciation of aluminum versus the U.K. version. The Yank engineer at PLEXICORP said transparent aluminum, not the ST-OS away-team members. However, Scotty using the antique keyboard was ridiculous. It was just like he was inadvertently hitting the advance button in HYPERCARD (early Apple presentation product) rather than just blind typing. (This Grammarly is awesome!)

        youtu . be/xaVgRj2e5_s (take out spaces)

  14. Transparent Aluminium. Cool, despite the colonial spelling, my favourite transparent metal it lead tungstate, yes thats LEAD and TUNGSTEN ally thats Water clear…check it out.

  15. If someone can devlope a slurry casting and no pressure firing method for this, the price will be able to drop a huge amount.

    Slip casting of pottery, porcelain and other ceramics is done by pouring a water based slurry (called slip) of various types of clays and other stuff into special pottery plaster molds. The mold absorbs some water from the slurry, causing a skin of it to solidify. Excess slurry is poured out (Lay the mold on one side, then tip pour hole down. If you just tip it upside down you end up with raised bumps in the bottom of your casting from drips.) and the skin allowed to dry to the point where it’s self supporting. Not too dry or you can’t get it out of the mold intact.

    The castings are allowed to fully dry. That state is called greenware. After being fired in a kiln, it’s called bisque. Bisque is strong and break resistant. Glaze is applied (by dipping, brushing, or spraying) then fired to seal, smooth, and color the surface. Colors called under-glaze can be applied to the bisque then fired before the glossy glazes are applied. Final decorating steps can involve special water slide decals made with glazes screen printed onto the carrier film and precious metal paints. Those are amazingly stinky during firing, probably pretty toxic but the metal coating left behind is durable and for non-gold metals doesn’t tarnish due to being fused into the glaze.

    Castable ALON slurry or slip would likely involve a carrier fluid other than water. The big trick would be making it vitrify without pressure. If a clear glaze coating (called clear brushing) could be applied to eliminate the surface polishing stage for transparency (except for uses where distortion free transparency is required) that would also drastically cut the cost.

  16. seems like only using it for armor is kinda limiting off the top of my head space and undersea craft, airplane windows, high rise buildings, not to mention windows in hurricane and tornado prone areas

    granted some of those would require finding a way to lower the price point but even a thin membrane of this over regular class might help in some places

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