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I'm currently bouncing around ideas for a sci-fi / cyberpunk world and one of the major technologies in this universe is the manufacture and usage of metallic glass. I don't want to handwave too much away, since one of the scenes I have in mind involves a gunfight inside a factory where such glasses are made, and I was thinking of having the main characters and the antagonist's goons fighting it out using sheets of these glasses for cover as they're being moved by overhead automated cranes. I'm unsure of how to proceed with this line, as I've found a great deal of academic papers, but I can't really wrap my head around the exact properties they have. What do I need to look out for when writing about these metallic glasses both at ambient and elevated temperatures?

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    $\begingroup$ Do you mind explaining what semi-ELI5 is? $\endgroup$ – L.Dutch Jun 11 at 19:00
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    $\begingroup$ Glass does not mean "transparent", it means "non-crystalline solid which exhibits a glass transition when heated". For example, porcelain (aka china) is a glass. Metallic glasses are more commonly known as amorphous metals. They look and behave pretty much like ordinary crystalline metals (they are opaque, conduct electricity etc.), but have certain useful properties; they don't look or behave like window glass. $\endgroup$ – AlexP Jun 11 at 21:44
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    $\begingroup$ Please update the question to clarify if you mean amorphous metals or clear metal-like plates. $\endgroup$ – Nosajimiki Jun 12 at 5:41
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    $\begingroup$ If you are after a strong glass sheet, consider Tempered glass or Chemically strengthened glass (used for fighter jet canopies!), or even bog-standard laminate "bulletproof" glass $\endgroup$ – Chronocidal Jun 12 at 8:25
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    $\begingroup$ @L.Dutch: This is the origin and pretty much best explanation of ELI5. I guess semi-ELI5 would be ELI10? $\endgroup$ – Flater Jun 12 at 14:37
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A metallic "glass" would be an amorphous metal or alloy. This material is commercially available in ribbon form (only, last time I checked), and is far from transparent (it looks like solder ribbon or metallic tape). It has most of the same properties as the metal it's made of, except that it has no crystal structure (this affects bending strength, for instance).

The material is made by directing a stream of molten metal at a chilled metallic roller, which cools the liquid too rapidly for crystals to form. The roller is turning very rapidly, and a combination of inertia and a sharp scraper sling the metallic glass off the roller, where it's caught and rolled in a continuous process. The commercial brand I'm aware of is MetGlas, and it's been around for decades (it's possible the company has been bought out and/or acquired competition since then).

Amorphous metal is likely to stay generally in this form, because of the cooling rate needed to prevent crystallization during cooling. You probably won't see it in large sheets or plates.

What you may see (what's been called "transparent aluminum" in the press) is aluminum oxide sheet. This is effectively clear sapphire; it's hard, very transparent, and fairly strong (but brittle -- exceed its strength by a tiny bit and it will fracture instantly, without any deformation as you'd expect from a metal). It's been used for high strength watch crystals for decades, in price ranges as low as consumer watches just above the "Timex" class.

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    $\begingroup$ "fairly tough but brittle" - eh? The former material scientist in me is boggled by this statement. Tough vs brittle are the opposite ends of a spectrum. It's like saying "fairly strong but weak" or "fairly stiff but floppy". $\endgroup$ – Martin Bonner Jun 12 at 10:12
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    $\begingroup$ @MartinBonner Yep, sorry, poor choice of words. Should be "fairly strong but brittle" -- like an overhardened steel or carbide. $\endgroup$ – Zeiss Ikon Jun 12 at 11:15
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Generally speaking, metallic glass (in terms of what you can see through) does not exist because metals have non localized electrons. This means that when light or electrons hit metal, they want to be bounced around or conducted instead of passing through.

Instead there are real-life materials which are actually very hard, clear ceramics that can offer similar protection to metals, but you can see through them. The most famous is aliglass which is a synthetic sapphire that offers similar protection as aluminum. The key difference with these materials is that they can not be deformed like true metal, but will shatter just like other ceramics if hit hard enough.

If you want a clear sculptable metallic substitute, Polycarbonate is probably your best bet. It is a very strong clear plastic which is used as a metal substitute in many industrial processes and for making see-through riot shields. While it does not have all of the same properties as metal (such as conductivity), it has a similar strength to steel.

Aliglass will be much more resistant to temperature with a melting point of ~2,000 °C vs Polycarbonate which melts at ~150°C.

If you need your Polycarbonate or Aliglass to be conductive, then layer it with graphene. Graphene is a mono-molecular sheet that conducts electrons better than gold and is several times stronger than steel. It is technically opaque, but since it is only one molecule thick, it takes hundreds of layers to actually block out light; so, it could be used to print super thin circuit boards or wiring inside your "glass" without blocking a significant amount of light.

Another option to consider is titanium dioxide doped with cobalt. It is the transparent semiconductor used in flexible screen technology. While technically crystalline it is both clear and flexible. Unto itself it is not going to have nearly the material strength of most metals, but it could be embedded in Polycarbonate or adhered to Aliglass depending on what this metallic glass is intended for. While you could probably do more with this than graphene, don't expect you metallic glass to still work after a heavy impact.

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  • $\begingroup$ As the answer from Zeiss Ikon explains, metallic glass absolutely does exist, and is for sale commercially. It's not transparent though. $\endgroup$ – Martin Bonner Jun 12 at 10:13
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    $\begingroup$ Yes, that is why I specified "in terms of what you can see through". Zeiss Ikon answers the question in the literal sense of glass as a molecular structure, but my answer is in the vernacular since of glass as a thing you can see through. The context of the OP makes me think he wants the latter since he is is looking to use it as a dramatic form of cover, but both answer the question in very legitimate ways. $\endgroup$ – Nosajimiki Jun 12 at 14:08
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Wave them hands!

You had me at gunfight in the factory, using sheets of glass for cover. Awesome. Make your metallic glass be what your story needs it to be for the story as regards bulletproofness and other properties. It is not so farfetched. Do it up!

I like a closing scene where the protagonist enters some stuff into his phone then curls up and plugs his ears. A piercing shriek is emitted from the phone, getting higher and louder. The goons wince and look around in confusion. One of them catches on faster than the rest and bolts for the door.

Then all the glass above them shatters and rains down on them. The phone itself cracks as well - its casing is made of the same glass.

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I am going to give you something of a frame challenge here - while you generally want to keep the properties of the glass realistic, don't forget to let your factory and production process of the glasses seem somewhat real too. I'm not sure if a lot of readers will care whether your characters are fighting among metallic glass, aluminium oxide sheets, or sheets of polycarbonate - the main point is that you have an image in mind which you want to enter into your story.

However, to keep my suspension of disbelief intact you don't just have to make the materials seem realistic-ish, you also need to make the factory in which the scene is set to seem real. Some questions which immediately popped into my mind after reading your question were:

  • why are the automated cranes moving the sheets about. Most production lines will try to minimize how much the product is handled, and in a lot of instances a monorail, robot, or conveyor will be more efficient than a ceiling-mounted crane.
  • talking about ceiling-mounted, how will several cranes move over the same area without the beams they are mounted on colliding?
  • how are the characters getting access to the production area of factory floor. With new HSE regulations, such areas will often be fenced off and require the machines in the area to be powered down before access is granted.

I realize that some of these issues are often ignored in sci-fi / cyberpunk, depending a bit on how realistic the author wants their setting to be, but I just want to warn you not to focus on this one issue regarding the exact properties or chemical structure of the materials encountered in the factory, while disregarding how realistic the rest of the situation seems.

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    $\begingroup$ Generally this is all true and valid, but cyberpunk settings generally don't have things like HSE regulations. As for the panes being suspended, this could be in preparation to be dipped in vats of some sort of coating. If they have to remain submerged for a certain time period, there may need to be many parallel lines at this point in the production to keep up with the flow. $\endgroup$ – Nosajimiki Jun 12 at 14:28
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    $\begingroup$ @Nosajimiki True, and I think you'll find I e.g. don't care that none of the walkways in Star Wars have handrails. My point is that when taking care to make parts of your story hard sci-fi with regards to material properties and so forth, you should also take care that other aspects of your setting seem believable as they'll stand out more. Ofc it's hard to say exactly what the OP is going for, judging from his description it sounds like it's mostly aesthetics, in which case I think he doesn't need to care about the real-world equivalent of the panes unless it has direct relevance to the plot. $\endgroup$ – eirikdaude Jun 12 at 21:19
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In terms of appearance, the sheets of metal glass should be shiny. As good as a mirror or highly polished chrome. They tend to have a high tensile strength. They are not very ductile, but are fairly tough, so it's unlikely for them to shatter like regular glass, unless you really hit them. They should probably be able to stop a bullet. The most likely process for making them is going to be fast cooling. Right now it's difficult to make sheets thicker than 1 mm because the cooling rate has to be way too high, but with better alloys we should be able to increase the thickness. One interesting property that metallic glasses have is that because they have no grain structure and because they soften in flow on heating they can be injection molded to form very fine features, even at the nanoscale. One can actually injection mold a knife with a sharp edge. So your sheets could potentially have sharp corners.

The most relevant property here is the high resilience of metallic glasses. Resilience is the ability to absorb and release elastic energy. This is best illustrated with a video. A ball dropped on to metallic glass bounces for a much longer time than a ball dropped onto regular metal. This means that ricochets might be more of a problem. It probably wouldn't be too much of a handwave to have multiple bounce ricoshets. I Video taken from here, which also has more information on metallic glasses

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