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In the past I've entertained the notion of space stations and spaceships having window panes or transparent viewing surfaces made from laboratory-created diamonds, but a recent answer to a different question on this site has led me to question how effective (or not) this would be even if it were possible- assuming it is even possible to create diamonds with the appropriate dimensions for a viewport on such a structure- would they serve as safe and effective for the task?

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    $\begingroup$ More likely you'd be working with something like synthetic sapphire, as sapphire is less brittle, has greater optical purity, and has a much higher heat tolerance than diamond. (For reference, diamond can ignite at 850C.) $\endgroup$
    – jdunlop
    Commented Sep 11, 2023 at 21:48
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    $\begingroup$ I don't get it. What is the real problem that diamond windows are supposed to solve? What can diamond do which (relatively) ordinary glasses such as fused silica cannot? $\endgroup$
    – AlexP
    Commented Sep 11, 2023 at 21:59
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    $\begingroup$ @jdunlop is right sapphire is better, artificial sapphire is even used for some real world applications where optics have to survive in really harsh environments. $\endgroup$
    – John
    Commented Sep 11, 2023 at 23:34
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    $\begingroup$ See Sapphire (wikipedia) > Synthetic Sapphire > Applications $\endgroup$
    – Atog
    Commented Sep 12, 2023 at 5:33
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    $\begingroup$ username checks out $\endgroup$
    – N. Virgo
    Commented Sep 13, 2023 at 5:03

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Diamond is very hard, but unfortunately it is also a bit brittle. If an object with enough kinetic energy hits it, the window can shatter completely. This is not an acceptable risk in space. Suitable window material should not shatter even if it breaks.

Eg. car windshields had this problem, and that is why they are today made of laminated glass to mitigate this risk. If the glass is hit, the glass cracks, but typically the windshield still stays as one piece. Maybe it is possible to do something similar with your spacecraft windows, ie. use diamond instead of glass and laminate it to prevent shattering.

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    $\begingroup$ Just to nitpick (for those not following the link): Windshields are intentionally designed to shatter, and in a specific way (many small pieces, no sharp edges). I do support the idea of laminated diamond/glass. $\endgroup$
    – Tom
    Commented Sep 12, 2023 at 19:57
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    $\begingroup$ @Tom: Modern windshields are indeed designed so that if they shatter they do so in a specific less-harmful way — but also to be highly shatter-resistant, compared to older forms of glass. $\endgroup$ Commented Sep 14, 2023 at 8:43
  • $\begingroup$ @PeterLeFanuLumsdaine agreed. Though we should tell that to the million or so idiots on YouTube who thought you could dance on a windshield or whatever and look all surprised when - omg! - glass does indeed shatter... $\endgroup$
    – Tom
    Commented Sep 14, 2023 at 9:30
  • $\begingroup$ This might be a bit about semantics, but they seem to make an intentional distinction between shattering and cracking in this context. Laminated glass is often called shatterfree or shatterproof. It can still crack, but usually it stays as one piece, held together with the the plastic or something similar. $\endgroup$ Commented Sep 14, 2023 at 10:07
  • $\begingroup$ Car windshields and spaceship windows are very different use cases. The primary concern with car windshields was to avoid sharp glass fragments from high-force impacts. For spaceships, on the other hand, the goal is presumably to prevent any hole whatsoever from generally-tiny meteors and potentially from accidents. $\endgroup$
    – NotThatGuy
    Commented Sep 14, 2023 at 15:30
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Diamond is good for some things like cutting, but not for things like resisting impacts. It is very hard, and consequently very brittle. Laminating might counteract that weakness, but I doubt it would make much sense in terms of weight and budget.

We're already in the future anyways.

Transparent ceramics are a thing already, and it will only get better and cheaper. ISS' Cupola module uses "fused silica and borosilicate glass panes" for its 7 windows, and shutters to protect them when not in use. It's been working fine for the last 13 years, they even managed to replace panes.

We've also created things like aluminium oxynitride which can make for much light bulletproof panes, or sapphire which is already used in iPhone lenses.

The military is very interested in those things, because lightweight and transparent materials have a lot of interesting applications, so it's safe to bet we'll be able to make transparent viewports that aren't total structural weaknesses by the time we're able to make cool spaceships.

But it won't be diamond. Diamond just isn't the right material for armor.

If you really want diamond, I can see two options.

You could imagine a carbon-based material, like a transparent carbon ceramic nanotube matrix thingamajig, and call it "diamond window" because diamonds are carbon and marketing will probably still exist in the future.

Or you could have a diamond pane under a proper transparent ceramic pane, and that's technically a diamond window (with non-diamond transparent armor).

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    $\begingroup$ "But it won't be diamond. Diamond just isn't the right material for armor." Minecraft lied to me $\endgroup$
    – 0x777C
    Commented Sep 12, 2023 at 13:26
  • $\begingroup$ I thought shuttles would have different material since they have to go back and forth between Earth and orbit, but turns out they also use fused silica with perfect record. $\endgroup$
    – Martheen
    Commented Sep 13, 2023 at 6:54
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    $\begingroup$ +1 for referencing aluminium oxynitride. Worth adding the Wiki link: en.wikipedia.org/wiki/Aluminium_oxynitride $\endgroup$
    – MBender
    Commented Sep 13, 2023 at 12:57
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    $\begingroup$ @MBender Ah, good old "transparent aluminium." Scotty would be proud 😄 $\endgroup$
    – Corey
    Commented Sep 15, 2023 at 0:24
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Diamonds isn't particularly resistant to impact, with a fracture toughness of 2 MPam1/2. If you want a resistant and transparent material, you could instead use Yttria-stabilized cubic zirconia (bonus for the cool name), with about 3.7 MPam1/2, or sapphire with 4.2 MPam1/2.

If the goal is to have highly impact resistant material, going for a composite structure is probably much better. Stacking layers of transparent materials in a similar way an armor is built could make for a very strong material. Laminated sapphire with graphene could be extremely resistant. Adding a shock absorbing material like polycarbonate can greatly improve impact resistance while staying transparent.

enter image description here

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  • $\begingroup$ Do you have a reference for the image? $\endgroup$ Commented Sep 12, 2023 at 16:25
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    $\begingroup$ @WaterMolecule Made it myself $\endgroup$
    – Elzaidir
    Commented Sep 12, 2023 at 16:27
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    $\begingroup$ LOL @typo "choc absorbing material". Sometimes, I'm made from that. $\endgroup$
    – Kingsley
    Commented Sep 14, 2023 at 0:44
  • $\begingroup$ @Kingsley My brain switched to French mid-sentence lol $\endgroup$
    – Elzaidir
    Commented Sep 15, 2023 at 10:27
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"Windows are structural weaknesses. Geth do not use them." - Legion, Mass effect 2

Why would you need windows anyway? If you want to look outside you can have a sensor outside and a screen inside. Same results with none of the engineering issues. And if you are afraid that an insane A.I., khm, your friendly computer will try to manipulate the view you can make it a closed system and not connect it to the network.

Because windows made of any material WILL be a weakness in the structure. And if you somehow create a transparent material better than what the hull is made of, then why not create the whole thing from that transparent material?

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    $\begingroup$ Also a window sized monitor will be much, much cheaper than a window sized diamond. Better view, no chance to burn your retina if there is a high energy flare. We are even replacing mirrors in cars with monitors to ensure perfect alignment as well as better view clarity under different conditions. $\endgroup$ Commented Sep 12, 2023 at 15:24
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    $\begingroup$ I'd say humans aren't robots, humans like to look out of windows and a screen just doesn't hit the same. $\endgroup$ Commented Sep 13, 2023 at 9:01
  • $\begingroup$ @AmiralPatate We can build screens today that a human eye cannot distinguish from a window. $\endgroup$
    – Negdo
    Commented Sep 13, 2023 at 9:08
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    $\begingroup$ @Negdo But you know it's not a window. $\endgroup$ Commented Sep 13, 2023 at 9:11
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    $\begingroup$ @AmiralPatate A few hundred years ago: "Humans are used to look through wall openings! Looking through that new material, glass, just doesn't feel the same. And how expensive that glass is! A window should be a wind opening, that's where the name comes from. You shouldn't call a glass pane a window. This stupid new fanciness will be gone in less than 5 years, I swear!" $\endgroup$ Commented Sep 14, 2023 at 7:01
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Synthetic diamond can be used as an armor material. It's no different from AlON, sapphire, or just plain glass in that regard. All armor ceramics are brittle, by their very nature. Diamond isn't particularly more brittle than the rest.

However, it's notoriously difficult to fabricate, the only means to make flat diamonds is through chemical or physical vapor deposition, which is hard to do in a thick layer. You also still need to layer it with tougher polymer layers. There's no massive advantage to using diamond over sapphire or AlON. But diamond-like coatings are used widely where a very hard surface is required. This includes optics.

The primary advantage of ceramics in armor is their hardness, allowing them to blunt incoming metal projectiles. In space, you are more likely to face hypervelocity projectiles, against which hardness doesn't help much. Brittleness, however, isn't such a big problem either.

A window with its outermost layer made out of diamond will likely retain its transparency longer, better resisting the effects of space dust than other ceramics. In all other respects, it won't be very different from AlON or glass. If you're in a high sci-fi setting, and don't want to use the same aluminum oxynitride as everyone else probably does, there's nothing very wrong with diamond.

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