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Are galvanised steel parts safe to use in space (high-vacuum environment), e.g. washers, fasteners, nuts? I've heard that zinc can sublimate at low pressures.

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  • $\begingroup$ From a quick search, it sounds like those wouldn't be safe in space. However, there would also be no point in using galvanised steel in space, since galvanisation is done to prevent rusting, which can't occur in the vacuum of space. $\endgroup$ – Pitto Aug 27 at 12:14
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    $\begingroup$ @Pitto: You would be surprised. Rusting in space isn't the same as rusting on earth, but taking protection for it is still a good thing, and almost anything launched in to space has rust protection. There are a lot of oxygen ions in the thin parts of the upper atmosphere. $\endgroup$ – PearsonArtPhoto Aug 27 at 12:16
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    $\begingroup$ I have no source I can link, so just a comment not an full-answer: galvanised steel was forbidden when I worked in space related hardware development (less than 10 years ago). Zinc tends to form needle-like structures in vacuum. So only stainless-steal was allowed. @Pitto: it is not called rust but oxidizing and it is a very big problem in space. We even need to coat aluminium! $\endgroup$ – CallMeTom Aug 27 at 13:05
  • $\begingroup$ @CallMeTom I wonder if zinc needles and tin whiskers are related phenomenon? What mitigation procedures are in place in space systems to prevent whisker growth? $\endgroup$ – uhoh Aug 27 at 23:37
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    $\begingroup$ @uhoh ... you made me unsure if I confound zinc and tin (lost in translation) because I was searching for the word "whiskers" when writing "neelde-like structures". Beside this confusion I want to confirm the main statement: galv. steel was forbidden! $\endgroup$ – CallMeTom Aug 28 at 8:07
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It's not just zinc. Pure tin coatings and cadmium coatings are also prohibited, at least in the vicinity of electronics. See the Prohibited Materials Section of the NASA Parts Selection List (NPSL).

NASA Technical Standard 6012 (NASA-STD-6102), Corrosion Protection for Space Flight Hardware, appears to prohibit zinc and cadmium coatings anywhere in a spacecraft.

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  • $\begingroup$ Interesting that the reason given is wisker formation rather than outgassing. Out of curiosity, is brass or leaded steel prohibited? $\endgroup$ – 0xDBFB7 Aug 28 at 3:30
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    $\begingroup$ @0xDBFB7 - Whisker formation apparently is much more likely to occur than is sublimation/redeposition for pure tin and zinc, and those whiskers can be particularly bad in an electrical setting. Note however that cadmium is also banned, and cadmium is not noted for forming whiskers, and also note that NASA-STD-6102 remarks that in addition to the whisker problem, zinc also is subject to sublimation and redeposition elsewhere. Finally, it does not seem that brass or leaded steel are prohibited. $\endgroup$ – David Hammen Aug 28 at 6:54

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