0
$\begingroup$

It is a common fact that without oxidation, a metal can reform it's lattice with a tad bit of pressure. Gold is often said to be non-oxidising(doesn't oxidise in ambient temperature and pressure) and that only aqua regia can oxidise gold. In that case, why doesn't gold reform it's lattice on applying pressure. I did try it and noticed that gold partially reformed it's lattice if we try to attach the pieces immediately, but even that eventually tore out as I put just a tad bit of force, I'd say something like 20g.wt. So, why does gold not reform it's lattice if it doesn't oxidise, which basically says gold does oxidise?

Edit: Okay, for context, I mean cold welding should be possible with gold if it doesn't oxidise. But that obviously doesn't happen, which means the surface gold does lose electrons. So I mean to say, gold should be considered as oxidisable in air, but slowly instead of saying it doesn't at all, which most resources claim. Am I right, if not, please correct me.

$\endgroup$
7
  • 4
    $\begingroup$ Oxidation, lattice reforming and reattaching 2 metal pieces are 3 different independent things. $\endgroup$
    – Poutnik
    Jul 30, 2023 at 9:33
  • $\begingroup$ But oxidation prevents lattice reforming, which causes us not to be able to reattach 2 metal pieces. For reference, see cold welding on wiki $\endgroup$
    – Sid N
    Jul 30, 2023 at 9:35
  • $\begingroup$ Or gas adsorption. Such reattaching is best done in vacuum. $\endgroup$
    – Poutnik
    Jul 30, 2023 at 9:38
  • $\begingroup$ Yep, because there is no reaction with air. Which means gold does react, though slowly, with air. $\endgroup$
    – Sid N
    Jul 30, 2023 at 9:41
  • 2
    $\begingroup$ You have not excluded gas adsorption. // Golden foil can have thickness down to lower nanometers, just few atoms thick. If it oxidated, such a foil would stop become a metal soon. BTW, gold oxides are not thermodynamically stable at low temperatures. $\endgroup$
    – Poutnik
    Jul 30, 2023 at 9:57

1 Answer 1

2
$\begingroup$

Gold most definitely does cold-weld in vacuo, or even with moderate pressure, extended clamping time and/or mild heating at 1 atm, That is how gold leads are attached to an IC. If you want to test in the lab, though, whether with gold or any other substance, start with clean surfaces. Clean, lapped gauge-blocks cannot be left wrung together lest they cold-weld.

However, reformation of a crystalline lattice is not necessary for cold welding. For example, glass vacuum tubes can be produced by cold-welding without heat sealing. Glass is noncrystalline.

Richard Feynman stated: "If we try to get absolutely pure copper, if we clean and polish the surfaces, outgas the materials in a vacuum, and take every conceivable precaution... the slider will not fall off — the two pieces of copper stick together... The reason for this unexpected behavior is that when the atoms in contact are all of the same kind, there is no way for the atoms to "know" that they are in different pieces of copper." On a quantum level, can one distinguish an atom in one piece from an adjacent one in what was the other piece?

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.