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If you could take a cube of metal (say one inch in size), which was a single crystal (not sure of that's important for this question) and somehow separated it down the middle to leave to two perfectly "flat" surfaces of metal atoms. Assuming they are in a perfect vacuum, if you brought the two back together again would they fuse into one cube again? Would you need to put in any energy for this fusing together to happen, i.e. would they repel each other initially?

I had first thought of asking this question by saying if you polished two metal cubes but then thought that the crystal faces might be different between the two cubes.

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  • $\begingroup$ Cold welding with an emphasis on the cleanliness of the surfaces which are going to be joined together - en.wikipedia.org/wiki/Cold_welding and Feynman in the section about friction mentions this. feynmanlectures.caltech.edu/I_12.html $\endgroup$
    – Farcher
    Commented Jan 27, 2018 at 14:14
  • $\begingroup$ It is called vacuum welding and it can be quite annoying when stuff gets stuck inside vacuum equipment. $\endgroup$
    – user137289
    Commented Jan 27, 2018 at 14:15
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    $\begingroup$ Possible duplicate of Why don't metals bond when touched together? $\endgroup$
    – Stéphane Rollandin
    Commented Jan 27, 2018 at 15:11
  • $\begingroup$ Only a few metals will do this, as I remember Indium is one. There is a similar phenomenon for steel "Jo blocks" ; they are exceptionally flat and smooth and when placed together they "stick". $\endgroup$
    – blacksmith37
    Commented Jan 27, 2018 at 17:16
  • $\begingroup$ @blacksmith37 Johansson blocks stick together because of surface tension of the greasy layer of adsorbed moisture and stuff between them. $\endgroup$
    – user137289
    Commented Jan 27, 2018 at 23:24

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