If you touch two CLEAN blocks of the same metal together in space, they weld! Atoms in solid metals move a bit. Touch two clean surfaces together, and the atoms can't tell they're in different blocks so they become one group of atoms, ie ONE SOLID. (Gif: https://www.homemadetools.net/forum/cold-welding-gif-56268 …)pic.twitter.com/WAfv3VwhnX
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The reason it doesn't happen on Earth when you put two of the same metals together is because of oxygen, which causes metal to rust. That oxide layer sits the two metal surfaces, so atoms in each block see a layer of different atoms, and know that's their "limit" for movement.
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Replying to @Astropartigirl
Why does this not work with, for example, gold on earth then?
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Replying to @logGo13 @Astropartigirl
Was wondering, too. In the video they use gold nano wires and write in the paper: "The good resistance to oxidization of gold is another useful property." So I guess it could happen. But maybe it oxidizes just enough to prevent it happening outside labs.https://www.nature.com/articles/nnano.2010.4 …
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It can be done with gold within the Earth's atmosphere, if you polish the surfaces first and push them together hardhttps://www.youtube.com/watch?v=mHAhfX7iRjs …
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Replying to @arthur_affect @kokemikal and
All of this stuff is on a spectrum, too -- like if you have two clean smooth surfaces of just regular stainless steel, the oxidation layer won't prevent it from cold-welding in atmosphere if you put it under enough pressure
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Like when metal under pressure sticks to itself but not to the degree of true "cold-welding" it's called "galling" and is a significant problem for engineers
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