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#21
Jan 13 2009 04:39am
old but cool
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#22
Jan 13 2009 04:47am
If the metal is brought to space from earth, then wouldnt those metals contain the oxidised layer?
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#23
Jan 13 2009 03:49pm
Quote (penguinhero @ Tue, Dec 16 2008, 05:21am)
In space, if unprotected pieces of metal touch each other, they stick together permanently.

This doesn't happen on Earth, because the oxygen in our atmosphere forms an extremely thin film of oxidized metal on every exposed surface. The oxidization layer acts as a barrier that conveniently prevents chunks of metal from sticking to other chunks of metal.

In the vacuum of space, however, there is no oxidation layer. If the atoms of two metal objects come in contact with each other, what you suddenly have is one continuous metal object, and a lot of explaining to do to your mission commander.

This is an issue on the space station. Metal tools used outside the station have to be coated with plastic or other materials that will not stick.




got it from here: http://www.coolsciencefacts.com/2006/metal.html



i coulda told them that.
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#24
Jan 13 2009 03:54pm
Old thread, but I didn't know that... Pretty cool.
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#25
Jan 13 2009 06:43pm
Quote (Karak @ Tue, Jan 13 2009, 05:47am)
If the metal is brought to space from earth, then wouldnt those metals contain the oxidised layer?


i think the oxidized layer would not be present because of the no oxygen in space
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#26
Jan 13 2009 07:25pm
Quote (Osirislives @ Wed, Jan 14 2009, 12:43am)
i think the oxidized layer would not be present because of the no oxygen in space


Okay...when a metal is in space, there is no oxygen around it, therefore there is nothing to oxidize the surface of the metal. On Earth however, any metal is subject to oxidation since there is an oxygen atmosphere around it. So the correct answer is, when you bring a metal from outer space onto Earth, an oxidized layer would FORM around it -- and likewise when you brought it back into space, the layer wears off (depends on the metal, but most metals' oxidation layer would wear off if you bang/use the metal).
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#27
Jan 13 2009 07:33pm
Quote (BovineDesi @ Wed, Jan 14 2009, 01:25am)
Okay...when a metal is in space, there is no oxygen around it, therefore there is nothing to oxidize the surface of the metal. On Earth however, any metal is subject to oxidation since there is an oxygen atmosphere around it. So the correct answer is, when you bring a metal from outer space onto Earth, an oxidized layer would FORM around it -- and likewise when you brought it back into space, the layer wears off (depends on the metal, but most metals' oxidation layer would wear off if you bang/use the metal).


the very last reaches of our atmosphere are very low in oxygen, therefore any loose oxygen would rapidly combine with loose hydrogen particles or what have you
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#28
Jan 13 2009 10:01pm
I told my dad this and he said there had to still be a considerable amount of force to push the two metals together making them one piece. It's not like they just stick together.
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#29
Jan 14 2009 06:01pm
Quote (kegman909650 @ Tue, Jan 13 2009, 11:01pm)
I told my dad this and he said there had to still be a considerable amount of force to push the two metals together making them one piece. It's not like they just stick together.


Does your dad work at the NASA?
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#30
Jan 14 2009 06:48pm
Vacuum welding, aka cold welding, is basically a myth. There are *no*
documented cases of it actually occurring in orbit, except in experiments
deliberately designed to provoke it (with susceptible materials, great
care to avoid contamination, and deliberate mechanical removal of oxide
layers etc.).

A number of early problems were ascribed to cold welding, but those are
now thought to have been mostly cases of galling -- surface damage due to
metal-to-metal rubbing -- with lubrication absent, inadequate, improper,
or migrated. A few others were simple design botches. No spacecraft
anomalies have been attributed to cold welding since 1966, around the time
when people started having doubts about its reality.

No cold welding was found anywhere in LDEF's mechanical systems. All
apparent cases of it were eventually shown to be galling damage during
installation, or improper removal techniques leading to galling then.
(Stainless-steel fasteners, in particular, gall very easily.)
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mail to henry at zoo.utoronto.ca instead. | he...@spsystems.net

http://groups.google.com/group/sci.space.history/msg/9f09b7136c1206f5
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