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Author Topic: What happens, on a molecular level, when a solid is cut?  (Read 4555 times)

Offline lancenti

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I was just thinking suddenly - what happens when you cut a solid on a molecular level?

Is it simply that you break bonds? If it is, why is it not possible that two solids become one solid again when you put them together at the same place you cut them?
« Last Edit: 01/01/2009 04:07:32 by chris »


 

Offline lightarrow

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Re: What happens, on a molecular level, when a solid is cut?
« Reply #1 on: 29/12/2008 18:40:48 »
I was just thinking suddenly - what happens when you cut a solid on a molecular level?

Is it simply that you break bonds? If it is, why is it not possible that two solids become one solid again when you put them together at the same place you cut them?
It's an interesting question, I have asked myself several times. The answer I gave to me is that to achieve it in practice would be very difficult: the atoms/molecules on the cut surfaces rearrange themselves immediately so the surfaces are not the same after a very short time; second, they would be immediately contaminated by other atoms/molecules in the air; third, to make the two surfaces correspond perfectly would be quite impossible because they are not completely smooth, but have microscopic holes and ridges. In the hypothesys that those effects could be negligible, I immagine that the two surfaces should perfectly re-attach upon contact.
« Last Edit: 29/12/2008 18:45:09 by lightarrow »
 

Offline lancenti

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Re: What happens, on a molecular level, when a solid is cut?
« Reply #2 on: 30/12/2008 02:58:50 »
Hmm, that is true, but let's consider a case.

Supposing we use a highly unreactive metal, such as Gold. After breaking the metallic bonds between a certain section, we wouldn't expect any real contamination via oxidation so we could still say it's pure gold. (Okay, maybe with tiny dust particle in the middle of nowhere if we're in a clean room) If there is indeed a sea of delocalized electrons in the metal, then putting them together should allow the sea to delocalize into each other (hence why two metals in contact conduct, right?) and so it should eventually become one again. Am I correct in thinking this way?
 

Offline Chemistry4me

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Re: What happens, on a molecular level, when a solid is cut?
« Reply #3 on: 30/12/2008 05:13:17 »
The two pieces needs enough activation energy to come together again, applying a bit of heat will certainly help. Thats how they usually do it.
 

Offline lightarrow

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Re: What happens, on a molecular level, when a solid is cut?
« Reply #4 on: 30/12/2008 15:03:19 »
Hmm, that is true, but let's consider a case.

Supposing we use a highly unreactive metal, such as Gold. After breaking the metallic bonds between a certain section, we wouldn't expect any real contamination via oxidation so we could still say it's pure gold. (Okay, maybe with tiny dust particle in the middle of nowhere if we're in a clean room) If there is indeed a sea of delocalized electrons in the metal, then putting them together should allow the sea to delocalize into each other (hence why two metals in contact conduct, right?) and so it should eventually become one again. Am I correct in thinking this way?
It's not only oxidation and dust (which is correct) but also air and all the other atoms/molecules present in the air which are adsorbed on the surface, so you should conduct the experiment in absolute void. Then you would still have the problem of making a good contact between the two surfaces for what I explained before. This said, I believe there wouldn't be much problems in recreating the bonds at the simple act of contact.

Chemistry4me: I'm not sure activation energy is significant in this case, I would tend to believe it is negligible (but I don't know it for certain).
The fact that to sold two metallic pieces we heat them is to increase diffusion of atoms from one surface to the other surface and to increase the contact with a pressure exploiting the material's softeness at high temperature.
 

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Re: What happens, on a molecular level, when a solid is cut?
« Reply #4 on: 30/12/2008 15:03:19 »

 

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