Does solid absorb or lose its atoms near the surface?

[kenny1999]

I know that atoms or molecules near the surface of liquid or water may absorb from or lose its molecules/atoms to the surrounding.

Does it also happen to solid?

When two solids of the same kind or different kinds are touched, pushed, or rubbed against each other, could they exchange their molecules or atoms at the touching surface?

Thanks for the concept.

[John Cuthber]

Some clearly do. Camphor and menthol have strong odours.
Diffusion in solids it slow, but it does happen.

 

[swansont]

I knew people in grad school who studied adsorption on solid surfaces, and other surface effects. The forces are different than in the bulk solid, since you don’t have the interaction from all directions. The lack of symmetry makes for some interesting physics.

Surfaces of the same material can have pretty strong attraction; the adhesion between metal surfaces is called galling 

https://en.m.wikipedia.org/wiki/Galling

(I “discovered” this problem putting some bolts into a frame in a vacuum system and having one seize up. Right after, I was introduced to the anti-seizing compound molybdenum disulfide)

[kenny1999]

12 hours ago, swansont said:

I knew people in grad school who studied adsorption on solid surfaces, and other surface effects. The forces are different than in the bulk solid, since you don’t have the interaction from all directions. The lack of symmetry makes for some interesting physics.

Surfaces of the same material can have pretty strong attraction; the adhesion between metal surfaces is called galling 

https://en.m.wikipedia.org/wiki/Galling

(I “discovered” this problem putting some bolts into a frame in a vacuum system and having one seize up. Right after, I was introduced to the anti-seizing compound molybdenum disulfide)

How about if they are not metals, but two different materials?

[exchemist]

16 hours ago, swansont said:

I knew people in grad school who studied adsorption on solid surfaces, and other surface effects. The forces are different than in the bulk solid, since you don’t have the interaction from all directions. The lack of symmetry makes for some interesting physics.

Surfaces of the same material can have pretty strong attraction; the adhesion between metal surfaces is called galling 

https://en.m.wikipedia.org/wiki/Galling

(I “discovered” this problem putting some bolts into a frame in a vacuum system and having one seize up. Right after, I was introduced to the anti-seizing compound molybdenum disulfide)

According to my recollection from the lubricants industry this phenomenon applies to sliding surfaces, rather than just a static contact. It leads to what is known as adhesive wear (as opposed to abrasive or corrosive wear).

With sliding surfaces, microscopic asperities come into contact, causing very high pressures and temperatures at the contact zone which leads to microscopic welding of the surfaces at these points. As the sliding continues, these microscopically welded areas are torn asunder. Often this does not occur at the point where the weld formed, so that material is torn out of one or both surfaces. It is often the practice to use dissimilar metals in bearings, chosen so that the welds are weaker than the parent metals. This encourages the adhesions to break without tearing lumps out and thus preserving the surface. (One example is in worm gears, where the worm is usually steel and the gear wheel is bronze. Worm gears have an extremely high rate of sliding relative to rotation, so the issue can be quite acute in such gears.)

The purpose of lubricants of course is to keep the surfaces apart and prevent this from happening. It is common practice to add anti-wear or extreme pressure agents - often sulphur/phosphorus containing organic molecules -  to lubricants where the nature of the motion does not ensure a constant pressurised film of lubricant to do this, another classic example being the cam followers in an engine. The anti-wear agents decompose under local temperature, adsorb on the surface and form a protective but weak layer, that easily breaks without damaging the parent surface. 

However one does also get "cold welding" of clean flat metal surfaces brought into static contact. This occurs especially with surfaces exposed under vacuum, so that no oxide layer has a chance to form: https://en.wikipedia.org/wiki/Cold_welding.  

 

Edited December 18, 2023 by exchemist

[studiot]

I think it is worth pointing out the difference between absorbtion and adsorbtion.

Adsorbtion is the interaction at the surface or interface only.

Absorbtion molecules of one material are incorporated into the body mass of the other.

The distinction may bit a bit blurred with 'solids' such as sponges which have a very large internal surface area.

[exchemist]

On 12/18/2023 at 12:00 PM, studiot said:

I think it is worth pointing out the difference between absorbtion and adsorbtion.

Adsorbtion is the interaction at the surface or interface only.

Absorbtion molecules of one material are incorporated into the body mass of the other.

The distinction may bit a bit blurred with 'solids' such as sponges which have a very large internal surface area.

Good point, and yes, we had that discussion with that person who had a bee in his or her bonnet about microwaving silica gel, some months ago. 

[Phi for All]

4 hours ago, exchemist said:

Good point, and yes, we had that discussion with that person who had a bee in his or her bonnet about microwaving silica gel, some months ago. 

I know it's a post hoc fallacy, but I'm convinced microwaving silica gel causes mental fixations.

[exchemist]

8 hours ago, Phi for All said:

I know it's a post hoc fallacy, but I'm convinced microwaving silica gel causes mental fixations.

Ssh, don’t tell Lara Knowles.