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Author Topic: Which metals diffuse into other metals and how?  (Read 1248 times)

Offline thedoc

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Which metals diffuse into other metals and how?
« on: 25/09/2015 21:50:02 »
Shashwat Sharma asked the Naked Scientists:
   
Which metals diffuse into other metals? How?  
please list all metals and the metals they diffuse into.  

What do you think?
« Last Edit: 25/09/2015 21:50:02 by _system »


 

Offline chiralSPO

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Re: Which metals diffuse into other metals and how?
« Reply #1 on: 04/10/2015 14:22:26 »
I believe most metals diffuse into other metals. It really a question of rates. There are also some major differences in the outcome depending on the difference in electronegativity between the metals.

Sodium and potassium metal (both soft solids, like cold butter) react most quickly because they are soft to begin with (atoms are mobile) end up making an alloy that is liquid at room temperature (
), which then dissolves the remaining solids and facilitating the mixing (
). Mercury metal is also liquid at room temperature, and will quickly form amalgams (https://en.wikipedia.org/wiki/Amalgam_%28chemistry%29) with many metals (including sodium, aluminum, potassium, copper, tin, gold, lead...)

There are also much slower reactions, like that between gold and aluminum, which is known as a failure mechanism in devices where a gold wire is connected to an aluminum component, and takes weeks to manifest under normal conditions (https://en.wikipedia.org/wiki/Gold-aluminium_intermetallic). Interestingly, because the electronegativity of gold and aluminum are so different, the resulting compounds aren't really metallic, and are brittle and poorly conductive.... and white or bright purple!

At higher temperatures, noble metals like gold and palladium react violently with aluminum (
)
In addition to increasing the temperature, one can speed up the reaction between two metals by pressing them into one another very hard (https://en.wikipedia.org/wiki/Cold_welding)
« Last Edit: 04/10/2015 14:31:26 by chiralSPO »
 

Offline evan_au

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Re: Which metals diffuse into other metals and how?
« Reply #2 on: 04/10/2015 23:25:32 »
On Earth, there is often a layer of oxide on the surface of metals, which discourages this diffusion of atoms from one piece of metal into another.

However, in space, cold welding occurs readily, and is a major problem for mechanical design of satellites.
 

Offline chiralSPO

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Re: Which metals diffuse into other metals and how?
« Reply #3 on: 05/10/2015 15:40:24 »
Another interesting point is that hydrogen diffuses into and through many types of metal. It is actually quite soluble in iron and nickel, and can cause steel pipes to become brittle. I believe that aluminum in impervious, but I am not certain if it is because of the nature of the metal itself, or the protective oxide surface.

Hydrogen is not a metal as we know it, but supposedly does become metallic under extreme pressures, such as found at the core of Jupiter.
 

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Re: Which metals diffuse into other metals and how?
« Reply #3 on: 05/10/2015 15:40:24 »

 

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