I would like to know what happens when gold leaf comes into contact with liquid gallium. Will the gold dissolve into (alloy with) the gallium, wet the gallium or have no reaction with gallium?

The reason I am asking this question is to figure out if I could gild some gold leaf onto a base metal (that is compatible with gallium) and use the gallium as an 'adhesive' between the gold and base metal. I am planning on using this as a gold plated cathode in electrolysis experiments.

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    $\begingroup$ I’m pretty sure the gold leaf will simply dissolve in the gallium. If I find anything definitive, I will post it as a comment. $\endgroup$ – Ed V Sep 17 '20 at 16:57
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    $\begingroup$ The wikipedia article on “Colored gold” says blue gold alloy is an alloy of gold with either gallium or indium. No idea how it is made. $\endgroup$ – Ed V Sep 17 '20 at 17:16
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    $\begingroup$ @MathewMahindaratne I think this is simply analogous to amalgamation: gold amalgamates very readily, so the melting point difference between Au and Hg does not factor in. In any event, a piece of gold leaf is inexpensive and presumably already available and a few drops of gallium are also inexpensive, so the experiment could be done easily. I think it is just a matter of dropping the gold leaf onto the gallium and seeing what happens. Alternatively, Ga wets glass, so wet a microscope slide, drop the Au leaf on it and see what happens. $\endgroup$ – Ed V Sep 17 '20 at 17:25
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    $\begingroup$ sciencedirect.com/science/article/pii/S0364591610000830 covers the Au-Ga phase diagram. There are 6 intermetallic phases, 4 of which are stable at and below room temperature. None of those could be considered an amalgam. The kinetics of phase formation are not covered. $\endgroup$ – Jon Custer Sep 17 '20 at 17:32
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    $\begingroup$ @EdV - from my perspective, Ga is a pretty boring and normal component of many binary phase diagrams. Perhaps the weirdest one is the strong positive heat of mixing in the liquid phase with Hg, leading to a liquid miscibility gap. But otherwise? Nope, pretty normal. $\endgroup$ – Jon Custer Sep 17 '20 at 17:48

Broadly speaking, looking at the Au-Ga phase diagram one gets:

enter image description here

(Now, this is based on a paper from 2011, a more recent 2017 paper is open access).

Several things to notice (or get from the paper):

  1. The solubility of gold in solid gallium can be considered to be zero.

  2. The solubility of gallium in gold is not zero, but is on the order of a few atomic percent.

  3. Slightly above the melting point of gallium, the solubility of gold in the liquid is also very small.

  4. There are multiple intermetallic phases across the diagram, 4 of which are stable at (and below) room temperature.

  5. Formation of an amalgam can be ruled out.

So, it is a pretty normal binary phase diagram. Now the phase diagram does not provide kinetics information, so the time needed to actually form any intermetallic compounds (and if those formed near room temperature would even be the equilibrium phases) is not known.

Now, if we look at how gold leaf is used, there is no glue used - the leaf is place, smoothed and hammered into place, and it just sticks. So try just sticking it.


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