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I'm curious whether any salt would at all dissolve in a liquid metal, such as gallium, mercury, or some other metal in the liquid phase?

A Google search of "solubility of NaCl in Mercury" results in papers on Mercury's solubility in molten salt. I have tried googling various combinations of salts and metals but with no success. I have little knowledge of searchable chemistry resources beyond google, and any suggestions of other places to look would be great.

Any ideas or resources that point me in the right direction would be appreciated (including better search terms).

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  • $\begingroup$ Well, obviously they are usually insoluble, at least the ones you can approximate as "ionic". If metallic character of these "salts" is bigger, you could expect some solubility. $\endgroup$
    – Mithoron
    Commented Jan 3, 2023 at 14:22
  • $\begingroup$ The AgCl-NaCl pseudo binary shows a miscibility gap at lower temperatures and complete solid solubility at higher temperatures. But you are only asking about liquid solubilities, with the salt as a unit or as separate entities? Please clarify. $\endgroup$
    – Jon Custer
    Commented Jan 3, 2023 at 16:25

3 Answers 3

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Yes, to varying extent. So just as a starter for your bibliographic research:

  • The solubility of salts in metals, a technical report by the US Department of Energy turned in by December 31st, 1960:

    "The results show that $\ce{BiCl3}$ and $\ce{Hg2Cl2}$ are most soluble, the former being completely miscible with Bi at 778 deg C, while the latter is soluble to the extent of 7 mole% at 600 deg C. $\ce{PbCl2}$ is slightly soluble (1 mole% at 1,000 deg C) while the remaining salts are considered insoluble in their metals. There does not appear to be any single criterion for predicting the solubility of salts in their metals."

  • Bredig, M. A.; Johnson, J. W.; Smith, T. M. Miscibility of Liquid Metals with Salts. I. The Sodium-Sodium Halide Systems. J. Am. Chem. Soc. 1955, 77, 307–312; doi 10.1021/ja01607a016. So far, there are 66 citations ACS identified just for this publication.

This equally is something to consider for e.g., molten-salt batteries (an entry on wikipedia, and an illustrative video).

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The solubility of oxygen, in effect cuprous oxide, in molten copper is important in the smelting and processing of this metal.

Silvain et al. 1 give the copper-oxygen phase diagram below:

enter image description here

Thus at $\pu{1200 °C}$, roughly $7$ atomic percent oxygen may be dissolved into molten copper; even at $\pu{1100 °C}$ about $2$ atomic percent may be dissolved. Since $\ce{Cu2O}$ is stable at these temperatures, the solution is effectively a solution of cuprous oxide in the metallic liquid. Above $\pu{1223 °C}$ where cuprous oxide decomposes, the metallic phase is effectively a nonstoichionetric oxide salt dissolved in copper. Above $\pu{1345 °C}$ the solubility limit disappears completely as metal and salt merge into a single phase.

Since copper is smelted and often processed as a liquid, this oxygen/oxide solubility must be considered in order to avoid contamination of the final copper product with precipitated oxide.

Reference

  1. J.F Silvain, J.L Bobet, J.M Heintz (2002). "Electroless deposition of copper onto alumina sub-micronic powders and sintering". Composites Part A: Applied Science and Manufacturing, 33(10), 1387-1390. https://doi.org/10.1016/S1359-835X(02)00153-7.
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    $\begingroup$ Similarly, molten silver is reportedly known as "misbehaving", dissolving oxygen too, excluding it while solidifying. That causes splashes of molten metal when breaking just formed and thin meta crust. $\endgroup$
    – Poutnik
    Commented Jan 3, 2023 at 14:34
  • $\begingroup$ One difference between silver and copper is that during solidification, silver has no stable oxides. So the oxygen is evolved as gas (silver spitting/splashing) rather than precipitated as a solid (contamination of copper metal). $\endgroup$ Commented Jan 3, 2023 at 20:26
  • $\begingroup$ Sure, I have not said otherwise. But the oxygen solubility in molten silver is very interesting. If I did not know it happens I would say "nonsense". $\endgroup$
    – Poutnik
    Commented Jan 3, 2023 at 20:28
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Bredig et.al. did an extensive study on the miscibility of liquid metals with salts especially alkali metal-alkali metal halide system. Later Dworkin et.al. worked together with M.A. Bredig and continued the study pertaining to alkaline-alkaline earth halide and rare earth-rare earth halides system. They together published a series of 11 papers under the title "Miscibility of Liquid Metals with Salts"

Simultaneously, Yosim et.al. worked with heavy metal-heavy metal chloride system. You can find the reference in @Buttonwood's answer.

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