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I wanted to electroplate aluminum onto a 3D printed part (treated with conductive paint). I found out that you can plate it with copper, zinc, gold, or palladium from an aqueous solution, but electroplating with aluminum seems to be difficult. I have two questions:

  1. Why is that?
  2. I found that you can use molten salt, benzene-tetrahydrofuran-AlCl3-LiAlH4 or AlCl3 in acetamide to electroplate aluminum onto a surface. Would it work if I use AlCl3 in DMSO?
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    $\begingroup$ Aluminium has too negative electrochemical potential to be deposited from water solutions. Hydrogen obtained by reduction of H+(aq) or even H2O is preferably produced. $\endgroup$
    – Poutnik
    Commented Apr 5, 2022 at 11:38
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    $\begingroup$ Exposing of 3D prints - or at least their conductive paint - to organic solvents may lead to damage or even destruction of the substrate aluminium is supposed to be deposited on. Check solvent - print-with-paint compatibility. $\endgroup$
    – Poutnik
    Commented Apr 5, 2022 at 12:57
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    $\begingroup$ Aluminum coating are made with vapor deposition. $\endgroup$
    – blacksmith37
    Commented Apr 5, 2022 at 14:22
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    $\begingroup$ In my notes, I got a report from the year 1950 saying that the metal aluminum can be obtained by electrolysis in a solution of $\ce{AlCl3}$ in ether, of which a concentrated solution of 2-ethyl-hexylamine in ethanol has been added. In case of necessity, I could find this review. I only have the code of my university library. $\endgroup$
    – Maurice
    Commented Apr 5, 2022 at 20:59
  • $\begingroup$ BTW, plated aluminum, if pure, would be very soft, easily scratched by a fingernail. If it is possible to plate that part, and to do so wit a thick enough layer, it might require anodizing to withstand handling. $\endgroup$
    – DrMoishe Pippik
    Commented Apr 5, 2022 at 23:37

2 Answers 2

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Aluminum can be obtained by electrolysis of $\ce{AlCl3}$ in DMSO, as shown by you in your answer, iblue. But it should be stated that

  1. the solution should be absolutely anhydrous

  2. once deposited on any metallic support by electrolysis, aluminum must be kept and stored in an absolutely dry atmosphere. This allows the aluminum metal to be in contact with oxygen $\ce{O2}$ to produce a thin, waterproof, and continuous layer of aluminum oxide $\ce{Al2O3}$. This continuous layer prevents the aluminum metal to get in touch with water. All pieces of aluminum metal in the world are covered by this thin film.

Without this oxide layer, aluminum reacts quickly and violently with water, as can be demonstrated by dipping an aluminum piece in a solution of mercury chloride $\ce{HgCl2}$ : $\ce{HgCl2}$ is able to cross the aluminum oxide layer and react with the metal according to $$\ce{3 HgCl2 + 2 Al -> 3 Hg + 2 AlCl3}$$ The deposited mercury produces an amalgam with aluminum $\ce{Al(Hg)}$. And then the continuous aluminum oxide layer is broken. As a consequence, the unprotected aluminum metal reacts violently with water according to $$\ce{2Al + 6 H2O -> 2 Al(OH)3 + 3 H2}$$ This demonstration was popular in the middle of the previous century. Nowadays it is obviously not feasible anymore, because of the toxicity of mercury salts.

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So, time went by and I got a little wiser. Answering my own question in the hopes that it may be useful to someone, somewhere, sometime.

  1. The issue is that aluminum has an electrode potential way lower than hydrogen, so in an aqueous solution instead of Aluminum being reduced on the cathode, the production of hydrogen will be favored strongly.

  2. Maybe. You can at least electroplate aluminium very well from DMSO2 (dimethylsulfone). The conditions reported were however 110-150 °C and the electrolyte has to be prepared in an argon-filled glove box (Source: https://doi.org/10.1016/j.surfcoat.2006.11.035), I suppose because AlCl3 is very hygroscopic.

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  • $\begingroup$ @Peterswift Don't spam people with comments. Such links are supposed to be mainly on questions that are more or less related. $\endgroup$
    – Mithoron
    Commented Sep 9 at 17:34

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