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The oxide layer formed on galinstan (or its component of pure gallium) when exposed to air increases wetting and dulls the appearance. Is there a clear liquid material in which a blob of liquid galinstan can be placed that would prevent oxidation of the surface long-term? Ideally the protective liquid would be cheap, relatively safe, not degrade with time, and have a viscosity of about that of water. The goal is to show off galinstan's un-oxidized appearance and surface tension in a sealed or nearly-sealed container.

I know that application of sulfuric acid can break down the oxide layer temporarily, but am unsure if weaker acids accomplish the same, whether this destroys part of the material, and how long the effect would last.

Clear oils could perhaps accomplish the protection goal, but I'm interested if there are less viscous alternatives (e.g., water, alcohol, etc...) and whether additives are necessary to maintain the galinstan's surface appearance.

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  • $\begingroup$ Those liquids should be in the first place inert. Liquids with active hydrogen like water or alkohols can react with gallium. $\endgroup$
    – Poutnik
    Oct 7, 2021 at 16:22
  • $\begingroup$ If oil is acceptable, but too viscous, try naphtha, kerosene or charcoal lighter fluid (if it contains no alcohols or ketones). Of course, these are flammable and attack some plastics,, so use a strong glass container. $\endgroup$
    – DrMoishe Pippik
    Oct 7, 2021 at 19:00
  • $\begingroup$ I'd prefer to avoid easily flammable liquids if at all possible, as larger volumes may eventually be used. Safety and clarity would take precedence over viscosity. Would PFCs carry too much oxygen? What about glycerin? $\endgroup$
    – Parallax
    Oct 7, 2021 at 20:23
  • $\begingroup$ What about an inert gas, like nitrogen or argon? $\endgroup$
    – Poutnik
    Oct 20, 2021 at 11:16

1 Answer 1

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I use dilute hydrochloric acid to keep my galinstan looking like mercury. The oxide doesn't just increase wetting it its the sole cause of it. You need at least 0.1 M HCl to get maximum surface tension and to keep the surface shiny. Paper on it

0.1 M is about 0.37% concentration. Any concentration of HCl under 5% is "safe" to handle and only over 15% is considered to have the ability to case serious harm. Muriatic acid from a store is usually around 28% - 36% but they don't always give an exact concentration. You'll either have to buy some from a chemical shop that specifies or do a titration on the common stuff.

I just started some trials with 12 sealed tubes of about 1 ml galinstan each ranging from pure water to 1.0 M HCl. Cool stuff. (Sorry for bad quality, phone camera glass is shattered) Only been a few hours and I plan to leave them for months but as of now at 0.1 M and higher concentrations it looks perfect. 0.05 M looks decent, lower and its no longer shiny. The highest (0.5 M - 1.0 M) have visible hydrogen forming from excess acid attacking the metal itself. So far seems like 0.1 M to 0.2 M HCl is best. Water only vs 0.2 M HCl bath

And try to only get clean metal in the acid without tons of oxidation or the dilute acid wont be able to dissolve it all. I always keep my galinstan under water and my syringes full of water when I work with it as soon as its cooled from the alloying heat to slow the oxidation.

In case you don't know the process going on here, the acid can react with the gallium oxide as it forms from the dissolved oxygen in the water. The products of this are gallium chloride and water. Gallium chloride is very soluble in water so the small amounts are invisible. The dilute acid also slowly (very, very slowly) reacts with the gallium, indium, and tin to form the metal chlorides and hydrogen gas. With dilute levels like 0.1 M the metal being lost is negligible. The container is completely full with water so no new oxygen can be dissolved like it would if there was air present above the water.

I'm thinking that if it is in a sealed container the oxygen dissolved in the water will eventually be consumed and converted to H2O and the system will reach an equilibrium. But I'm no expert. If it can last a year or more I'd be satisfied. (Making non toxic liquid metal snow globes with the centerpiece floating on galinstan.)

Liquid metal is fun to work with. I especially like watching it bounce and rebound off the glass when its in a small enough amount to form a bead. I will update this with my results in weeks or months. Best of luck!

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  • $\begingroup$ Argon or nitrogen should work yes, but getting galinstan with zero oxidation in a sealed container with zero oxygen contamination in the gas is not feasible unless you have the right equipment. I don't, but maybe you have access to some. Even just a small amount of oxygen will dull the metal and the argon can't remove that oxidation. You would still probably need to have the galinstan in a dilute acid bath before putting it in the inert gas anyways to get rid of oxidation beforehand. Putting a few drops of muriatic acid in some water and adding galinstan is easy enough for me. $\endgroup$
    – GalinCam
    Oct 20, 2021 at 16:07

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