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I'm looking for a wet etch of Bismuth Oxide that does not etch $\ce{Bi}$ itself.

There are obviously chemicals that etch $\ce{Bi2O3}$, but $\ce{Bi}$ is pretty fragile, so almost everything I've found that can etch $\ce{Bi2O3}$ also etches Bi, and usually more rapidly than the $\ce{Bi2O3}$ itself.

However, someone recently mentioned to me in passing that there was a chemical that could do this, but they didn't remember what it was.

Searching Google, I found this, but that's RIE -- not wet etching.

I've also read about people using $\ce{H2}$ gas to reduce the oxide back to $\ce{Bi}$, but again, not wet etching.

Does anyone have any idea? I know it's a specific and uncommon question.

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    $\begingroup$ I saw on wikipedia that bismuth oxide is transformed to bismuth trioleate by a mixture of acetic anhydride and oleic acid. I'm not 100% sure but I doubt either of those materials does much to bismuth metal. Maybe that could be the basis of a wet etching? $\endgroup$
    – Curt F.
    Jul 7, 2015 at 21:36

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In order to achieve what you're looking for you can use buffered hydrochloric acid solution. This solution can be adjusted to increase or minimize the etching rate of bismuth while selectively dissolving bismuth oxide.

For you to prepare this buffered HCl solution, take some concentrated hydrochloric acid and mix with appropriate buffer agent.

One of the widely used buffer agent for HCl or any other acidic solution is ammonium chloride and this helps in maintaining the ph balance.

Increase or decrease the concentration of HCl and the ammonium chloride solution to obtain the desired etching rate and corrosive nature. The pH of the solution should be optimized to minimize etching of elemental bismuth while effectively dissolving bismuth oxide.

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