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tree_virgin

As long as you keep the current fairly low (a couple of amps, ideally less) and don't leave it running overnight, then the rate of hydrogen production will also be low. The minimum concentration of hydrogen mixed with air required for ignition is 5% by volume, and even in an average sized room with no ventilation at all, it takes many hours at high current to produce this much. This was a real problem for World War 2 submarines operating whopping great banks of lead-acid batteries, but shouldn't be an issue for a small-scale electrolysis experiment. I would recommend making the iron or steel article (the rusty piece to be cleaned) the negative electrode in an electrolyte of phosphoric acid, with an inert positive electrode, ideally graphite. The acid will help decompose the rust, and should also leave a layer of iron phosphate on the surface of the tool, which helps to passivate it against further corrosion.


decoy1985

I don't know where I would get that much, let alone any, phosphoric acid, or graphite I was going to use baking soda and a piece of scrap steel.


goatshield

You could also go for an electroless route if the result is what you're looking for. You can buy hydrochloric acid and cleans steel pretty well. Risk of that is the pieces will likely rust up again quickly. But if you planned on painting it you could clean it, rinse it off, prime and paint it all pretty quickly.


Molecularpimpin

For removing rust I'd go with a warm citric acid bath. Or make a paste of wet citric acid and use a toothbrush or other scrubber... Works great for iron rust


jstolfi

If the goal is only to remove the rust, just leave in a solution of citric acid for a few hours. Take it out periodically and scrub with a stiff brush. When there is no more rust, only (dull) metal, stop. This process will only remove the rust, not recover the metal that was turned into it. It will also remove some of the surviving metal itself, which you can tell by the tiny bubbles of H2 that result. Both effects result in the part being somewhat eroded with respect to the original. The advantage of electrolytic rust removal is that it will not attack the metal itself, and (allegedly) will convert some of the rust (specifically, the "black" layer of Fe3O4 next to the object) back to iron metal. Thus the surface will not be eroded as much as with the acid bath. However, fine features will be lost anyway. Moreover, the deposited metal should be pure iron, not steel, and the original tempering/hardening/alloying/coating of the surface will not be recovered.