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A common problem in shooting sports is precipitation of lead onto aluminum suppressor baffles. (The lead presumably comes from both lead styphnate priming compound and from the base and bearing surface of lead bullets that vaporize during propulsion.)

If the lead precipitate is allowed to build up a contiguous layer it requires mechanical removal, which tends to damage and degrade the aluminum alloys used.

A common solution for ferrous baffles is to strip the lead with H2O2-boosted acetic acid, but that goes after aluminum almost as fast as lead.

What practical electrochemical methods could be used to strip the solid lead from the aluminum?

(Bonus if you can propose a method that would also leave titanium baffles intact!)

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You could try hard anodizing Al and Ti (e.g., Calphalon cookware) to give them a non-delicate surface, and go on from there. Black is a good gun component color. CVD deposition of titanium boride, ion plating of titanium nitride or carbonitride gives exceptionally survivable hard surfaces.

http://www.brycoat.com/coating-services/pvd-coatings/titanium-nitride-tin.html
http://www.brycoat.com/coating-services/pvd-coatings/ticn.html

Among mostly cheap and harmless diddles, I'd try 1:2 mole ratio of choline chloride with urea or ethylene glycol ("all natural," etc.). Mix, the deep eutectic liquefies, soak. Both eutectics conduct electricity, so you could make lead contamination the anode and plate it out on a closely spaced but not touching copper foil cathode. Test on contaminated waste Al or Ti. Careful with the voltage - too high and you mobilize Al and Ti. Avoid contact with skin pro forma, do not ingest, keep away from eyes.

Try vacuum thermal deposition of a micron or so thickness of the Parylene family on the newly fabricated and cleaned metal - intrinsic, especially C, or F. Parylene polymer surface coats survive the insides of excimer lasers, protecting the excitation electrodes. If the lead still sticks, chemical cleaning should stop at the polyparylene film. Or not. Gotta test it. You are worried about vapor deposition not abrasion, so an inert barrier film is reasonable.

Google, parylene coating services

For aluminum or titanium vs. lead in chemistry, I'd pull one out of left field to try on test coupons: Rauchfuss' elixir: elemental sulfur dissolved in N-methylimdiazole (pyridine less so, very smelly, toxic, and don't get it on your skin or breathe the awful vapors). It goes through polysulfide-forming metals like a buzz saw, giving soluble products. I would expect aluminum to be inert; titanium is a toss-up. It should hit lead hard, probably. Test it small scale.

Inorg. Chem. 30 (11): 2514 (1991)
DOI:10.1021/ic00011a011
http://dx.doi.org/ (resolve a DOI)

Last gasp: Weapon Shield to clean before and after firing.

Concentrated nitric acid (already a bad idea) passivates aluminum and eats lead. Toxic and corrosive NOx fumes come off. However...aluminum plus lead in galvanic contact make aluminum the sacrificial anode. Homeland Severity does not like people possessing concentrated nitric acid.

Wear gloves and goggles, have ventilation. None of this stuff is good for you.

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  • $\begingroup$ Thanks. Prophylactic coating (as with Weapon Shield) is the current best practice -- along with cleaning frequently enough that no solid deposition layers form. Hard anodizing is often done but doesn't seem to help with this problem substantially. Parylenes look interesting, but I have read that PTFE has been tried and failed because propellant temperatures can exceed 650F. Assuming I can source it I'll certainly like to test the sulfur/methylimidazole. First search shows methylimidazole to be super expensive. Any ideas for cheaper sources? I don't need lab grade. $\endgroup$ – feetwet Apr 30 '14 at 4:16
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    $\begingroup$ chemistry.illinois.edu/faculty/thomas_rauchfuss.htm Talk with Rauchfuss. Pyridine is workable but terrible for the stink and some toxicity. If you stop smelling it you are OD'd. 340 C is beyond Parylenes dying about 200 C, event too high for phenyl silicones. Give deep eutectics a whack, especially with voltaic stripping. Cheap, non-hazardous, available in bulk. It could be a kit for general civilian and military armory use. $\endgroup$ – Uncle Al Apr 30 '14 at 15:06
  • $\begingroup$ Choline chloride is a bulk chicken feed additive. Urea is a bulk nitrogen fertilizer. You certainly don't need reagent grade. Choline chloride is 139.62 g/mol, urea is 60.06 g/mol, ethylene glycol is 62.07 g/mol. Thus one part by weight choline chloride to 0.86 parts urea or 0.89 parts ethylene glycol, both by weight. It works or it doesn't work. As you said, the problem is keeping Al and Ti inert while moving the lead - and disposing of it. You want Pb out net, not dissolved in a gallon of goo. $\endgroup$ – Uncle Al Apr 30 '14 at 15:20
  • $\begingroup$ Looks like two excellent options. I've contacted Prof. Rauchfuss about his elixir. I'm drawing a blank on "eutectics" here. Can you point me to some background on that chemistry? Also basic parameters to try for the voltaic reaction -- e.g., what range of voltage likely to move the lead but not the light metals, and what that's a function of: e.g., distance to cathode, purities, masses of anything? And when do the various components need to be refreshed -- e.g., will the cathode be impaired by some thickness of lead? Thanks! $\endgroup$ – feetwet Apr 30 '14 at 15:46
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    $\begingroup$ en.wikipedia.org/wiki/Deep_eutectic_solvent en.wikipedia.org/wiki/Ionic_liquid www2.le.ac.uk/departments/chemistry/research/lil chemspecevents.com/europe/images/uploads/chemsource/… (deep eutectics start about 55% down, including lead) Cell voltage depends on cell resistance in part, and the chemistry. This is not an aqueous cell. Try Pb-fouled metal around a volt oxidizing, see what happens. Closer electrode spacing is a more efficient cell. The cathode can keep accumulating lead. Cu is a better conductor. $\endgroup$ – Uncle Al Apr 30 '14 at 18:10

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