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I weld carbon steels all the time, and sometimes I get parts from the scrapyard. Unfortunately, these parts are generally oxidized, so I've been assembling an electrolysis tank for it. This tank removes the oxidation in about a day. I'm getting the feeling that I can make it go faster if I step up the current or voltage. What combinations of currents or voltages would make the fastest method of removal?

NOTE: I'm familiar with the risks of doing electrolysis, including hydroxy production, and the restriction on stainless steel electrodes.

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  • $\begingroup$ What is the applied voltage? Did you try just HCl? $\endgroup$ Sep 17, 2015 at 10:42
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    $\begingroup$ I use 12V at 2A. I'm using NaOH for the electrolyte. Approximately 1 tablespoon per gallon with 15 gallons. $\endgroup$ Sep 18, 2015 at 3:36
  • $\begingroup$ and what about the HCl? $\endgroup$ Sep 18, 2015 at 10:12
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    $\begingroup$ @SarahSzabo Washing soda ($\ce{Na2CO3}$) might work just as well as the $\ce{NaOH}$ and for much cheaper too... $\endgroup$
    – ManRow
    Jan 30, 2023 at 11:05

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This is what I found (only in Czech):webpage

Power source should be around 15V/5A. The cleaned part acts as negative electrode- applied voltage should be as high as needed to reach 2A. The electrolyte (described in the source) is based on water and sodium carbonate. Derusting should be done between 2 to 4 hours. Let us know if it helps or how it works.

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In order to answer the question we also need how large a part you are electrolyzing.

The current density in $mA/cm^2$ is the key number. For electrolysis on stainless steel, I would say you need to stay less than about $ 1~mA/cm^2$ to stay safe.

The voltage is hard to gauge. In any two electrode system like yours, the electrochemical potential is only one part of the total potential. The total potential includes contributions from the resistance of the solution, resistance of the contacts, overpotential of the counter reaction, etc... The current should be a decent gauge of what you are seeing.

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I run graphite plate electrodes (anodes), to avoid consuming them I try to stay below 15A/square foot, much depends on the area of both workpiece and electrode. Example, I'm currently de-rusting a motorcycle tank (Damn You, E10 "petrol") using a 20x2 inch, quarter-inch thinck graphite (50cm x 5cm x 6cm), about a mugfull of wash soda (sodium carbonate) in 5 gallons and with a 12v supply (old transformer battery charger) it's taking 8 Amps - near enough the 15A/square-foot. For awkward access like inside tanks etc, the graphite's wrapped in the non-slip mat sold for car dashboards etc, cable tied in place to prevent shorting to the tank or whatever.

I started out using scrap steel sheet as the electrode, but it grows barnacles that need to be scraped and brushed off regularly to maintain current and effectiveness, with graphite this does not happen and the process can be ignored for as long as it takes :)

NEVER, EVER use stainless steel as the anode - this will produve hexavalent chromium in the solution, which must be disposed of as toxic waste by a licenced waste processor and legally MUST be transported as toxic waste by a licenced handler. It's neurotoxic, hepatotoxic, implied carcinogen - you REALLY don't want it anywhere near you/

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I've just set up a small tank. My smart ass charger no good so I've borrowed a bigger one with a gauge on it. Its set to minimum but if the gauge is to be believed, it is showing 5 amps and it is fizzing away nicely. I wanted 2 amps so I will check it soon!!

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