December 12, 2019, 06:30:51 AM
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Topic: Rust removal with citric acid: black residue  (Read 276 times)

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Lewis

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Rust removal with citric acid: black residue
« on: October 09, 2019, 08:50:35 AM »
Hello,

I would like to know how to remove the black residue, that remains on the surface of carbon steel after rust removal by treatment with citric acid. Household-typical means and minimal abrasive action would be preferred, although the surface is pitted under the rusted areas.

Thanks,
Lewis

Offline hollytara

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Re: Rust removal with citric acid: black residue
« Reply #1 on: October 14, 2019, 11:36:10 AM »
If it is carbon steel, the black may be residual carbon - the citric acid would dissolve the metal but leave behind the carbon. 

The carbon might be removable with hydrogen peroxide - you could either use hydrogen peroxide from the pharmacy, or use something like Clorox2, which has hydrogen peroxide mixed with surfactants. 

If you test it on a small area, usually if the hydrogen peroxide is working you will see bubbles forming.

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