Electropolished stainless steel has a high corrosion resistance due to the oxide film that is created during electropolishing. The film mainly consist of chromium(III) oxide.

Phosphoric acid is used as a rust removing agent:

$\ce{2 H3PO4 + Fe2O3 -> 2 FePO4 + 3 H2O}$

My question is: will 5% $\ce{H3PO4}$ solution remove this protective layer as well? It should, but how fast will be the protective layer removed? Does anyone have personal experience?

  • $\begingroup$ The phosphoric acid will remove the coating if it's concentrated enough but the time it takes to do this depends on how concentrated the acid is and how much of the acid it is exposed to. $\endgroup$
    – Technetium
    Jun 23 '15 at 3:37

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