I have several NIST stainless steel standards that have rusted over time. I would like to remove the rust while preserving the composition of the samples. Is there an effective way to do so? For instance, is there something that would react exclusively with metal oxides rather than with metals themselves?
Passivation will remove free iron on the surface, and should remove any corrosion products as well. It creates an iron-free surface layer on the order of 10 Angstroms thickness. It is up to you if that constitutes an acceptable chemical change to the steel, as removing corrosion is also a chemical change.
ASTM A967 or SAE AMS2700 provide passivation procedures for stainless steels. For simple corrosion removal, I would recommend a process without a dichromate sealer.
You can use SiC paper to remove the rust if it's only on the surface. If not, you can use appropriate chemical cleaning procedures described in ASTM G1 standard. For instance, for iron you can use 500 ml HCl + 3.5 g Hexamethylene Tetramine + water (to make a 1000 ml solution) and put your samples for 10-12 minutes to remove rust. Attach is the link to ASTM G1. Hope it helps.
https://www.astm.org/Standards/G1.htm
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