Ask A Scientist Chemistry Archive

name         Michael A.
status       educator
age          40s

Question -   Is their something that can be applied to pickled 
steel, such as a chloride or similar substance, which would cause a very 
rapid (i.e. a matter of minutes) oxidation of the surface of the steel so 
that it would be readily apparent?
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You sent me on a search, since I did not know for sure what "pickled" 
steel is.
     ANSWER: Basically, it is a hot acid treatment during production to 
remove rust,  scale and oils from the surface of steel.
    You could probably use concentrated HCl, H2SO4, or H3PO4 but all of 
these acids are very corrosive at high concentrations and especially at 
elevated temperatures, so I would not recommend them unless you are 
equipped to handle those materials.
    There are a number of steel "brighteners" commercially available. I 
do not know what chemistry they involve, but you could certainly contact 
the vendors for direction and/or method for the application you have in mind.

BRIGHTENERS AND PICKLING AGENTS

http://www.ecki.com/vst/prdt543.htm

http://www.seatexcorp.com/newProducts.asp

http://www.iams.org/iamsorg/p2iris/metalfinish/1197-p.htm

http://metal-plating-chemicals.com/

      Pickling
     A process to chemically remove scale or oxide from steel to obtain a 
clean surface. When applied to bars or coils prior to bright drawing, the 
steel is immersed in a bath of dilute sulphuric acid heated to a 
temperature of around 80oC. An inhibitor is added to prevent attack and 
pitting of the cleaned metal. After pickling, a washing process takes 
place followed by immersion in a lime-water bath to neutralize any 
remaining acid. For environmental reasons shot blasting has largely 
replaced pickling.

Vince Calder
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