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"Nitric acid as a component to balance pH for chromate bath"

February 21, 2010

Good day everyone,

I have a question and inquiry but cannot find any definite answer hope experts around can help me.

I am wondering for black chromate normally there is 3 component for black chromating, lets maybe just call it black a/b/c, I wonder if a and b are main component for the bath make up and c is just the pH buffer.

but now if I don't add c and I replace it with nitric acid to control the pH at 1.9 - 2.1 and I am adding it in bulk, so my question is will there be reaction between my parts and the chromate bath.

will there be excessive hydrogen stuck in burrs or pores of fastener and screw and cause embrittlement.

please advise.

Lindy Lam
hobbyist - Singapore

February , 2010

Hi, Lindy. This is awfully cryptic! You have mystery ingredients "a" and "b", and you want to know what will happen if, in lieu of adding mystery ingredient "c" to them, you add nitric acid to them instead? :-)

I believe that a small amount of nitric acid may be present in commercial chromates, and chromic acid is an oxidizer just as nitric acid is, so I don't think you will ruin the parts through hydrogen embrittlement. Do you bake the parts after plating and before chromating?

Please start by telling us what you are up to :-)


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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