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Letter 22011
ASSURING STEEL IS UNPASSIVATED
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1. I AM USING GALVANIZED STEEL, I WANT TO TAKE OFF THE
PASSIVATION, WHAT PRODUCT SHOULD I USE?
2. IS THERE A TESTING METHOD TO MAKE SURE THE METAL IS
UN-PASSIVATED?
THANK YOU,
SERGE DORE
MOELLER ELECTRIC INC - GRANBY, QUEBEC, CANADA
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The meaning of the word "passivation" is very tricky in this
instance. Generally the term "passivation" is applied to stainless
steels, and refers to the building of a chrome-rich surface skin. The
term "passivation" is also sometimes used, however, to refer to the
chromate conversion coating that is applied to zinc plated and zinc
galvanized surfaces. But the way you are using the term, it seems
like you are really asking how to remove the zinc, not just the
chromate?
The zinc will almost instantly dissolve in hydrochloric acid; in
fact the reaction can be violent.
If you are trying to remove just the chromate conversion coating,
I think scrubbing it with
Trisodium Phosphate [link is to product info at Amazon] and
Pumice [link is to product info at Amazon]
will do it. There
are ASTM standard "spot tests" for the presence of the chromate.
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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