[TheForge] Hydrochloric acid and galvanising

Fri Jul 18 12:16:00 2003

I strongly doubt that PURE hydrochloric acid would make galvanized turn
black.  What else have you had in this acid?  

If you pickle the zinc off the steel, the steel should be shiny, not
black.  I think you've left something behind, but I don't know what.

Black is often due to finely divided metal.  I'm wondering whether you
may be precipitating out some less-active metal on the surface of your
galvanized steel.  If this is the case, no telling how stable it would
be.  Finely divided metal could be loose as a powder.  Even if not
loose, it would react with air fairly readily.  So, I doubt this would
be a stable color.

Zinc and other metals can be turned black by sulfide - but you won't
find sulfide in hydrochloric acid.

Don't know whether this helps.

Bruce
NJ

>>> [email protected] 07/17/03 11:23PM >>>
Does anyone know if the blackend look adding H Ch acid to galved steel
is as
durable to corrosion as plain galv? whats the reaction that makes it
go
black? have I even got the right acid, I did this a long time ago and
havent
used it since. Does it actually react or just remove the galv and show
black
steel?

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