[TheForge] Hydrochloric acid and galvanising

Fri Jul 18 13:02:01 2003

Amusingly enough I cast allot of zinc, and I play with some of the drop slag
with Hydroclhoric acid to generate hydrogen gas, yes Zinc will turn black
however you can damage the black finish with a light touch.  I have take a
few pieces of galvanize, pickled then and then carefully coated with
lacquer, but then whets the point of galv, if you are going to turn it into
finely divided metal, it doesn't have much corrosion protection any more.

----- Original Message -----
From: "Bruce Freeman" <[email protected]>
To: <[email protected]>
Sent: Friday, July 18, 2003 9:10 AM
Subject: Re: [TheForge] Hydrochloric acid and galvanising

> 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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