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February 2002

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Subject:
From:
Ahne Oosterhof <[log in to unmask]>
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Date:
Thu, 7 Feb 2002 10:07:57 -0800
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Hi Kathy,
My knowledge of passivation is somewhat limited. I have only seen it used
for stainless steel (steel with typically high nickel content). I also found
a little on how/why it is done:

With austenitic stainless steel, such as the 300 series, once a corrosion
site has started it only gets worse, being continuous and self-catalyzing.
In corrosive environments the growth of the corrosion site will accelerate
rapidly! Thus, proper cleaning and passivation of surfaces prior to use is
essential to achieve maximum resistance to corrosion.
Most companies have used and continue to use methods for cleaning and
"passivating" stainless steel which utilize mineral acids such as nitric
acid and phosphoric acid. Their effect is limited to surface iron, although
in many cases this method redeposits contaminant iron on the surface again.
Nitric acid is known to many times produce pitting corrosion. There are many
problems with long term use of mineral acid applications, especially under
corrosive environments.
Although not really "new", an emerging technology that is proving to be a
vast improvement over the mineral acids is the use of safer organic acids
such as citric acid. These are very effective materials which complex and
remove a variety of metallic ions that would otherwise adversely affect the
corrosion resistance of the stainless steel. These acids are materials that
work in aqueous solutions to tie up metal ions so that they are no longer
effective or able to have a negative impact. After stripping the metal ions
from the surface, the citric acid forms a water soluble complex with a metal
ion. It will not precipitate the metal ions again like the mineral acids are
known to do.

I cannot vouch for the correctness of the claims in this information nor
comparing one method versus another.
In your application I wonder why you would do this to a "pure" nickel
deposit and what it would do to all the other metals that may be nearby.

Have fun,
Ahne.

-----Original Message-----
From:   TechNet [mailto:[log in to unmask]] On Behalf Of Kathy Kuhlow
Sent:   Thursday, February 07, 2002 06:50
To:     [log in to unmask]
Subject:        [TN] Nickel Passivation

 << File: TEXT.htm >> What has actually happened to the nickel on a pad when
it is passivated?  Can this nickel also be unpassivated?

TIA

Kathy

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