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topic 1653

Acid cleaning - alloy oxide removal, brightening processes



1998

Hello everybody,

Im hoping that someone out there can help me out with a production/environmental problem we are having with one of our pickle house processes. Currently, our pickling department in our Huntington, WV plant uses various mineral acids (sulfuric, nitric, hydrofluoric) to remove oxides and scale from copper-nickel alloys, nickel-iron alloys, and nickel-chromium alloys. My problem is as follows:

As a final step after pickling our alloys in a sulfuric acid solution, the alloys are dipped into a tank of ammonia to prevent the copper salts contained within the sulfuric acid tank from plating out onto the finished product ("copper-kiss" prevention). This plating problem really presents itself on rolled wire products that have a lot of surface area. In addition to preventing to preventing "copper-kisses" the ammonia solution leaves the alloys with a bright finish as required by customers. The ammonia has always worked great but it has one major drawback, it reacts with the sulfuric acid and nitric acid fumes within the pickle house to produce adverse atmospheric emissions. We are currently looking for a replacement for ammonia (chelating agent) that will prevent the formation of "copper kisses" and will allow for the expected bright finish. We have tried a 5% solution of tetra-sodium EDTA in water (alkaline solution) and received favorable results with Nickel-Iron Alloys but unacceptable results with Copper-Nickel and Nickel-Chrome Alloys (copper kisses formed on wire where any wire strands touched one another) although all alloys had a bright finish. Would anyone have any experience in dealing with a problem of this type or know of a suitable replacement product for ammonia.

Luke Pokrajac
Inco Alloys International, Inc - Huntington, West Virginia


1998

Hi Luke:

We have a chemical deburring solution that is completely free of mineral acids. It removes the oxide layers and brightens the parts. If you can send us your sample parts, we can test them in our lab. This solution also improves adhesion of cyanide-free copper on Zamak, ZA, ACuZn, steel and other substrates.

Thanking you,
-Agi

Agi D'Mello
- Newark, Delaware


2000

Dear Mr Pokrajac,

We have pickle lines at our facility as well. You mentioned "adverse atmospheric emissions" in your inquiry posted at finishing.com. We are in the process of trying to "measure" the constantly irritating conditions surrounding our pickling operations. Typical atmospheric samplers seem to yield very low results based on the very noticeable and irritating conditions. Do you sample the atmosphere near your pickling operations and measure for HNO3, NO2, and/or NO fumes? I wondered if we were doing the best we could to get a true picture of the conditions which workers were exposed. Any comment would be appreciated.

Melanie Beard
- Elmore, Ohio


2004

Hi Luke,

I was looking up ways to clean Minerals and found this inquiry. If you do a net search for "nitric acid cleaning minerals", You will find a number of rinsing steps/methods for removing traces of acids. Including one or more of these rinsing processes in an appropriate place in your process could contain a solution to your problem.

Don Allen
lapidary - Maine, USA

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