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Can using Porous Pots Increase Sulfates in Chrome Plating?

June 4, 2010

Hi!

We have 4 hard chrome plating baths that we have recently been "porous potting" more regularly in the last 2 to 3 months. We do 2 tanks per week as we only have 2 porous pots. The pots are taken out once a day for cleaning/maintenance and replaced in the tank. Not long after, we observed our sulfates steadily rising. In the 3 years I've worked with the solutions, this is the first time I've seen the sulfates rise so fast. Usually, it's a very boring test because we can almost predict what the results would be. (We use the Kocour method to check sulfates.)

Could the porous pots be removing contaminants that may have been binding with the sulfates and now that those contaminants are gone, are we just seeing the "freed" sulfates? (Or is that too weird to even consider?)

We do use tap water for bath make up (always have). We have been monitoring the sulfates in the tap as well. Nothing alarming there. Just normal ranges.

Any ideas what's causing the rise in sulfates?

Romina Garcia
Plating Engineer - Winnipeg, MB, Canada

Possible-Yes. Probable-?
I used porous pots for years and never had a problem. Dragout always required sulfate additions.
If you had a lot of metallic ion contamination in your tanks-as in several years old, the ions would exist as chlorides and sulfates. The chlorides are converted to chlorine gas and leave in the air. Sulfates would be liberated by the removal of the tramp metals, so it is possible to see a sulfate increase, especially if you plow back the first rinse tank. The sulfate increase should gradually be reduced as you will eventually have very little tramp metals.
PS, you will have better luck if you go to a DI or RO water makeup for your chrome tank.

James Watts
- Navarre, Florida

The increased sulfates aren't a result of the porous pot treatment. It must be coming from somewhere else. City water is a likely source as you already know. Even if that is not the source of your current sulfate problem, you should really think about upgrading there. Aside from sulfate, there is probably some chloride in the water that can really throw your bath out of wack. Even if you don't measure much in your City water sample, the problem is that all of those contaminants accumulate in the chrome bath.

Jon Barrows, MSF, EHSSC
GOAD Company

Independence, Missouri

Thank you so much for the feedback!

Romina Garcia
- Winnipeg, MB, Canada

Romina,

Do you have high sulfate activation before chrome ?
may be drag out sulfate into the chrome or bad racks holding sulfate then drag into the chrome tank.

Check city water for contamination or any sulfuric acid aerosol in air and go into the chrome tank.

Popatbhai B. Patel
electroplating consultant - Roseville, Michigan

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