Letter 15017

Help with sulfate concentration in a chrome plating bath  

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We have been having problems lowering our Sulfate concentration in our chrome plating bath. I have analyzed the bath and determined that the concentration is .14 oz/gal (I know I hate standard too). We have added a total of 1 3/4lbs of Barium Carbonate and my analysis still shows no change in sulfate. I KNOW that barium precipitates sulfate rapidly so I don't know what the problem could be. If you have any suggestions please feel free to share them.

Thank you,

Hope Bearbower
- Las Vegas, NV, USA

Assuming this is a conventional 100:1 bath, why is 0.14 oz/gal too high? It sounds too low.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

What is the volume of the chrome tank? Are you using the centrifuge method for analysis? Are you having a problem with the deposit, poor throwing power? How many mm of coverage do you have in a 267 ml Hull Cell panel plated at 5 amperes for 3 minutes?

Tom Pullizzi Platronica.com Falls Township, PA

Our tank is 830gal. our ratio is 224:1. i am getting 55mm of coverage in the hull cell at 5amps. I had them add 2000mls of floride catalyst and it seems to have fixed the problem but it is too soon to be sure.

P.S. What is this about a 100:1 ratio. I have heard this a couple times, but on all of the spec sheets that I have seen for chrome tanks it says the ratio should be around 170-230:1??? Is this wrong???

Thank you,

Hope Bearbower
- Las Vegas, NV, USA

I thought that you were using a conventional bath when you said you hated standard, I thought this was what you meant, (without other catalysts like fluoride), 100:1 is correct. With fluoride catalyst in a mixed catalyst bath, the 200:1 ratio for sulfate is usually correct.

55 mm coverage is marginal, I like to see 70 mm. Why would you add fluoride, but try to remove sulfate to cure the same problem? They are both catalysts and too much of each would tend to reduce throwing power. What problem were you trying to solve? I don't know why the barium did not work, filter your sample next time.

Tom Pullizzi
platronica.com
Falls Township, PA

The precipitation of sulfate with barium is not as quick as you think. Because the solution has a lot of chromium and relatively only a little sulfate, the first precipitate will be of barium chromate and only with time (in lab it will take at least an hour)it wil create the barium sulfate. So you cannot add the barium carbonate mix and recheck the result righ away.

If you use a centrifuge for the analysis, you MUST filter the solution prior to the analysis ( even prior to the first analysis prior to the addition of the barium). The reason for it is that the solution contains lead chromate which might precipitate when the centirifuge is used.

Sara Michaeli     chemical process supplier Israel

Listen to Sara, she has it right. What is your procedure for sulfate analysis? There are a number of things that can go wrong, not filtering your solution is only one. As a rule I give Barium 8 hrs to do it's thing, only then will I re-sample.

Steve Delaney
- Ontario

Make sure that you stir up the sludge in the bottom of the tank. I use a one foot stainless steel disc ,stainless welded to a stainless pipe. Do this every morning of use, and every thousand amp hours, to ensure even solution uniformity, better absorbtion of sulphate and a true hull cell test. Works for me!

Mark Gunn
- NSW, Australia

Barium chromate is yellow in colour due to the chromium. Barium chromate precipitates sulfate as a barium sulfate. I want to determine sulfate concentration using barium chromate. But I do not know solubility of barium chromate and how long it will take to precipitate sulfate as a barium sulfate at room temperature?

Patel Rahul P
University of tasmania - Hobart, Tasmania, Australia

We are trying to find a technical data sheet or procedure on determination of sulfate in chrome tank (HEEF-25).
Any assistance is appreciated.

Joe Faitak
Quality Manager - Warsaw, In, USA

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