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"Determine Sulfates in Chromium Plating Baths"



Current question:

July 4, 2021 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I determine the concentration of sulfuric acid in chromium bath using a centrifuge using HCl and barium chloride 20% .
I need another way to determine the concentration of sulfuric acid in chromium bath other than centrifuge.

Thanks in advance.

Hanan Fathy
- Egypt Cairo
^




Closely related historical postings, oldest first:

2004

Q. Dear Sirs,

We would really appreciate if you could help us on the following problem which we are facing in our labs ( Hellenic Aerospace Industry - Physical Science Labs):

In our labs we have to determine Sulfuric Acid in Chromium plating bath.The limits for Chromic Acid in the bath is 225-270 gr/l and for Sulfuric Acid is 2.25-2.70 gr/l (a very small concentration range of 2.70 - 2.25 = 0.45 g/l) . We tried two methods for the determination of Sulfuric Acid in the solution but taking into account the very small limits range of Sulfuric Acid in the solution and the time the methods need, we are not satisfied by the results of both methods

More specifically:

A. The first (titration) method is as follows:

In above method (A), a difference of 0.1 ml of 0.1 Magnesium Chloride (titrant) results in a deviation of result equal to 0.1 gr/l Sulfuric Acid (that is, a very high deviation of approximately 22% in comparison with the very small limits range of 0.45 g/l of Sulfuric Acid).

B. The second (weighing) method is as follows:

In above method (B) we face the difficulty to clean up the filter from the Chromium during filtration. Additionally a small difference of 0.002 gr in weighing gives a deviation of result equal to 0.084 gr/l of Sulfuric Acid ( that is, again a very high deviation of approximately 19% in comparison with the very small limits range of 0.45 g/l of Sulfuric Acid).

We tried to perform above analyses using a higher quantity of sample to eliminate the error, but we faced difficulty during the reduction of Chromium due to rapid expansion (explosion) of the solution during the reaction.

Angela Nikolaou
aerospace - Tanagra, Viotia, Greece
^


simultaneous 2004

A. I think that you have set your limits tighter than necessary. Chrome is constantly depleting with plating. Sulfate is only lost to drag out, so the ratio is constantly changing throughout the day.

The Kocour centrifuge method is fairly quick, simple, reasonably repeatable and more than accurate for chrome plating needs. Use the electric centrifuge and not the hand one. If you like, you can do a correlation of the centrifuge method and your lab method as well as samples from reagent grade materials to establish a correction factor if you really think that it is required. My centrifuge tubes were calibrated in oz rather than grams. They may offer one in grams, but if not it is a very simple conversion. I am a chemist and truly appreciated this adequate method.

James Watts
- Navarre, Florida
^


2004

A. My method of choice would be (b). That's the standard accepted method. I do not know that barium sulfate would completely dissolve even in a solution containing EDTA, as it is notoriously insoluble in just about anything. If you are determined to avoid the gravimetric method, it might work to fuse the recovered barium sulfate with sodium carbonate (washing soda) [affil. link to info/product on Amazon], dissolve the melt in dilute nitric acid, then adjust the pH to about 10 with ammonium hydroxide. The EDTA could then be added, then titrated away with your standard magnesium solution.

If I were you, I would just do the gravimetry. The boiling over you describe can be avoided by adding the ethanol slowly to the mixture, and heating it gradually. And, it is not necessary to ignite the precipitate. It is good enough to filter it with a Gooch crucible and glass filter mat and dry it at 105 C.

dave wichern
Dave Wichern
Consultant - The Bronx, New York
^


simultaneous 2004

A. A quick and easy way to measure sulfate is precipitation with barium chloride, then centrifuge and measure volume of precipitate. Kocour company makes a centrifuge and graduated tubes for this purpose. it is quite accurate.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina
^


2004

A. GO FOR IC TECHNIQUES IT CAN DETERMINE SULFATES TO ppm levels. Otherwise the techniques you use are the ones commonly used in industry. TRY KOCOUR sulfate testing kits .

vikram dogra
Vikram Dogra
Irusha India - Chandigarh, India
^


2004

A. 1. The deviation is not much of a problem. There is little or no difference in performance of the chromium plating solution with the small error in the analysis. To do a simple analysis, Kokour Co. provides a Kit that includes a centrifuge that runs at a specified RPM The procedure is simple and quick and may even be more precise than the ones you have mentioned. Sulfate is precipitated by a barium salt in a centrifuge tube with a small diameter tip that is calibrated. Simply read the number after centrifuging.

don baudrand
Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [affil link to the book on: Amazon or AbeBooks ])
^


2004

Q. Thank you all very much for responding. Here are some very questions and comments

1. Could I have some info as concerns the supply of the Kocour Kit? Could you describe briefly, what the kit consists of. Is any "Kocour solution" included in the kit and what is it exactly?

2. Have in mind that the hexavalent Chrome must be reduced to trivalent, otherwise insoluble Barium Chromate would form along with the sulfate.

3. The sulfate limits are really tight, but this is because of our clients' specifications.

4. Do you think that the 19-20% deviation in the sulfate determination is a small one?

4. The precipitate has to be ignited at 600 °C because it holds water strongly, as it is suggested in the "Electroplaters' Process Control Handbook" [affil. link to book on Amazon], edited by Gardner Foulke.

Thanks again,

Angela

Angela Nikolaou [returning]
aerospace - Tanagra, Viotia, Greece
^


simultaneous 2004

A. The kit comes with 2 solutions, the centrifuge of choice and special centrifuge vials.You can get the desired information from Kocour or your plating supply vendor.

As far as the accuracy of the kit, I will hazard a guess that over 95% of chrome platers use that method as it is sufficiently accurate to maintain a 100:1 plating solution.As I said in my first post, the ratio is constantly changing and it is the ratio that is important.

James Watts
- Navarre, Florida
^


2004

Q. Hi again, Please give me the address, web site, fax and/or e-mail of Kocour company, to come in contact with. I tried the web site www.kocour.com [but it didn't work].

Thanks,

Angela Nikolaou [returning]
aerospace - Tanagra, Viotia, Greece
^

Their URL is www.kocournet.com, Angela.
Dec. 2019: That link no longer works any more. Please remind them that lacking presence on the world's most popular finishing website, and making you wait until their competitors get around to providing you their updated contact info, makes things hard for you :-)


2004

A. If you use the Kocour method and want very accurate results, you will want to calibrate the tubes yourself against a prepared 100:1 chromic/sulfate standard. You will find that you will need to apply your own correction factor to most tubes. Repeat the calibration every three months on each tube. This will account for interior scratches that tend to occur with use and cleaning.

Jon Barrows
Jon Barrows, MSF, EHSSC
Independence, Missouri
^


2005 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear all
I've heard that there is a centrifuge method for determining sulfate concentration in chrome plating solution. However, I don't know how it works and what shall I do. I'll be grateful if any body could advise.

Regards,

Sani [last name deleted for privacy by Editor]
- London, UK
^

Interested readers might also wish to review thread 44422, "Sulfate Analysis of Chrome Plating Solution".


May 19, 2009

A. The Kocour test is easy and very accurate. Repeatable if you follow the steps accurately. I personally have used it 16 years off and on as they had some others testing the baths over the years. Our company has used it for 20 something years and our tanks stay optimum.

I put the entire testing process on my site, here is the link. Hope it helps:
rodneystephens316.webs.com

Rodney Stephens
industrial plating - Anniston, Alabama
^

----
Ed. note: Sorry readers, that link is broken :-(

Our site has been 'on the air' since 1989, and we are striving to be a permanent reference, like a book.
Nearly all links break in a few months or years, making them difficult to maintain across our quarter million postings. If you provide a link, please give title & author or other info so we have a fighting chance to fix broken links. But we urge you to put your stuff directly here (we have all the room in the world) rather than at a link that will almost surely soon fail :-)
We thank Rodney for his input, but we heard the librarian say she has put him on her "naughty" list for ripping pages out of this reference work :-)




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