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topic 44422

Sulfate Analysis of Chrome Plating Solution


A discussion started in 1999 but continuing through 2018

(1999)

Q. We wish to purchase a centrifugal unit for the analysis of sulphate in chrome. Can anyone recommend a product and supplier?

Thanking You,

Kenneth Kelleher
- Ireland


(1999)

A. Kenneth, your best bet for a centrifugal unit is Kocour Co. in Chicago, IL. They have several types of units available.

jim conner
Jim Conner
Anoplex - Dallas, Texas USA


(1999)

A. Kocour used to sell an open hand crank unit --somewhat dangerous-- and an enclosed unit with the chemicals and centrifuge tubes.

The only stand alone unit that I am aware of is ion chromatography. This is a bit expensive.

James Watts
- Navarre, Florida


44422-2
February 2014

thumbs up signAh, for life in simpler times ... Toxic, carcinogenic, hexavalent chrome whirling around atop the desk in fragile glass test tubes. With a "Be Careful" label the sum of the vendor's safety responsibilities :-)

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



Suggested RPM and other parameters for Sulphate Analysis

(1999)

Q. I use a Kocour centrifuge but I am not sure that the results are so accurate.

Does anyone know the recommended type of centrifuge for the sulfates in chrome? (I mean info like RPM, G, swing rotor etc).

sara michaeli
sara michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel



(1999)

A. I think the RPM for the centrifuge should be between 600 and 900 for 3 minutes if using the manually operated one. Kocour has a nice electric one that sure saves your arm if you have more than one or two samples to run.

jim conner
Jim Conner
Dallas, Texas USA


How to dispose of these Chromic Acid Test Samples?

(2005)

Q. At my facility, we hard chrome plate our injection molds for wear resistance and part release. Recently, I purchased new testing equipment to replace our current outdated equipment. I have ordered the following four test kits from Kocour: chromic acid (titration), trivalent chrome (color match), sulfate (centrifuge), caustic strength (titration).

My question is pretty basic but our safety is number one so I'll ask the people who know. I believe everyone here is familiar with the Kocour tests so I'll spare an explanation. I'm new to chroming so the descriptions wouldn't be any good anyway. Once the testing is complete, I have a fairly small sample left over from each test. We have a company that disposes of our waste that will readily accept the tested samples.

Can these tested samples be combined and then disposed of? Combining the samples will make shipping the sample a lot easier. This seems like a simple question but I'm not sure. Again, I'm fairly new to the plating world so any information would be helpful.

William Belanger
- Morristown, Tennessee, US


(2005)

A. Contact your local sewer authority. Usually there is an exemption which allows a few gallons per day of laboratory waste to be disposed directly to sewer without treatment or reporting.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina


(2005)

A. It is safe to combine all the waste from the chromic acid titration, sulphate test and trivalent test, just chuck them in a old, properly labeled 25L container.

I can't help but wonder what the caustic test is for on a ACIDIC chrome plating solution? it must be to test your cleaners.. this one should be disposed of in a separate container or you will probably end up with a drum full of nasty sludge.

Peter Van de Luecht
- Melbourne, Vic, Australia



(1999) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Can anyone direct me to the method for testing sulfates using a centrifuge? Thank you.

Kristine Campiola
  - Wichita, Kansas



Comparison between Centrifuge Method and Gravimetric Sulphate Test

2007

Q. We chrome plate gun barrel bores. Typical chemistry is 33 oz/gal, at 100:1 sulfate ratio. Due to the thickness required, plating cycle may be 10 hours or more. Our problem is that apparently the ratio is critical to controlling taper in the bores. If we go out of the 90-100:1 ratio, taper becomes excessive. Obviously, we need a more reliable method for sulfate analysis than the Kocour centrifuge test. I know there are gravimetric tests for sulfate -- does anyone have a proven, reliable method to share with me?

George Brackett III
Sr Manufacturing Engineer - Saco, Maine


2007

A. I can easily see where the ratio could cause problems with plating control of a gun bore, especially at the top.

My personal feeling is that the Kocour method is very repeatable and accurate if and only if your spin cycle is exactly the same RPM and length of time.

The Sulfate ion is a catalyst and is not consumed during the process and the only loss is dragout. Therefore, if you are having a problem in a 10 hour cycle has to be due to the change in the chrome concentration, which would tell me that you do not have enough replenishment of the plating solution in the gun bore.

The sulfate can be analyzed by a gravimetric analysis method, but it is long and complicated. So bad, that virtually no one will do it. Look at any college level chemistry book for the method. Also, the Metal Finishing Guidebook has the identical method in the analysis section.

I would make up a lab solution of 100:1 plating solution from Reagent grade material, both the chromic acid and the sulfuric acid, and analyze it several times by the Kocour method and then apply a "correction factor", if required, to your analyses of the tank solution. Assuming that you have highly repeatable results, which you should have.

James Watts
- Navarre, Florida


February 2014

thumbs up signThat was a great response, James. Thanks!

Unfortunately the MFG doesn't include that info anymore, but it can be found in olde editions --

44422

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


2007

A. Someone may suggest an alternative method for sulfate analysis, however my experience with the Kocour method is that it is quite reliable. make sure you are doing it by an exactly repeatable method -- same centrifuge time, etc.

Since sulfate is not consumed during plating, and since you can easily control chromic acid within 10%, why does the ratio get away from your range? If you maintain constant chromic acid concentration, the ratio should change only very slowly as solution is lost to fume scrubber or drag out.

Is something else changing during plating? It is easy to imagine temperature and chemistry changes within the bore unless provision is made for constant circulation of the solution in the bore.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg,
      South Carolina


2007

A. I cannot quote the method from memory. It involves mixing the bath sample, acetic acid, ethanol, and water, boiling, then adding a good excess of barium chloride solution to drop the sulfate as BaSO4. The resulting mixture is then filtered through a Gooch crucible of known weight, the precipitate rinsed, dried, then weighed.

I once attempted to develop a method for doing this analysis via turbidimetry, a method used for sulfate in water. I had NO LUCK AT ALL. I messed with it for over a year, off and on.

An important source of sulfate in some shops is drag in from the nickel bath that precedes the chrome bath. Good rinsing here is essential.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


2007

thumbs up signThanks for the responses. Incidentally, we don't nickel plate, so sulfate from drag-in isn't a problem. We initiated a testing method where once a week we run 5 tests on each chrome tank (there are 4). We look at the results, and reason which ones are most likely to be correct. If no two are alike, of course we resample and retest. We use this weekly result for any adjustments needed during the week. Usually we have to cut the solution weekly due to formation of trivalent chrome (we use platinum-clad anodes, and of course the anode to cathode ratio is skewed towards rapid trivalent generation, and the platinum doesn't allow conversion back to hex. We use the weekly sulfate analysis result to rebuild the solution, and so far it's working great.

George Brackett III
- Saco, Maine



2007

Q. Hi, I'm a chemist that's doing plating for aviation company. Since the specification has been set up by Boeing, I would like to ask how much actually is the deviation between centrifuge method and gravimetric method to determine the sulphate content; the claim by Boeing is that the centrifuge method is not valid to be used for the test method. Regards to the chemistry side, there is no significant difference on the sulphate precipitation by both method but only the byproduct of the analysis? Do you have any idea or research work on that?
I hope you can help me on this.

Regards,

Riexal
- Subang, Malaysia


2007

A. Sir:
In Hot Dip Galvanizing the flux solution becomes contaminated with sulfate (in plants using sulfuric acid) and a volumetric titration using standard barium chloride is used to determine sulfate. The test takes 5 minutes. It determines sulfate as 0.1%, 0.2%, 0.3% etc. These percents are changed to grams/liter by multiplying by 11.4. This method can be modified by changing the sample size and/or the standard barium chloride solution to attain the required accuracy. A centrifuge is required, which is low cost on ebay.
Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota


2007

A. Working for Boeing can be difficult at times, especially with some inspectors.
Step 1 is to ask Boeing for a copy of their procedures, including analysis for chrome plating.
If it were me, I would use their procedure and the Kocour method on split samples and track their agreement. Eventually, you will have enough data to ask for a variance in the procedure.
The gravimetric method is a time consuming pain in the rear method that is only minorly better than the Kocour method after you have run it on a bunch of reagent grade standards to come up with any fudge factors required.

James Watts
- Navarre, Florida


2007

A. Just to add to James' post, we carry out the sulphate analysis by the gravimetric method and it is a right royal pain in the posterior. Add to that that it is a multiple stage process, with each stage open to inaccuracies ... by the time you get to weigh your sample it is no more accurate than the Kocour method, in fact if you are carrying out analysis on several baths then I bet you will end up trying to find shortcuts and introduce new inaccuracies.

Follow James' advice, run concurrent samples by both methods, build up a database of results and offer these as objective evidence of satisfactory analysis.

Brian Terry
aerospace - Yeovil, Somerset, UK


May 15, 2009

A. I have used the Kocour test myself for many years. The key is making sure you add your B solution slowly and that your math in processing your data is correct. I am currently thinking of contacting Kocour to see if they would like to distribute my calculator that I wrote with their test kits. With it you tell the program where you want your solution in ration, put in your baumé and your sulfate reading and it tells you the exact amounts of acids you need.

Rodney S [last name deleted for privacy by Editor]
industrial plating. - Anniston, Alabama



Centrifuge speeds for testing sulfates in chromium plating baths

February 13, 2014

Q. what is the correct "RPM" for the Kocour centrifuge method of testing for sulfates in Chromium baths, I am currently using a 4-tube "Clay Adam" centrifuge...

GEORGE SKEET
- SAN ANTONIO, TEXAS, USA


February 14, 2014

A. The only reference I found was in an old British lab book, "Electroplating Laboratory Manual", by Armet, 1965.

They say 1000 RPM for 2 minutes.

Chris Owen
- Nevada, Missouri, USA


February 2014

Chromium Plating
by Weiner & Walmsley
from Abe Books

or

A. Thanks Chris. Doing some scouting myself, I see that Weiner & Walmsley agrees with that 1000 RPM for 2 minutes =>

Dubpernell's "Electrodeposition of Chromium from Chromic Acid Solutions" [link is to info about book at Amazon] doesn't either agree or disagree, but stresses that what matters is consistency and proving the correlation between your centrifuge results and the actual sulfate content:

44422-3

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


February 22, 2014

A. In the dark ages, when I worked in the Udylite lab in L.A., we used a hand-cranked centrifuge made by Kocour, I believe. We kept a bottle of a standard chrome bath with a known amount of H2SO4 to test our techniques.

Chris Owen
- Nevada, Missouri, USA



April 14, 2014

Q. I used centrifuge to check for the sulphate content in hexavalent chrome and chrome pre dip. Why is the sulphate content in the pre dip higher than the hexavalent chrome. And what are the standard techniques to check for the sulphate content?

james parker
- selangor malaysia


April 2014

A. Hi James. George Brackett seems to have implied that if you do nickel plating the sulphate will run high in the pre-dip. Do you do nickel plating before the chrome plating or not?

This whole thread is about the standard techniques to check for the sulphate content -- can you study it and phrase your question in terms of the responses already provided please? Thanks!

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



October 14, 2014

Q. Hello everyone!

I'm buying a centrifuge for determination of sulphate in chromium bath. I would like to know which one to choose if it's possible somewhere in Europe not in USA?
I have found this one: hettichlab.com/web/global/prod/EBA+200/6455
But I'm not sure if it is the best option.
What should be the volume of centrifuge tubes? 50 mL?

Bojan Koren
- Bovec, Slovenia

----
Ed. note: We don't recommend or comment on brand names on these pages (why?), but if anyone has recommendations on generic issues like tube volume, etc., they are welcome of course.


October 15, 2014

A. The centrifuge you've posted the link to will not work for that analysis: it's a medical centrifuge and only holds vials that hold 15 mL.
When I formerly worked in a lab doing metal finishing analyses, we used a simpler centrifuge that held Kokour tubes that are specifically designed for the sulfate analysis. for instance, check out this link:
www.kocour.net/productDetail.asp_Q_catID_E_91_A_subCatID_E_92_A_productID_E_92
These tubes are glass, hold 50 mL, and have a completely different shape that 'normal' centrifuge tubes.
The sulfate analysis requires 20 mL of sample, 5 mL of 50% HCl, 5mL of 30% BaCl2, so the 50 mL is optimal.

Fauna Tester
- Seattle, Washington USA



September 6, 2018

I have a Koch set centrifuge but have lost the manual. Also need to know what chemicals to use i.e. A and B. I'm in kenya east Africa. It's for sulphate for hard chroming bath. Need good advice. shahid

Shahid sidi
- Nairobi kenya


September 2018

A. Hi Shahid. The method is explained and discussed on our thread 32838, and at
https://www.hettweb.com/sulfate.html
and
http://www.plating.com/anapro.htm

If you tell us the model number of the centrifuge maybe someone can find a copy of the manual. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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