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Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)

by Randy Taylor, Advanced Tooling Corporation.
June, 2008

High Sulfates in a H/C Bath

Q. Dear Mr. Taylor, I have been out of the plating industry for a while and recently returned, have any of the old methods of lowering high sulfates changed such as with Barium Carbonate? Has there been new chemistry introduced or changes/revisions to bath temperatures using Barium concentrations?

A. Joe, welcome back.

I know of nothing new regarding treating for high sulfate. We don't see all that many high sulfate levels unless someone botches an addition or an error was made in the lab. It is also feasible for sulfate levels to rise when adding chromium trioxide with a particularly high level of sulfuric in it from the supplier. Ask for product certifications on raw materials.

Whether it's done in house, or at an outside lab, the sulfate analysis is one of the most important to get right. I like the koucor tube centrifugal method for checking sulfate. However, if you run only one tube per bath sample, and something is amiss, you're scratching your head and probably have to run the test over until you find the mistake.

I recommend two or even three koucor tubes be run per bath sample to ensure accuracy. It doesn't take more than a couple minutes to duplicate, but at least when done, you can compare the results with a higher level of confidence.

The keys to being confident about the sulfate analysis is: 1) perfecting technique, 2)use the best equipment, glassware and reagent chemicals, 3)ensure that the bath samples have been properly taken and bath volume is verified, 4) perform all tests on schedule and take your time.

There are more accurate methods of testing sulfate levels but they involve longer more involved test cycles, specialized equipment or an outside laboratory.

Best of luck.

Randy Taylor





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