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topic 47214

Cadmium plating turning black

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A discussion started in 2003 but continuing through 2019

(2003)

Q. We have a situation where Cadmium plated and chromate passivated parts are being rejected following short term storage due to black patches on the surface. This is not the white rust normally associated with corrosion of cadmium, could anyone help with advice on the possible causes.

(note - my research suggests that inadequate rinsing - aided by a porous coating - could produce this, could anyone confirm this or offer an alternative cause)

Regards

Nick Clark
- Bristol, Avon, England


(2003)

A. Sounds like a sulfide. Check to see how they are stored. Many papers and cardboards have enough sulfur in them to spoil cad plating, even chromated. At the right temp, humidity and air movement, it does not take long. Solution-wrap the parts in crystal paper and store in plastic tote bins.

James Watts
- Navarre, Florida


(2003)

A. Copper contamination in the cadmium plating solution.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como
and co-author of The Sulfamate Nickel How-To Guide


(2003)

A. Cadmium sulfide is yellow. I agree that porosity is likely the cause. Porosity in the basis metal most likely. I have found that plating porous metal, one can help the situation by a pre dip in clean hot water at a temperature above that of the alkaline cleaner. Water is drawn into the pores and usually stays there throughout the processing so that cleaner and acid cannot enter to later bleed out causing black spots. Also, alternate hot and cold rinsing is helpful after plating and before the chromate.

don baudrand
Don Baudrand
Consultant - Poulsbo, Washington

(Don is co-author of the
book "Plating on Plastics")



Cad plating turns black in a few days

2007 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We are cadmium plating fasteners in a cyanide bath and we are finding that the finish is turning black after 4-6 days. Parts come out of he process more or less bright white.
After the cad plate we rinse and apply a chromate, rinse and dry.

We have been doing this for more than 20 years and sometimes the plated parts turn yellowish to brown, but never black.

I'm enclosing a picture so that you can se the magnitude of the black color, together with a freshly plated part. You can see one fastener is a little yellowish after a couple of weeks, but the others that are black, where plated only 4 days ago.

 Cad plated parts turn black

Can the brightener be the culprit? I've heard that to much Nickel in the brightener can cause this black spots.

Also, if we submerge a black stained part in a cyanide containing solution, we get a bright clear finish, so we think this stain is over the cad deposit.

Thank you for your help.

Carlos Cielak
plating shop - Mexico City, DF, Mexico


simultaneous 2007

A. I never had the problem, so can not truly say. Typically, you have a sour rinse, probably with a high sulfide content or your packing containers have a high sulfide content (which is common in some cardboard and some paper)and you storage area is in slightly high humidity(IE: not air conditioned) Not that some plastic bags can cause problems also.

James Watts
- Navarre, Florida


2007

A. Off line in buckets, set up a 1/4%/vol nitric acid to neutralize the cyanide, then another bucket of fresh made chromate. Wait 5 days and let us know. I suspect your chromate pH is out of spec due to CN drag-in. So neutralize in nitric first, then chromate.

robert probert
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina


2007

A. I WOULD LIKE TO REQUEST TO YOU GET YOUR CAD BATH ANALYSED PROPERLY FOR IMPURITY CONTAMINATION -- SAY COPPER, IRON, ETC.
IMMEDIATELY YOU CAN DO ONE THING: PREPARE A NEW PASSIVATION BATH AND TRY SOME SAMPLES (YOU CAN MAKE 20 LTS)
AFTER PASSIVATION, DO WATER RINSE,THEN HOT WATER RINSE, THEN DRY COMPONENTS PROPERLY.
I THINK YOUR PROBLEM WILL GET SOLVED.
WITH BEST WISHES,

ajay raina
Ajay Raina
Ludhiana, Punjab, India



June 21, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We have some parts that we currently produce for a customer, the parts are Bright Cad plated. Once we get parts back from plater they look great, however over time they begin to show black spot through the Cadmium. we have had several labs look at this products and they say that it is due to the cleaning process, we have tried 3 different vendors and they all get the same results, are we missing something. We have had parts stripped and replated and same thing happens, material be used is a C1018. We have asked platter for titration results and they look ok from what we can tell. we have asked to have parts baked prior to plating and platter stated that they could not do it because they would rust as they do not have in line dryers. We are total lost as to what this could be any help would be great.

Thanks
Brian

Brian A
- Jefferson, Ohio USA



Black stain in cadmium deposit after chromate

January 7, 2019

Q. We regularly, but not always, end up with parts having black or gray little stain all over after chromate conversion. It seems to be done at the plating stage as we have changed the chromate solution for a new one but the problem still occurs.

Pierre Legault
shop employee - Montréal, Québec, Canada
  ^- Privately contact this inquirer -^


January 9, 2019

A. If the "stain" is in the low current density areas then we suspect copper contamination of the cadmium plating solution.

robert probert
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina


January 17, 2019

thumbs up sign Thank you for your comments!
I attach some photos that can help you understand our problem. Pierre

47214-2a

47214-2b

Pierre Legult [returning]
shop employee - Montréal, Québec, Canada

January 18, 2019

A. OK, so it is not the LCD area. so now I suspect the cyanide was not neutralized before going into the chromate.
Recommendation: Dip in 1/4 %/vol Nitric Acid before the chromate.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como
and co-author of The Sulfamate Nickel How-To Guide



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