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topic 17612

White Spots on Cadmium Plating?




An ongoing discussion from 2002 through 2015 . . .

2002

Q. I am having problems with corrosion on the threaded portion of a safety critical item. After being subjected to 48 hours of humidity at 40 degrees and 90% R.H., I have noticed the formation of what seems like white pustules/spots on the steel component (S96) which is Cadmium plated to a thickness of 15 microns and subsequently coated with molybdenum disulfide. Does anybody know what species these white spots could be?

David Moore
- Stevenage, Hertfordshire, England


2002

A. I would expect that the white spots are cadmium corrosion products. I would expect cadmium to start corroding to white rust within 48 hours unless the post treatment was protecting it. It sounds like the molybdenum disulfide is not providing 48 hours of protection. Is there a chromate conversion coating between the cadmium and the molybdenum disulfide?

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


2002

A. Hi Dave,

I agree the white spots are the cadmium corroding. What are your expectations of the coating? One of the main engineering characteristic of cadmium is its corrosion. The fastener industry is flooded with cad plated threads specifically because of the lubricity of the corrosion. This coupled with eliminating corrosion of your base material are the main reasons for cadmium plate. In testing, don't confuse cadmium corrosion as a failure. Typically testing criteria is base corrosion. I also agree that increased corrosion resistance of the cadmium can be attained through secondary chromate treatments. Take a look a what your requirements are, and good luck.

Tim Martin
plating shop - Springfield, Massachusetts



To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



2004

Q. I have cadmium corrosion on equipment tie-down shackles, what do you recommend as the safest way of removing this corrosion and preventing its return.

Thanks,

Mark Hoods
- North Yorkshire, UK


A. Cadmium is a chronic, cumulative poison like lead and mercury. It isn't safe to try to deal with these corrosion products except at a plating shop which recognizes the hazards and has the necessary protective gear and medical monitoring programs. Take the items to a plating shop for stripping and replating.

There was a time when zinc and cadmium plating were used interchangeably. Today, cadmium is applied to parts only when its unique combination of properties is important. It is quite possible that these shackles can simply be zinc plated this time.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



February 15, 2009

Q. I have a problem of widespread white blooming on aerospace components, some after a very short lifespan (nearly new); is this due to porosity of the original plating, or some kind of other chemical component in the process. Disposal issues aside, how long can this equipment be expected to last before base metal corrosion is a problem, and is there any alternative to complete re-plating or replacement.

John Eaton
- Sleaford, Lincolnshire



Cause of white powder on cadmium or zinc plated components?

November 4, 2009

Q. We have a plating facility doing cadmium and zinc cobalt. After plating we are inspecting components 100 % but some of the components at customer end are rejected due to a white powdery deposit. We are carrying out cad/zinc cobalt plating over aluminium and aluminium die cast parts.

Our cleaning is as follows:
Degreasing, soak clean,rinse,desmutting HNO3 50 + H2SO4 25 + 100 gm/lts ammonium bifluoride.
rinse , albond zincating ,rinse,HNO3 50 % strip, rinse, albond zincating, rinse, electroless nickel undercoat, rinse (2), cadmium plating / zinc co plating, Olive green passivation, rinse(2), dry. Oven test 1 hr. 150 °C.

Bhatt k.m. Bhatt
PLATING MANAGER - PUNE, MAHARASTRA, INDIA


November 4, 2009

A. You are turning the chromate to a powder. Above 140 °F it basically becomes worthless. Notice that it is F and not C.

James Watts
- Navarre, Florida



November 30, 2009

Q. Regarding the white spots on the cadmium plating. Can we use an 'over the counter' cleaner, or use a Dremel [linked by editor to product info at Amazon] and polishing pad, or is this best left to replacement?

Jeff Willis
- San Diego, California


November 30, 2009

A. Hi, Jeff. As mentioned above, cadmium is a bio-accumulating poison. For that reason I would not use a Dremel or polishing pad or other method that might spread cadmium dust around. I would strip and replate.

This is the fourth mention on this thread of cadmium corroding, but no one has discussed their chromate conversion coating which is what keeps the cadmium from corroding. After replating, I would include a proper chromate conversion coating. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



White film on Cadmium Plated connectors with Olive Drab finish

April 30, 2012

Q. My name is Nick and I am an Engineer with a cable manufacturing company. I have a problem with cadmium plated connectors. I make a junction box assembly that has a lot of Olive Drab Cadmium plated military circular connectors on it. I recently received about 10 of these unused boxes back from my customer's stock because all of the olive drab connectors have a white film on them. The film has a slightly acidic smell to it. The connectors are from a variety of different manufacturers, but all have the same finish.

58498

Any ideas what could be causing this?

Thanks.

Nick Kochey
Engineer - Saint Petersburg, Florida


May 2, 2012

A. Hi Nick,

This sounds like you have a storage issue, especially as the fault occurs across a number of manufacturers.

Cadmium is susceptible to corrosion (that is what you are seeing, cadmium corrosion products) when stored in certain conditions such as in wooden containers or in corrosive atmospheres. I think your first step is to check out the storage conditions.

Brian Terry
aerospace - Yeovil, Somerset, United Kingdom


May 4, 2012

Q. Brian,

Thanks so much for your helpful response. As a matter of fact, these assemblies have been stored in a wooden crate for the last couple of weeks. The crate is made from OSB board (commonly known as chip board). Do you know what it is about the wood that may cause corrosion of the cad plate?

I am running a test in another crate now to see if I can duplicate it. It's only been one day, but no sign of corrosion yet.

Nick

Nick Kochey [returning]
Engineer - Saint Petersburg, Florida


May 8, 2012

A. Hi Nick,

Chip boards are bound using a resin. The resin leaches into the box and is corrosive to several metals, but is most noticeable on zinc, zinc alloys and cadmium, all of which seem to be particularly susceptible to this particular corrosion issue.

Replacing with solid wood boxes won't help either, especially pine as the sap is is corrosive to the cadmium.

The best bet is to have them packaged in plastic containers if you can. If it has to be wood then I would suggest the parts need to be individually wrapped in polythene bags or similar, the boxes need to be vented and some form of corrosion inhibitor could be added. Saying that do not use VPI/VCI type papers as these can also corrode cadmium. You may want to look at VpCI type corrosion inhibitors.

Brian Terry
aerospace - Yeovil, Somerset, United Kingdom


May 14, 2012

thumbs up signThanks Brian. The wood box did in fact cause the corrosion. After 5 days we saw the white film all over the connectors. The odd thing is that these connectors have a chromate conversion coating on them that is supposed to prevent the corrosion of the underlying cadmium, at least until it gets into service. It doesn't seem to work very well. In any case we are going with the plastic bag and some desiccant material. That should take care of it.

Thanks very much for your responses. They have been extremely helpful.

Nick Kochey [returning]
Engineer - Saint Petersburg, Florida


May 15, 2012

A. Hi Nick,

The passivation is unfortunately not very good at stopping corrosive vapours, that's why the cadmium was able to be attacked. The mechanism for corrosion is a little different from that of a moisture laden environment, where the hexavalent chromium is mobile and able to protect the cadmium. Good to see that you got to the bottom of the problem.

Brian Terry
aerospace - Yeovil, Somerset, United Kingdom



Cad plating turns white during storage

June 3, 2015

Q. We store a lot of CAD plated items. We have trouble with stored items turning white. The parts are stored in wooden boxes in an un-climate controlled warehouse. Is there anything we can do to stop the CAD plating from turning white? Items left out in the weather do not seem to have this issue.

John Eberling
Plant Engineer - Monroe North Carolina USA


simultaneous June 4, 2015

A. Hi John,

First step is to stop storing cadmium plated parts in wooden boxes. Corrosion of cadmium stored this way is a well known phenomenon.

If you can't avoid storing in wooden boxes then you need to isolate the parts from the wood as much as possible. I would suggest you bag everything and use a corrosion preventative compound to protect the parts.

Brian Terry
Aerospace - Yeovil, Somerset, UK


June 4, 2015

A. Good day John.

There is good info in letter #59662.
I think you need to address the sulfides, as they are also in paper packaging products for shipment.
Also, I have found using latex gloves during processing/handling also causes defects.
I am using nitrile .
Hope this helps.

Regards,

Eric Bogner
Lab Tech.- Whitby, On. Can.


June 4, 2015

A. I suspect your plater is not neutralizing off the cyanide film before applying the chromate, then with temp/humidity cycling the cadmium corrodes. Or that it is one of those lately tri-valent chromates that is failing.

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


June 8, 2015

thumbs up signGentlemen,
I thank you all for the quick responses. We will not be able to abandon the wooden boxes but we will explore some dry film lubricants to coat the CAD plated parts before assembly. Thanks again for all the help.

John Eberling [returning]
- Monroe North Carolina USA


August 5, 2015

A. Bonjour,
It is not recommended to store or to transport the olive green passivated cadmium plated parts in wooden boxes. The vapors from adhesives based on formaldehyde or formic aldehyde are harmful and likely to produce this phenomenon. We see in the photo that the box is made of chipboard and heavily impregnated with glue.

Denis Nicollet
- Mieussy,Haute-Savoie, France



Cadmium plating corrosion

November 12, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We store a lot of CAD plated(type II) items. We have trouble with stored items turning white, which I understand is cad plate corrosion. The parts come from multiple plating houses, and every part that has cad plating exhibits this corrosion. I do not believe this is a problem with the plating process, most likely a problem with our storage conditions. The parts are oil dipped and wrapped in paper(not VPI/VCI type paper) or stored in plastic bags. These parts are not cad plated all over, so we need to be able to protect the surfaces that are not plated from corrosion also (hence the reason for the oil). Is there anything we can do to stop the CAD plating from turning white?

Katey Grubisa
Plating shop emoployee - Park City, Utah



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