What's so special about Cadmium Plating? 

Letter 10089

Hi I need help!

What is the use of Cadmium? What is so special about it? We do a nickel, cadmium, gold plating series. We now want to do away with cadmium. What can we use in place? Core metal is aluminum alloy 60601 - T6 IAW ASTM B 209.

Susan Snow
- New Hampshire

Assuming radiation control is no part of the function of your product line, then the features that make cadmium attractive are: good corrosion resistance, cathodic protection of steel, galvanic compatibility with aluminum, excellent lubricity, and freedom from gummy and voluminous corrosion products.

However, it is unusual to plate both cadmium and nickel on a part. When it is done it is usually for the purpose of making a diffused nickel-cadmium coating which is a rather different thing than cadmium plating.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

Cadmium plating is wonderful. I want all landing gear on every plane I ride to NOT have a substitute for cadmium, NiCd, chromate conversion coating, etc.

I still don't get why we have to eliminate cad and chrome, and I am a card carrying tree hugger. (Keep hard chrome on those chain saw blades too!) All we have to do to waste treat the effluent from the plating shops, and we are done.

Tom Pullizzi platronica.com Falls Township, PA

Here's why NASA doesn't like Cadmium plating:

1. Cadmium is known to sublimate in a hard vacuum environment (especially at temperatures above 75°C). The sublimation products, which are conductive, can redeposit resulting in short circuits. The sublimation products may also interfere with sensitive optics.
2. Cadmium is a toxic material that should not be used in manned space flight applications
3. Cadmium is subject to the spontaneous growth of Cadmium whiskers. The propensity of Cadmium to grow whiskers appears to be lower than that of zinc and especially tin. Cadmium whiskers (like tin whiskers) grow spontaneously and are capable of causing electrical failures ranging from parametric deviations to sustained plasma arcing that can result in catastrophic short circuits. See prohibition against pure tin plating for additional insight regarding the risks of metal whiskers.

I also think that when it's exposed to certain types of radiation it becomes extremely toxic, emitting a deadly gas. I heard long ago that a nuclear devices' potential for rendering an area uninhabitable can be enhanced by covering the device with cadmium. Items sold to the government are prohibited from having cadmium plated parts for this reason.

Shawn Barnett
- Shingle Springs, California

Thanks, Shawn. Good points, all . . . except your last sentence, which simply isn't true. There are countless military and aerospace parts that must be cadmium plated per military spec. In fact, if you research the background scandal behind the Fastener Quality Act, I think you'll find that the heart of it was that lives were endangered by plating shops substituting zinc plated fasteners where cadmium was specified.

Cadmium is certainly unsuitable for some applications, and it is a cumulative poison we are all working to get out of the environment -- but we can't substitute anything for cadmium without design review of each individual component.

Ted Mooney finishing.com Brick, New Jersey

I believe some bar stock I am working with is cadmium plated. It's solderable, and there are advantages in that. Does anyone here know of a test to differentiate between "bright tin", and cadmium?

Jim Canale
manufacturing - Tully, New York

Hi, Jim. Letter 31938 and 38853 suggest spot tests for cadmium. The majority of cadmium plated work receives a yellow chromate, which wouldn't be mistaken for tin. Good luck.

Regards,

Ted Mooney finishing.com Brick, New Jersey

Thanks! Do you know of anyone making small test kits of the chemicals necessary to make the tests? We try to minimize the amount of hazardous chemicals and reagents we have in house.

Jim Canale
manufacturing - Tully, New York

Hi, Jim. Although there may be a few such suppliers, your local metal finishing chemical distributor will be familiar with all of them, and is always your best best for small quantities because they are often able to split orders and stock locally. If your company buys no chemicals, so you are unfamiliar with this, look in the yellow pages of your town or the nearest city.

Regards,

Ted Mooney finishing.com Brick, New Jersey

We are a supplier of Oilfield Equipment and our customer needs ASTM A193 [link is to spec at TechStreet] GR B7 Studs and Nuts with Cadmium plating. Why do they need cadmium plating,
what is the difference between Zinc and cadmium?
Your explanation will be very useful for me,

Thanks and Regards

Palavesam Subramanian
- Dubai, U.A.E.

Hi, Palavesam. Please see my response to Susan (the 2nd entry on this thread). Your customer may decide to change the spec for the coating after considering the toxicity of cadmium; but zinc is not a proper substitute for cadmium in many cases because of lower malleability, incompatibility with aluminum, stick-slip problems on fasteners, and gummy corrosion products. Good luck.

Regards,

Ted Mooney finishing.com Brick, New Jersey

  opt  

Ted, what is a suitable substitute for cadmium plating in automotive applications (we are striving for 20-year performance in our trucks....)

Is "cadmium plating" a good choice for automotive? -- I always understood that if it has cadmium plating, it's going to be quite costly....

Do you have a rough feel for how much more costly cadmium plating should be, compared to yellow or clear zinc?

Thanks,
Jeff Bonn

Jeffrey Bonn
- Springfield, Ohio

Hi, Jeff. Auto manufacturers do not use cadmium plating anymore and you probably should not either. A zinc alloy like tin-zinc or zinc-nickel may be appropriate but, as mentioned, you need to look at which properties of cadmium you need and select a replacement coating that offers those particular properties. Nothing has all the properties of cadmium. If something had all the properties of something else, it would be that other thing :-)

At one time cadmium was very cost competitive with zinc. The only thing to say about cadmium cost now is that it is on an upward trajectory as it gets harder to find. Good luck.

Regards,

Ted Mooney finishing.com Brick, New Jersey

Ted,

You mentioned you don't see many reasons for plating both Cadmium and Nickel on the same part, yet Nickel (usually Electroless) is quite often applied as an underplate on Mil/Aero Aluminum based Electrical connectors and accessories that are top coated with Olive Drab Chromate over Cadmium. What would be the benefits of the Nickel under the Cadmium? And doesn't the galvanic potential between the two create corrosion issues?

Thanks,

John van den Enden
- Toronto, Ontario, Canada

Hi, John. That's not quite what I said, but no matter. Cadmium offers sacrificial protection to nickel just as it does to steel, so I don't see a galvanic issue. I am not familiar with the connectors in question, but sometimes the cadmium and olive drab is required for camouflage color, or perhaps for fungus resistance.

Electroless nickel is an extremely corrosion resistant, highly conductive, barrier layer finish. Also, to plate onto aluminum requires either cyanide copper or electroless nickel after the zincate anyway, so it's more of a question of choosing between the two than choosing to do electroless nickel or not do it.

Regards,

Ted Mooney finishing.com Brick, New Jersey

October 4, 2009 I am making a small bracket that requires military part number to be stamped or etched.(the part is Cadmium plated) We prefer to Laser Etch instead of stamping, but I am wondering if any toxic fumes are produced when Cadmium plating is etched by laser marking??? Can anyone tell me if this is true??? Thanks Sam Rearick - Apollo, Pennsylvania October 6, 2009 Hi, Sam. I would expect the cadmium plating to vaporize from the heat of the laser. So I would not suggest this operation unless there is fume removal capacity in the system. If good provision is made for fume removal, though, I wouldn't think it would be a big deal. Cadmium is not plutonium, and in the old days muffler repair shops would burn off cadmium plated bolts and brackets, releasing hundreds of times as much fumes without fume extraction systems. Regards, Ted Mooney finishing.com Brick, New Jersey