Letter 10089

Cadmium Plating 

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
- NH

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, NJ

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, CA, USA

Cadmium is a cumulative poison we are all working to get out of the environment; but we can't substitute anything for cadmium except upon individual design review of each individual component.

Ted Mooney, P.E.  finishing.com Brick, NJ

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