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topic 0125

Implications of phasing out Cadmium and Chromium

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Environment Canada is considering new regulations that could phase out Cr & Cd plating . I am looking at the status of commercially useable replacements for Cr & Cd plating.

I do have some information for I attended the fall meeting of the American Society for Metals in Cleveland last month :Surface Engineering Symposium.

I also know that the USAF is doing research in this area. I am trying to evaluate the importance the growth of Cr & Cd replacement and the need of our industry in Canada to look to replacement processes. Could you suggest some names of experts who could fill me in on the status of this trend and what is driving it? Thanks

Emile Beauchamp
MTR - Canada

Hi, Emile. What is driving the trend is recognition of the toxicity of cadmium and hexavalent chromium.

Cadmium is a chronic, cumulative poison like mercury and lead; the booklet "Using Cadmium Safely" by the Cadmium Council, Reston, Virginia USA provides a good introduction to the issue.

Hexavalent chromium is a carcinogen; NIOSH Technical Report 85-102, "Control Technology Assessment: Metal Plating & Cleaning Operations" summarizes and references numerous studies of the subject over the last 60 years that seem to prove it pretty conclusively.

Twenty years ago cadmium was used rather indiscriminately-- interchangeably with zinc. And for two decades we've been chipping away at its use, replacing it in the easier applications first. Now it's never used by informed people simply for corrosion protection, but only where its combination of properties (compatibility with aluminum, freedom from gummy corrosion products, sacrificial protection, lubricity, and softness) make replacement quite difficult. It is one thing to say muffler hardware, which will be torched off by mechanics, ought not be cadmium plated -- but it is an altogether different thing to tell an airplane manufacturer that the only fastener coating that he has found to not cause catastrophic failure of airplane wings is now forbidden, or to tell a fire extinguisher manufacturer that he must use a plating on his trigger mechanisms which is known to cause jamming by buildup of gummy corrosion products.

Similarly with chrome. Where hardness is required, electroless nickel may do. Where low coefficient of friction is required, teflon may suffice. Where preventing nickel from tarnishing is required, a proprietary cobalt may be fine. But where hardness, wear resistance, freedom from galling, low coefficient of friction and the ability to retain oil are required, it's hard to replace chromium plating.

At a recent A.E.S.F. meeting our European lecturer was showing slides about eliminating the use of toxic metals. His brand new slide projector kept snagging and hanging up. He couldn't understand why some of us surface finishers were impolitely tittering each time it did so. But the irony of the situation was just too much: here we were suffering through trying to watch a slide presentation about eliminating cadmium and chrome, constantly interrupted by an expensive new projector that was a hopeless piece of junk because cadmium and chrome had been designed out of it!

It is in society's interest to keep the pressure on toward reducing cadmium and chrome usage. But it gets progressively more difficult and costly, and there is surely a place, beyond the point of diminishing returns, where chemical paranoia is not free of mortal cost. I find it disconcerting that we judge chemicals by arbitrary ethereal statistical formulae like "1 in 100,000 increase in cancer mortality" without being mindful that unrelenting pressure on engineers to prescribe obviously inferior substitute finishes is predictably causing catastrophic failures.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

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