Guest Editorial -For Plateworld.com                                                 

 Don Baudrand, Don Baudrand Consulting,   e-mail:donwb@tscnet.com

 

CHROME REPLACEMENT

(and other plated metals and that are present a hazard)

 

The EPA's Final Report IIPB 85-115905, "Health Assessment Document For Chromium," documented that hexavalent chromium has been shown to cause mutations by causing problems with DNAl: "Therefore, long known as a material which can cause or contribute to dermatitis, breathing problems and cancer, is also a possible cause of birth defects."

It is not difficult to predict that the reduction or elimination of hexavalent chrome plating is in sight.

How can chrome plating be replaced? Several possible substitutes are now available with no doubt more to come as the pressure mounts to remove hexavalent chrome from plating shops.

Trivalent chrome is gaining popularity for decorative chrome plating, and may in the future be available for hard chrome applications.

Electroless nickel can offer application in many areas where hard chrome is now used. Electroless nickel can be hardened to give a good wear surface. It can be plated bright to produce a reflective surface.

Electroless nickel has already served to replace hard chrome in many applications. For example, plated drills and taps, rolls for printing, rolls and guides for moving materials such as in textile production, bearings and journals, and so on. The characteristics of electroless nickel deposits from certain nickel phosphorus and nickel boron solutions are
similar to hard chrome in wear, abrasion resistance, coefficient of surface friction, and electroless nickel is superior to chromium in corrosion resistance and protection in most environments.

Also contending as chrome replacements are plasma spray and detonation spray processes. Many materials, including hard metals, stainless steel, and even ceramics, can be deposited this way. Ion implantation is another contender, along with laser surface modifications.

Cadmium plating is disappearing. The toxicity of cadmium and the difficulty in waste treating it to meet the new standards have caused people to try to find substitute materials. MIL-Std-186D "Protective Finishes for Army Missile Weapon Systems" states, "4.16 Cadmium Plating. Cadmium plating shall be restricted to essential applications only. Use zinc plating, tin plating or aluminum coating instead."

Tin plating is not likely to be satisfactory since it is not very protective. However, some tin-containing alloys may be suitable.

Zinc, zinc nickel, and aluminum by ion vapor deposition have been used to replace cadmium in some applications. New, better alloys are needed to completely fill the need. Boeing has a patented zinc-nickel process for license which claims equivalent or better corrosion protection to that of cadmium. Because of the low couple to aluminum, electroless nickel is used for some cadmium replacement.

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