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topic 2064

Rumor: hexavalent chromate conversion coatings cause skin cancer?


(1998)

I am working on a project concerning the future of cadmium and hexavalent chromium plating. At the last Ontario Regional, I heard a rumor that General Motors Corp. had discovered that assembly workers who handled chromate conversion coated parts had a higher incidence of skin cancer, and that GMC was looking into ways to phase out the use of this coating. Is this just a rumor, or did anyone else hear of something like this in their neighborhood?

tom pullizzi monitor
Tom Pullizzi
Falls Township,
   Pennsylvania 


(1998)

Hi Folks,

I did not hear it before but hear it now. It is an interesting news. I wish it would not be true. But I believe it is just a matter of time. It looks like a warning signal. I suggest all professionals in this field had better take this as seriously as possible. I would like to say that this is a piece of good and bad news. Good: this encourages new technologies to take place; Bad: this cost is too high to affordable to metal finishers. Accordingly, we probably have to change our cars more frequently because of corrosion problem or pay more to buy a new car due to extra cost for corrosion protection.

Indeed, chromates are very bad to human health and our environment. Unfortunately, there is no other alternative treatments able to provide the corrosion resistance comparative to that offered by chromating treatments. It is a time to respond to this issue. We have to look for any possible candidates in order to replace chromating treatments eventually. Non-chromate passivation or oxidation with organic or inorganic peroxides (e.g. permanganate formulation with some additives), anodizing in corrosion inhibitor-containing solutions, and phosphating may be potential alternatives for chromating treatments. I am really interested in any ideas about this topic.

Ling

Ling Hao
- Grand Rapids, Michigan


(1998)

I would not panic to that extent, Mr. Hao. It is Hexavalent form that is carcinogenic, not the trivalent, and trivalent conversion treatments are commercially available.

My question is, why are these trivalent baths not commonly accepted as of today? Is it the specs that need to be changed? Or these are not as good as what they were thought to be?

Mandar Sunthankar
- Fort Collins, Colorado


(1998)

Mandar is right: there are some proprietary trivalent chromium formulation available to the post treatment of plating.

However, trivalent chromium formulations cannot provide the corrosion resistance comparable to that resulting from hexavalent chromate solutions. In addition, trivalent Cr baths are usually hard to control and maintain in practice. In other words, the appearance and quality of trivalent Cr conversion coatings are not stable and consistent. The adhesion of trivalent Cr conversion coatings to plated metals is not so good as that of hexavalent Cr conversion coatings. Trivalent Cr formulations are limited to clear and blue colours on zinc, Zn-Co and Zn-Fe platings at the present. Most importantly, trivalent Cr formulations generally involve the utilization of oxidizing agents which convert trivalent Cr to hexavalent Cr at the metal coating surfaces.

Ling

Ling Hao
- Grand Rapids, Michigan


(1998)

Tom:

The concern over chrome seems to stem from a European Union Directive on End of Life Vehicles(ELV). This directive has labeled hexavalent chrome as a hazardous substance and requires the manufacturer to be responsible for removal prior to recycling. This directive is scheduled to take effect January 1, 2003.

General Motors has issued a industry leading directive to be hexavalent chrome free by January 1, 2000. They are currently in the process of releasing several worldwide specs that are hexavalent chrome free. These specs will replace current hexavalent chrome containing processes.

Ford has suggested taking a multi-phase approach to elimination. This approach requires Ford to be chrome free by year 2003.

Although this is causing concern within the plating industry, rest assured it is responding. Much effort is being directed towards development of Cr+6 free processes. Some progress has been made but improvements are still necessary. In addition, post dipping solutions have been developed to compliment Cr+6 free treatments. Some dip/spin applications have been chrome free for years and can meet many zinc/zinc alloy plating requirements.

Edward Koneczny
- Birmingham, Michigan



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