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RoHS testing for Hex chrome in chrome plated brass
Q. I wanted to have a few components tested to show due diligence for RoHS compliance reasons. My understanding is that chrome plating from a hexavalent chrome bath will deposit chrome metal with a valence or oxidation state of 0, not 6. I contacted a reputable lab to initiate testing and got this response from a PhD of something...."If you use hex chrome to coat your parts, the chrome layer will be +6 oxidation state not 0. On the other hand, stainless steel has high concentration of metallic chrome with oxidation state of 0." The statement about the chrome is not consistent with what I'm hearing, although the stainless steel part is. Is he mistaken about the chrome?
Hal WilliamsMedeco - Salem, Virginia
2006
A. Better find another lab, Hal, maybe one that specializes in plating and metal finishing issues :-)
The PhD is off base but I understand his confusion. Chrome has traditionally been used in two very different ways in the plating industry, and it confuses people.
First, as chrome plating, which is that shiny finish we are all familiar with and which is usually deposited from a chromic acid (hexavalent chromium) bath, although a percentage is deposited from trivalent plating baths. In this case what is deposited is chromium metal, valence 0.
Second, as a "chromate conversion coating" often used on aluminum parts and zinc plated parts. This involves a dip (usually no electricity) in a chromating solution consisting largely of dilute chromic acid. This chromate conversion coating stays hexavalent (a large effort in the industry right now is to convert these conversion coatings over to trivalent or chrome-free processes).
But, indeed, if the chrome plating is very poorly rinsed, there could remain some hex chrome on it. I have seen this in hard chrome plating, but it's probably very unlikely in decorative plating because the item simply can't look good if stained with chromic acid. Highly unlikely though it may be, your testing is probably a good idea.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ted is available for instant help
or longer-term assistance.
A. Hi Ted,
Indeed. For decorative hex chrome plating which employs 3 drag out tanks, 3 rinse tanks (the last 2 with spray and counter flow ) , the residue Cr+6 is below 5 ppm. This meets RoHS requirement, set at 1000 ppm .
- Malaysia
2006
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