Ioan,
Where can I find this paper on testing coated galvanized steel for
RoHS compliance?
My understanding is that some steel applications use sheet metal with
two coatings on it. The first coating is a Zn or Zn-Al alloy applied
by either a galvanic or a hot-dip process. The second, outer coating
is the chromate process. [Can chromite process be substituted?] If
you obtain a depth profile of this multi-layer structure you see a
blurring of the interfaces between materials. At the surface, there
is carbonaceous matter. Underneath that is the Cr-bearing layer
which gradually incorporates Zn (and Al if present) as it morphs into
the galvanic or hot-dip coating. Deeper yet, the Zn or ZnAl layer
increases in Fe content as it transitions into the surface of the
steel. The extent of intermixing depends on whether there was an
annealing step included prior to the application of the Cr
coating. None of the layer boundaries are sharp and all contain
other elements either as contaminants or as alloy constituents. In
addition, none of the layers are uniform in thickness and composition
across the entire area of the sheet metal.
This description is meant to impress on you that coatings are ugly
beasts that make terrible analytical specimens. Probably many of you
already know this. From the perspective of an analytical chemist,
there is nothing homogeneous about them. Depth profiles have been
obtained using glow-discharge atomic emission spectrometry, which
does not tell you the oxidation state of the Cr. One can probably
study the outer Cr-containing coatings using X-ray photoelectron
spectrometry and other microanalysis techniques. I'd be surprised if
very many coatings companies have these techniques available for
manufacturing QA.
regards,
John Sieber
At 12:34 PM 9/20/2006, you wrote:
>The galvanised coat is not homogeneous with the steel in respect of the
>RoHS definition of homogeneous. If it were then no one would be worrying
>about all the other plated finishes!!
>
>Regards,
>
>Chris
>
>
>-----Original Message-----
>From: Leadfree [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
>Sent: 20 September 2006 17:20
>To: [log in to unmask]
>Subject: [LF] Galvanized RoHS
>
>Hi everybody,
>
>Steve has been kind enough to post a document I have sent to him. The
>paper practically says that galvanized steel is not considered a coated
>structure, therefore the homogeneous material take on galvanized steel
>considers the base material and coating to be one element.
>
>What do you think about this?
>
>Thanks,
>
>Ioan
>
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John R. Sieber, PhD
Research Chemist
National Institute of Standards and Technology
Chemical Science and Technology Laboratory
Analytical Chemistry Division
100 Bureau Drive, Stop 8391
Gaithersburg, MD 20899-8391 USA
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Tel: 1.301.975.3920
Fax: 1.301.869.0413
www.cstl.nist.gov/
Identification of commercial items in this document does
not imply endorsement by NIST or that items are
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