What is the criterion for successful removal of a layer by grinding
so that one can test its composition? I'd like to see someone
demonstrate the removal of a chromate layer of 10 nm to 100 nm
thickness without contaminating it or changing its chemical composition.
People are challenging the statement that layers must be consider
homogeneous substances because they can, in principle, be disjointed
by grinding. Sure you can remove it, but is that really
"disjointing" if the layer is destroyed in the process?
John Sieber
NIST
At 03:33 PM 5/18/2006, Davy, Gordon wrote:
>Bev Christian has raised the question of how to determine the ppm level
>of chromium that he finds on a component, since he doesn't know the
>weight, thickness, or density of the layer that has the Cr. He refers to
>a colorimetric test. The color of a Cr-bearing coating on, for example,
>aluminum sheet metal, might be used to distinguish between Cr (VI) from
>any other form of Cr. The only method that I can think of that could be
>used to establish the oxidation state of Cr in a coating is ESCA, and
>that would be totally impractical. If Cr (VI) is found, then it must be
>assumed that the amount present in the coating layer itself (which
>could, of course, be removed by grinding and is therefore homogeneous)
>is more than 0.1 percent.
>
>But what to do if the Cr is found below the surface, for example below a
>layer of paint? X-ray fluorescence can find the Cr, but it can't tell
>one oxidation state from another. The Cr in this coating might be
>present as conventional chromate, or it might be present as a permitted
>chromium-bearing substitute (i.e., Cr(III)). I can think of no
>practical way to way apply colorimetry or any other method to an
>underlayer alone.
>
>Here's another way of coming at it. If you can't determine the oxidation
>state of a buried coating, then neither can anyone else. The reason for
>being concerned about the presence of Cr in the first place is that an
>enforcement agency might find it and claim that it is Cr(VI). Can an
>enforcement agency on the basis of a suspicion impound hardware or issue
>monetary penalties until conformance is established to their
>satisfaction? Perhaps. Europeans seem willing to do some pretty strange
>things. But is it likely? Take into account the overwhelming number of
>manifest noncompliances that the agencies will surely be dealing with
>for the foreseeable future. What is the probability that a penalty for
>use of Cr(VI) would be imposed on the basis of a suspicion? How high on
>your list of concerns is this, anyway?
>
>
>
>Gordon Davy
>
>Baltimore, MD
>
>
>-------------------------------------------------------------------------------Leadfee
>Mail List provided as a service by IPC using LISTSERV 1.8d
>To unsubscribe, send a message to [log in to unmask] with following text in
>the BODY (NOT the subject field): SIGNOFF Leadfree
>To temporarily stop/(start) delivery of Leadree for vacation breaks
>send: SET Leadfree NOMAIL/(MAIL)
>Search previous postings at: http://listserv.ipc.org/archives
>Please visit IPC web site
>http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
>information, or contact Keach Sasamori at [log in to unmask] or
>847-615-7100 ext.2815
>-------------------------------------------------------------------------------
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
[log in to unmask]
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
-------------------------------------------------------------------------------Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL)
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-------------------------------------------------------------------------------
necessarily the best for the purpose stated.
|
