RE>Impedance Spectroscopy 12/4/96
Hi Doug,
I have some experience in this technique, but it's been a while. I used it about 15 years ago to characterize the corrosion susceptibility of underground gas pipelines and then about 5 years ago at DEC to investigate solder flux corrosivity and some cursory examinations into SIR degradation behavior. I seem to remember that there was an excellent group at IBM many years ago that was also working with this, but I believe that they've disbanded by now. I agree that it's an exciting concept, but there are some challenges to implement it to provide useful information. Perhaps the two largest challenges that I remember (and it's a little fuzzy!) were getting a stable reference electrode built into the SIR interdigitated comb pattern and to suppress electrical noise to take valid measurements.
As a summary for those who aren't familiar with the technique, a small amplitude AC voltage relative to a known reference is applied to a specimen that's resting at its Open Circuit Potential. This is done for a variety of frequencies. The ratio between this applied voltage and the resulting current gives you an impedance value which can be described by both real and imaginary components. Analysis of these components provides information about the resistance of the solution between the specimen and the reference/counter electrode (which approximates SIR), the polarization resistance (susceptibility of the metal specimen to corrosion), and information about any oxide or boundary layers which are present. It's relatively quick to perform (maybe a couple of hours, depending upon your selected frequency range), and it tends to be non-destructive to your sample.
There is an outstanding group at the University of Virginia that has done a lot of work with this technique in a variety of applications. In the past, they've offered good short courses on the subject. Contact Dr. John Scully of the Materials Science dept at 804-982-5786 for more info.
Good luck,
Greg Bartlett
Mercury Computer Systems
Chelmsford, MA
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--------------------------------------
Date: 12/4/96 5:16 AM
To: Greg Bartlett
From: [log in to unmask]
Good afternoon all.
I had a discussion this morning with a customer regarding the relative merits
of DC-based SIR testing vs. the newer impedance spectroscopy, which is
AC-based. I know of it and the basic operating theory, but not much more.
Is there anyone in the TechNet crowd who has started to use impedance
spectroscopy as a research or production tool? Or more to the point, willing
to share information on this new tool? I think it is an exciting concept.
Thanks for any input.
Doug Pauls
CSL
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