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topic 1704

Testing electrical resistance/conductivity of chromated aluminum

Not a response, a question. Need info on test procedures/equipment/ companies selling ways to test electrical resistance/conductivity of chromated aluminum. Is the "Sunshhine Tester" still applicable? Just heard of it today. Please respond!

Robert Heiney
LECO Corp.


I do not quite understand the reason for measuring the conductivity of chromated aluminum. The cromate layer is either nonconductive or highly resistive. That does not change the conductivity of underlying aluminum. If the chromate layer is thick enough, about 1 micron, then method such as a "four point probe" may be convenient on flat surfaces, about 1/2 to 1 in.sq. Companies like VEECO used to make such equipment. One thing to emphasize, the four-point probes were made for measuring higher conductivity layers on lower conductivity substrates.

Mandar Sunthankar
- Fort Collins, Colorado


I am not certain, but I am guessing that the purpose for needing to determine the conductivity of chromated aluminum is arising from the old Mil-Spec requirement for certain conductivities on specific alloys.

If that is the case, the piece of equipment is not that difficult to assemble, and getting a copy of that mil spec should be more than sufficient to describe its construction, as this is to be done under a small load of 200 psi.

David Brader
Concurrent Technologies Corporation - Johnstown, Pennsylvania


Is it possible to use a four-point probe to test the resistance of a graphite/epoxy plate? since the surface is contact sensitive, I would prefer some un-contact ways. The reason to do this is to detect the change of resistance at areas where internal delamination exists.

lijie yu


As far as my understanding goes, and I have used the technique extensively for thin films, the four point probe is more suited for coatings that are only a few microns thick. It is developed for near-surface resistivity measurements because most of the current flows near the surface. If there are defects near the surface affecting the restivity, these could be detected but not defined.

Mandar Sunthankar
- Fort Collins, Colorado
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