General > General Technical Chat
Iron Filings Conductivity
nickbild:
I've got a jar of fine iron filings that are not conducting electricity as expected. They respond to magnetism as they should, so it seems to be iron, and was bought from a reputable brand. Any ideas on why this might be? Corrosion? Thanks in advance.
TimFox:
For some applications of iron filings, such as inductor cores, the particles may have been coated to eliminate conduction. This would avoid eddy current loss in that application.
nickbild:
Good info. This is just a jar of raw filings for hobbyist/educational use, so I doubt there is a special coating in this case though.
Ian.M:
Cutting or grinding iron to dust is a fairly high energy operation, and the particles typically come off hot enough to form an oxide layer. That oxide layer may insulate if thick enough or when thinner can even form a point contact Schottky type diode junction with an adjacent particle. This has interesting effects on the electrical properties of bulk iron (and other metal) filings. See https://en.wikipedia.org/wiki/Coherer
floobydust:
OP it does depend on how much current and voltage you are attempting to pass through the iron filings.
Most multimeters do not push enough current to punch through any passivation layer. Try using a bench power supply and more current, like a light bulb.
The early radio detectors circa 1890, before galena crystals, the "coherer" was iron filings in a glass tube and I think it was the oxide layer doing rectification.
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