iron powder conductivity

For some experiment I need a conductive powder which is reasonably easy to clean. One of my options is iron powder, because it is easy to clean -- pick up with a magnet. To my surprise, the powder turned out to be non-conductive -- if I stick multimeter probes in a heap of powder there is no conductivity, not below 1Kohm anyway.

Any clue why and how to make it conductive? The only theory I have is it is oxidized, but still it seems counterintuitive.

The powder is clean, freshly out of the package, bought here http://www.amazon.co.uk/gp/product/B007JTMVD4?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s01.
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gremwellAsked:
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JohnBusiness Consultant (Owner)Commented:
Iron conducts electricity of course. So in a powder, there is no direct path and then powder elements make only loose contact with each other, so there is going to be resistance there. And there will be a lot of these points.

So your reading makes sense to me.
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rindiCommented:
The problem with iron is that it oxidises (rusts) quickly when exposed to oxygen, which of course is in the air, and rust isn't very conductive. The powder just increases the surface exposed to air. You'd have to create the powder (with a file for example), then immediately do your experiment. Then chances are that it will not yet have oxidized enough.

Or use stainless steel powder, that shouldn't oxidize that quickly and it is also magnetic.
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JohnBusiness Consultant (Owner)Commented:
True, but even so, powder elements are loosely coupled. Copper wires with loose contacts make for high resistance as well.
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☠ MASQ ☠Commented:
You have discovered the Branly effect!  

Although iron has good conductivity, this is all about the form you have it in.  Actually with different voltages and arrangements you will see different effects.

Some academic stuff for you here if you want the science behind particles and conductivity: http://arxiv.org/pdf/cond-mat/0407773.pdf
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gremwellAuthor Commented:
@John, resistance between copper wires maybe due to an oxide too? Or you suggest high resistance is really due to very small surface of contact between the grains, so this will be an inherent problem?
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gremwellAuthor Commented:
@rindi, making it right before the test is tricky, I need quite lot of it (100ml) and all the noise and mess associated with the process make this solution less practical for me.
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gremwellAuthor Commented:
@MASQ, thanks for your input. It appears the effect I observe is due to Branly effect indeed.
For the same of other readers, I give a link to wikipedia article which describes the same in slightly more accessible form.
http://en.wikipedia.org/wiki/Édouard_Branly
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dbruntonQuid, Me Anxius Sum?  Illegitimi non carborundum.Commented:
Following on from Masq's comment see http://en.wikipedia.org/wiki/%C3%89douard_Branly
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gremwellAuthor Commented:
Thanks to everyone for the input. I have just realised my experiment will not work out anyway, regardless of the properties of the powder. The objective was to short-circuit two contacts by pouring powder on top of it, but the electrodes (some copper alloy I think) will also be covered with an oxide, so even if the powder is perfectly conductive, they will not be short circuited.
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d-glitchCommented:
If you can compress the powder, it will conduct.  But the resistance will be a function of the pressure.  

If you can share more about your experiment, we might be able to help.  
Why do you need powder?  Would a pair of wire brushes do the job?  Or a drop of mercury?
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gremwellAuthor Commented:
@d-glitch, I've made another, corrected question.
http://www.experts-exchange.com/Other/Math_Science/Q_28636565.html
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JohnBusiness Consultant (Owner)Commented:
@gremwell2015 - Thanks.

"Or you suggest high resistance is really due to very small surface of contact between the grains, so this will be an inherent problem? "

Broadly yes. A carbon resistor is compressed carbon granules in a composite (plastic) shell with wire leads.  One a precision instrument in my shop, I was having problems with an input. When I unsoldered the resistor, one lead fell out. The compressed carbon has loosened to a powder and I got the same effect as above. New resistor and problem solved.
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