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Is aluminium lose its electrical conductivity when it is oxidised ? Answered

I have a soil moisture probe that is generally use for gardening projects. So I read some articles that tell about oxidation of this probes in a week. I wanna make soil moisture sensors that I can use it in my experiments and you know inexpensiveness is important rule of DIY :). I planned to use aluminium plates as resesitive soil moisture sensor but I have still some doubt that oxidation of aluminium affects to conductivity or not ? 

I will use the sensors for a year or at least 7-8 months. So I worry that couldn't measure soil moisture properly.


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Jack A Lopez

Best Answer 2 years ago

Some metal oxides are electrically conductive, and some are not.

I will guess that aluminum is probably a poor choice for conduction cell electrodes, because the usual, most stable, aluminum oxide (Al2O3 I think) is a good insulator.

In fact there is a well known recipe for making electrolytic capacitors, which relies on the fact aluminum will grow an insulating layer, when acting as an anode, under the influence of direct current (DC).

Which reminds me, I think the usual technique for pushing current through a conductivity probe, is to use an alternating current (AC) signal, and this is done intentionally so as to avoid the usual stuff that happens to a DC electrolysis cell, like eroding metal from the anode, or passivating it, or plating metals onto the cathode, or covering it with hydrogen bubbles.

Anyway, you wanted some suggestions for inexpensive probe materials, that you could leave buried, and have the probe still work, without the probe character drifting, or the probe itself corroding.

I am not sure what will work best, but some ideas for things to try:

? coins, the kind with low monetary value

? brass, rod stock, bolt stock, plate, etc.

? copper wire

? nichrome wire, like from discarded hairdryer or toaster

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JeoleXJack A Lopez

Answer 2 years ago

It was so informative reply. Thank you so much, you lighted to my bulb :)

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seandogue

2 years ago

fyi the classic for a dyi humidity or soil moisture tester is a pair of galvanized nails. Some I've seen in the old days suggested copper roofing nails, but as any gardener knows copper isn't very nice to plants.

From a few years ago when I was looking into moisture probes, I *think the nice commercial probes are stainless.

Aluminum rots too easily in soil and I wouldn't recommend it, in part for the same reasons I wouldn't recommend copper., especially if this is for ingestable plants (fruit, vegetable, herb.)

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JeoleXseandogue

Answer 2 years ago

I think so that stainless steel is appropriate material for probe. I will try to use steel plates.

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rickharris

2 years ago

The grey aluminium oxide coating you find on aluminium exposed to air is an insulator, however it is normally so thin it is easily scratched off to giv electrical connection.

Clean your probe with some fine abrasive.

Aluminium when polished is bright shiney and silver looking.

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JeoleXrickharris

Answer 2 years ago

I will bury my sensor under the soil. So I don't have a chance that clean it.

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Downunder35mJeoleX

Answer 2 years ago

Use a piece of stainless steel.
It will oxidise, but is still conductive and won't corrode.

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Josehf Murchison

2 years ago

Use stainless steel spoons total DIY.

The oxidation of aluminium can effect the impedance of soil contact.

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JeoleXJosehf Murchison

Answer 2 years ago

I need 24 pieces of sensor that are have to be standard. So if I use spoons, I couldn't get homogeneous meaurement. I planned to use plate or folio that are durable metal to oxidation

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rickharrisJeoleX

Answer 2 years ago

Stainless plate should be available to you.