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Physics/Ferromagnetic fluid


I have learnt that a simple ferro magnetic fluid can be made by mixing Black Iron Oxide (Fe3O4) and a viscous fluid like oil. I purchased black oxide from a hardware store. When I bring the powder near a magnet(loudspeaker magnet - the only magnet at my disposal) it is not at all responding, why is that? is that the same powder that is used as thin film in hard disks?

I saw many videos on the internet making ferro magnetic fluids by mixing black oxide and some viscous media.

My question is if it is working for them why is it not working for me? what went wrong?

Hello veeru,

I suspect that the black oxide you got from a hardware store is not truly Fe3O4. Check the website
The site describes 3 different processes for ferrous objects using different temperatures. The hot and the mid temperature processes apparently "convert the surface of the ferrous metal to magnetite". This is done using baths of alkaline cleaner, water, and caustic soda. The room temperature process is called cold black oxide but uses a copper selenium compound. This may be the product that you got from your hardware store.

I hope this helps,


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Steve Johnson


I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.


I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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