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Old 3rd May 2005, 06:22 AM   #1
tade is offline tade  United States
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Default Do not understand ferrofluid.

how viscous is the stuff? It seems to me like a crazy idea to put fluid in between a quickly moving object and a stationary one. the gap between coil and magnet. it certainly must not kill your high frequency response as logic dictates.
interesting stuff.
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Old 4th May 2005, 03:28 AM   #2
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Viscosity will be highly dependent on the carrier fluid, and the magnetic particle size. I made some with engine oil, that was fairly thick. I'll probably try it with diesel next time.

The viscous drag is not necessarily a bad thing, as it will increase damping.
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Old 4th May 2005, 03:30 AM   #3
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interesting. do you use fine ground iron for the particles?
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Old 4th May 2005, 03:38 AM   #4
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Normally, it's made of very fine iron particles suspended in silicone fluid. There's a lot of flexibility regarding the rheology.
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Old 4th May 2005, 04:14 AM   #5
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The magnetic particles need to be around 20 microns or smaller, in order to stay in suspension in the fluid. I made mine by running an equimolar solution of FeCl2 and FeCl3 (ferrous and ferric chloride) into boiling NaOH solution. Fine magnetite particles precipitate immediately. Then its washed several times and dried.

Suspension is achieved by adding a surfactant (like oleic acid - which I extracted from olive oil) to the powder, then mixing into a suitable carrier oil.

Nice idea SY, I'll have to get some silicone oil.

I'm also going to try making nickel ferrites and cobalt ferrites the same way. Should have higher mu than magnetite.
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Old 4th May 2005, 05:02 AM   #6
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Thanks for the info. What concentration of the solutions?

Warning!
Perhaps for those who have forgotten (or never learned) their high school chemistry boiling NaOH is to be respected don't get any into your eyes (possible blindness) and it does a pretty good job of consuming skin - it is used to clean clogged drains.
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Old 4th May 2005, 05:47 AM   #7
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Default making your own iron dust

Would it be practical to take the iron particles that one can collect from beach sand with a magnet and then mechanically screening it for fine particle size? Perhaps it could be separated by letting it fall near a magnet, the finer particles would be pulled off course to a different degree than the heavier ones, very much like the principle of a mass spectrometer. This would be safer than playing with hazardous chemical operations.
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Old 4th May 2005, 06:36 AM   #8
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In a class I help run for high-achieving 5th graders, the students make a 'ferro-fluid' by burning old audio tape stock, grinding it up with a morter+pestel and adding red lamp oil. If you suspend the whole deal in blue h20, the lamp oil seperates and the magnetic tape dust sticks to the lamp oil. The kids get to move it around with a magnetic, adding teflon fluid helps the keep the stuff off the sides of the glass beakers.

Excellent for science-fair fodder. I think NASA originally made this stuff for moving rocket propellent around in zero-G.


dan

(who recently built his first head-phon tube amp! Score!)
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Old 4th May 2005, 07:57 AM   #9
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rcavictim: no, screening beach sand wont work. You need extremely fine particles , under 20 um (thats micro metres) in diameter. The stuff is finer than talcum powder, as fine as paint pigment. Get the idea?

Grinding up old audio tape is a great idea!

Yes, boiling NaOH must be treated with respect! Thats gloves, mask, goggles, coat at least folks.

Soln concentrations: weeell thats a bit indeterminate , I'm a little impatient sometimes so I didn't bother to dry,weigh and redissolve the FeCl2 I made by dissolving nails (!) in 30% HCl. I just took half the FeCl2 solution, converted to FeCl3 with peroxide and HCl, combined the result and ran it slowly into the NaOH (which was about 100g in 500ml water).

Have a look at these two links:Ferrofluids 1
Ferrofluids 2

Intriguing how this topic sparks so much interest here, when I got zero response at the Chemistry forum I hang out at.
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Old 4th May 2005, 10:16 AM   #10
SY is offline SY  United States
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When you obtain the particles by precipitation, are they dendritic?
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