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Kostas Ampatzis

How to Make Ferrofluid in a Bottle

Danu Novmanu  Follow

You have to be sure to use the type of toner powder that is made to print "machine readable type" like on checks. It is magnetic, the regular toner powder is not magnetic and does not work. It makes a mess.

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Charles Offiong  Follow

I have not yet tried it but there is a youtuber who has made excellent ferrofluid at home. The broad steps are as follows :

  1. Making the magnetic nanoparticles (Fe3O4)
  2. Coating them with a surfactant (Oleic acid)
  3. Dissolving in suitable carrier solution (petrol/kerosene)


Making the magnetic nanoparticles

Add FeCl2 and FeCl3 solution in 1:2 ratio in a beaker and continue mixing it while adding NH3 drop wise. First the solution will turn brown. Keep adding until the solution turns black

$$3NH_3+3H_2O+FeCl_3→3NH_4Cl+Fe(OH)_3$$

$$2NH_3+2H_2O+FeCl_2→2NH_4Cl+Fe(OH)_2$$

$$Fe(OH)_2+2Fe(OH)_3→4H_2O+Fe_3O_4$$

This leaves us with Fe3O4 in NH4Cl solution.

You can also heat the solution for sometime at about 80 ℃

Note - some people suggest adding the iron solution to ammonia and not he other way around.



Separating out the Fe3O4 from the solution

To the solution add small amount of Oleic acid and some excess of ammonia which will form ammonium oleate which binds to the magnetic particles and is soluble

$$OleicAcid+NH_3→AmmoniumOleate$$

heat the solution to about 80 ℃ – 90 ℃ . The ammonium oleate will decompose to again form oleic acid (which is hydrophobic) and it will separate out the magnetic particles from the solution.



Purification

We don't want

  1. Particles that are too big
  2. Particles that are not properly coated with Oleic acid

To deal with them follow these steps

  • Dissolve the Oleic acid coated particles in petrol/kerosene and then keep the beaker over a big magnet to precipitate the unwanted big particles. Then Decant the useful Oleic acid coated particles which stayed in the solution

  • Now add double the volume of Acetone to extract these particle out of the solution. They stay coated with Oleic acid.

This was the purification process. Note that you can also use paint thinner in place of petrol and isopropyl alcohol in place of Acetone.



Dissolving in carrier fluid

Now let the particles dry out and then add a few drops of kerosene/petrol to make a concentrated solution. The ferrofluid should be ready now.



Additional information

If you don't have oleic acid then you can obtain it by saponification of olive oil.

$$OliveOil+CausticSoda/NaOH \xrightarrow{\text{boil}} soap$$

Dissolve the soap in water with some acid (sulphuric). The oily substance collected at the top is mostly Oleic acid with stearic acid and linoleic acid. This can be further purified by refrigeration.

Melting point of oleic acid is 13–14℃ while that of stearic acid is 68℃ and linoleic acid is -12℃

You can also make ferrous chloride from ferric chloride by adding irin nails to it.

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Nate Wyatt  Follow

It is always easier to buy ferrofluid than to make it. Some of the steps don't work well unless the conditions are just right and it is hard to get them right on your first attempt. Luckily there are plenty of suppliers (this UK supplier is top of my Google search for "ferrofluid sales" and they also supply lots of cool magnets).

Ferrofluid is a suspension of small magnetic particles (often magnetite, the magnetic oxide of iron) in a fluid. To avoid the heavy and magnetic particles clumping together or precipitating, they need to be coated in a surfactant. And this only works if the particles are the right size (very small) and you have the right mix of surfactant that works in the carrier fluid (the fluid is usually mineral oil or vegetable oil; alcohols will be a poor choice).

Laserprinter toner isn't usually a mix of suspended magnetic particles: only specialty toner inks are (the ones used for machine readable printing). If you can get the right sort, it will save a lot of effort, but the wrong toner won't work at all and will just make a mess.

There are quite a few recipes on places such as Youtube, but some of them don't work well or don't explain some of the important details. So, if you don't want to spend a lot of time experimenting to get the synthesis right, just buy the ferrofluid.

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