One of the most fun experiments that can be performed at home! Ferrofluid is a magnetic liquid that takes the shape of the magnetic field applied to it and can be used to visualize magnetic fields. This experimental explains how a ferrofluid can be made multiple ways by using simple household items.
Introduction to Ferrofluid
It is generally difficult to make a magnetic liquid because once you melt a magnetic material (for example iron) it will no longer be magnetic. This is because the melting point for iron is 1000˚C, but its Curie point (the temperature when magnetic materials lose their magnetism) is 800˚C. A ferrofluid, however, is liquid at room temperature and becomes strongly magnetized in the presence of a magnetic field.
They are made from ferromagnetic nanoparticles approximately 10 nm in diameter suspended in a carrier fluid. The nanoparticles will remain suspended in a solution as long as they do not aggregate. To prevent aggregation from occurring each nano particle is thoroughly coated with a surfactant to inhibit clumping. There are many commercial applications for ferrofluid from liquid seals in hard drives to contrast agents for magnetic resonance imaging. One of the more interesting applications is in the use of ferrofluid based ink by the US government to print the one dollar bill. These bills can be read by vending machines, capable of to recognize different magnetic patterns of different denominations. This technology also helps to US government to identify counterfeit bills. To prove this at home (if you live in the US) hold a neodymium magnet to a one dollar bill and you will see it would be attracted to the magnet. Ferrofluid can be bought relatively cheaply online. It can also be made simply from home in two ways.
Homemade Ferrofluid from Laser Jet Toner
One of the quickest and easiest ways to make a ferrofluid is to made a 1:1 mixture of laser jet toner (or magnetic ink developer) land vegetable oil.
Homemade Ferrofluid from Compact Cassettes
The magnetic tape contained in the compact cassette is made of a thin magnetizable coating on a long, narrow strip of plastic. The magnetizable tape coating is made from ferric oxide (Fe2O3).It is this ferric oxide that needs to be isolated and mixed with vegetable oil to make the ferrofluid.
Materials and equipment
- Compact Cassettes
- Two Large bowls
- Neodymium magnets
- Vegetable oil
- Break the cassettes and remove the magnetic tape and unravel.
- Place the unraveled tape in to one of the large bowls and submerge with acetone. Leave for a hour allowing time for the acetone to dissolve the tapes coating.
- Decant the acetone solution into the second bowl.
- Push the neodymium magnets into a balloon and swirl through the acetone solution. The ferric oxide will be attracted to the magnet and form a brown sludge on the outside of the balloon.
- Collect the brown sludge by removing the magnet from the balloon. This can be achieved by cutting the top of the balloon off and inverting. This method will also prevent any get the sludge on the magnet.
- Add a small amount of vegetable oil (You will need to experiment to get the correct concentration)
There is a third option but it requires using less available ferrous chloride, ammonium hydroxide and citric acid. Ferrofluids are well known for forming regular patterns of peaks and valleys (spikes) when a strong vertical magnetic field is applied. The spikes are formed along magnetic field lines when the magnetic surface force exceeds the stabilizing effect of the fluid weight and surface tension. Ferrofluids have an exceptionally high magnetic susceptibility and large spikes will form using a small neodymium magnet.
Neodymium is a rare-earth element and was first discovered in 1885 by Austrian chemist Carl Auer von Welsbach. Neodymium magnets are made from an alloy of iron, boron and neodymium (Nd2Fe14B) and are the most powerful permanent magnets known to man capable of lifting a thousand times their own weight. Neodymium magnets appear in products such as microphones, loudspeakers, bass guitar pick-ups and headphones.
Materials and equipment
- Petri dish
- Neodymium magnets
- Nitrile gloves
- Magnetic objects (screws, bolts, etc)
- Be sure to wear nitrile gloves before starting this experiment as ferrofluid will dye your hands.
- Connect the neodymium magnets to your magnetic objects but keep them separated by placing a Petri dish between them. Next place them on the glass.
- Using a pipette, pipette out a small amount of ferrofluid on the magnetic object.
- To reuse the ferrofluid simply remove the neodymium magnets and collect using the pipette.