Download Ferro-fluid

Multi-grade CHEMISTRY/FORCES
FERRO-FLUID
Time: 45 min, good to combine with other magnet exploration exercises like ‘magnetic
sizzlers’, ‘wooly wally’, and extraction of iron filings from cereal
Topics: invisible forces (g3), forces and simple machines (g5), the Earth’s crust (g7), forces,
fluids and density (g8), motion in our world (g10)
What is a ferro-fluid?
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A ferro-fluid is a colloidal suspension of magnetic particles in a fluid matrix, or surfactant
What are ferro-fluids used for?
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Liquid seals on metal joints in vehicles – they are held in place by magnetic attraction
Thermal regulators in audio-speakers
Computer components
Medical purposes including Magnetic Resonance Imaging, or MRI
Many other commercial purposes!
For Science Students, ferro-fluids provide a visual way to understand magnetic
attraction and the concept of a magnetic field
Instructions: Make a ferro-fluid
 A high quality ferro-fluid requires magnetic nano-particles, a near weightless surfactant,
and very strong magnets
 This is a low-tech, non-toxic version:
o Pour 1/2 cup of granular iron oxide into a container that you will be okay
disposing of (this is very difficult to clean out of a beaker)
Add 6 tbs vegetable oil
Add 3 drop of dish soap
Add 1 tbs of acetone
Stir thoroughly
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 This is best done as a demonstration at the front of the room
o Ask the students:
 Why would a weightless surfactant make a more ‘reactive’ ferro fluid?
Because the magnetic particles move most easily through a lighter, less
viscous medium, but they also need to be supported – water will not
support them, and oil is lighter than water
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Why add dishsoap? Dishsoap breaks the bonds between oil molecules,
making the surfactant less viscous, so that the iron particles can move
more easily
Why add acetone? Acetone is an extremely light weight fluid – it
evaporates very quickly for this same reason (girls will have noticed this if
they ever used it to clean off nail polish – it dries much faster than water
because the molecules are light and it takes little energy to evaporate
them)
Demonstrate the ferro-fluid’s responsivity using a retrieval magnet – see if
it will be drawn to the side of the container, or, if you tip the container, if it will be held
by the magnet and resist flowing down. The movement of a large ferrofluid mass can be
quite eery and magnificent, depending on the strength of the magnets used
Now, let them visualize magnetic fields for themselves:
 Use a straw to transfer a small drop of ferrofluid into the bottom of a plastic cup
 Choose a small magnet to place under or on the side of the cup (I suggest some round
fridge magnets, some small medium strength bar magnets, one ree magnet, and a
bunch of oblong ‘magnetic sizzlers’)
 DO NOT ALLOW THE MAGNET TO TOUCH THE FERRO-FLUID – and ** warn the students
not to touch the ferro fluid as it can make its way onto metal desks, watches, and
electronics and can be very hard to get off **
What will happen?
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The magnetic particles in a ferro-fluid will line themselves up with the magnetic field
generated by a magnet – providing visible evidence of its shape and strength
Once aligned, the fluid is ‘stabilized’ by the magnetic force – try turning the cup upside
down with the magnet on the bottom of the cup
Remove the magnet and magnetic field, and the fluid will ‘liquify’ once more
Allow the students to experiment with different sizes, shapes and stregths of magnets
Visualization exercise:
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After they’ve had a chance to experiment, ask each to choose a magnet for the
following exercise:
o Place the magnet near your ferro-fluid and allow it to stabilize
o Using a pencil and paper, draw the shape of your ferro-fluid, and the magnet
beneath it
o Using a pencil crayon – draw the shape of the invisible magnetic field that is
passing through your ferro-fluid
o Arrange the drawings on a bulletin board, or clear space on the floor, and have
them discuss the shapes and sizes of magnetic fields associated with different
magnets
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FOR GRADE 7, the Earth’s Crust: Discuss how iron in cooling, solidifying magmatic rocks
is stabilized by the Earth’s magnetic field and explain how this discovery contributed to
the theory of Plate Tectonics
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ADDITIONAL SUPPLEMENTAL ACTIVITY: If there is a parent or community member who
has apprenticed as a mechanic, you might have them come in to talk about some
practical uses of ferrofluids in the garage – including the product Magnaflux