1. Ferrofluids

2. Ferrofluids: Magnetic Liquids
Liquid That Responds to a Magnetic Field =
Colloidal Suspension of Superparamagnetic Magnetic Material

3. How Does A Magnetic Liquid Work?
2FeCl3 + FeCl2 + 8NH3 + 4H2O → Fe3O4 + 8NH4Cl
Tetramethylammonium
Cation
(NH4+)
Electrostatic
Repulsion
Hydroxide
Anion
(OH-)
~ 10nm
Berger, P.; Adelman, N. B.; Beckman, K. J.; Campbell, D. J.; Ellis, A. B.; Lisensky, G. C. Journal of Chemical Education 1999, 76,

4. Synthesis of Magnetite Nanocrystals
FeCl3 + 3NH4OH → FeO(OH) + 3NH4Cl + H2O
FeCl2 + 2NH4OH → Fe(OH)2 + 2NH4Cl
2FeO(OH) + Fe(OH)2 → Fe3O4 + 2H2O
Processes:
1) Nucleation ) Growth ) Termination + + + + → + → + + + + +
Fe(III) coordinates to 6 water molecules and
Fe(II) coordinates to 4 water molecules (not
shown) until the solid forms
The water molecules on the periphery of the
magnetite are ultimately replaced by
tetramethylammonium hydroxide + + + + + + + + +

5. Unique Properties Stick to Magnets Take on 3-Dimensional Shape of a
Magnetic Field
Change Density in Proportion to
Magnetic Field Strength

6. Applications Inks Biomedical Damping Seals money
attach drugs to magnetic particles,
proposed artificial heart
Damping
speakers, graphic plotters, instrument
gauges
Seals
gas lasers, motors, blowers, hard drives
Berger, P.; Adelman, N. B.; Beckman, K. J.; Campbell, D. J.; Ellis, A. B.; Lisensky, G. C. Journal of Chemical Education 1999, 76,

7. Damping: Speakers
Rosensweig, R. E. Scientific American 1982, 247,
See how a speaker works at:

8. Damping: Rotating Shafts
Cross-sectional view of a ferrofluid viscous inertia damper
Energy band gap apparatus
Ray, K.; Moskowitz, B.; Casciari, R. Journal of Magnetism and Magnetic Materials 1995, 149,

9. Seals Atmosphere Vacuum Rotating Shaft Ferrofluid Magnetically
Permeable
Material
Permanent Magnet
Rosensweig, R. E. Scientific American 1982, 247,