Transcript Ferrofluids Slides - University of California, Los Angeles

Ferrofluids
Ferrofluids: Magnetic Liquids
Liquid That Responds to a
Magnetic Field
=
Colloidal Suspension of
Superparamagnetic Magnetic
Material
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, 943-8.
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
2) Growth
3) 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
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Unique Properties
• Stick to Magnets
• Take on 3-Dimensional Shape of a
Magnetic Field
• Change Density in Proportion to
Magnetic Field Strength
Applications
• Inks
• money
• Biomedical
• 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, 943-8.
Damping: Speakers
Rosensweig, R. E. Scientific American 1982, 247, 136-45.
See how a speaker works at:
http://electronics.howstuffworks.com/speaker6.htm
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, 174-180.
Seals
Atmosphere
Vacuum
Rotating
Shaft
Magnetically
Permeable
Material
Ferrofluid
Permanent Magnet
Rosensweig, R. E. Scientific American 1982, 247, 136-45.