magnetic fluid otherwise magnetic liquid; ferrofluid; liquid magnet (rus. магнитная жидкость otherwise феррожидкость abbr., МЖ) — a stable colloidal system of fine ferro- or ferrimagnetic particles dispersed in a liquid carrier.

Description

Magnetic fluids are colloidal solutions of fine magnetic particles (particle size from 5 to 50 nm), usually in the superparamagnetic, ferro- or ferrimagnetic states (particles of metals, iron oxides, etc.). Magnetic fluids (MF) demonstrate a unique combination of fluidity and ability to interact with the magnetic field. Properties of magnetic fluids are determined by the characteristics of their components (solid magnetic phase, dispersion medium and stabilizer); changing of those characteristics allows the MF parameters to be changed over a wide range.

There are two types of magnetic fluids: surfactant-containing MFs and ion MFs, in which the magnetic nanoparticles are stabilised by surface-active substances or by surface charge, respectively.

The MF production process consists of two main stages: obtaining magnetic particles of the required size, and their stabilisation in a liquid medium (liquid carrier). The main difficulty of this process is that the two phases should be aligned in time to prevent aggregation of the particles.

Magnetic fluids based on non-polar media with particle size of about 1 micron are called magnetorheological fluids. They are characterised by a sharp increase in viscosity under the influence of the magnetic field, while in strong fields they can "harden" completely. This property characterises them as "smart" materials with a nonlinear response to external stimuli.

Thanks to the unusual combination of properties of magnetic materials, fluids and colloidal solutions the magnetic fluids are promising materials and find application in various fields of technology – in creation of magnetic fluid seals in the chemical industry, as magnetic-based lubricants, in processes of magnetic concentration of nonmagnetic materials, in cooling systems (e.g. ferrofluid cooling of speaker voice coils), in biology and medicine.

Illustrations

а — Behavior of magnetic fluids in magnet field. Author: 
а — Behavior of magnetic fluids in magnet field. Author: Vladimir Ya. Shur, Ural State University. b — Showpieces at the II International Nanotechnologies Forum (German sector) — syringes with magnetic fluid for hyperthermia.

Author

  • Goldt Anastasia E.

Sources

  1. Makarov V.M., Kalaeva S. Z., Shipilin A.M. et al. Iron-containing waste processing and nanoparticles recovery for producing magnetic liquid(in Russian).// Nanotekhnika. 2004. V. 4, №12. P. 66–69.
  2. Scherer C. and Figueiredo Neto A. M. Ferrofluids: Properties and Applications // Brazilian J. Phys. 2005. V. 35. P. 718–727.

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