Ferrofluids applications

In recent years, the growing numbers of publications are concerned with ultra-fine metal oxide structures because of their useful applications as bactericides, adsorbents, energy storage media, magnetic data storage, and ferrofluids and specifically as catalysts [6, 7]. 

Ferrofluids find several technical applications, which include rotary shaft seals, damping fluids, accelerometers, optical switches and shutters, and magnetic inks. The earliest application was in the construction of wear-free seals for rotary shafts. A similar seal is used in computer disc drives. Using ferrofluids, high-pressure differential seals which work in multiple stages have been constructed. When the seal is pressurized, each stage develops a momentary leak into the next chamber. The total pressure that can be contained is the sum of the pressure differences across all the stages. Pressure seals... 

Odenbach S. (Ed.), Ferrofluids Magnetically Controllable Fluids and Their Applications, Springer-Verlag New York, 2003. 

Thus, in a field /uqH of 0.1 T, with = 4.5 x 10 A/m, at room temperature, we obtain from Eq. (8-25) that particles of around diameter 10 nm and above will orient their magnetic dipoles with the field. Furthermore, if only part of the ferrofluid is exposed to the magnetic field particles larger than 10 nm will be drawn into the field and will enneentrate where the field is strongest. Thus, in practical applications of ferrofluids, the particles must be kept small to avoid field-induced particle segregation. 

The properties of ferrofluids seem now to be well understood, and numerous applications have been found. Unlike ER and MR fluids, particles in ferrofluids have permanent (magnetic) dipoles thus the particles must be small, around 10 nm, to prevent permanent clumping. If single-domain ferromagnetic particles this small are made, and coated with surfactant to prevent clumping by van der Waals forces, stable ferrofluids can be made whose properties are readily predicted from theory. 

The Shliomis Stepanov approach [9] to the ferrofluid relaxation problem, which is based on the Fokker Planck equation, has come to be known in the literature on magnetism as the egg model. Yet another treatment has recently been given by Scherer and Matuttis [42] using a generalized Lagrangian formalism however, in the discussion of the applications of their method, they limited themselves to a frozen Neel and a frozen Brownian mechanism, respectively. 

Kim, D.K. et al., Biomedical application of ferrofluids containing magnetite nanoparticles, in Materials Resource Society Symposium Proceedings, Vol. 676, Materials Research Society, Warrendale, PA, 2001, p. 1, cited after [1313]. 

We may summarize the contents of this chapter in more detail as follows. In Section I we demonstrate how the explicit form of Gilbert s equation describing Neel relaxation may be written down from the gyromagnetic equation and how, in the limit of low damping, this becomes the Landau-Lifshitz equation. Next the application of this equation to ferrofluid relaxation is discussed together with the analogy to dielectric relaxation. 

The stable colloidal dispersion of iron oxide nanoparticles in a liquid carrier medium is known as magnetic ferrofluid. The iron oxides mostly used are magnetite Fe304 and maghemite y-Fe203. The carrier medium can be chosen to be aqueous or organic, depending on the application. The stability of the ferrolluids is the main... 

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