Synthesis and Properties of Novel Magnetorheological Fluids Having Improved Stability and Redispersibility

Abstract

A novel class of relatively stable and redispersible MR fluids based on meso-scale magnetic particles of iron or nickel zinc ferrite and nano-scale additives is described. For a flux density B ~ 1 Tesla, the iron based MR fluids exhibited yield stresses of ~100 kPa. For ferrite based fluids the yield stress values were as high as ~15 kPa at B ~ 1T. The yield stresses at the flux density required for magnetic saturation increase quadratically with the saturation magnetization of the particulate material, in good agreement with a model for the yield stress of uniformly saturated particle chains. At lower flux densities, the yield stress was generally observed to increase as B 3/2, consistent with models of the role of local saturation of the particle magnetization. The additives were found to enhance the stability and redispersibility of the MR fluids: they appeared to promote a small non-zero yield stress in the absence of a field but were found not to have a substantial effect on the field-dependent yield stresses.

An improved properties of bidispersed magneto-rheological fluids

“…Recently, it was reported that the use of ferrouid (FF) is an effective way to reduce the settling rate of micron-sized particles in MR uid. [15][16][17][18][19] On the application of a magnetic eld, the micron-sized particles become polarized and gather in chains or clusters due to dipole-dipole interaction. It is seen that formation of these clusters creates microcavities within the structures.…”

Magnetorheological Finishing: A Review

“…In order to reduce particle aggregation and settling, different procedures have been proposed: (1) adding thixotropic agents (ex. Carbon fibers, silica nanoparticles) (Bossis, Volkova et al 2003;De Vicente, López-López et al 2003); adding surfactants(ex Oleic or stearic acid) (Phulé and Ginder 1999); (3) adding magnetic nanoparticles López-López, de Vicente et al 2005); (4) the use of viscoplastic media as a continuous phase (Rankin, Horvath et al 1999) and (5) water-in-oil emulsions as carrier liquids . Glycerol and surfactants are used in water based fluid as stabilizers.…”

Magnetic Nanoparticles and Their Applications

“…(10)(11)(12) and T 2 is the transverse relaxation time associated with the dephasing of different spins. T 2 is generally shorter than T 1 .…”

“…There has been a recent spate of interest in the use of metallic Fe nanoparticles for environmental remediation of subsurface chlorinated hydrocarbons, [8][9][10][11] but here the Fe (0) chemistry is central, rather than the magnetism. Micrometer-scale particles are used in magnetorheological fluids, [12] whose viscosities change by orders of magnitude when a magnetic field is applied. Although nanoparticles may be mixed in as well, [13] the magnetism of these materials is dominated by the multidomain structure.…”