Synthesis and magnetorheology of suspensions of submicron-sized cobalt particles with tunable particle size

Abstract

. Synthesis and magnetorheology of suspensions of submicronsized cobalt particles with tunable particle size. Journal of Physics: Condensed Matter, IOP Publishing, 2010, 22, pp.324106 Abstract. Different samples of cobalt powder were synthesized. Particle size and shape were characterized by electron microscopy and light scattering. These measurements showed that the synthesized powders consisted of monodisperse spheres with average diameters ranging between 63 and 760 nm. These powders were used for the preparation of magnetorheological (MR) fluids by dispersing them in silicone oil. The MR properties of these MR fluids were investigated. It was found that particle size did not have much influence on the MR response of MR fluids, for average particle diameters larger than 100 nm. On the other hand, the MR response decreased appreciably when average particle diameter was diminished below 100 nm; a theory based on the change of the aggregates'shape with the size of the particles could explain these observations. IntroductionSuspensions of colloidal magnetic particles are complex fluids that exhibit magnetic field-dependent rheological (flow) properties. This feature is known as magnetorheological (MR) effect. According to the size of the dispersed particles, these suspensions can be divided in: (i) ferrofluids (FF), which are dispersions of ferro-or ferrimagnetic nanoparticles (approx. 10 nm in diameter) in a carrier liquid (Odenbach 2006); and (ii) MR fluids, which are dispersions of micron-sized particles of magnetizable materials in a carrier liquid (Bossis et al 2002). Upon magnetic field application, particles of FF and MR fluids experience attractive magnetostatic forces, which lead to the formation of particle structures aligned in the field direction. The formation of these structures, which strengthen the suspension and oppose to the flow, is the basic phenomenon underlying the MR effect. The formation of field-induced particle aggregates, i.e. the intensity of the MR effect, will depend on the ratio of the magnetic interaction energy to the thermal energy. For two magnetic dipoles this ratio is given by:

Synthesis and magnetorheological characteristics of ribbon‐like, polypyrrole‐coated carbonyl iron suspensions under oscillatory shear

“…[22][23][24][25] However, in real applications, the MR suspensions are mostly stressed dynamically. This behavior is usually examined through measurement in the steady shear mode.…”

“…This behavior is usually examined through measurement in the steady shear mode. [22][23][24][25] However, in real applications, the MR suspensions are mostly stressed dynamically. This indicates that oscillatory shear measurement is an adequate method for performance evaluation.…”

Particle Dynamics of Polydisperse Magnetorheological Fluids

“…[x, y, z] = sphere (4) x = x * radius (5) y = y * radius (6) z = z * radius (7) xinit(i) = rand*length (8) yinit(i) = rand*width (9) zinit(i) = rand*height (2*uf))^2)*uf) (27) Dworadius = 6*pi*vis (28) cubaf = cuba(f) (29) Qfgfacaf3 = Qfgfac*cuba(f) (30) Q1Bupufaf3 = Q1Bupuf*cuba(f) (31) delx(f,g) = xsys(t,f)-xsys(t,g) (32) dely(f,g) = ysys(t,f)-ysys(t,g) (33) delz(f,g) = zsys(t,f)-zsys(t,g) (34) crit = a(f)+a(g) (35) Fx(f,g) = Fmx(f,g)+Fpx(f,g) (36) Fy(f,g)=Fmy(f,g)+Fpy(f,g) (37) Fz(f,g)=Fmz(f,g)+Fpz(f,g)+dvis(f)*U*(xsys(t,f)-a(f))/length (38)…”

“…However due to sedimentation problem, usage of larger sized particles [7][8] are discouraged. Similarly, retainability of magnetic field in submicron particles [9] is disadvantageous as quick reversibility in shear stress is an essential functionality of MR fluids.…”

Effect of Particle Size on Shear Stress of Magnetorheological Fluids

“…However due to sedimentation problem, usage of larger sized particles [7][8] are discouraged. Similarly, retainability of magnetic field in submicron particles [9] is disadvantageous as quick reversibility in shear stress is an essential functionality of MR fluids. It is interesting to note that the cost of larger sized particles is just 28% of the cost of smaller sized particles [10].…”