Bidisperse Magnetorheological Fluids using Fe Particles at Nanometer and Micron Scale

Abstract

Conventional magnetorheological (MR) fluids are suspensions of micron-sized particles in a hydraulic or silicone oil carrier fluid. Recently, research has been conducted on the advantages of using bidisperse fluids, which are mixtures of two different powder sizes in the MR suspension. The MR fluids investigated here use a mixture of conventional micron- sized particles and nanometer-sized particles. The settling rate of such bidisperse fluids using nanometer-sized particles is reduced because the nanoparticles fill pores created between the larger particles, thereby reducing fluid transport during creeping flow. This reduction in the settling rate comes at a cost of a reduction in the maximum yield stress that can be manifested by such an MR fluid at its saturation magnetization. There is a measurable and predictable variation in rheological properties as the weight percent (wt%) of the nanometer-sized particles is increased relative to the weight percent (wt%) of micron-sized particles, while maintaining a constant solids loading in the MR fluid samples. All bidisperse fluids tested in this study have a solids loading of 60 wt% of iron (Fe) particles. This study investigates the effect of increasing the wt% of 30 nm (nominal) Fe particles relative to 30 mm (nominal) Fe particles on rheological characteristics, such as yield stress and postyield viscosity. The goal of this study is to find an optimal composition of the bidisperse fluid that provides the best combination of high yield stress and low settling rate based on empirical measurements. The applicability of the Bingham-plastic rheological model to the measured flow curves of these MR fluids is also presented.

Effect of Magnetic Nanoparticle Additive on Characteristics of Magnetorheological Fluid

“…To overcome these problems, many researchers studied various methods. Representatively, the coating magnetic particles with polymer not only decreases the density of magnetic particles but also well matches with lubricant medium oil [17]. Moreover, the abrasion for surface of the CI particles could be reduced during the reversing forming clusters of magnetic particles.…”

Optimal Design Methodology of Magnetorheological Fluid Based Mechanisms

“…The interaction between the particles impedes to a certain level of the shear stress without breaking and simultaneously increases the viscosity of the fluids [32]. In many cases, the effect of MRF is described by Bingham Plastic model [33]. A modified or extended Bingham model, or a combination of Bingham model with other models such as viscous and coulomb friction have also been used to describe the behaviour of MRF [34].…”

Microdynamics of Magnetic Particles Dispersed in Complex Media

“…On the contrary, ferrofluids, which are stable dispersions of magnetic nanoparticles, show almost negligible rheological changes because magnetic attraction is dominated by Brownian motion [2]. Some attempts of increasing the strength of magnetic forces between microparticles have been done by dispersing them in a ferrofluid, and several authors have actually demonstrated that the field-induced yield stress could be substantially increased in this way [3][4][5]. In addition, it has been shown that suspensions of ferromagnetic microparticles in ferrofluids also exhibit a better colloidal stability against irreversible aggregation and sedimentation [6][7][8][9].…”