Abstract
In this study, magnetorheological fluid (MRF) was prepared with several kinds of hydrophobic fumed silica in order to improve MRF stability while maintaining desirable fluidity. We conducted steady flow measurements and oil separation tests under gravity and centrifugal conditions. The linkage of fumed silica particles was also observed morphologically by transmission electron microscopy. We found that the MRF sedimentation stability correlated with viscosity in the lower shear rate range. The oil separation ratio improved with the addition of the fumed silicas examined in this study. The surface characteristics of the silica particles affected the stabilization ability. The addition of hydrophobic fumed silica can desirably increase MRF magnetic properties.
Highlights
Magnetorheological fluid (MRF) is a slurry prepared with oil and magnetic particles that have an average diameter of several micrometers
The trend and the order were similar to the results shown in Figure 1, except for MRF-E; we cannot explain this phenomenon in detail because the relationships among the iron particles, fumed silica particles, and oleic acid are not clear
Fumed silica additives having different surface characteristics were used as MRF stabilizers
Summary
Magnetorheological fluid (MRF) is a slurry prepared with oil and magnetic particles that have an average diameter of several micrometers. The quick and large variations in the rheological property of MRF with respect to a magnetic field (Weiss et al, 1994; Carlson, 1994) are desirable for applications such as automotive dampers, brakes, and clutches (Kordonsky, 1993; Carlson, 1996; Jolly and Nakano, 1998; Nakano et al, 2009). The difference in density between the oil and the particles in MRF is large, resulting in particle sedimentation and liquid separation of the upper layer. Such unstable slurries simultaneously cause unstable magnetic properties of MRF, leading to various problems such as device malfunction and damage due to the occlusion and deposition of magnetic particles. Higher-viscosity MRF is not attractive for use in rotating devices such as brakes and clutches from the viewpoint of energy saving, because a high shear rate is applied in the drive part of the device
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