Iron–sepiolite magnetorheological fluids with improved performances

Abstract : This work is focused on the characterization and magnetorheological study of magnetorheological (MR) fluids composed of iron particles and sepiolite fibers, used as a thickening agent. The work is aimed at (a) understanding the effect of the sepiolite addition on the MR response; and (b) finding an appropriate formulation allowing a good sedimentation stability keeping a relatively low off-state viscosity and providing an enhanced MR effect. In the presence of an applied magnetic field, the composite MR fluid exhibits a yielding behavior with a progressive enhancement of the field-induced static yield stress with increasing volume fractions of both iron and sepiolite. Such effect is attributed to a friction between gap-spanning aggregates composed of iron particles and sepiolite-oil viscoplastic matrix. The field-induced dynamic yield stress shows an initial increase with the sepiolite concentration (explained by a partial expulsion of the sepiolite fibers from the aggregates) followed by a decrease. The proposed mechanisms are supported by developed qualitative theoretical models, one of which is based on homogenization approach of Château et al. J. Rheol. 52, 489 (2008). From the practical point of view, the formulation containing 10 vol% of iron and 4 vol% of sepiolite seems to combine a perfect sedimentation stability with moderate values of the plastic viscosity and of the off-state static yield stress (only 5 Pa) and with a relatively important static and dynamic yield stress enhancement (30% and 60%, respectively).
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Submitted on : Sunday, January 6, 2019 - 8:04:01 AM
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Jessica Marins, Tomáš Plachý, Pavel Kuzhir. Iron–sepiolite magnetorheological fluids with improved performances. Journal of rheology, American Institute of Physics, 2019, 63 (1), pp.125-139. ⟨hal-01970783⟩

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