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).

Gelatine-Coated Carbonyl Iron Particles and Their Utilization in Magnetorheological Suspensions

“…Nevertheless, the coating process of the particles did not fully suppress the sedimentation process. In the case of the MR suspensions, this has to be achieved through the use of thickening agents or other additives [ 38 ], whose effects can be emphasized using coated particles. The uneven start of the particles can possibly arise from different characteristics of the particles affecting the interaction between the sedimentation probe and the liquid itself; nevertheless, it should not further affect the sedimentation process.…”

Surface-initiated mechano-ATRP as a convenient tool for tuning of bidisperse magnetorheological suspensions toward extreme kinetic stability

“…The upward shift in the flow curves occurred due to increased viscous dissipation that usually transpires through increase in the concentration of an additive. 17,51 Such a rise evident herein most likely stemmed from the greater hydrodynamic volume of the supplemented additives lent by the lightweight coatings. Furthermore, enhanced interaction with the silicone oil played a significant role in heightening the rheological response, as discussed below.…”

“…Similar behaviour was observed in the MR suspensions after incorporating high surface-tovolume ratio additives, such as carbon nanotubes 17 or sepiolite clay. 51 The formation of a gel-like structure was also evidenced through a gradual drop in the n-index value, reflecting its non-Newtonian properties. The off-state n-index extracted from the R-S equation equalled 0.78 for the reference MR suspension, decreasing to 0.76, 0.59 and 0.51 after incorporating the neat NPs, NPs-Br and NPs@PMA, respectively.…”

Performance and Stability of Magnetorheological Fluids—A Detailed Review of the State of the Art

“…A magnesium silicate clay, called sepiolite, was studied as an additive by Marins et al [ 133 ] in iron‐based MRFs. The addition of sepiolite did not change the magnetic properties of pure iron significantly.…”