SEM micrographs of the two types of particles used for the preparation of the MR fluids. Solid carbonyl iron (A) and (B) and porous iron particles obtained from the reduction of a magnetite precursor (C) and (D).
Diameter distribution of the synthesized porous iron particles.
Mass magnetization of the dry powders (A) and suspensions with 78.7 mg/ml of iron (B).
Small-amplitude oscillatory shear magnetosweep curves for suspensions prepared with porous iron (open symbols) or solid iron (solid symbols) with the same gravimetric iron content. (A) Storage modulus (G′). (B) Loss modulus (G″).
Small amplitude oscillatory shear magnetosweep curves for suspensions prepared with porous iron (open circles) or solid iron (solid circles) with the same particle volume fraction (φ = 0.10). (A) Storage modulus. (B) Loss modulus.
Storage modulus at saturation, G′sat, (A) and scaled storage modulus at saturation, G′sat/(μ o M s 2), (B) as a function of volume fraction (φ) for both types of particles. Solid circles: solid iron. Open circles: porous iron. Lines in (A) are a guide to the eye.
Dependence of the static yield stress (A) and the dynamic yield stress (B) on the applied field for porous and solid iron suspensions. Note that one of the solid iron suspensions (that with φ = 0.010) had the same mass concentration as the porous iron suspension (78.7 mg/ml), whereas the other solid iron suspension was prepared with the same particle volume fraction as the porous iron suspension (φ = 0.021). Bottom: scaled static (C) and dynamic (D) yield stresses. The range of four orders of magnitude in the y-axis has been preserved to facilitate the comparison with the data before scaling.
Viscosity curves for the two types of suspensions at four different field strengths. (A) Viscosity as a function of the shear rate. (B) Viscosity as a function of the Mason number (Mn, see Eq. (1)). Suspensions had the same particle volume fraction (φ = 0.021).
Viscosity (η) as a function of shear stress (τ) for suspensions prepared with solid particles (A) and porous iron particles (B). Particle volume fraction was the same (φ = 0.021) for both types of suspensions.
Shear stresses that mark the onset of flow (static yield stress), the onset of shear thickening (critical stress) and the end of the shear thickening for different field strengths and for a porous iron suspension with a particle vol. concentration of φ = 0.021. The boundaries of the shear thickening region are given by the local minima and maxima of the curves shown in Fig. 9 (bottom).
Gravimetric iron concentrations and the equivalent particle volume fractions for the porous iron and the solid iron suspensions used in this study.
Values of the static yield stress and the dynamic yield stress obtained from the ramp-up shear flow rheograms for both the porous particle and the solid particle based suspensions. Iron content in both types of suspensions was 78.7 mg/mL.
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