R. V. Upadhyay

Plate-like iron particles based bidisperse magnetorheological fluid

Magnetorheological (MR) properties are experimentally investigated for bi-dispersion suspension of plate-like iron magnetic particles dispersed in carrier liquid to see the influence of small size particle on large size MR fluid. As a first step, structural, magnetic, and morphology of two different micron size magnetic particles are described in details. The three different weight fractions of MR fluid samples are then prepared, followed by measuring their magneto-viscous and visco-elastic properties. In the steady-state shear, the Bingham yield stress obtained by extrapolating the shear stress to the zero shear rate increases by augmenting the weight fraction of small micron size magnetic particles and the strength of magnetic field. In the oscillatory strain sweep test at an angular frequency of 10u2009radu2009s−1, a transition from visco-elastic solid to visco-elastic liquid is observed and a strong chain formation is proposed to explain the mechanism for transition. The storage modulus also increases with in...

Rheological properties of soft magnetic flake shaped iron particle based magnetorheological fluid in dynamic mode

In this work, the effect of particle shape (flakes) on the magnetorheological (MR) properties of an iron based MR fluid, constituted of two different volume fractions of particles dispersed in a liquid carrier, is studied. To compare the MR effect, spherical iron carbonyl particle based MR fluid is studied. In both MR fluids, linear viscoelastic behavior has been extensively investigated using small amplitude oscillatory analysis and magnetic sweep tests, in the presence and absence of a magnetic field (H). The amplitude sweep tests reveal that flake-based MR fluid shows a higher storage modulus compared to sphere-based MR fluid and saturates at a lower magnetic field strength. The variation of storage modulus with magnetic field strength shows an Hn dependence, where n varies from 2.2 to 2.4 for 20% volume fraction while it varies from 1.6 to 2 for a dilute sample. In the case of sphere-based MR fluid, at 20% volume fraction the variation of storage modulus is nearly linear with the magnetic field at low strain amplitude, and with increasing strain amplitude shows H2 dependence. At lower volume fraction in both cases, the loss modulus increases linearly with the magnetic field strength. The observed enhancement in the MR effect in the flake-based MR fluid is likely due to the stronger particle–particle interaction which results in higher friction between the particles. The sedimentation rate decreases by nearly 50% when flakes are used. The study reveals that one can use the irregular shaped particles for MR applications at low fields (~80 kA m−1).

Ultrasonic propagation: A technique to reveal field induced structures in magnetic nanofluids

The paper reports the study of magnetic field induced structures in magnetic nanofluid investigated through ultrasonic wave propagation. Modified Tarapovs theory is used to study variation in velocity anisotropy with magnetic field. The types of field induced structures depend upon the chemical structure of the carrier in which magnetic nanoparticles are dispersed. Our study indicates formation of fractals and chain respectively, in transformer oil and kerosene based fluid. This difference is explained on the basis of particle-particle interaction and particle-medium interaction.

Maneuvering thermal conductivity of magnetic nanofluids by tunable magnetic fields

We report an experimental investigation of magnetic field dependent thermal conductivity of a transformer oil base magnetic fluid as a function of volume fractions. In the absence of magnetic field, thermal conductivity increases linearly with an increase in volume fraction, and magnitude of thermal conductivity thus obtained is lower than that predicted by Maxwells theory. This reveals the presence of clusters/oligomers in the system. On application of magnetic field, it exhibits a non-monotonous increase in thermal conductivity. The results are interpreted using the concept of a two-step homogenization method (which is based on differential effective medium theory). The results show a transformation of particle cluster configuration from long chain like prolate shape to the aggregated drop-like structure with increasing concentration as well as a magnetic field. The aggregated drop-like structure for concentrated system is supported by optical microscopic images. This shape change of clusters reduces t...

Augmentation of chain formation in a magnetic fluid by the addition of halloysite nanotubes

The study aims to investigate the effect of the addition of nanotubes of halloysite on the augmentation of chains observed in an aqueous magnetic fluid consisting of co-precipitated magnetite particles stabilized with lauric acid. Three samples of the mixture containing 0.5%, 1% and 2% of halloysite nanotubes (HNTs) and a pure magnetic fluid are used for this study. A room temperature magnetization study shows that for 0.5% and 1% of HNT, the magnetization of the mixture significantly increases, while for the higher concentration (2%) it decreases. Such concentration dependent behaviour on the addition of a nonmagnetic system to a magnetic fluid has not previously been observed. The increase in the magnetization is attributed to smaller sized (<5‐6nm) magnetite attached to the HNT, forming a magnetite‐HNT composite. Additionally, field-induced chaining is augmented by the addition of HNT in the magnetic fluid. The augmentation of chain formation is confirmed by optical microscopy, field-induced transmission changes and field-dependent diffraction effects. The augmentation will be useful in enhancing other properties of the composite, such as the viscosity and thermal conductivity of nanofluids.

Role of inter-particle force between micro and nano magnetic particles on the stability of magnetorheological fluid

The concept of phase condensation of larger size particles in a poly-dispersed magnetic fluid (also known as ferrofluid) is employed as a tool to investigate the interaction of nanoparticles with micro particles in magnetorheological (MR) fluid. Two different shapes iron micron sized particles are used in MR fluid formulation: spherical and flake shaped. The magnetic fluid is used as a base carrier having three different magnetic nanoparticles volume fraction (0.2%, 0.6% and 0.8%). The study suggests that the interaction of magnetic nanoparticles with micron sized particle depends on the geometrical shape of the particle as well as surface roughness. The sedimentation ratio of flake shaped MR fluid increases with nanoparticles volume fractions while for spherical particles it remains virtually constant. The supernatant fluid analysis suggests that, larger sized particle fraction from magnetic fluid are attached to the surface of micron sized flake shape particles, which results in reduction of sliding fri...

Mechanism of acid corrosion inhibition using magnetic nanofluid

The inhibition effect of magnetic nanofluid on carbon steel in acid solutions was investigated using gravimetric, potentiodynamic and SEM measurement. The inhibition efficiency increases up to 95% and 75% for 51.7 mM concentration, respectively, in 1 M HCl and 1 M H2SO4 medium. The adsorption of nanoparticles to the steel surface forms a barrier between the metal and the aggressive environment, which is responsible for observed inhibition action. The adsorption of nanoparticles on steel surface is supported by the Langmuir and Freundlich adsorption isotherm and surface morphology scanned through SEM.

The effect of spherical nanoparticles on rheological properties of bi-dispersed magnetorheological fluids

In the present investigation, the rheological properties of bi-dispersed magnetorheological (MR) fluid based on Fe3O4 nanosphere and microsphere of iron particles are experimentally investigated. The MR fluid is prepared by substituting nanosphere of 40nm Fe3O4 particles in MR fluids having microsphere iron particles (7-8 μm). Three different weight fractions (0%, 1% and 3%) of nanosphere-microsphere MR fluids are synthesized. In the absence of the magnetic field, substitution of magnetic nanosphere decreases the viscosity lower than without substituted sample at high as well as low shear rate. Upon the application of the magnetic field, the particles align along the direction of the field, which promotes the yield stress. Here too the yield stress value decreases with magnetic nanosphere substitution. This behaviour is explain based on the inter-particle interaction as well as formation of nanosphere cloud around the magnetic microsphere, which effectively reduces the viscosity and works as weak point wh...

Anomalous increase in the magnetorheological properties of magnetic fluid induced by silica nanoparticles

Magnetorheological properties are experimentally investigated in aqueous magnetic fluid containing spherical silica nanoparticles. A bi-dispersed system is prepared using aqueous suspension of silica nanoparticles and aqueous magnetic fluid. Both these fluids exhibit Newtonian viscosity with nominal values of 1.3 and 5.8 at 20 °C. Three different samples are prepared by varying silica and magnetic fluid concentrations and keeping the total volume constant. The addition of silica nanoparticles leads to enhancement of the magnetic field induced viscosity up to the order 107 . The magnetic field induced viscosity is analyzed using the structural viscosity model. Magnetic field induced static and dynamic yield stress values to reveal the existence of field induced clustering. An attempt is made to explain this yielding behavior using chain-like and micromechanical models. It is found that high silica fraction leads to the formation of chain-like structure. At low silica fraction, chains overlap and result into layer aggregates, which are responsible for the anomalous increase in the magnetorheological properties. This is further confirmed using magnetic field microscopic chain formations.

Nano-MRF: A Material for Damping Application

A magnetorheological fluid (MR), a suspension of micron-sized magnetic particles in a carrier fluid, has vast applications in the field of vibration dampers, seismic vibration dampers, shock absorbers, clutches, break system, vehicle suspensions, seat suspensions, Robotics, design of buildings and bridges etc. The biggest issue in MR fluid is the settling of particles under gravity. To overcome this, one of the approaches is to mix micron size particles in a magnetic fluid (MF) known as Nano-MRF. In the present paper, we report a technique to synthesis Nano-MRF suspension having high stability under gravitation as well as magnetic field. X-ray diffraction (XRD) and dynamic light scattering are used to characterize the solid/liquid system. Magnetic and Magnetorheological properties are studied and results indicate that: instead of decreasing stress with increasing temperature we have observed an increase until 40°C and thereafter, it decreases. This is explained based on, inter and intra particles/chain interaction as well as synergetic effect between small and large sized magnetic dispersion.