Nonmagnetic Particles Research Articles

A comparative study on magnetic and non-magnetic particles in nanofluid propagating over a wedge

The purpose of this paper is to investigate convective heat and mass transfer of nanofluid in the context of improving physical properties through magnetic and non-magnetic nanomaterials under the ...

Investigation on the sorting regularity for non-magnetic micro-particles by negative magnetophoretic coupled sorter

Separation of micro-particle have great potential applications in the fields of bioengineering, material engineering and environment engineering and so on. In order to sort non-magnetic micro-particles with a very close diameter, a negative magnetophoretic coupled sorter is designed on the basis of hydrodynamic sorter. For assuring the excellent sorting performance of designed sorter, numerical simulations for the calculation of distribution of non-magnetic micro-particles with a diameter of 3, 4, 5 μm after separation process were carried out under different magnetic flux densities, at different inlet velocities and velocity ratios of two inlets in the microchannel with different parameters. The numerical results show that, greater lateral deflection of non-magnetic particles can be induced by more powerful magnetic field and bigger particle diameter. However, the deflection doesn’t increase with the magnets number continuously. Separation efficiency of non-magnetic particles was increased at lower inlet velocity and greater inlet-velocity ratio. Moreover, the smaller H a/ H b can lead to greater space between two particle-bands for facility separation. Finally, the micro-PIV experiments were conducted to calculate the bandwidth and space of particle-band. The agreements of experimental and numerical results verify the validity of our numerical approach. It is instructive to guide the design of non-magnetic sorter.

The Influence of Admixtures to the Signal of an Electromagnetic Flow Meter

Measurement error in an electromagnetic flow meter appears if magnetic and electric properties of admixtures are different from that of the fluid. Expressions of the error, which depends on volume concentration, permeability, and electric conductivity of particles were obtained by approximating the particles’ shape as an ellipsoid. Components of the error, which appear inside particles and outside particles in active zone of flow meter, with any canal form are investigated. Expressions of the error are presented assuming that particles are oriented in various directions with respect of the flow direction and are spinning. Different cases of magnetic and electric admixtures properties are discussed. Error expression obtained for flows with nonconductive and nonmagnetic particles coincides with experimental and modelling results obtained by other explorers for flows with air bubbles. Magnetic particles with high electric conductivity are especially dangerous. Extra measurement error in this case greatly depends on the shape of the particle. Measurement error increases if particle shape differs from a sphere. The complementary measurement error can exceed the volume concentration of particles by ten times if the ratio between the longest and the shortest axes of ellipsoid exceeds 3.

Optical manipulation with electric and magnetic transverse spin through multilayered focused configuration

We theoretically analyzed the electric and magnetic transverse spin properties of the highly focused cylindrical vector beams under a multilayered configuration, which revealed a rich nontrivial structure of local spin densities and exhibited a potential applications in optical manipulation for non-magnetic and magnetic particles. An isolation-metal-isolation structure can trap non-magnetic particles with the electric field force and achieve rotation owing to the electric transverse spin, while a metal–dielectric waveguide enables a magnetic transverse spin and hence achieves trapping and rotation of magnetic particles. Various topological charge and materials were analyzed to modulate the optical torques for multiparticles manipulation.

Trajectory of a Non-Magnetic Particle Transported by a Rotating Magnetic Particle Chain

Transportation of microscale subject is important in the MEMS application. In this paper, movement of a non-magnetic particle driven by a chain consisted of several magnetic particles in a rotational field is experimentally manipulated and observed. The results reveal two distinct motion behaviors of the non-magnetic particle depending on its initial position. For an “outer” particle, whose initial position is at the edge of gyration region, the angular movement is most significant at the timing when contacting with the chain. The net rotating angle of an outer particle per contact remains nearly constant regardless of the length of the rotating chain. Nevertheless, interaction with an “inner” particle, whose initial position is well covered by the gyration, would cause the chain drifting, so that its radial distance to the rotational origin varies continuously. As a result, the overall movement of an inner particle follows a spiral-like trajectory with varying radius in each cycle. Based on the experimental measures, a kinematic model is developed, which enables to numerically predict the trajectory of a non-magnetic particle.

Magnetorheological Fluid Finishing of Soft Materials: A Critical Review

Magnetorheological Finishing (MRF) is one of the precision finishing processes and recently commercialized method for finishing of various materials like optical glasses, metals, non-metals etc. This method utilizes a suspension consisting of a fluid carrier which can be water or oil, both magnetic and non-magnetic particles and stabilizing agents. Rheological behavior of this mixture of magnetorheological (MR) fluid with abrasives changes under the influence of magnetic field which in turn regulates the finishing forces during finishing processes. Present study critically reviews the MRF process used for achieving nano-level finishing of soft materials and the advancements made in this process

Active microrheology in two-dimensional magnetic networks.

We study active microrheology in two-dimensional (2D) magnetic networks. To this end, we use Langevin dynamics computer simulations where single non-magnetic or magnetic tracer particles are pulled through the network structures via a constant force f. Structural changes in the network around the pulled tracer particle are characterized in terms of pair correlation functions. These functions indicate that the non-magnetic tracer particles tend to strongly affect the network structure leading to the formation of channels at sufficiently high forces, while the magnetic tracer particles modify the network structure only slightly. At zero pulling force, f = 0, both non-magnetic and magnetic tracer particles are localized, i.e. they do not show diffusive behavior in the long-time limit. Nevertheless, the friction coefficient, as obtained from the steady-state velocity of the tracer particles, seems to indicate a linear-response regime at small values of f. Beyond the latter linear response regime, the diffusion dynamics of the tracer particles are anisotropic with superdiffusive behavior in force direction. This transport anomaly is investigated via van Hove correlation functions and residence time distributions.

Rheological Characterization of Vegetable-Oil-based Magnetorheological Finishing Fluid

Abstract Magnetorheological (MR) finishing fluids are the backbone of MR finishing technology. The rheological behavior of MR finishing fluid helps to attain required abrading force during a finishing operation. The rheological properties of MR finishing fluid changes with the applied magnetic field strength as well as with the fluid composition. Magnetizable iron particles, non-magnetic abrasive particles and non-magnetic carrier liquid are the main constituents of MR finishing fluid sample. The selection of a carrier liquid is equally important along with other constituents of MR finishing fluid. In the present work, coconut oil, as an eco-friendly carrier liquid, was selected for the preparation of MR finishing fluid. The performance of the developed sample in terms of rheological properties was tested under different magnetic field strengths. The structure of the prepared sample exhibits more strength at the higher magnetic field strengths.

Magnetic responsive brushes under flow in strongly confined slits: external field control of brush structure and flowing particle mixture separation.

In the present work magnetic brushes under flow conditions and confined inside narrow slits have been studied using Langevin dynamics simulations. It has been observed that the structural properties of these confined magnetic brushes can be tuned via the application of an external magnetic field, and this control can be exerted with a relatively low content of magnetic colloidal particles in the filaments that form the brushes (20% in the present study). The potential of these brushes to perform a separation process of a size-bidispersed mixture of free non-magnetic colloidal particles flowing through the slit has also been explored. Numerical results show that it is possible to induce a two-fold effect on the bidispersed particle flow: a lateral separation of the two types of flowing colloidal particles and an enhancement of the differences in their velocities. These two features are key elements sought in separation processes and could be very relevant in the design of new chromatographic columns and microfluid separation devices.

Comparing flow regime transition of magnetized fluidized bed with Geldart-B particles between magnetization-FIRST and -LAST operation modes

Different flow regimes existed for the magnetized fluidized bed with purely Geldart-B magnetizable particles (pure MFB) or their admixture with Geldart-B nonmagnetizable particles (admixture MFB). Several unresolved issues about the flow regime transition were addressed first for both the pure and admixture MFBs. Then the flow regime transition was thoroughly compared for the first time between the magnetization-FIRST and -LAST operation modes. The magnetic stabilization flow regime was observed to no longer exist under the magnetization-LAST operation mode. The comparison further indicated that the operating range covered in the literature and this work could be roughly divided into four zones. Particularly in operating zone II, the MFB state was found to depend not only on the magnetic field intensity and superficial gas velocity but also on the operation mode. Such a dependence feature in essence referred to the dependence of the MFB state on the path taken to achieve it. The reason why the bed state was path-dependent in operating zone II lay in that the MFB therein could have two different equilibrium states and different paths led to the two states, respectively. Of the two equilibrium states, the magnetic stabilization was demonstrated to be a metastable equilibrium state. Such unique characteristics of the magnetic stabilization state explained why it could not be obtained under the magnetization-LAST operation mode. Furthermore, the reason why the MFB could have an additional metastable equilibrium state aside from the stable equilibrium state in operating zone II lay in the difficulty in forming a new phase under the magnetization-FIRST operation mode.

Railway Actuator Made of Magnetic Elastomers and Driven by a Magnetic Field.

We fabricated a mono-link using bimodal magnetic elastomers that demonstrate drastic changes in the elastic modulus by magnetic fields. The magnetic elastomer is bimodal consisting of large magnetic particles and nonmagnetic fine particles. The storage modulus for bimodal magnetic elastomers was altered from 2.2 × 105 to 1.7 × 106 Pa by a magnetic field of 500 mT. Compression tests up to a strain of 20% also revealed that the on-field stress for the bimodal magnetic elastomer was 1.24 times higher than the off-field stress. The bimodal magnetic elastomer was synthesized for the mono-link and was mounted on the bogie of a railway vehicle. A running test exhibited that the wheel lateral force was reduced by 20% by applying a magnetic field of 390 mT.

Synthesis and characterization of molybdenum complex supported on magnetic and non-magnetic supports: comparing their catalytic activity, selectivity, and reusability

A molybdenum complex was immobilized on Schiff-base-modified magnetic and non-magnetic particles by covalent linkage. The characterizations of the obtained materials were carried out by means of TG–DTG, SEM, TEM, VSM, XPS, IR, and Raman microprobe techniques. All of them exhibited efficient activities in the oxidation of sulfides to sulfoxides by urea hydrogen peroxide oxidant. The advantages and disadvantages of these catalysts are discussed in detail. Molybdenum complex immobilized on silica bead can be recycled and recovered by simple filtration, but it demonstrated low activity in catalytic oxidation reaction. Immobilization on nano-SiO2 leads to the formation of nanocatalyst having high catalytic activity but inefficient reusability. The best results were obtained with nano-Fe3O4 magnetic support. The immobilized molybdenum complex on silica-coated magnetic nanoparticles can easily be recovered from the reaction system using an external magnet and reused several times with high yields.

Magnetic Field-Driven Convection for Directed Surface Patterning of Colloids.

Drying sessile droplets is a promising route to transform colloidal dispersions into surface coatings, which are widely used in material design and biochemical detection. However, directing the assembly of the particles within drying droplets and achieving surface patterns beyond the well-known coffee-ring formation remain a challenge. Here, we present a new principle of directing the assembly of nonmagnetic colloidal particles dispersed in a magnetic fluid and generating unusual surface patterns. We use the ability of ferrofluids to change phases with the application of magnetic fields to program the assembly of nonmagnetic microparticles present in drying sessile droplets. We show that in the absence of external magnetic field, the superparamagnetic nanoparticles in the magnetic fluid are spontaneously transported to the droplet edge because of solvent evaporation. This nanoparticle transport leads to the formation of nanoparticle-rich edge and nanoparticle-depleted center of the drying droplet. Upon the application of a uniform external magnetic field, the asymmetry in the magnetic nanoparticle distribution drives a magnetostatic convection and finger-like instability from the droplet edge to the center. This magnetic microconvection from droplet edge-to-center reverses the particle transport from center-to-edge, well-known for drying droplets in the absence of external field. We use this magnetostatic microconvection to assemble secondary nonmagnetic microspheres in droplets, overwriting ring formation and direct their assembly into four distinct kinetically stable states. The method presented here offers an active control over the colloidal assembly achieved by drying sessile droplets and thus enables a new route for fabricating complex patterns and functional surface coating.

Separation of steelmaking slag with mechanical stirring by fluctuated magnetic field

Steelmaking slag is by-product of the steelmaking process and has a high content of iron. In order to recover this iron, steelmaking slag is processed with various methods such as crushing, sieving and magnetic separating. Magnetic separators process steelmaking slag in multiple layers for mass production and non-magnetic particles are attracted to a magnet roll by magnetic particles [1]. Therefore, precision of separation is low with conventional pulley magnetic separator. This study proposes an efficient magnetic separating technology. In proposal magnetic separation, a fluctuating magnetic field is generated by rotation of a magnet roll with multiple poles. This quick change of the magnetic field generates strong agitation in the attracted particles and eliminates non-magnetic particles [2]. As the result of separation test with steelmaking slag, the iron content of magnetic side and the overall separation efficiency is higher in proposal method than in conventional method.

Structured spin angular momentum in highly focused cylindrical vector vortex beams for optical manipulation.

We investigate the spin properties of a family of cylindrical vector vortex beams under a focusing condition. The spin-orbit interaction is demonstrated by comparing the energy flow and spin flow density of the focused field to those of the incident field. This spin-orbit interaction is analyzed to construct the desired distribution of spin angular momentum for optical manipulation. The structured spin angular momentum of the focused field can transfer to the optical torque for the non-magnetic absorptive particle. The influences of polarization topological charge, vortex topological charge and wavelength on optical torque in the hot-spot of focused field are summarized for three typical particles. Such results may be exploited in practical optical manipulation, particularly for optically induced rotations.

Magnetic and SEM-EDS analyses of Tilia cordata leaves and PM10 filters as a complementary source of information on polluted air: Results from the city of Parma (Northern Italy)

In this work, both PM10 filters and leaves have been collected, on a daily basis, over a period of five months and compared systematically. Filters were taken from an air-quality monitoring station and leaves from two Tilia cordata trees, both located near the railway station of Parma.SEM-EDS analysis on the surface and across the leaves shows that magnetic particles are almost entirely made of magnetite, and that they are found invariably on the leaves surface. The saturation isothermal magnetic remanence (SIRM) shows that for both filters and leaves the magnetic fraction mainly consists of a low coercivity, magnetite-like phase.The magnetic signals of filter and leaves and atmospheric PM concentrations are compared. The correlation is better for filters, mostly with parameters related to vehicular pollution, and improved for both filters and leaves once data were averaged on a 10 days basis. Filters and leaves equally show an increase in magnetic signal during the fall-winter period together with PM10 content. The comparison between leaves and filters shows that: 1) leaves give a qualitative picture, and in our case they could be used as environmental proxies after averaging the results over multiple days; 2) the correlation with PM10 is weaker, indicating that there is a PM10 contribution from non-magnetic particles, like calcite and clay minerals, pollen and spores; 3) multidomain particles contribution from filters indicates a strong relation with vehicular polluters, suggesting the important role of larger particles; 4) magnetization from leaves and filters are weakly related, due to the different sampling lapse.

A Rapid Method for Estimation of Cariogenic Bacteria Based on a Stationary Liquid Phase Lab-on-a-chip

Salivary levels of Streptococcus mutans and Lactobacillus sp. are important risk factors for dental caries. Application of current test methods is limited because of the requirement for a time-consuming incubation step or expensive laboratory instruments. In this study, we developed a rapid method for determination of the representative cariogenic bacteria, S. mutans and Lactobacillus plantarum, based on a stationary liquid phase lab-on-a-chip (SLP LOC). The method utilized two types of particles, i.e., magnetic capture particles (CPs) for capture of target bacteria and nonmagnetic labeling particles (LPs) for labeling of the captured bacteria with horseradish peroxidase (HRP). Complexes of CP-bacteria-LP were formed in a sample chamber of the LOC and transported to a detection chamber containing the chromogenic substrate of HRP by moving a magnet under the LOC. The method is simple and enabled detection of the two bacteria in a range required for caries risk diagnosis within 40 min without the use of any complicated instruments. Accordingly, this method may have applications in the rapid diagnosis of dental caries risk.

Magneto-optical properties of binar ferrocolloids

In this work, a new method for increasing optical anisotropy of a ferrocolloid through introducing the coiled polymer molecules or elongated nanosized non-magnetic particles is realized. Since the dimensions of structural elements comprising such a binary colloidal solution are small compared to the wavelength, the ferrocolloid remains optically homogeneous. Type I binary ferrocolloids are obtained by introducing polybutadiene molecules into a magnetic fluid (magnetite + kerosene + oleic acid). In this case, an increase in the double refraction (DR) is due to the deformation and stretching of the polymer coils along the magnetic field. In weak fields, double amplification of the signal was detected for the concentration of polymer molecules of about 0.5 %. A further increase in the concentration of impurity molecules weakens DR due to a disturbance of the sedimentation stability of the solution and precipitation of colloidal particles. Type II binary solution is synthesized on the basis of a magnetic fluid and rod-shaped impurity nanoparticles of goethite ( αFeOOH). The transverse dimension of the impurity particles (10 − 30 nm) was close to the average diameter of single-domain magnetite particles, and the longitudinal dimension was an order of magnitude larger. An increase in the DR occurs due to the orientation of long axes of impurity particles along the magnetic field caused by the difference in the ”demagnetizing” coefficients along and across the axis of the particle. The magnetic double refraction has been studied depending on the concentration of magnetite and impurity particles and the strength of the magnetic field. For the first time, an experimental substantiation of the multiple amplification of the DR signal by impurity particles was obtained. In the fields (up to 10 kA/m) and for the volume fraction of impurity particles of the order of one percent, the DR signal is amplified by more than an order of magnitude. In stronger fields, the signal gain, associated with the influence of impurity particles, reaches saturation and, with further increase in the field strength, remains practically unchanged, while the total anisotropy of the solution continues to increase due to the orientation of the magnetite particles.

Modeling of segregation in magnetized fluidized bed with binary mixture of Geldart-B magnetizable and nonmagnetizable particles

Abstract For the magnetized fluidized bed (MFB) with the binary mixture of Geldart-B magnetizable and nonmagnetizable particles, the magnetically induced segregation between these two kinds of particles occurs at high magnetic field intensities (H), leading to the deterioration of the fluidization quality. The critical intensity (Hms) above which such segregation commences varies with the gas velocity (Ug). This work focuses on establishing a segregation model to theoretically derive the Hms–Ug relationship. In a magnetic field, the magnetizable particles form agglomerates. The magnetically induced segregation in essence refers to the size segregation of the binary mixture of agglomerates and nonmagnetizable particles. Consequently, the segregation model was established in two steps: first, the size of agglomerates (dA) was calculated by the force balance model; then, the Hms–Ug relationship was obtained by substituting the expression of dA into the basic size segregation model for binary mixtures. As per the force balance model, the cohesive and collision forces were 1–2 orders of magnitude greater than the other forces exerted on the agglomerates. Therefore, the balance between these two forces largely determined dA. The calculated dA increased with increasing H and decreasing Ug, agreeing qualitatively with the experimental observation. The calculated Hms–Ug relationship agreed reasonably with the experimental data, indicating that the present segregation model could predict well the segregation behavior in the MFB with the binary mixture.

Adsorption Performance and Mechanisms of Methylene Blue Removal by Non-magnetic and Magnetic Particles Derived from the Vallisneria natans Waste

Vallisneria natans (V. natans) is a submerged aquatic plant, and its dried biomass waste was used to prepare magnetic particle biomass adsorbent by chemical co-precipitation via FeSO4·7H2O and FeCl3·6H2O as iron precursors. Brunauer–Emmett–Teller specific surface area, total pore volume, and average pore width were 7.434 m2 g−1, 0.013 cm3 g−1, and 6.992 nm for magnetic V. natans, correspondingly, and 3.575 m2 g−1, 0.004 cm3 g−1, and 4.476 nm for non-magnetic V. natans, respectively. The adsorption kinetics of methylene blue (MB) is a more appropriate fit for pseudo-second-order kinetic model than pseudo-first-order and intraparticle diffusion kinetic models. Isotherm results showed that the adsorption of MB onto the non-magnetic and magnetic adsorbents agrees well with Dubinin–Radushkevich isotherm model. Moreover, the thermodynamics study implied that the adsorption of MB onto both adsorbents is a spontaneous and exothermic process. The maximum adsorption capacities of MB on non-magnetic and magnetic V. natans were 657.90 and 473.93 mg g−1 at 303 K, correspondingly.