Concentration Of Magnetic Particles Research Articles

Soft hybrid magnetorheological elastomer: Gap bridging between MR fluid and MR elastomer

Two major branches of the magnetorheological (MR) materials are MR fluids and MR elastomers. The MR fluids largely suffer from the sedimentation problem. On the other hand, MR elastomers conquer the sedimentation problem but have a lower MR effect. A magnetic field is required when an anisotropic configuration of the magnetic particles in the MR elastomer is desired. In this paper, we present a gap bridging material between MR fluids and MR elastomers, which may overcome the sedimentation problem of MR fluid as well as exhibits the anisotropic MR effect but avoids the need of a magnetic field during the crosslinking process as required for the fabrication of conventional anisotropic MR elastomer. A soft hybrid MR elastomer has been developed by forming a core-shell structure. The core consists of a mixture of magnetic particles and a carrier medium. Two types of carrier media have been adopted, named as fluid core and solid core. The shell is made from an elastomer. The investigation was performed to understand the effect of the concentration of magnetic particles in both liquid and solids cores as well as the effect of viscosity of the carrier fluid in the liquid core. The magnetorheological study revealed that the high viscosity carrier fluid is not as good as a low viscosity carrier fluid for the shear stress enhancement. However, for the core-shell soft hybrid MR elastomers, MR effect exhibited by the high viscosity carrier fluid core (>1000 Pa.s) was found to be as good as the low viscosity carrier fluid core. The high viscosity carrier fluid also overcomes the sedimentation problem of MR fluids and also exhibits a remarkable MR effect even in a moderately strong magnetic field. Similarly, it also exhibits the anisotropic MR effect when the direction of the applied magnetic field is changed, however, no magnetic field was applied during the crosslinking as typically required for conventional anisotropic MR elastomers. Such core-shell soft hybrid MR elastomers with high viscosity fluid core potentially bridge the gap between MR fluids and MR elastomers and open a new door of MR materials’ applications that might have not been achieved by the exclusive utilization of the previous MR materials.

NONLINEAR BEHAVIOR AND THERMAL DAMAGE OF THERMAL LAGGING IN CONCENTRIC LIVING TISSUES SUBJECTED TO GAUSSIAN DISTRIBUTION SOURCE

The effects of thermal lagging with high-order became essential to describe non-equilibrium heating in tissues. This paper studies the temperature rise behavior in living tissues theoretically during the treatment by magnetic tumor hyperthermia based on the non-linear form of the dual-phase-lag model. Experimentally, it was found that the concentration of magnetic particles is in Gaussian distribution through the radial direction when magnetic fluid is injected into the living tissue space. Hence, the governing partial differential equation in concentric spherical space is solved in the Laplace transform domain. Some comparisons between the non-linear and linear effects of phase-lag time’s parameters on bio-heat transfer have been studied and discussed. The thermal damage quantity for the tumor has been calculated with different values of the phase-lag times. The results show that the nonlinear and linear effects of phase-lag times on bio-heat transfer have significant effects on the tumor, the tissue, and the thermal damage quantity.

Effects of physicochemical properties on heavy metal, magnetic susceptibility and natural radionuclides with statistical approach in the Chennai coastal sediment of east coast of Tamilnadu, India

The aim of the study was to determine the effects of physicochemical properties of sediment samples on the heavy metal, magnetic susceptibility, and natural radioactivity concentration. Spectroscopic techniques like energy-dispersive X-ray fluorescence, dual-frequency susceptibility meter, and gamma ray spectrometry measurements are commonly employed for the determination of heavy metals, magnetic particle, and radioactivity concentration in sediment sample collected from Pulicat Lake to Vadanemmeli, of Chennai Coast, Tamilnadu. The relations between the physical and chemical properties and studied parameters of sediment samples were mainly clarified with Pearson correlation, factor, and cluster analysis. Silt content was the most effective parameter on the studied parameter. The results are discussed and the conclusion is drawn.

Magnetic, geochemical and granulometric properties of street dust from Warsaw (Poland)

The study presents variations in the magnetic properties and heavy metal concentrations of five granulometric fractions, i.e. 1000–500 μm, 500–250 μm, 250–100 μm, 100–71 μm and <71 μm, for street dust collected at two locations in Warsaw. Combination of grain-size determination, magnetometry, electron microscope observation, mineral composition and chemical analyses was applied as an effective and multidisciplinary approach for the complete characterization of individual fractions of street dust. The magnetic properties of street dust are influenced by its grain size; concentration-dependent magnetic parameters, e.g. magnetic susceptibility, saturation magnetization, saturation remanence and anhysteretic remament magnetization of the finest fraction (d < 0.071 mm) are about three times higher than that of the coarsest fraction (d > 0.5 mm). For all fractions the main magnetic mineral is near stoichiometric magnetite. The dust fractions with grain size <250 μm additionally contain a phase with a Curie point ~770 °C, ascribable to metallic iron. The smallest contribution to the total mass is from the finest size fractions, which contain the highest concentrations of the traffic-related heavy metals. Traffic intensity are well reflected at the two sites studied by the concentration of anthropogenic magnetic particles which are strongly associated with traffic-related heavy metals. Magnetic extracts of the finest dust fraction contain a mixture of spherical magnetic particles and irregular angular particles of iron-oxides with traces of Mg, Al, Na, Ca, K, and Si. Detailed studies preferentially oriented toward to the finest fractions of street dust are a critical issue in terms of potential effects on population health.

Chain Structure in a Cross-Linked Polyurethane Magnetic Elastomer Under a Magnetic Field.

The morphology of magnetic particles with a size of 7.0 μm was observed for magnetic elastomers with a concentration of magnetic particles of 70 wt% using an X-ray microscope remolded into high resolution. Computed tomography images revealed that magnetic particles were distributed isotopically in the absence of a magnetic field, but they formed a chain structure in the polyurethane network under a magnetic field of 270 mT. It was also established, by image analysis, that magnetic elastomers had an anisotropic structure under the magnetic field.

Efficient Removal of Ultrafine Particles from Diesel Exhaust by Selected Tree Species: Implications for Roadside Planting for Improving the Quality of Urban Air.

Human exposure to airborne ultrafine (≪1 μm) particulate pollution may pose substantial hazards to human health, particularly in urban roadside environments where very large numbers of people are frequently exposed to vehicle-derived ultrafine particles (UFPs). For mitigation purposes, it is timely and important to quantify the deposition of traffic-derived UFPs onto leaves of selected plant species, with particularly efficient particle capture (high deposition velocity), which can be installed curbside, proximal to the emitting vehicular sources. Here, we quantify the size-resolved capture efficiency of UFPs from diesel vehicle exhaust by nine temperate-zone plant species, in wind tunnel experiments. The results show that silver birch (79% UFP removal), yew (71%), and elder (70.5%) have very high capabilities for capture of airborne UFPs. Metal concentrations and metal enrichment ratios in leaf leachates were also highest for the postexposure silver birch leaves; scanning electron microscopy showed that UFPs were concentrated along the hairs of these leaves. For all but two species, magnetic measurements demonstrated substantial increases in the concentration of magnetic particles deposited on the leaves after exposure to the exhaust particulates. Together, these new data show that leaf-deposition of UFPs is chiefly responsible for the substantial reductions in particle numbers measured downwind of the vegetation. It is critical to recognize that the deposition velocity of airborne particulate matter (PM) to leaves is species-specific and often substantially higher (∼10 to 50 times higher) than the "standard" Vd values (e.g., 0.1-0.64 cm s-1 for PM2.5) used in most modeling studies. The use of such low Vd values in models results in a major under-estimation of PM removal by roadside vegetation and thus misrepresents the efficacy of selected vegetation species in the substantial (≫20%) removal of PM. Given the potential hazard to health posed by UFPs and the removal efficiencies shown here (and by previous roadside measurements), roadside planting (maintained at or below head height) of selected species at PM "hotspots" can contribute substantially and quickly to improve in urban air quality and reductions in human exposure. These findings can contribute to the development and implementation of mitigation policies of traffic-derived PM on an international scale.

THE EFFECT OF THE CONCENTRATION OF MAGNETIC PARTICLES ON THE OPERATING PARAMETERS OF A SLIDE JOURNAL BEARING LUBRICATED WITH FERRO-OIL

This paper presents an analysis of changes in basic operational parameters of a slide journal bearing in an aspect of a concentration of magnetic particles in ferro-oil as a lubricant. The first part of the article presents an analytical-numerical calculation model. This model is based on experimentally determined physical parameters describing the dependence of ferro-oil viscosity on changes at basic operating parameters. Moreover, dimensionless load carrying capacity, dimensionless friction force and dimensionless coefficient of friction numerical calculations have been obtained by solving the Reynolds type equations using the finite difference method in Mathcad 15 program and the author’s own calculation procedures. The obtained results have been presented in the form of graphs taking into account the influence of the following factors: external magnetic field, corrections related to the influence of pressure changes, corrections related to the influence of temperature changes and corrections related to non-Newtonian properties of the ferro-oil. The analysis of the obtained characteristics in the paper has been carried out, observations have been made as well as conclusions have been drawn regarding the optimal concentration of magnetic particles in the ferro-oil lubricating the slide journal bearing.

Coarse-grained molecular dynamics simulations of particle behaviors in magnetorheological polishing fluid

Material removal in magnetorheological polishing (MRP) process is primarily caused by abrasive particles. To analyze the particle behaviors in MRP fluids, a biphasic coarse-grained molecular dynamics model including magnetic dipoles and abrasive particles is built. The effects of magnetic field gradient, magnetic strength and abrasive particle concentration are studied both from theoretical analysis and numerical simulation. The results show that the increased magnetic field gradient and intensity increase the probability that abrasive particles contact the workpiece significantly, while increased abrasive particle concentration reduces the probability. Moreover, increased magnetic field gradient and abrasive particle concentration greatly increase the response time of MRP fluid system undesirably, but the increased magnetic field intensity leads to a firstly increased but then dropped response time.

Synthesis of absorbing coating based on magnetorheological gel with controllable electromagnetic wave absorption properties

Owing to the increasingly complicated electromagnetic environment and changeable battleground, it is especially urgent to study electromagnetic wave absorbing coating with enhanced absorbing capacity and adaptive ability. Magnetorheological gel (MRG) is prepared by mixing magnetic particles with high viscosity polymer matrix. Under magnetic field, these magnetic particles move to form columnar or chains, which allows electromagnetic (EM) waves to penetrate and scatter along the chains. Accordingly, the MRG-based coating that absorbs electromagnetic waves was successfully synthesized. Moreover, flower-like carbonyl iron particles (FCIPs), as the filled magnetic particles, were prepared by in situ method. We studied the effect of magnetic field, particle concentration and matrix curing on electromagnetic (EM) absorbing properties of the MRG-based coating. With the purpose to test absorption performance of the MRG-based coating under different magnetic field intensity, a device that regulates the magnetic field is essential. Thus, we built the device that contains permanent magnet, frame, lifting table. From the results, magnetic field can make absorption peak frequency (APF) move toward high frequency. The amount of shifting to high frequency increases as the magnetic field increases. The magnetic-induced frequency offsets of four samples with different mass fractions (40 wt%, 50 wt%, 60 wt%, 70 wt%) are 2.88 GHz, 1.26 GHz, 1.52 GHz and 0.64 GHz from 0 to 300 mT, respectively. Meanwhile, a suitable magnetic field is beneficial for the coating to absorb more electromagnetic waves. This characteristic of MRG will make it have a wide application prospect in real-time electromagnetic protection and electromagnetic stealth.

Effective and universal tool for evaluating heavy metals—passive dust samplers

The study presents designating, accomplishing, optimizing, and validating a new tool - “passive sampler” (PS) that can be effectively used as a proxy to assess the level of traffic-related pollution. To construct the PS, a drainage pipe filled with a mixture of coarse sand and peat in a volume ratio of 1:1 was used; this was previously verified to exhibit high ability to accumulate pollutants. Magnetic methods supplemented with chemical method evaluating heavy metal content and electron microscopic observations were used to detect the effectiveness of the PS. The PS was validated in Warsaw, Poland, by observing the capacity and trends in the accumulation of traffic-related heavy metals as well as magnetic particles and by comparison of the properties of magnetic fraction of PS filling and street dust collected from the surface of road. A depth decreasing trend in distributions of magnetic susceptibility related to the concentration of magnetic particles and the content of heavy metals confirmed a very strong accumulation of pollution in the surface layer of samplers and their depth-migration. Magnetic fraction of PS filling and street dust revealed similarities in terms of magnetic mineralogy, grain size, domain state, morphology, and chemical composition. The good correlation of concentration of magnetic particles with traffic-related heavy metals indicates their similar transport pathway from road to sampler. Passive sampler is a compact, mobile, low-cost tool that does not require electricity for installation and can be effectively used for the identification of traffic-derived pollution. Moreover, the PS can overcome disadvantages of street dust arising from different geological backgrounds, cleaning of the road surface, runoff of deposited dust, etc., which cause the underestimation of pollution level.

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.

Magneto-ultrasonic heating with nanoparticles

Abstract Recently, there has been a great interest in the application of multimodal hyperthermia. Hyperthermia, a controlled increase of temperature in tissues up to 42–45 °C, is a very promising anti-cancer medical treatment. Hyperthermia can be induced by means of ultrasound wave, alternating magnetic field, radiowave, laser light, etc. In our research, we combine magnetic hyperthermia with ultrasound thermal treatment to facilitate a more efficient, innovative sonomagnetic therapy. The experiments are performed using ultrasound phantoms doped with magnetic nanoparticles. These nanoparticles act like sonosensitizers and become the source of supplementary ultrasound attenuation which consequently leads to the increase of temperature. Because of their sensitivity to magnetic field they are also the source of heat in magnetic hyperthermia. In order to investigate the thermal effect of multimodal hyperthermia, phantoms are simultaneously irradiated with a focused ultrasound beam and exposed to the AC magnetic field. We demonstrate that this double thermal stimulation of phantoms doped with nanoparticles provides better heating efficiency which enables more precise control over the heating process. Magneto-ultrasonic heating creates more effective hyperthermia and has a big application potential in treating cancer at a lower magnetic particle concentration. The coupling of magnetic and ultrasonic hyperthermia gives the possibility for developing the new, innovative sonomagnetic thermal therapy.

Boundary interface condition of magnetic fluid determines the magnetic levitation force experienced by a permanent magnet suspended in the magnetic fluid

The buoyancy experienced by a permanent magnet suspended in magnetic fluid is studied, and the expression for calculating the magnetic fluid buoyancy is derived. The magnetic fluid buoyancy or magnetic fluid levitation force, which can be obtained by calculating the sum of Archimedes levitation force and magnetic levitation force, depends on the boundary interface condition of magnetic fluid. The type of the boundary interface and the pressure over it determine the boundary interface condition, and the dependence of boundary interface condition of magnetic fluid and magnetic fluid levitation force is studied. If the boundary interface of the magnetic fluid is a liquid-gas interface in contact with air, the magnetic fluid levitation force will be equal to the gravity of the magnetic fluid. A sudden change in magnetic fluid levitation force can be seen when the liquid-gas boundary interface of magnetic fluid is broken by the wall of a container. Or, in other words, the emergence of a solid-liquid boundary interface will influence the magnetic fluid levitation force, and the magnitude of the change is proportional to magnetic field intensity over the solid-liquid boundary interface. Once the liquid-gas boundary interface is close to a horizontal plane, the magnitude of magnetic fluid levitation force will reach a relatively stable value. In the experiments, the volume of magnetic fluid, the location of the magnet, and the magnetic particle concentration in magnetic fluid are used to control and change the boundary interface condition of magnetic fluid.

Landfill leachate treatment by sorption in magnetic particles: preliminary study

Leachates are still an open issue in environmental protection. Many of the applied methods for their treatment present low efficiency and thus need to be used collectively. In practice reverse osmosis is mostly used, as it is the most effective option, regardless of its cost. Magnetic methods to treat effluents have been used for water and wastewater treatment by the use of magnetic particles together with magnetic separation for the removal of contaminants. However, large-scale applications are few or even non-existent when we deal with complex contaminated media such as landfill leachates, for which not even research studies at laboratorial scale with real samples have been done yet. In this work, we apply for the first time magnetic sorption for the treatment of leachates, and close the full cycle by studying the regeneration and re-use of the magnetic particles; we also study the influence of the concentration of magnetic particles, the use of several pre-treatment methodologies and the type of particle used in the process, in real landfill samples from the waste treatment plant of Salamanca (Spain), for the removal of COD, NO3−, NO2−, NH4+, Total-N, PO43−, SO42− and Cl−. Regeneration of the magnetic particles after being used in the sorption stage is also studied, as well as their efficiency regarding their re-use. It is also determined the optimum number of batches for complete desorption and for regeneration of the particles, the effect of successive regeneration and re-use cycles, the use of two different regeneration methods, the efficiency of the desorption, the effect of the quantity of solvent and the influence of the time of sorption. Due to its innovative character and the complexity of the media, this work represents a first preliminary approach and, although some promising results have been obtained, further studies are required to completely understand and evaluate the proposed treatment process.

Fe-Cr-Nb-B ferromagnetic particles with shape anisotropy for cancer cell destruction by magneto-mechanical actuation

We introduce a new type of magnetic particles (MPs) prepared by wet milling of superferromagnetic Fe-Cr-Nb-B precursor glassy ribbons for cancer treatment by magneto-mechanical actuation in low magnetic fields (1 ÷ 20 Oe). The rectangular shapes of MPs and the superferromagnetism of the glassy alloys of which are made the MPs induce important magnetic shape anisotropies which, in association with a large saturation magnetization, generate an improved torque in a rotating magnetic field, producing important damages on the cellular viability of MG-63 human osteosarcoma (HOS) cells. The specific parameters such as MPs concentration, frequency and intensity of the applied magnetic field, or the time of exposure have a strong influence on the cancer cells viability. The specific behavior of the Fe-Cr-Nb-B MPs offers them destructive effect even in low magnetic fields such as 10 Oe, and this characteristic allows the use of coils systems which provide large experimental spaces. The novel MPs are used for the magneto-mechanical actuation alone or in association with hyperthermia, but also can be transported to the tumor sites by means of stem cells carriers.

Rheology of magnetic alginate hydrogels

Magnetic hydrogels are becoming increasingly in demand for technical and biomedical applications, especially for tissue engineering purposes. Among them, alginate-based magnetic hydrogels emerge as one of the preferred formulations, due to the abundance, low cost, and biocompatibility of alginate polymers. However, their relatively slow gelation kinetics provokes strong particle settling, resulting in nonhomogeneous magnetic hydrogels. Here, we study magnetic hydrogels prepared by a novel two-step protocol that allows obtaining macroscopically homogeneous systems, consisting of magnetic microparticles embedded within the alginate network. We describe a comprehensive characterization (morphology, microstructure, and mechanical properties under shear stresses) of the resulting magnetic hydrogels. We pay special attention to the effects of particle volume fraction (up to 0.33) and strength of the magnetic field on the viscoelastic properties of the magnetic hydrogels. Our results indicate that magnetic hydrogels are strongly strengthened against shear stresses as magnetic particle concentration and applied field intensity increase. Finally, we report an adaptation of the two-step protocol for the injection of the magnetic hydrogels that might be adequate for implementation in vivo. Interestingly, injected magnetic hydrogels present similar morphology and mechanical properties to noninjected hydrogels. To conclude, we report magnetic alginate hydrogels with adequate homogeneity and injectability character. These characteristics, together with the broad range of their mechanical properties, make them perfect candidates for cutting-edge technology.

Magnetic Biomonitoring as a Tool for Assessment of Air Pollution Patterns in a Tropical Valley Using Tillandsia sp.

Recently, air pollution alerts were issued in the Metropolitan Area of Aburrá Valley (AVMA) due to the highest recorded levels of particulate matter (PM2.5 and PM10) ever measured. We propose a novel methodology based on magnetic parameters and an epiphytic biomonitor of air pollution in order to improve the air pollution monitoring network at low cost. This methodology relies on environmental magnetism along with chemical methods on 185 Tillandsia recurvata specimens collected along the valley (290 km2). The highest magnetic particle concentrations were found at the bottom of the valley, where most human activities are concentrated. Mass-specific magnetic susceptibility (χ) reaches mean (and s.d.) values of 93.5 (81.0) and 100.8 (64.9) × 10−8 m3 kg−1 in areas with high vehicular traffic and industrial activity, while lower χ values of 27.3 (21.0) × 10−8 m3 kg−1 were found at residential areas. Most magnetite particles are breathable in size (0.2–5 μm), and can host potentially toxic elements. The calculated pollution load index (PLI, based on potentially toxic elements) shows significant correlations with the concentration-dependent magnetic parameters (R = 0.88–0.93; p &lt; 0.01), allowing us to validate the magnetic biomonitoring methodology in high-precipitation tropical cities and identify the most polluted areas in the AVMA.

Application of monodisperse Fe3O4 submicrospheres in magnetorheological fluids

Steady shear response of a magnetorheological fluid (MRF) system containing porous mono-disperse magnetite (Fe3O4) spheres synthesized by solvothermal method is demonstrated. In applied magnetic field the interaction between the spherical particles leads to form strong columnar structures enhancing the yield strength and viscosity of the MRFs. The yield strengths of the MRFs also scale up with the concentration of magnetic particles in the fluid. Considering magnetic dipolar interaction between the particles the magneto-mechanical response of the MRFs is explained. Unlike metallic iron particles, the low-density corrosion resistant soft-ferrimagnetic Fe3O4 spherical particles make our studied MRF system efficient and reliable for shock-mitigation/vibration-isolation applications.

Weak Coupling Effect on the Magnetic Freedericksz Transition in a Ferronematic Liquid Crystal

The magnetic Freedericksz transition in a ferronematic representing a diluted suspension of magnetic nanoparticles in an N-(4-methoxybenzylidene)-4-butylaniline (MBBA) nematic liquid crystal was experimentally studied. The transition point was determined by means of dielectric capacitance measurements in cells of different thickness for samples with various volume fractions of ferroparticles. The effect of weak coupling between the magnetic and liquid-crystal subsystems was studied. Low concentrations of quasispherical magnetic particles were shown to decrease the magnetic Freedericksz transition threshold in comparison with a pure liquid crystal. The obtained results were theoretically substantiated. The phase diagram of the suspension was plotted, and the method of estimating the energy of coupling between magnetic particles and a liquid-crystal matrix was proposed.

Development and validation of an MRI-based method for 3D particle concentration measurement

A novel method, denoted MRP (short for Magnetic Resonance Particle concentration), was developed to obtain 3D volume fraction measurements for a dispersed particulate phase in turbulent water flows using Magnetic Resonance Imaging (MRI). MRI images taken near a single stainless steel particle suspended in agarose gel showed good agreement with the analytical solution for the disturbance to a uniform magnetic field induced by an immersed sphere. For a random distribution of particles, a linear relationship between the MRI signal decay rate (R2*) and particle volume fraction (ϕv) has previously been predicted in the MRI literature. This relationship was investigated for various types of particles suspended in agarose gel vials. Good agreement with theory was observed for particles with a high magnetic susceptibility difference from water. R2* was also measured in a square channel flow containing a uniform distribution of titanium particles at two fully turbulent Reynolds numbers. Experimental results again agreed well with theory in the majority of the channel for both Reynolds numbers studied. Data from this flow were used to examine the expected SNR and dynamic range for MRP in future experiments. Some discrepancy was observed near the entry region of the channel, with possible explanations including inflowing fluid and large-scale flow structure effects behind the channel’s mixing pin array. Finally, the new method was used to measure the 3D concentration distribution for a streak of titanium particles injected into a turbulent square channel flow with angled ribs. The transport of the streak was analyzed quantitatively, and a minor asymmetry in the channel geometry was shown to have important implications for the mean transport of the particle streak.