Applications Of Ferrofluids Research Articles

Ferrofluids and their applications

Abstract

Fabrication of cobalt hollow microspheres via a PVP-assisted solvothermal process

Cobalt hollow microspheres were prepared by a surfactant-assisted solvothermal method in water and ethanol mixed solution. The outer diameter ranged from 1.5 to 2μm, and the shell with average thickness of about 250nm was constructed by smaller cobalt nanoparticles. The surfactant polyvinylpyrrolidone (PVP) was found to play an important role in the formation of such novel morphology. Room temperature magnetic measurement of the hollow microspheres demonstrated its enhanced ferromagnetic property with a coercivity of 202Oe. The possible formation mechanism was also discussed. The result showed a potential application in ferrofluids and other related magnetic devices.

Soft-Chemical Synthetic Route to Superparamagnetic FeAs@C Core–Shell Nanoparticles Exhibiting High Blocking Temperature

Superparamagnetic FeAs nanoparticles with a fairly high blocking temperature (TB) have been synthesized through a hot injection precipitation technique. The synthesis involved usage of triphenylarsine (TPA) as the As precursor, which reacts with Fe(CO)5 by ligand displacement at moderate temperatures (300 °C). Addition of a surfactant, hexadecylamine (HDA), assists in the formation of the nanoparticles, due to its coordinating ability and low melting point which provides a molten flux like condition making this synthesis a solventless method. Decomposition of the carbonaceous precursors, HDA, TPA and Fe(CO)5, also produces the carbonaceous shell coating the FeAs nanoparticles. Magnetic characterization of these nanoparticles revealed the superparamagnetic nature of these nanoparticles with a perfect anhysteretic nature of the isothermal magnetization above TB. The TB observed in this system was indeed high (240 K) when compared with other superparamagnetic systems conventionally utilized for magnetic storage devices. It could be further increased by decreasing the strength of the applied magnetic field. The narrow hysteresis with low magnitude of coercivity at 5 K suggested soft ferromagnetic ordering in these nanoparticle ensembles. Mössbauer and XPS studies indicated that the Fe was present in +3 oxidation state and there was no signature of Fe(0) that could have been responsible for the increased magnetic moment and superparamagnetism. Typically for superparamagnetic nanoparticle ensemble, the need for isolation of the superparamagnetic domains (thereby inhibiting particle aggregation and enhancing the TB) has been in constant limelight. Carbonaceous coating on these as-synthesized nanoparticles formed in situ provided the physical nonmagnetic barrier needed for such isolation. The high TB and room temperature magnetic moment of these FeAs@C nanoparticles also make them potentially useful for applications in ferrofluids and magnetic refrigeration. In principle this method can be used as a general route toward synthesis of other arsenide nanostructures including the transition metal arsenide which show interesting magnetic and electronic properties (e.g., CoAs, MnAs) with finer control over morphology, composition and structure.

Rheological study and applications of ferrofluids

Rheological study and applications of ferrofluids

Current and emerging applications of ferrofluids

Current and emerging applications of ferrofluids

Calculation of magnetic levitation force exerted on the cylindrical magnets immersed in ferrofluid

The magnetic levitation force exerted on the magnets immersed in ferrofluid is the theoretical basis of various application of ferrofluid. In this paper, based on the equivalent magnetic charge models and the equivalent current models of cylindrical magnets, magnetic charge image method and current image method are used to calculate the magnetic levitation force exerted on the cylindrical magnets immersed in ferrofluid respectively. The magnetic levitation force under the same conditions is calculated by the Comsol Multiphysics software according to the mechanical formula after the distribution of the magnetic field is obtained using finite element method. The magnetic levitation force is also measured experimentally, whose results are compared with the theoretical results obtained by the three methods. The analysis shows that the variation law of the magnetic levitation force and the influence by various parameters can be evaluated by the calculation with magnetic charge image method and current image method, but there is great difference between the theoretical results and the experimental results, and the greatest difference are 46% and 62% respectively. The agreement between the theoretical and the experimental results is quite good when the finite element method is used, whose greatest difference is 9%.

Optical Properties and Applications of Ferrofluids—A Review

Optical Properties and Applications of Ferrofluids—A Review

Solvothermal synthesis and characterization of cobalt microcrystals with hierarchical radial structure

Three-dimensional (3D) hierarchical cobalt microcrystals composed of well-aligned dendrites radiating from the shaft axis were prepared using cobalt chloride hexahydrate as starting materials via a facile hydrothermal route. The structures and morphologies of products were investigated by X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) measurements. It was found that the dosages of ethylenediamine, sodium hydrate played an important role in the morphology control of the final products. A unique growth mechanism for the radial cobalt microcrystal was tentatively discussed, which offers a fresh and possible solution to the design and fabrication of materials with hierarchical structure. Additionally, Magnetization measurements revealed that the products exhibited ferromagnetic characteristics with a saturation magnetization of 151.7 emu/g and a coercivity of 355.8 Oe at room temperature. The result shows a potential application in ferrofluids and other related magnetic application.

Synthesis and stabilisation of superparamagnetic iron oxide nanoparticle dispersions

Superparamagnetic iron oxide nanoparticles (magnetite (Fe 3O 4) and/or maghemite (γ-Fe 2O 3)) were precipitated with ammonium hydroxide from a solution of Fe(II)- and Fe(III)-chlorides in water under ambient conditions. The agglomerated nanoparticles were dispersed by addition of nitric acid to a sol and stabilised with a polycarboxylate backbone polyethylene oxide side chain combpolymer (MELPERS4343, BASF, Germany). In this work focus was put on studying the colloids stability in great detail which is of uttermost importance for technical applications of ferrofluids. It was possible to demonstrate that the resulting nanoparticles showed a good colloidal stability in water over a wide pH range from 2 to 12 as well as in ethanol or ethanol/water/ammonium hydroxide mixtures. Remarkable is the stability of the ferrofluid even at very high electrolyte concentrations present, such as NaCl. The stabilisation is steric or electrosteric, depending on the pH. Superparamagnetism is preserved in all cases. At pH > 12 the ester bonds to the polyethylene oxide side chains were hydrolysed, steric stabilisation was lost. Electrostatic stabilisation was hampered due to neutralisation by Na + where particles agglomerate. From the results of this study, an innovative binding scheme of the stabilising polymer to the nanoparticle, showing the changes of the polymer at different pH values leading to different stabilisation mechanisms, is proposed. The work describes an elegant way towards the synthesis of a very pH and electrolyte indifferent, stable ferrofluid. A ferrofluid, stable in such a remarkable way has not yet been reported to be obtained with such ease and in such a short time using mild, non-toxic, and cheap synthesis conditions.

Gd[formula omitted] substituted of Mn[formula omitted]Zn[formula omitted]Gd[formula omitted]Fe[formula omitted]O[formula omitted] ([formula omitted], 0.2, 0.3, 0.4) ferrites for ferrofluids application

Gd3+ substituted MnZn ferrites [ Mn0.5Zn0.5GdxFe2−xO4 (x=0.1, 0.2, 0.3, 0.4)] nanoparticles have been explored for ferrofluid applications. The oleic acid coated water base ferrofluids of these ferrites are prepared by chemical co-precipitation. The effect of Gd3+ ions on structural morphological and magnetic properties of these samples are characterized by X-ray diffraction, FTIR, EPR and dc magnetization techniques. The crystallite size, particle size and saturation magnetization increases with the increase of Gd3+ ions concentration while lattice parameter and lattice strain reduces. The g-value, peak-to-peak linewidth and spin concentration evaluated from EPR spectra correlated with cations occupancy.

Applications of ferrofluids in Micro Electro Mechanical Systems (MEMS) and micropumps

The micro-pump is one of the most promising micro-flow devices. At micro-level electronically controlled pumping of any fluid by a mechanical pump is not so easy and reliable. In the realm of nano-tech materials, ferrofluids have unique properties in both liquids and solids and have potential applications for MEMS/NEMS devices. This paper presents two new types of concepts, a micro-flowmeter based on a micro-turbine made using MEMS technology and the other is a micro-pump based on ferrofluidic. actuation. In our first device an optical photovoltaic sensor has also been integrated with this device. and the, micro-turbine rotates with a Speed of 50000 rpm. We have fabricated a ferrofluid-based glass micro-pump of size 20 x 20 x 10 mm(3). in which micro actuation is electrically, controlled by NdFeB (N50) permanent magnets (diameter 5 x 3mm, B(r) = 1400 mT, coercive field H(c) = 840 kA/m) with a ferrofluid bearing. The device is able to pump the fluid at the rate of 10 mu L/actuation.

Effect of initial pH and temperature of iron salt solutions on formation of magnetite nanoparticles

We report the effect of initial pH and temperature of iron salt solutions on formation of magnetite (Fe 3O 4) nanoparticles during co-precipitation. We synthesized nanoparticles by keeping the initial pH at 0.7, 1.5, 3.0, 4.7, 5.7, 6.7 for two different temperatures of 30 and 60 °C. When the initial pH (prior to alkali addition) of the salt solution was below 5, the nanoparticles formed were 100% spinel iron oxide. Average size of the magnetite particles increases with initial pH until ferrihydrite is formed at a pH of 3 and the size remains the same till 4.7 pH. The percentage of goethite formed along with non-stoichiometric magnetite was 35 and 78%, respectively, when the initial pH of the solution was 5.7 and 6.7. As the reaction temperature was increased to 60 °C, maintaining a pH of 6.7, the amount of goethite increased from 78 to 100%. These results show that the initial pH and temperature of the ferrous and ferric salt solution before initiation of the precipitation reaction are critical parameters controlling the composition and size of nanoparticles formed. We characterize the samples using X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The results of the present work provide the right conditions to synthesis pure magnetite nanoparticles, without goethite impurities, through co-precipitation technique for ferrofluid applications.

Determination of the magnetic particle distribution in tumour tissue by means of x-raytomography

In biomedical applications of ferrofluids, the resulting distribution of the magneticnanoparticles is a crucial parameter for the effect of the therapeutic approach. In order toincrease the efficacy of local cancer treatments incorporating ferrofluids like magnetic drugtargeting and hyperthermia, the bio-distribution of theses fluids in the respective tissue hasto be optimized. Usually, the distribution of particles is determined by histological cuts ofthe investigated specimen, a technique which provides only local information about theoverall distribution of the magnetic material, e.g. in a tumour. Radioscopic techniques basedon gamma or x-rays are well established, suitable for in vivo examination andnon-destructive, but only provide two-dimensional integral information in thedirection of the beam. Here we have used micro-tomography—incorporating aconventional x-ray tube as well as monochromatic synchrotron radiation—as a toolfor a three-dimensional analysis of the distribution of magnetic nanoparticles inbiological applications. Compared to biological matter, the iron-based magneticnanoparticles provide sufficiently high absorption for x-rays and thus serve as an intrinsiccontrast agent for the examinations. The results show the principle feasibility of themethod for a quantitative determination of the agglomeration behaviour of thenanoparticles within carcinogenic tissue after intravascular or intratumoural injection.

Magnetoviscous control of wall channeling in packed beds using magnetic nanoparticles—Volume-average ferrohydrodynamic model and numerical simulations

A theoretical framework for analyzing ferrofluid magnetoviscosity in anomalous non-magnetic porous media is constructed. Upscaling the pore-level ferrohydrodynamic model resulted in a volume-average model with 15 closure equations. A simplified zero-order three-dimensional axisymmetrical model for Forchheimer non-turbulent flows is cast for steady-state isothermal incompressible Newtonian ferrofluids through a Müller porous medium of spherically shaped grains and subjected to external constant gradient (bulk-flow oriented) magnetic fields, ferrofluid self-consistent demagnetizing field and induced magnetic field in the solid. The model reveals interesting potential chemical engineering applications of ferrofluids in contexts where wall flow maldistribution due to low column-to-particle diameter ratios exists. Judicious magnetic field arrangement mitigates wall channeling by inflating wall flow resistance through magnetoviscothickening and Kelvin body force density rerouting thus a fraction of wall flow towards bed core. Depending on whether the Kelvin force density acts against or in favor of the flow direction, the pressure drop is, respectively, larger or smaller than that without magnetic field, though, in all cases, magnetoviscothickening is the prevailing mechanism.

Identification of magnetic minerals by scanning electron microscope and application of ferrofluid

Magnetic minerals are mostly identified by a combination of rock magnetic and microscopic techniques and the ferrofluid method in combination with an optical microscope was applied during the last decades. But today, scanning electron microscopy (SEM) is preferred for the observation of mineral phases because its depth of focus and resolving capability at the same magnification. In this study, we report on a method, which allows ferrofluid application under the SEM. We coated a polished basalt sample containing titanomagnetite grains with high demagnetizing fields, with a colloidal suspension containing magnetite particles (ferrofluid) ranging in size between 11 and 20 nm. Due to large gradients of multidomain grains the ferrofluid particles adhered to their surfaces. Other grains of similar composition present (ilmenohematite) but with low demagnetizing fields do not generate large magnetic gradients and therefore do not attract the colloidal particles. Upon evaporation of the ferrofluid and covering the sample with conducting material the magnetic grains with high demagnetizing field are easily identifiable under the scanning electron microscope. The different mineralogy observed by this method is confirmed by temperature dependent variation of magnetic susceptibility, revealing titanomagnetite and ilmenohematite as magnetic carriers in the basaltic samples.

Determination of magnetic particle distribution in biomedical applications by X-ray microtomography

In biomedical application of ferrofluids the resulting biodistribution of the magnetic nanoparticles is a crucial parameter for the effect of the therapeutic approach. Usually the biodistribution is determined by histological cuts of the investigated specimen, a technique which provides only a very local information about the overall distribution of the magnetic material, e.g. in a tumor. Here we will introduce X-ray microtomography as a tool for a three-dimensional analysis of the distribution of magnetic nanoparticles in biological applications. Within the experiments presented here a spatial resolution of 80 μm could be achieved which can be enhanced to approximately 2 μm by the use of a synchrotron as X-ray radiation source.

Stabilization of spinel structure during combustion synthesis of iron nanooxides

Iron oxide nanoparticles were synthesized by direct metal combustion in the oxygen-containing environment. A pure Fe powder as well as its mixtures with powders of some other metals (Mg, Co, Zn) were burnt in oxygen-containing environment. The synthesized oxide nanoparticles were examined with transmission electron microscopy, X-ray diffractometry, atomic adsorption spectroscopy, and magnetization measurements. The results of the study of the nanoparticle properties showed that the doping of the other metal to the Fe fuel led to the spinel phase stabilization. The synthesized non-agglomerated ferrimagnetic nanoparticles possess the extremely high magnetization, which makes them attractive for ferrofluid applications.

The synthesis of spinel–ferrite nanoparticles using precipitation in microemulsions for ferrofluid applications

Magnetic maghemite nanoparticles with a narrow size distribution were prepared in water–CTAB–hexanol–butanol microemulsions. The particle size was controlled with the composition of the microemulsion (water-to-CTAB ratio) and the temperature during synthesis. The saturation magnetization of the nanoparticles depended mainly on their size, ranging from 22 emu/g for a particle size of 3.4 nm to 64 emu/g for a size of 15.3 nm.

Enhancement of AC-losses of magnetic nanoparticles for heating applications

Aqueous ferrofluids of maghemite nanoparticles coated with carboxydextran were investigated with respect to their specific loss power (SLP) in dependence on frequency and field amplitude of magnetic AC-fields. In order to elucidate the effect of the size distribution on SLP fluid fractions with different mean particle core size were prepared by a magnetic separation procedure from the original ferrofluid. Structural characterisation by means of TEM and XRD as well as reconstruction of core size distributions from magnetisation curves reveals that the narrow size distributions of the fractions cover a range of mean core sizes from about 8 up to 20nm. Spectra of the complex susceptibility were measured for a frequency range of 20Hz to 1 MHz. From the imaginary part of the susceptibility the specific loss power is calculated in dependence on frequency. The results are compared with calorimetrical measurements performed in dependence on field amplitude up to 11kA/m at 410kHz. A very high specific loss power in the order of 400W per gram maghemite was found at 410kHz and 11kA/m for the fluid fraction having the largest mean core diameter. A deviation from linear response behaviour is found for this sample showing a power law field dependence of the specific loss power SLP∼H2.5. In addition to liquid suspensions measurements were performed with particles immobilised in mannitol or gel in order to elucidate the role of Brownian relaxation. The experimentally found dependence of SLP on the mean particle core diameter may be understood in the frame of the Debye dispersion model. Results are discussed with respect to applications of ferrofluids in RF-magnetic hyperthermia.

Ferrofluids: magnetically controllable liquids

The make up, properties and applications of suspensions containing magnetic particles with a size of about 10 nm - usually called ferrofluids - will be discussed. The specific interest in these fluids bases on the fact that they show normal liquid behavior coupled with superparamagnetic properties. That means that it is possible to control the flow and the properties of ferrofluids by means of moderate magnetic fields in the order of about 50 mT. The magnetically controllable forces on ferrofluids open wide fields for basic research as well as for technical applications. Some of the applications of ferrofluids entered everyday live meanwhile and gained high commercial importance. Beside the discussion of the basic properties of these liquids, particular interest will be drawn to the change of their viscosity in the presence of magnetic fields. This effect usually called magnetoviscous effect is one of the most vivid fields of ferrofluid research at present.