Applications Of Ferrofluids Research Articles

Ferrofluids in electric motors-a numerical process model

The number of technical applications of ferrofluids is constantly increasing. Their main purpose in terms of electric effects is to fill air gaps in magnetic circuits in order to lower the magnetic resistance. In this paper, a method to increase the efficiency of electric motors by filling the gap between the rotor and stator with a ferrofluid is proposed. The magnetic field and torque in a simplified model of an electric motor are calculated using orthogonal expansion.

Clinical Applications of Magnetic Drug Targeting

Cancer patients often present with localized disease. Yet, surgical eradication or radiation treatment is not always possible or meaningful. Site-directed drug targeting is one way of local or regional antitumor treatment. Magnetically controlled drug targeting is one of the various possibilities of drug targeting. This technology is based on binding established anticancer drugs with ferrofluids that concentrate the drug in the area of interest (tumor site) by means of magnetic fields. Then, the drug desorbs from the ferrofluid and enfolds its mechanism of action. This paper gives the reader an overview of current applications of ferrofluids (magnetic liquids) in conjunction with magnetic fields as they relate to the latest advances in medical applications and in particular to anticancer treatment.

Biomedical application of ferrofluids containing magnetite nanoparticles

ABSTRACTFerrofluids containing superparamagnetic Fe3O4 nanoparticles have been prepared by a controlled co-precipitation method.The aggregation of the particles was prevented by using a polymeric starch network as a coating agent. Structural and magnetic measurements reveal a particle size of around 6 nm, with a clear evidence of a uniform particle coating. The ferrofluids have been used as a contrast agent for MR imaging in biological tissue.

Numerical Simulation of Ferrofluid Flow for Subsurface Environmental Engineering Applications

Ferrofluids are suspensions of magnetic particles of diameter approximately 10 nm stabilized by surfactants in carrier liquids. The large magnetic susceptibility of ferrofluids allows the mobilization of ferrofluid through permeable rock and soil by the application of strong external magnetic fields. We have developed simulation capabilities for both miscible and immiscible conceptualizations of ferrofluid flow through porous media in response to magnetic forces arising from the magnetic field of a rectangular permanent magnet. The flow of ferrofluid is caused by the magnetization of the particles and their attraction toward a magnet, regardless of the orientation of the magnet. The steps involved in calculating the flow of ferrofluid are (1) calculation of the external magnetic field, (2) calculation of the gradient of the external magnetic field, (3) calculation of the magnetization of the ferrofluid, and (4) assembly of the magnetic body force term and addition of this term to the standard pressure gradient and gravity force terms. We compare numerical simulations to laboratory measurements of the magnetic field, fluid pressures, and the two‐dimensional flow of ferrofluid to demonstrate the applicability of the methods coded in the numerical simulators. We present an example of the use of the simulator for a field‐scale application of ferrofluids for barrier verification.

Experimental studies of the flow of ferrofluid in porous media

This paper presents laboratory-scale experimental results of the behavior of ferrofluids in porous media consisting of sands and sediments. Ferrofluids are colloidal suspensions of magnetic particles stabilized in various carrier liquids. In the presence of an external magnetic field, a ferrofluid becomes magnetized as the particles align with the magnetic field. We investigate the potential for controlling fluid emplacement in porous media using magnetic fields. These experiments show that in laboratory-scale porous media experiments (up to 0.25 m), with both vertical gravitational forces and lateral magnetic forces acting simultaneously, the magnetic field produces strong attractive forces on the ferrofluid, particularly in the vicinity of the magnet. These holding forces result in a predictable configuration of the fluid in the porous medium which is dependent on the magnetic field and in- dependent of flow pathway or heterogeneity of the porous medium. No significant retention effects due to flow through variably saturated sands are observed. While the proposed field engineering applications of ferrofluids are promising, the observations to date are particularly relevant at the laboratory scale where the decrease in magnetic field strength with distance from a magnet is less of a limitation than in larger scale applications. Ferrofluids may find immediate application in any situation where it is desirable to control the motion or final configuration of fluid in an experimental flow apparatus without direct physical contact.

Some biomedical applications of ferrofluids

Ferrofluids are colloidal solutions of iron oxide magnetic nanoparticles in either a polar or no polar liquid. We present here two biological applications using maghemite (γFe2O3) ferrofluids: magnetic cell sorting and magnetocytolysis. The first application employs magnetic particles binding a biological effector, which is capable to recognize the target cells specifically. These cells become magnetic and can be sorted in a gradient of magnetic field. We describe first the various steps of the synthesis of a biocompatible ferrofluid and the grafting an effector protein onto the particles. We then describe the use of particles carrying annexin V in the separation and quantification of damaged erythrocytes in blood samples. This very sensitive technique can be used to follow the erythrocytes ageing of normal blood samples during their storage under blood bank conditions or to detect the membrane modifications that are associated with some pathologies such as malaria or Alzheimer's disease. The dependence of the magnetic susceptibility versus the frequency is a way to transform magnetic energy into thermal energy. Magnetocytolysis is the destruction of cells, carrying magnetic particles, through the action of an alternating magnetic field (about 1 MHz). We present here preliminary experiments with macrophages, which demonstrate the method's feasibility and the formation of the non-specific interactions between the cells and the magnetic particles.

Study of an optimal configuration of an X-Band ferrofluid insulator

Results of investigation concerning a new application of ferrofluids (magnetic fluids) in the doMayn of non-reciprocal X-band devices are shown. Values of ferrofluid slab position x 0 , biasing field and ferrofluid saturation magnetization are determined for the optimum performance of an insulator. The advantages of using ferrofluids in non-reciprocal devices are also highlighted.

Experimental investigation of longitudinal magneto-optic effects in four ferrite ferrofluids in visible-near infrared spectrum

We present an extensive experimental work concerning measurement of longitudinal magneto-optic effects (Faraday rotation and circular dichroism) induced in magnetic liquids. Seven ferrofluid samples allow the study of the influence of numerous parameters: magnetic suspension and carrier liquid characteristics, magnetic field strength (up to 10 kOe) and frequency (dc to 50 kHz), light wavelength (400 to 2000 nm) and, temperature (253 to 373 K). These topics, especially the spectral area, have rarely been studied before. Most of the studies show interesting behaviors and aid in the understanding of magneto-induced phenomena. They also contribute to the conception of new optical applications of ferrofluids: 1) a pure Faraday rotator (free of circular dichroism) obtained by a ferrofluid mixing method and 2) a Faraday light modulator working up to 50 kHz.

The Materials Science of Field-Responsive Fluids

Scientists and engineers are most familiar with single-crystal or polycrystalline field-responsive or “smart” materials with responses typically occurring while the materials remain in the solid state. This issue of MRS Bulletin focuses on another class of field-responsive materials that exhibits a rapid, reversible, and tunable transition from a liquidlike, free-flowing state to a solidlike state upon the application of an external field. These materials demonstrate dramatic changes in their rheological behavior in response to an externally applied electric or magnetic field and are known as electrorheological (ER) fluids or magnetorheological (MR) fluids, respectively. They are often described as Bingham plastics, and exhibit a strong field-dependent shear modulus and a yield stress that must be overcome to initiate gross material deformation or flow. Prototypical ER fluids consist of linear dielectric particles (such as silica, titania, and zeolites) dispersed in nonconductive liquids such as silicone oils. Homogeneous liquid-crystalline (LC) polymerbased ER fluids have also been recently reported. MR fluids are based on ferromagnetic or ferrimagnetic, magnetically nonlinear particles (e.g., iron, nickel, cobalt, and ceramic ferrites) dispersed in organic or “aqueous liquids. Unlike ER and MR fluids, ferrofluids (or magnetic fluids), which are stable dispersions of nanosized superparamagnetic particulates (~5–10 nm) of such materials as iron oxide, do not develop a yield stress on application of a magnetic field. Applications of ferrofluids are primarily in the area of sealing devices (see Rosensweig for more information). Since ferrofluids are well-known and have been extensively discussed elsewhere in the literature, they will not be treated in detail here.

Ferrofluids‐ Magnetisable Liquids and Their Application in Density Separation

Stable suspensions of magnetic particles exhibit specific features making them an innovative liquid material for numerous applications as well as for basic research. In particular ferrofluids can be used for density separation of non‐magnetic materials immersed in the liquid under the influence of magnetic fields. In this article the basic properties and applications of ferrofluids will be reviewed, and the principles of magnetic density separation will be discussed on the basis of the available literature. In addition we will try to show the possibility and problems of a commercial use of this technique.

The Application of Heterogeneous PolarisableFluids in Mineral Processing

The paper deals with the application of ferrofluids in mineral processing. The efficiency of primary and secondary raw material separation by the magnetohydrostatic method is dependent on convenient distribution and on the stabilisation of density of the ferrofluid. To determine this density, the effective dynamometric method based on measurement of the buoyant force was constructed. A density controller has been developed for stabilisation and control of the density. Influence of some factors on the separation process, as well as the results of magnetohydrostatic separation are described.

Magnetic fluids in sealing and lubrication – a state of the art review

AbstractThe paper is a review of the properties and functions of magnetic fluids and their potential use in tribological applications, such as seals and bearings. They offer new possibilities for achieving low friction, low wear, and no leak‐ age.Magnetic fluids or ferrofluids consist of magnetic particles suspended in a carrier fluid and a coating on the particles. The coating prevents the agglomeration of the particles through magnetic and molecular attraction by keeping the distance between them sufficiently large. The magnetic fluids have the basic properties of liquids and they act like ferromagnetic materials in the presence of an external magnetic field.Shaft sealing is the most promising potential application for ferrofluids. Magnetic seals have zero‐leakage and low friction, they are non‐stick and they have high‐performance properties. Lubrication is another important application of ferrofluids. The advantage over conventional lubricants is the possibility of keeping the lubricant exactly and only where it is needed. They provide the possibility of increasing the life of components. Furthermore, because they do not contaminate, ferrofluids are also used as lubricants in clean environments.

Commercial applications of ferrofluids

Ferrofluids have been in the commercial arena for over two decades. In this paper, the most advanced, successful commercial applications of ferrofluids are discussed. These applications center around the tribological characteristics of ferrofluids, e.g., sealing, damping and hydrodynamic bearings. Also, an account of some lesser known applications is presented.

Formation of ultra-fine amorphous alloy particles by reduction in aqueous solution

Amorphous alloys are normally prepared as thin ribbons or films by the liquid quench technique or by vapour deposition. Recently we have shown1 that ultra-fine amorphous Fe–C alloy particles can be prepared by thermal decomposition of Fe(CO)5 in an organic liquid; that is, by a chemical reaction. Here we report the preparation of small alloy particles by reduction of metal ions by KBH4 in aqueous solutions. Mossbauer and X-ray diffraction studies show that the particles are amorphous. The amorphous phase is formed because the chemical reaction takes place below the glass transition temperature and because boron atoms are present in the particles. The method may be used for the large-scale production of ultra-fine amorphous alloy particles, which may have applications in ferrofluids, magnetic memory systems and catalysis.

Technological applications of ferrofluids

Ferrofluids have novel properties and their behaviour in magnetic fields leads to many interesting applications. Although magnetic fluids are already used in some devices they have not yet been exploited to any extent

Application of ferrofluids to separation of particulates

Potential applications of ferrofluids as a carrier medium for control of separation processes of particulates are considered. The variable magnetization of ferrofluids can be used to monitor flow of mono- and polydispersed mixtures across magnetized elements such as ferromagnetic wires.

Lesser known applications of ferrofluids

This paper describes applications of ferromagnetic liquids, referring to less well publicised devices. Examples are of commercial applications, where ferrofluid is an essential component of the system, or is an addition, which enhances performance. Ferrofluids can be excitingly positioned, without containers, to perform damping, thermal contact and sealing functions. They can also be used to label chemicals, illustrate magnetised areas, indicate hidden dimensions, or levitate objects. Reference will be made as to how designs have exploited these abilities. The paper puts the described applications in perspective by classifying the general range of applications for magnetic liquids.

Application of ferrofluids as an acoustic transducer material

Application of ferrofluids to electroacoustic transduction is discussed. A design of a piston-type transducer is described, and power transfer calculations are given, showing that useful levels of acoustic power emission can be obtained at intermediate frequencies (100 to 3000 Hz). A toroidal configuration is proposed as an alternative that essentially utilizes the fluid properties of the material and that, in principle, can be employed in large dimensions for very low frequencies.

A review of damping applications of ferrofluids

Applications of magnetic liquid technology to damping phenomenon are reviewed. Products utilizing ferrofluids, such as a rotary viscous inertia damper, linear damper, damper/seal assembly, and dashpot are discussed. The rotary dampers are used to enhance stepper motor performance. A magnetic liquid film sheared between a moving and stationary component forms the basis of these devices. The fluid is retained by magnetic forces and does not leak out. Examples of actual use of these dampers on operating systems, along with the test results, are presented.