Magnetic Field Gradient Force Research Articles

In Situ Analysis of Three-Dimensional Electrolyte Convection Evolving during the Electrodeposition of Copper in Magnetic Gradient Fields

A novel three-dimensional particle tracking velocimetry technique was used to examine the flow during electrodeposition of Cu. For the first time electrode-normal, circumferential, and radial velocities were spatially resolved during deposition in superimposed low and high magnetic gradient fields. In this way the complex interaction of magnetic field gradient force and Lorentz force induced convective effects could be measured and analyzed. Magnetic field gradient force induced electrolyte flow was detected only in high gradient magnetic fields, and it was found to be directed toward regions of gradient maxima. Since this electrode-normal flow causes enhanced transport of Cu(2+) ions from the bulk electrolyte to those regions of the working electrode where maxima of magnetic gradients are present, a structured deposit is formed during diffusion-limited electrodeposition. Lorentz force driven convection was observed during deposition in the low and the high magnetic gradient experiments. The overall fluid motion and the convection near the working electrode were determined experimentally and discussed with regard to the acting magnetic forces and numerical simulations.

Electrodeposition of separated 3D metallic structures by pulse-reverse plating in magnetic gradient fields

We present a new technique for electrodeposition of separated three-dimensional metallic structures solely by the superposition of magnetic gradient fields. Separate columns and stripes of Cu are generated by pulse reverse plating controlled by tailored magnetic field gradients. It is demonstrated that structures of μm-dimension are accessible with this technique and that the height of deposited structures can be adjusted by the number of plating cycles. The experimental observations are explained by the action of the magnetic field gradient force on the paramagnetic Cu2+-ions during the deposition and the dissolution part of the cycle. Additional influences of the Lorentz force are also discussed.

Studies on the patterning effect of copper deposits in magnetic gradient fields

Electrochemical Cu deposition was performed from electrolytes containing 0.1–1 M CuSO 4 in a well-defined magnetic gradient field. Patterned deposits resulted in all cases showing a strong correlation to this gradient field. It was observed that with increasing Cu 2+ concentration the structuring effect decreases in terms of differences in topography and morphology. An explanation of this effect is presented based on local convection induced by the magnetic field gradient force which is dependent on the concentration gradient established during the deposition. Superimposed effects of Lorentz force driven convection were observed for high Cu 2+ concentrations, and their influence on the deposition process was discussed.

Impact of magnetic field gradients on the free corrosion of iron

Abstract The influence of magnetic fields oriented parallel and perpendicular to the electrode surface on the corrosion behaviour of differently shaped iron samples in low concentrated sulphuric acid solutions has been studied. It is demonstrated, that the relative sample-to-magnet configuration, which determines the magnetic flux density distribution in front of the electrode surface, is decisive for the free corrosion activity. In a configuration generating low magnetic flux density gradients the Lorentz force driven micro-convection leads to an anodic shift of the free corrosion potential. In contrast, a configuration yielding high magnetic flux density gradients causes a cathodic potential shift and leads to a suppression of the corrosion reaction. These effects are discussed on the basis of the Lorentz force and the magnetic field gradient force acting on the partial reaction steps during the corrosion process.

Magnetic field effect on the anodic behaviour of a ferromagnetic electrode in acidic solutions

The magnetization of a ferromagnetic electrode in an external homogeneous magnetic field leads to a stray field in front of the electrode. This stray and its gradients can alter the anodic behaviour of the electrode significantly. Potentiodynamic polarisation measurements of an iron wire in a 0.5 M sulfuric acid solution (pH 0.25) and in a 0.5 M phthalate buffer solution (pH 5) without and with applied magnetic fields up to 0.6 T in different orientations to the electrode surface were performed. In sulfuric acid solution an increase of the diffusion-limited dissolution current density and a shift of the active–passive transition potential to more noble potentials was observed when the magnetic field was applied parallel to the electrode surface. In contrast, in perpendicular field configuration the diffusion-limited current density is lowered and the active–passive transition potential is shifted to less noble values. In phthalate buffer no significant influence of the magnetic field on the current density was observed in the active region, but a shift of the active–passive transition to less noble potentials occurred irrespective of the magnetic field configuration. The observed effects of a superimposed magnetic field on the anodic behaviour of iron are discussed with respect to an increase of the mass transport due to the Lorentz-force-driven magnetohydrodynamic (MHD) effect, the magnetic field gradient force and its interaction with the paramagnetic iron ions. The results of this paper show that the effect of the field gradient force can become very important due to the high magnetic field gradient at ferromagnetic electrodes.

Development of Magnetic Separation of Water-Soluble Materials Using Superconducting Magnet

In traditional usage of magnetic separation, it had been applied only to the separation of ferromagnetic materials such as iron related compounds from kaoline minerals. If paramagnetic or diamagnetic materials are to be efficiently and rapidly separated at the level of practical use, applicable fields of magnetic separation is widely enlarged. To accomplish this goal, developments of appropriate magnetic seeding process and design of the separation system consisting of superconducting magnets should be required. Recently, we succeeded in developing a high gradient magnetic separation system for purification of wastewater from paper factory. Here we extended the previous study and consider efficient recovery of the soluble molecules and ions using a magnetic absorbents and bulk superconducting magnet in order to enlarge the application field. In the present paper, the threshold of the required magnetic field gradient and magnetic force were discussed for designing the bulk superconducting magnet. It has also reported that the originally prepared magnetic absorbents can effectively recover the organic dyes and phosphate ions, and that separation process using superconducting magnet shows the feasibility for the practical application.

Magnetic biosensors for genetic screening of cystic fibrosis

The paper reports on the development of a magnetic biosensing platform for genetic analysis. The sensing technique is based on the on-chip manipulation of magnetically labelled biomolecules by the magnetic field gradient force created by current-carrying conductors; on biomolecular reactions such as the binding of complementary DNA material; and on the detection of the fringe field of the magnetic label by a magnetoresistive spin valve sensor. Different experiments will demonstrate the advantages, difficulties, prospects and potential of the combination of magnetic bead manipulation and detection on a single microchip. Early detection of DNA coding for the cystic fibrosis (CF) gene is used as a model system for proof-of-concept of the magnetic DNA biosensor platform.

Inducing Convection in Solutions on a Small Scale: Electrochemistry at Microelectrodes Embedded in Permanent Magnets

Magnetic field-induced convection in solutions containing electroactive species that can undergo reduction-oxidation (redox) chemistry has been demonstrated using a 125-/spl mu/m-diameter platinum disk electrode embedded in Nd-Fe-B bonded magnets. Stirring near the electrode surface occurs through several convective forces: the Lorentz force (magnetohydrodynamics), the magnetic field gradient force, and the paramagnetic gradient force. Stirring was determined by comparing the mass transport-limited current before and after magnetization of the bonded material. Magnetic field effects were studied by performing cyclic voltammetry (CV) in a solution of nitrobenzene at different concentrations. The CV responses showed that with concentrations from 0.25 to 2.0 mol/L, the limiting current increased as large as 54% because of magnetic forces being parallel to and in the same direction as natural convection. Above 2.0 mol/L, the solution viscosity in the diffusion layer dominates, resulting in a decrease in current and, hence, less convection. Embedding microelectrodes in magnetic materials yields measurable enhancements of stirring of a small volume (/spl sim/1 /spl mu/L), defined by the diffusion layer adjacent to the electrode, even at weak magnetic fields of /spl sim/0.13 T.

Magnetic field effect on electrochemical oscillations during iron dissolution

A fairly low magnetic field of ca. 30 mT was found to affect the period and the amplitude of the self-sustained current oscillation of an iron electrode. This was observed much distinctively when the direction of the applied field was normal to the electrode surface, i.e., non-magnetohydrodynamic (MHD) configuration. The Flade potential of the iron electrode was not affected by the magnetic field intensity of up to 4 T. The observed magnetic field effect was attributed to the depression of the natural convection in the vicinity of the electrode surface which was caused by the two local paramagnetic body forces, the magnetic field gradient force and/or the concentration gradient force.

Magnetic field effects on the rest potential of ferromagnetic electrodes

The application of a magnetic field unexpectedly alters the rest potential of ferromagnetic electrodes in paramagnetic solutions of their salts. Anodic shifts of up to 60 mV in a field of 1 tesla were observed for 1 M iron electrodes in iron nitrate solution. The magnitude of the shift depends on magnetic field strength and orientation and it varies with the anion used. The shift is smaller for cobalt and nickel (/spl sim/ 2 mV) than for iron. The effect is attributed to modifications in the rate of mass transport under the influence of the magnetic field gradient force.

Collisional heating by nonthermal electrons in a tapered magnetic loop

We examine the behavior of non-thermal electrons injected into a tapered magnetic loop, under the action of both Coulomb collisional and magnetic field gradient forces. An approximate analytic formula for the heating rate as a function of distance along the loop is developed, and found to be in good agreement with exact numerical solutions of the relevant equations. Such a formula is useful as a source term in many situations, such as hydrodynamic simulations of atmospheric response to flare energy input.

Superconductive helical flow magnetic ore separator

A high field helical flow-through separator to concentrate weakly magnetic ores is described. The process is to flow slurry helically around a current carrying conductor in a cylindrical annulus. The magnetic field gradient forces magnetic particles inwards towards the conductor. Nonmagnetic particles (gangue, sands, etc.) are deflected outwards by centrifugal force. Separation occurs at the exit end of the channel where a divider separates inboard from outboard slurry. The experimental part of this experimental and theoretical study is reported here. Carefully sized synthetic ore particles with and without sand in a slurry are used. Experiments cover a wide range of particle sizes (100 - 800 microns), magnetic moments (1.4 - 4.8 Am2/kg), velocities (1.5 - 4 m/sec), magnetic flux densities (0 - 1.6 T), input solid concentrations (2.6 - 15% by weight), and input grades (16.5 - 100%). Satisfactory separation is found within the above parameter regions.