Magnetic Field Gradient Force Research Articles

Selective capture of rare earth mineral particles in Bayan Obo by matrix parameters in superconducting magnetic separation

The rare earth minerals in Bayan Obo are poor, fine, scattered and variegated, so it is very difficult to achieve efficient separation. Superconducting magnetic separation technology is an efficient separation technology for refractory minerals. In this paper, the magnetic field induced by a matrix in a superconducting magnetic field is studied based on a finite element method and a separate numerical calculation method, and a model for the trajectories of rare earth mineral particles in Bayan Obo is obtained. The matching relationship between the matrix parameters and the capture radius is obtained through model calculation, as is the optimal capture radius and capture efficiency. The results show that the magnetic field gradient and magnetic field force decrease with increasing distance from the surface of the matrix and that the critical distance of the magnetic field induced by the matrix is 1.5 times the diameter of the matrix. The particle capture radius and capture efficiency are inversely proportional to the matrix diameter. When the matrix diameter is 0.06 mm, the capture efficiency is higher than at other diameters. The theoretical capture efficiency of rare earth mineral particles of size 20–38 µm is approximately 98%, but for particles below 10 µm, the capture efficiency is only 30%. The research results provide a quantitative selective capture law for the matrix diameter and particle diameter, which provides theoretical guidance for production practice.

Numerical simulation for magnetic field analysis and magnetic adsorption behavior of ellipse magnetic matrices in HGMS: Prediction magnetic adsorption behavior via numerical simulation

Magnetic matrices are the core components of HGMS systems. In this study, the induced magnetic field distribution characteristics of ellipse magnetic matrices are investigated via numerical simulation. Besides, the effects of magnetic matrices structure parameters and magnetic field distribution characteristics on the cumulative adsorption behavior of magnetic particles are also discussed. First, the numerical simulation results indicated that compared with the simulation results of a single magnetic matrix, the multi-matrix composite system simulation results demonstrate that an interaction of the induced magnetic fields generated by the superposition of magnetic fields is enhanced with the increase in the long axis size or the decrease in the gap between the matrices, heightening the magnetic induction but leading to the magnetic field gradient and magnetic field forces to significantly decrease near the surface of the matrix. And the rapid reduction of the magnetic field forces around the single matrix leads to a reduction in the range of action. However, to a certain extent, the interaction of the induced magnetic fields also will make the scope of the magnetic field force expand with the decrease in the gap between the matrices. The magnetic cumulative adsorption tests prove that it is feasible to infer the adsorption behavior of magnetic particles through the numerical simulation and theoretical calculations. The adsorption morphology of magnetic particles on the surface of magnetic matrices show that the repulsive region of magnetic particles is perpendicular to the direction of magnetic field, and the adsorption region of magnetic particles is parallel to the direction of magnetic field and with the increase of the size of magnetic matrices, the effective adsorption area of magnetic particles on the surface of magnetic matrices decreases gradually. Besides, with the increase of the horizontal gap between adjacent magnetic matrices, the adsorption thickness of magnetic particles on the surface of magnetic matrices decreases. Moreover, with the expansion of the horizontal gap between the adjacent magnetic matrices, the adsorption amount of the magnetic particles gradually decreases due to the decrease of the adsorption area and fill rate. The adsorption amount of magnetic particles will decrease as the long axis size increases when the fill rate of the magnetic matrices is similar.

Magnetic field effects on the corrosion and electrochemical corrosion of Fe83Ga17 alloy

FeGa alloys are competitive as new magnetostrictive materials due to their excellent comprehensive properties. These alloys are used under seawater coupled with a magnetic field; therefore, it is essential to study the effect of a magnetic field on the corrosion and electrochemical corrosion behaviors. Uniform magnetic fields of 0.15 T were applied in the tests. The corrosion tests indicated that the presence of a parallel magnetic field inhibited corrosion. Conversely, the presence of a perpendicular magnetic field promoted corrosion. These effects were attributed to the action of the magnetic field gradient force. The electrochemical corrosion tests showed that an applied parallel magnetic field enhanced the electrochemical corrosion, and the Lorentz force was responsible for these magnetic field effects.

Neutron imaging of liquid-liquid systems containing paramagnetic salt solutions

The method of neutron imaging was adopted to map the concentration evolution of aqueous paramagnetic Gd(NO3)3 solutions. Magnetic manipulation of the paramagnetic liquid within a miscible nonmagnetic liquid is possible by countering density-difference driven convection. The formation of salt fingers caused by double-diffusive convection in a liquid-liquid system of Gd(NO3)3 and Y(NO3)3 solutions can be prevented by the magnetic field gradient force.

Magnetic mirror end-plugged by field-reversed configurations formed via rotating magnetic fields

A novel magnetic mirror concept with field-reversed configurations (FRCs) formed via rotating magnetic fields (RMFs) serving as end plugs is proposed to improve the mirror's axial confinement. Single-particle orbit calculations suggest that the FRCs in the end plugs can reflect ions back into the central cell if their parallel speeds are not so fast that they can overcome the magnetic field gradient force from the X-point of the FRC to the midplane outside of the FRC. However, this effect is limited and is no different from that of adding a weak mirror cell to the central cell. When the inward Hall electric field generated by the RMFs is considered, an additional Lorentz force emerges that pushes the incoming ions back to the central mirror, thereby dramatically improving the confinement. The Lorentz force is related to the azimuthal drift speed times the radial component of the magnetic field. By surveying the particle phase space of the speeds, we find that this Lorentz force can reflect back or trap >90% of ions escaping from the central mirror given a sufficient Hall electric field in the RMF region. Finally, preliminary experimental results from the Keda Mirror with AXisymmetricity RMF/FRC are reported and show that with the RMFs on, the axial mirror confinement can increase by a factor of ∼1.4 on average.

Combining magnetic forces for contactless manipulation of fluids in microelectrode-microfluidic systems

A novel method to drive and manipulate fluid in a contactless way in a microelectrode-microfluidic system is demonstrated by combining the Lorentz and magnetic field gradient forces. The method is based on the redox-reaction [Fe(CN)6]3−/[Fe(CN)6]4− performed in a magnetic field oriented perpendicular to the ionic current that crosses the gap between two arrays of oppositely polarized microelectrodes, generating a magnetohydrodynamic flow. Additionally, a movable magnetized CoFe micro-strip is placed at different positions beneath the gap. In this region, the magnetic flux density is changed locally and a strong magnetic field gradient is formed. The redox-reaction changes the magnetic susceptibility of the electrolyte near the electrodes, and the resulting magnetic field gradient exerts a force on the fluid, which leads to a deflection of the Lorentz force-driven main flow. Particle Image Velocity measurements and numerical simulations demonstrate that by combining the two magnetic forces, the flow is not only redirected, but also a local change of concentration of paramagnetic species is realized.

(Invited) Magnetic Gradient-Assisted Physical and Chemical Structuring of Electrodeposits

Magnetic thin films, micro and nano structures are key features in magnetic sensors and for data storage in hard drives. To date often physical deposition methods are more frequently employed than electrodeposition to produce these magnetic structures. This is due to the fact that the usually inexpensive alternative production by electrodeposition requires sophisticated masking or templating if structured deposits are desired. Magnetic-field assisted electrodeposition has been demonstrated as a method to produce structured deposits by employing reusable magnetic gradient templates. [1] The working principle is based on a locally enhanced mass transports thanks to a magnetic gradient force induced local convection in the electrolyte during electrodeposition. In regions of high magnetic gradients, typically film thickness and roughness are increased for paramagnetic ions like Cu2+, Co2+ or Fe2+. Here, we demonstrate that not only single component metals, but also bimetallic alloy electrodeposits can be deposited in a desired structure by this approach. By suitably selecting the electrolyte composition and deposition parameters, we demonstrate that the current efficiency can be increased for the electrodeposition of transition metal-based alloys. This is evidenced by electrochemical quartz crystal microbalance studies during electrodeposition of CoFe in the presence of varied magnetic gradients. [2] In addition, we show that also chemical structuring of bimetallic deposits can be achieved by means of magnetic gradient-assisted electrodeposition, which is shown or CuNi electrodeposits. For both systems the observed local morphological and compositional changes are characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. The experimental findings are then discussed in terms of magneto-hydrodynamic effects, which are attributed to the magnetic field gradient force. Thus, magnetic-gradient assisted electrodeposition is suggested as a new route to magnetic patterning of surfaces. [1] Tschulik, Kristina; Koza, Jakub Adam; Uhlemann, Margitta; Gebert, Annett; Schultz, Ludwig Electrochemistry Communications, 2009, 11(11), 2241–2244 [2] Karnbach, F.; Uhlemann, M.; Gebert, A.; Eckert, J.; Tschulik, K. Electrochimica Acta, 2014, 123, 477–484

Effect of Magnetic Field on Anodic Dissolution and Pitting of Iron in a Molybdenum Nitrate Solution with Chlorides

Magnetic fields would affect electrochemical reactions for metallic materials in aqueous solutions. The main effect of a magnetic field applied on an electrochemical system is the introduction of additional forces on the ions in the electrolyte, such as Lorentz-force driven magnetohydrodynamics (MHD) effect and Kelvin-force-driven magnetic field gradient force (MFGF) effect. There are some published reports on the influence of magnetic fields on the pitting corrosion, and apparently contradictory results have been reported. In this work, we focused on the effect of magnetic field on anodic dissolution of iron in a molybdenum nitrate solution with chloride ions. The typical potentiodynamic polarization curves of iron in a 0.2 mol L-1 Na2MoO4 +0.2 mol L-1 NaCl solution at a potential sweep rates of 0.833 mV/s and under 0 T and 0.4 T magnetic field are shown in Fig. 1. Magnetic field decreased the limiting current densities at high potentials. The results in Fig. 1 were confirmed by potentiostatic polarization measurements, which were used to study the effect of magnetic field on the anodic corrosion of iron. After a relatively long period of polarization at 0.4V(SCE) at 0T, imposing a magnetic field will result in a sudden increase and then a slowly decrease of the current density, as shown in Fig. 2(a). The electrode surface morphologies after potentiostatic polarization at 0.4V for 200s under 0T are shown in Fig. 2(b), which are corresponded to the conditions in Fig. 2(a). The pits have propagated deeply. The mass transfer process between occluded pit bottom and the pit mouth would became difficult with the deepening of the pits. The retarding effect of magnetic field on anodic dissolution of iron in a molybdenum nitrate solution with chloride is ascribed to its effect on the mass-transport process between the occluded pit bottom and the pit mouth and finally the resultant disturbance of the autocatalysis process involved in pitting Figure 1

Potentiodynamic Polarization and Potentiostatic Polarization Behaviors for Iron in Sulfuric Acid Solution with or without a Magnetic Field

The behavior of iron during the corrosion process has been already studied in great detail due to its importance as a main constituent of many metallic construction materials. Magnetic field generated by electromagnetic facilities such as power generators, motors and solenoid valves and electric transmission lines can affect the corrosion of these facilities and their surrounding materials. Effects of imposed magnetic fields on the anodic behavior of iron has been investigated and discussed with respect to the modulation of the mass transport due to the Lorentz-force-driven magnetohydrodynamic (MHD) effect and magnetic field gradient force (MFGF) effect. Hydrogen evolution reaction (HER) on different metals/alloys in acidic or alkaline media is one of the most investigated cathodic reactions in the field of corrosion electrochemistry. Meanwhile, hydrogen is a potential energy source for fuel cells and other applications and the HER supplies the highly pure hydrogen. Its reaction kinetics of HER has been generalized. The effect of magnetic field on the kinetics and mechanism of HER needs investigation in details. In the present study, the effect of a magnetic field on the cathodic reaction of iron in a sulfuric acid solution was studied. Potentiodynamic polarization curves with or without a 0.4 T magnetic field and potentiostatic polarizations under the intermittent imposing or withdrawing of the magnetic field were used to determine the magnetic field effect on hydrogen evolution reaction. An electromagnet with a direct current source was used. The magnetic field was horizontal and oriented parallel to the electrode surface. Results of potentiostatic polarization curves show that the cathode current density at high acthodic over-poentials increased due to the presence of a 0.4T magnetic field while the shape of the polarization curve was not significantly changed by magnetic field, as shown in Fig. 1. The phenomenon has been described in previous studies that the magnetic field generates a new overpotential which leads to accelerating the hydrogen reaction. Figure 2 shows the impact of an applied magnetic field on the current vs. time curves under potentiostatic polarization for iron in sulphuric acid solution. The effect of magnetic field on cathodic current was related to the polarization sequence and the sequence of applying magnetic field. When the iron electrode has been polarized after many cycles of imposing or withdrawing the magnetic field, the magnetic field could cause a sudden decrease of the current density and then the current density maintained at a relatively low value, and withdrawing the magnet caused a sudden increase of the current density and then the current density maintained at a relatively high value. It has been found that if the magnetic field was applied at the start of polarization, withdrawing the magnetic field for the first time caused to a sudden but not big decrease of the current density and then the current density maintained at a relatively low value. The results the applied magnetic field effect on cathodic hydrogen evolution could be different depending on the cathodic polarization mode and the test sequence. One possible reason is that iron electrode would be subject to hydrogen charging that will change the properties of the iron electrode itself thus making the magnetic field effect different. Another possible reason can be the memory effect of magnetic field on solution properties or cathodic reaction. Systematic measurements are required for clarifying these issues. Figure 1

Magnetic Field simulation and experimental tests of Special Cross-section Shape Matrices for High Gradient Magnetic Separation

The cross-sectional shape has great influence on the magnetic field characteristics of magnetic matrices in high gradient magnetic separation (HGMS). Suitable cross-sectional matrices can improve the recovery of fine weakly magnetic minerals and reduce mineral processing energy consumption. The performance of four types of cross-sectional shape matrices in the axial configuration of HGMS was studied through numerical simulation combined with experimental tests. The magnetic field generated by the matrices was simulated with ANSYS software, and the magnetic field strength, gradient, and magnetic force were analyzed and compared. The simulation results showed that diamond shaped, elliptical, square, and circular steel matrices reach magnetization saturation successively with increasing the magnetic induction, and the required magnetic induction is approximately 0.7, 0.8, 1, and 1.1 T, respectively. The magnetic field gradient increases with increasing the magnetic induction and then keeps constant when the matrices reach magnetization saturation. Within a wide range of the magnetic induction, the elliptical and square matrices present good magnetic field characteristics. The magnetic force near the surface of the square matrices is the largest but decreases rapidly and consequently has a small effect depth. The magnetic force near the surface of the elliptical matrices is relatively lower but decreases slowly and has a larger effect depth. The diamond-shaped matrices are easy to reach magnetization saturation, and the magnetic force decreases most rapidly. Magnetic matrices were manufactured, and magnetic separation experiments were conducted to verify the simulation results. The experimental results show that the elliptical and square matrices can obtain higher recovery in a wide range of magnetic induction, and the recovery of the elliptical matrices is the highest. The experimental results correspond well with the numerical simulation results, and the results indicate that the magnetic force effect depth is a very important factor influencing the performance of the matrices.

In situ analysis of copper electrodeposition reaction using unilateral NMR sensor

The uses of high-resolution NMR spectroscopy and imaging (MRI) to study electrochemical reactions in situ have greatly increased in the last decade. However, most of these applications are limited to specialized NMR laboratories and not feasible for routine analysis. Recently we have shown that a bench top, time domain NMR spectrometer can be used to monitor in situ copper electrodeposition reaction and the effect of Lorentz force in the reaction rate. However these spectrometers limit the cell size to the magnet gap and cannot be used with standard electrochemical cells. In this paper we are demonstrating that unilateral NMR sensor (UNMR), which does not limit sample size/volume, can be used to monitor electrodeposition of paramagnetic ions in situ. The copper electrodeposition reaction was monitored remotely and in situ, placing the electrochemical cell on top of the UNMR sensor. The Cu2+ concentration was measured during three hours of the electrodeposition reactions, by using the transverse relaxation rate (R2) determined with the Carr–Purcell–Meiboom–Gill pulse sequence. The reaction rate increased fourfold when the reaction was performed in the presence of a magnetic field (in situ), in comparison to the reactions in the absence of the magnetic field (ex situ). The increase of reaction rate, in the presence of the UNMR magnet, was related to the magneto hydrodynamic force (FB) and magnetic field gradient force (F∇B). F∇B was calculated to be one order of magnitude stronger than FB. The UNMR sensor has several advantages for in situ measurements when compared to standard NMR spectrometers. It is a low cost, portable, open system, which does not limit sample size/volume and can be easily be adapted to standard electrochemical cells or large industrial reactors.

Levitation forces of a bulk YBCO superconductor in gradient varying magnetic fields

The levitation forces of a bulk YBCO superconductor in gradient varying high and low magnetic fields generated from a superconducting magnet were investigated. The magnetic field intensity of the superconducting magnet was measured when the exciting current was 90 A. The magnetic field gradient and magnetic force field were both calculated. The YBCO bulk was cooled by liquid nitrogen in field-cooling (FC) and zero-field-cooling (ZFC) condition. The results showed that the levitation forces increased with increasing the magnetic field intensity. Moreover, the levitation forces were more dependent on magnetic field gradient and magnetic force field than magnetic field intensity.

Modification of Electrodeposited Co-Pd Alloy Catalysts By Superimposed High Magnetic Field

Palladium and its alloys have been a subject of interest in many research centers all over the world. Due to the price and accessibility of Pd, intensive tests are conducted aiming to invent alloys with catalytic properties similar to those of platinum, but much cheaper than palladium itself. Alloys of Co-Pd, Pd-Fe, Pd-Ni and Pd-Cr exhibit high catalytic activity for the four electron oxygen reduction reaction.The properties of Co-Pd alloys for the hydrogen evolution reaction are close to the properties of pure platinum. This makes it possible to use them, for example, in fuel cells. Tests performed so far have demonstrated that the Pd-Co alloys are characterized by much better electrocatalytic properties for HER than pure palladium. Application of an external magnetic field during the deposition of an alloy causes an additional convection at the electrode surface through the magnetohydrodynamic effect (MHD), paramagnetic force and magnetic field gradient force. This additional convection results in changes of the alloy composition, structure and morphology, and these, in turn, affect the further properties as magnetic as catalytical of the produced alloys. Magnetic field applied parallel to the surface of the electrode generates convection (magnetohydrodynamic effect MHD) of the electrolyte; it results in a laminar flow on the surface of the electrode which reduces the diffusion layer and increases the concentrations gradients. This results in change of the size of the grains and thus can also influence the texture and formation of various phases of the deposits. These various effects can be caused at the same time by the above mentioned convection but also by the magnetic properties, when the field is superimposed the growth in the direction of easier magnetization appears. Optimal conditions of electrolytic deposition of cobalt matrix nanoalloys will be sought through selection of proper composition of electrolyte, changes of electrolysis parameters and by application of external electromagnetic field with intensity up to 12 Tesla. Initial experiments, when the magnetic field was limited up to 1 T, show the improvement of catalytical properties together with increase of magnetic field orientated parallel to the surface of electrode. The influence of magnetic field with higher strength on electrodeposition of alloys with catalytical properties is needed to be clarified. Acknowledgement This work was supported by Polish National Science Center under grants 011/01/N/ST5/05509 and 2013/09/B/ST8/00211. This work was also supported by Polish Ministry of Science and Higher Education under grant IP2012/001072.

Enhanced paramagnetic Cu2+ ions removal by coupling a weak magnetic field with zero valent iron

A weak magnetic field (WMF) was proposed to enhance paramagnetic Cu2+ ions removal by zero valent iron (ZVI). The rate constants of Cu2+ removal by ZVI with WMF at pH 3.0–6.0 were −10.8 to −383.7 fold greater than those without WMF. XRD and XPS analyses revealed that applying a WMF enhanced both the Cu2+ adsorption to the ZVI surface and the transformation of Cu2+ to Cu0 by ZVI. The enhanced Cu2+ sequestration by ZVI with WMF was accompanied with expedited ZVI corrosion and solution ORP drop. The uneven distribution of paramagnetic Cu2+ along an iron wire in an inhomogeneous MF verified that the magnetic field gradient force would accelerate the paramagnetic Cu2+ transportation toward the ZVI surface due to the WMF-induced sharp decay of magnetic flux intensity from ZVI surface to bulk Cu2+ solution. The paramagnetic Fe2+ ions generated by ZVI corrosion would also accumulate at the position with the highest magnetic flux intensity on the ZVI surface, causing uneven distribution of Fe2+, and facilitate the local galvanic corrosion of ZVI, and thus, Cu2+ reduction by ZVI. The electrochemical analysis verified that the accelerated ZVI corrosion in the presence of WMF partly arose from the Lorentz force-enhanced mass transfer.

Magnetic Separation of Paramagnetic Ions From Initially Homogeneous Solutions

The concentration change in an initially homogeneous paramagnetic solution is studied interferometrically upon applying sufficiently strong inhomogeneous magnetic fields. For this purpose, five different magnetic field configurations are analyzed. Clear evidence is provided that an enrichment of paramagnetic ions occurs in the field gradient. In particular, we show that the shape of this enrichment layer maps the spatial distribution of the magnetic field gradient force.

Weak magnetic field significantly enhances selenite removal kinetics by zero valent iron

The effect of weak magnetic field (WMF) on Se(IV) removal by zero valent iron (ZVI) was investigated as functions of pH and initial Se(IV) concentrations. The presence of WMF significantly accelerated Se(IV) removal and extended the working pH range of ZVI from 4.0–6.0 to 4.0–7.2. The WMF induced greater enhancement in Se(IV) removal by ZVI at lower initial Se(IV) concentrations. The influence of WMF on Se(IV) removal by ZVI was associated with a more dramatic drop in ORP and a more rapid release of Fe2+ compared to the case without WMF. SEM and XRD analysis revealed that WMF accelerated the corrosion of ZVI and the transformation of amorphous iron (hdyr)oxides to lepidocrocite. XANES analyses showed that WMF expedited the reduction of Se(IV) to Se(0) by ZVI at pH 6.0 when its initial concentration was ≤20.0 mg L−1. Se(IV) dosed at 40.0 mg L−1 was removed by ZVI via adsorption followed by reduction to Se(0) at pH 7.0 but via adsorption at 7.2 in the presence of WMF. Regardless of WMF, Se(IV) applied at 40.0 mg L−1 was removed by reduction at pH 4.0–6.0. The WMF-induced improvement in Se(IV) removal by ZVI may be mainly attributable to the Lorentz force and magnetic field gradient force. Employing WMF to enhance Se(IV) removal by ZVI is a promising and environmental-friendly method since it does not need extra energy and costly reagents.

Analysis of the Electrolyte Convection inside the Concentration Boundary Layer during Structured Electrodeposition of Copper in High Magnetic Gradient Fields

To experimentally reveal the correlation between electrodeposited structure and electrolyte convection induced inside the concentration boundary layer, a highly inhomogeneous magnetic field, generated by a magnetized Fe-wire, has been applied to an electrochemical system. The influence of Lorentz and magnetic field gradient force to the local transport phenomena of copper ions has been studied using a novel two-component laser Doppler velocity profile sensor. With this sensor, the electrolyte convection within 500 μm of a horizontally aligned cathode is presented. The electrode-normal two-component velocity profiles below the electrodeposited structure show that electrolyte convection is induced and directed toward the rim of the Fe-wire. The measured deposited structure directly correlates to the observed boundary layer flow. As the local concentration of Cu(2+) ions is enhanced due to the induced convection, maximum deposit thicknesses can be found at the rim of the Fe-wire. Furthermore, a complex boundary layer flow structure was determined, indicating that electrolyte convection of second order is induced. Moreover, the Lorentz force-driven convection rapidly vanishes, while the electrolyte convection induced by the magnetic field gradient force is preserved much longer. The progress for research is the first direct experimental proof of the electrolyte convection inside the concentration boundary layer that correlates to the deposited structure and reveals that the magnetic field gradient force is responsible for the observed structuring effect.

Optical velocity measurements of electrolytic boundary layer flows influenced by magnetic fields

Magnetic fields are applied to electrically conducting fluids in order to influence electrochemical processes through the magnetohydrodynamic effect. Various phenomena, e.g. on electrodeposited metal layers, which can be attributed to forced convections were observed. To provide information about acting forces, the laser Doppler velocity profile sensor was applied to measure the transition layer of a Lorentz force influenced flow over a backward-facing step and the velocity boundary layer during copper deposition. With this sensor, the electrolyte convection within < 500 μm of the front of an electrode is measured with a spatial resolution down to 15 μm. The interaction of buoyancy, Lorentz and magnetic field gradient forces is studied by measuring the velocities down to 10 μm in front of the cathode. Inside the concentration boundary layer, complex electrolyte convection is induced, which varies not only in time but also in its structure, depending on the forces present and their influence over time. In inhomogeneous magnetic field configurations, the magnetic field gradient force dominates the velocity boundary layer at steady state and transports electrolyte toward regions of high magnetic gradients, where maximum deposit thicknesses are found. In this way, the measurements confirm the predicted influence of the magnetic field gradient force on the structuring of copper deposits.

Enrichment of Paramagnetic Ions from Homogeneous Solutions in Inhomogeneous Magnetic Fields.

Applying interferometry to an aqueous solution of paramagnetic manganese ions, subjected to an inhomogeneous magnetic field, we observe an unexpected but highly reproducible change in the refractive index. This change occurs in the top layer of the solution, closest to the magnet. The shape of the layer is in accord with the spatial distribution of the largest component of the magnetic field gradient force. It turns out that this layer is heavier than the underlying solution because it undergoes a Rayleigh-Taylor instability upon removal of the magnet. The very good agreement between the magnitudes of buoyancy, associated with this layer, and the field gradient force at steady state provides conclusive evidence that the layer formation results from an enrichment of paramagnetic manganese ions in regions of high magnetic field gradient.

Effect of high gradient magnetic fields on the anodic behaviour and localized corrosion of iron in sulphuric acid solutions

The influence of high gradient magnetic fields on the anodic dissolution of iron in sulphuric acid solutions and the localization of the corrosion attack is investigated by means of potentiodynamic and potentiostatic polarization experiments and subsequent surface profile analysis. A localization of the material loss is observed in every potential region of the anodic Fe dissolution except from the passive region. The impact of the magnetic field on the anodic current density and the localization of the corrosion attack are explained by the action of the Lorentz force and the magnetic field gradient force.