Magnetohydrodynamic Electrochemistry in the Field of Nd−Fe−B Magnets. Theory, Experiment, and Application in Self-Powered Flow Delivery Systems

Leventis, Nicholas; Gao, Xuerong

doi:10.1021/ac010172u

Cited by 95 publications

(100 citation statements)

References 30 publications

(29 reference statements)

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“…However, close to an electrode interface where a concentration gradient exists, the force is able to induce local convective flows. There is growing interest in the influence of nonuniform magnetic fields on electrochemical reactions, ranging from confinement of organic species at disc microelectrodes [17], remapping of MHD flows [18], electrodeposit patterning by magnetized iron wires [19], and spatially correlated suppression of corrosion of iron wires [20]. Here we show how electrodeposits of both magnetic and nonmagnetic cations can be structured using nonuniform fields.…”

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confidence: 92%

Magnetic Structuring of Electrodeposits

2011

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Metal electrodeposition reflects the pattern of the magnetic field at the cathode surface created by a magnet array. For deposits from paramagnetic cations such as Co 2þ or Cu 2þ , the effect is explained in terms of magnetic pressure which modifies the thickness of the diffusion layer, that governs their mass transport. An inverse effect allows deposits to be structured in complementary patterns when a strongly paramagnetic but nonelectroactive cation such as Dy 3þ is present in the electrolyte, and is related to inhibition of convection of water liberated at the cathode, in the inhomogeneous magnetic field. The magnetic structuring depends on the susceptibility of the electroactive species relative to that of the nonelectroactive background. ( 1) where j is the current density in the cell and B is the applied magnetic field. Another force is operative when the field is nonuniform and induces a magnetization, M ¼ H, in the electrolyte. Here is the susceptibility, which is expressed as m c where m is the molar susceptibility and c is the concentration of ions in the electrolyte in mol m À3 . Since ( 1 for the electrolytes used in electrochemistry, the difference between B and 0 H can be neglected. The Kelvin force then takes the form F K ¼ 0 MrH. Provided the cell current is also negligible as a source of H, the field gradient force can be written as F rH ¼ 0 HrH orThis may exceed the Lorentz force when the electrolyte is paramagnetic [15]. The ratio of the magnitudes of the two forces isThe magnetic field gradient does not drag ions in solution into the vicinity of a magnet, because the energy of a single ion with spin S at temperature T in the field B, g 2 2 B SðS þ 1ÞB 2 =6 kT, is about 5 orders of magnitude less than kT, the thermal energy driving diffusion. ( B =kT ¼ 0:67 K T À1 , where B is the Bohr magneton and k is Boltzmann's constant). Taking the curl of F rB it is possible to distinguish two regions where the influence of the field gradient force is different [16],In the bulk solution, where there is no concentration gradient, the force is conservative, meaning it cannot induce convection, but it can modify or bifurcate existing convective flows. However, close to an electrode interface where a concentration gradient exists, the force is able to induce local convective flows. There is growing interest in the influence of nonuniform magnetic fields on electrochemical reactions, ranging from confinement of organic species at disc microelectrodes [17], remapping of MHD flows [18], electrodeposit patterning by magnetized iron wires [19], and spatially correlated suppression of corrosion of iron wires [20]. Here we show how electrodeposits of both magnetic and nonmagnetic cations can be structured using nonuniform fields. The deposits of magnetic ions are governed by the magnitude of the field at the cathode surface, and on the difference Á between the susceptibility of the electrolyte with and without electroactive cations. The ratio R is ) 1 in our experiments, so the field gradient force dominates.Elect...

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confidence: 92%

Magnetic Structuring of Electrodeposits

2011

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“…This displacement in the reverse direction was also recorded 15 min after each measurement. We do not have a simple explanation for this phenomenon, but it is believed to be related to the interaction of anisole 6 and buffer with the Teflon capillary surface. For the rest of this work, we focused on system with 5 cm long teflon capillaries and avoided the backflow problem.…”

Section: Backflowmentioning

confidence: 93%

“…The results presented in Eqs. (6) and (7) can also be used to show that the volumetric flow rate scales with the magnetic field: …”

Section: Measurements In Nmr Superconductive Magnetmentioning

confidence: 99%

“…Redox-based MHD pumping was All values for voltage (U), current (I), channels' cross-sectional area (A), total length of electrodes along the pumping channel (l), MHD flow mean velocity in the pumping channel (v MHD ) and MHD flow rate (Q MHD ) were experimental data, and were taken from Refs. [1,2,6,[8][9][10]. Most of the values for the electrodes cross-sectional area (A J ) and current density (J) across the pumping channel had to be calculated.…”

Section: Introductionmentioning

confidence: 99%

“…If calculated with relation (3), the predicted velocity and flow rate would be 0.16 mm s −l and 4 L min −l , respectively. studied by Leventis and Gao [6] and more recently by Clark and coworkers [7]. Other groups studied MHD pumping of saline solutions with combined AC magnetic fields and an AC current at high frequencies (≥1 kHz) to avoid bubble formation at the electrodes [8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

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Magnetohydrodynamic pumping in nuclear magnetic resonance environments

Homsy

Linder

Lucklum

et al. 2007

Sensors and Actuators B: Chemical

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We present a DC magnetohydrodynamic (MHD) pump as component of a nuclear magnetic resonance (NMR) microfluidic chip. This is the first time that MHD pumping in an NMR environment was observed and demonstrated. This chip generates a maximum flow rate of 1.5 L min −1 (2.8 mm s −1 in the microchannel) for an applied voltage of 19 V with only 38 mW of power consumption in a 7 T superconductive magnet. We developed a simple method of flow rate measurement inside the bulky NMR magnet by monitoring the displacement of a liquid-liquid interface of two immiscible liquids in an off-chip capillary. We compared and validated this flow measurement technique with another established technique for microfluidics based on the displacement of microbeads. This allowed us to characterize and compare the flow rate generated by the micropump on top of a permanent magnet (B 1 = 0.33 T) with the superconductive magnet (B 0 = 7.05 T). We observed a 21-fold increase in flow rate corresponding to the ratio of the magnetic field intensities (B 0 /B 1 = 21) in accordance with the theoretical flow dependence on the magnetic field intensity. The final aim is to integrate MHD pumps together with planar coils in a microfluidic system for NMR analysis. The high performance of MHD pumps at relatively low flow rates is seen as an asset for NMR and MRI applications.

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