Application Of DC Current Research Articles

Heat Treatment of AA7075 by Electropulsing and DC Current Application

Electrical resistivity was used in this test methodology to estimate the relative precipitate density in AA7075. Various electrical test parameters were explored to determine the difference between pulsed and DC-type currents. No difference between these test conditions could be distinguished. Furthermore, an electroplastic effect was not needed to explain these results and the effects are likely to be caused by purely joule heating.

Electrothermal Actuation and Release of Adhesiveness of Conductive Carbon Nanotube/Epoxy Composites by Joule Heating

AbstractThe effect of an embedded electro‐conductive multi‐walled carbon nanotube (MWCNT) nanopaper in an epoxy matrix on the release of the frozen actuation force and the actuation torque in the carbon nanotube nanopaper/epoxy composite after heating above its glass transition temperature is assessed. The presence of the nanopaper augments the recovery of the actuation stress by the factor of two in comparison with the pure epoxy strip. The strengthening of the composite is attributed to the interlocking of the carbon nanotubes with the epoxy. Moreover, the internally heated electro‐conductive carbon nanotube nanopaper/epoxy composite not only substantially shortens curing time while retaining comparable strength of the adhesive bonding of the steel surfaces but also enables a release of such bonds by repeated application of DC current.

Protection of silver electrodeposit surfaces against accelerated and natural atmospheric corrosion by Ge incorporation in Ag structure; a microstructural investigation

Silver, as the most reactive noble metal, tarnishes immediately after exposure to industrial atmosphere or indoor S-bearing air. In this study, tarnish resisting and long term microstructural stability of silver-germanium (Ag-Ge) coating in industrial atmosphere is investigated and compared to silver electrodeposits. Ag-Ge coatings were electrodeposited on copper from cyanide base bath by DC current application. Coatings consisting about 0.5 to 6wt.% Ge have been studied and the optimum content of Ge in the coating was found to be 6 wt.% regarding dense and uniform microstructure along with best tarnish resistance and long term microstructural stability that has been discussed in this work. Ge forms a thin protective oxide layer, so a small incorporation of Ge in Ag structure, could improve tarnish resistance to a large extent. Tarnish resistance of samples have been evaluated according to ISO 4538 standard and considering color and reflectivity change detected by UV-Visible spectrometer. In addition, X-ray Diffraction (XRD) results were used to determine the crystalline structure of coatings before and after tarnish resistance and atmospheric corrosion. XRD patterns in grazing mode indicated the formation of Ge-Oxide passive layer on the Ag-6Ge surface which is known as the key factor for this sample's best performance. Scanning Electron Microscopy (SEM) along with Field Emission Scanning Electron Microscopy (FESEM) equipped with Energy Dispersive Spectrometry (EDS) were used for microscopic analysis and surface characterization of samples. The various tarnish behavior of the coatings were evaluated and discussed via correlation to their microstructural characteristics in both severe and low aggressive conditions.

Investigating Liquid Metal Galinstan as a High Current Carrier and Its Interaction with Collector Electrodes

In this work, we demonstrate the potential application of liquid metal galinstan as a means of carrying high currents between two collector electrodes. The room-temperature liquid metal was placed between two electrodes made either of stainless steel (SS) or of copper, where the electrical performance at applied currents as high as 250 A was monitored and found to be highly stable. The surface interaction between galinstan and the collector electrodes in the presence and absence of such high DC currents was also investigated. After 12 h of contact with Cu electrodes, analysis by X-ray diffraction and energy-dispersive X-ray experiments revealed the presence of Ga and Cu as well as evidence of very minor InSn phase separation from liquid galinstan to form a solid alloy. However, after the application of a DC current of 250 A for 12 h, extensive Cu-Ga alloy formation was observed in the form of CuGa2, as well as a more pronounced phase separation of the In and Sn components into islands of InSn. It was found that the slight temperature rise during electrical testing favored alloy formation but was not the origin of the phase separation of the In-Sn components. In contrast, analysis of the SS electrode after 24 h of an applied DC current of 250 A did not reveal any form of alloy formation. This work shows that the electrical performance of liquid metal galinstan is stable upon the application of high DC currents using two different contact materials even though the interaction with the contacts differs. In addition, this provides an interesting pathway that can be explored for alloy production using galinstan and Cu materials under the application of an applied current, which may have other uses apart from high-current-density carriers.

Accelerated Shape Forming and Recovering, Induction, and Release of Adhesiveness of Conductive Carbon Nanotube/Epoxy Composites by Joule Heating.

The versatile properties of a nanopaper consisting of a porous network of multi-walled carbon nanotubes were applied to enhance the mechanical and electrical properties of a thermosetting epoxy polymer. The embedded nanopaper proved useful both in the monitoring of the curing process of the epoxy resin by the self-regulating Joule heating and in the supervising of tensile deformations of the composite by detecting changes in its electrical resistance. When heated by Joule heating above its glass transition temperature, the embedded carbon nanotube nanopaper accelerated not only the modelling of the composites into various shapes, but also the shape recovery process, wherein the stress in the nanopaper was released and the shape of the composite reverted to its original configuration. Lastly, in comparison with its respective epoxy adhesive, the internally heated electro-conductive carbon nanotube nanopaper/epoxy composite not only substantially shortened curing time while retaining comparable strength of the adhesive bonding of the steel surfaces, but also enabled a release of such bonds by repeated application of DC current.

Potential of Vetiver grass for the phytoremediation of a real multi-contaminated soil, assisted by electrokinetic.

Phytoremediation assisted by electrokinetic is a potential technology for remediation of contaminated soil, but little is known about its application on real contaminated soils. This study aims to evaluate the Vetiver grass application on the electro-phytoremediation of a real contaminated soil around a metal smelter factory. Different types of the electric field (AC-DC), voltage gradient (1-2V/cm), saturation and unsaturation condition, and Eh-pH variation were investigated for Vetiver electro-phytoremediation performance. Vetiver grass had been grown for 21 days. Then three different voltage gradients (1, 2DCV/cm and 2ACV/cm) were applied for 8h/d across the soil domain for the next 21 days in comparison with a control cell without electric field (PR). The results showed that despite the AC current application which induced small changes, the application of DC current significantly changed the Eh-pH values. The maximum accumulation of extractable metals in Vetiver grass occurred in 2DCV/cm that shows approximately 50% increase in comparison with the AC and PR cells. The presence of contaminants poisons the Vetiver in all cells and all plants under 2DCV/cm dried out at the end of the experiment. Despite the significant reduction of heavy metals, there was no noticeable phytoextraction due to the application of DC current. Therefore, DC current can be used for phytoremediation through phytostabilization. However, the overall metals uptake in plants shoots under AC treatment with BCF>1 was much higher than the PR and DC treatment. Considering the translocation rate and plants health, if the AC current is applied in a long treatment time, it could have better results in electro-phytoremediation of the Vetiver grass through phytoextraction process. However, the maximum removal of heavy metals was in the cathode part of the cell under 2DCV/cm that shows 65% improvement in comparison with the PR cell.

Anisotropic grain growth in iron-carbon films at high electric current densities

We investigate the effect of direct electric current (DC) on grain growth in 100 nm thick iron-carbon films with carbon concentrations between 0.7 to 4.4 at%. The application of DC-current during annealing at 550 °C confirms the expected transport of carbon in the direction of the electric current and the unexpected formation of elongated, abnormally large carbide and ferrite grains along the current direction in the carbon-rich regions. The formation of elongated grains is explained by electromigration-induced carbon flux divergences that result from the carbide precipitates. This presents a possible scenario for controlling microstructure evolution in iron by using DC electric currents. Changes for alternating current (AC) pulses had been observed before.

Anisotropic Grain Growth in Iron-Carbon Films at High Electric Current Densities

We investigate the effect of direct electric current (DC) on grain growth in 110 nm thick iron-carbon films with carbon concentrations at 2.7 at%. The application of DC-current during annealing at 550°C confirms the expected transport of carbon in the direction of the electric current and the unexpected formation of elongated, abnormally large carbide and ferrite grains along the current direction in the carbon-rich regions. The formation of elongated grains is explained by electromigration-induced carbon flux divergences that result from the carbide precipitates. This presents a possible scenario for controlling microstructure evolution in iron by using DC electric currents.

Effect of magnetic sheath on filament AC losses and current distribution in MgB2 superconducting wires: numerical analysis

Finite element method (FEM) analysis is employed to study and compare AC losses in a wide frequency range in two MgB2 superconducting wires in self-field and in the presence of external AC field. The modelled wires, of the same external dimensions, are mono- and 36-superconducting filaments embedded in either magnetic Monel or a nonmagnetic metallic wire sheath. We demonstrate that in a multifilamentary wire in self-field the Monel sheath serves as a ‘pole piece’ at the filament outer surface and alters local magnetic fields, current flow and AC losses distribution within the filament. In comparison with the nonmagnetic sheath with the same electrical conductivity, AC current in the wire with the magnetic sheath penetrates significantly deeper into the filaments and AC losses in the filament and in the magnetic sheath increase significantly. In contrast, the symmetry of the monofilament wire makes the current and loss distributions in the filament practically indifferent to the sheath composition. Still, losses in the magnetic sheath are much higher than in the nonmagnetic sheath due to increased flux dynamics. The application of DC current, on which the AC current is superimposed, sharply reduces the AC losses in the magnetic sheath material due to the drop in its permeability. Filament losses are also reduced in the presence of DC current, but to a much lesser extent. Results also show that in the kHz frequency range, the magnetic permeability of the sheath increases the skin effect in both the wire and filaments complex. As a result, at such frequencies, a significant portion of the current is carried by the metallic part of the wire instead of the superconductor, contributing to a further increase in losses. The analysis also shows that in the presence of external AC magnetic field, the Monel can provide magnetic shielding for inner filaments, thus reducing coupling effects between filaments. However, if magnetically saturated by the DC current, the Monel behaves quite similarly to a nonmagnetic sheath.

Contributions to yield strength in an ultrafine grained 1050 aluminum alloy after DC current annealing

The ultrafine grained (UFG) 1050 aluminum alloy was prepared by equal channel angular pressing at cryogenic temperature (cryoECAP). The evolution of the yield strength and microstructures of UFG 1050 aluminum alloy after direct electric current (DC current) annealing at 150–400°C for 1h were investigated by tensile test, electron back scattering diffraction pattern (EBSD) and transmission electron microscopy (TEM). For the cryoECAPed and annealed samples at 150–250°C, the predominant boundaries are high angle boundaries (HABs) (>60%), many dislocations accumulate at subgrain and/or grain boundaries, the yield strength (126–159MPa) mainly comes from the dislocation and grain boundary strengthening contributions. While an unusual increase in the yield strength (by 8.1–11.2%) observed in samples annealed at 150–200°C is attributed to an additional strengthening contribution from the more HABs having stable structures which can act as effective barriers to dislocation motion during tensile deformation. When annealing at 300–400°C, the microstructures are free of dislocations, the yield strength (29–45MPa) comes from the grain boundary strengthening contribution. With the application of DC current, the larger grain size, lower dislocation density and higher fraction of LABs having misorientation angle between 3−7° in samples annealed at 150–250°C result in the lower yield strength, while the smaller average grain sizes in samples annealed at 300–400°C cause the higher yield strength.

Bioimpedance spectroscopy method for investigating changes to intracranial dose during transcranial direct current stimulation.

Tissue resistance changes upon application of DC current. We posit that in a similar fashion, that scalp and skull resistances during trancranial direct current stimulation (tDCS) are variable, resulting in changes to intracranial dose. Transcranial magnetic stimulation (TMS), electoencephelogram (EEG), functional magnetic resonance imaging (fMRI), proton magnetic resonance spectroscopy ((1)H MRS) and functional near infrared spectroscopy (fNIRS) are technologies used to measure individual neural response to tDCS. These technologies are complex and may not be directly correlated to intracranial dose. We therefore present a bioimpedance spectroscopy method of measuring changes to the intracranial dose in vivo. Scalp resistance changes are measured during tDCS. Current flow through the scalp is calculated as the ratio of voltage measured on the scalp and scalp resistance. Variation of intracranial current is indirectly calculated from changes in the current shunted through the scalp. We thus demonstrate a novel methodology of on-line monitoring of scalp resistance and current as an objective feedback of estimated individual tDCS dose.

Pharmacological Modulation of the Short-Lasting Effects of Antagonistic Direct Current-Stimulation Over the Human Motor Cortex

Combined administration of transcranial direct current-stimulation (tDCS) with either pergolide (PER) or d-cycloserine (d-CYC) can prolong the excitability-diminishing effects of cathodal, or the excitability enhancing effect of anodal stimulation for up to 24 h poststimulation. However, it remains unclear whether the potentiation of the observed aftereffects is dominated just by the polarity and duration of the stimulation, or the dual application of combined stimulation and drug administration. The present study looks at whether the aftereffects of oral administration of PER (a D1/D2 agonist) or d-CYC (a partial NMDA receptor agonist), in conjunction with the short-duration antagonistic application of tDCS (either 5 min cathodal followed immediately by 5 min anodal or vice versa), that alone only induces short-lasting aftereffects, can modulate cortical excitability in healthy human subjects, as revealed by a single-pulse MEP (motor-evoked-potential) paradigm. Results indicate that the antagonistic application of tDCS induces short-term neuroplastic aftereffects that are dependent upon the order of the application of short-duration stimulation. The administration of d-CYC resulted in a marked inhibition of cortical excitability under the application of tDCS in both stimulation orders. Intake of PER resulted in an increase in cortical excitability in both stimulation orientations, but was non-significant compared to the placebo condition. These results indicate that the aftereffects of tDCS are dependent upon the order of stimulation applied, and also demonstrate the prolongation of tDCS aftereffects when combined with the administration of CNS active drugs.

GPU-accelerated indirect boundary element method for voxel model analyses with fast multipole method

An indirect boundary element method (BEM) that uses the fast multipole method (FMM) was accelerated using graphics processing units (GPUs) to reduce the time required to calculate a three-dimensional electrostatic field. The BEM is designed to handle cubic voxel models and is specialized to consider square voxel walls as boundary surface elements. The FMM handles the interactions among the surface charge elements and directly outputs surface integrals of the fields over each individual element. The CPU code was originally developed for field analysis in human voxel models derived from anatomical images. FMM processes are programmed using the NVIDIA Compute Unified Device Architecture (CUDA) with double-precision floating-point arithmetic on the basis of a shared pseudocode template. The electric field induced by DC-current application between two electrodes is calculated for two models with 499,629 (model 1) and 1,458,813 (model 2) surface elements. The calculation times were measured with a four-GPU configuration (two NVIDIA GTX295 cards) with four CPU cores (an Intel Core i7-975 processor). The times required by a linear system solver are 31 s and 186 s for models 1 and 2, respectively. The speed-up ratios of the FMM range from 5.9 to 8.2 for model 1 and from 5.0 to 5.6 for model 2. The calculation speed for element-interaction in this BEM analysis was comparable to that of particle-interaction using FMM on a GPU.

In vivo transungual iontophoresis: Effect of DC current application on ionic transport and on transonychial water loss

The potential use of iontophoresis to improve drug penetration into the nail has been suggested. However, there is little information concerning transungual iontophoresis in vivo. This work describes the application of transungual iontophoresis to six healthy human volunteers in order to investigate key issues such as the effect of current application on ionic transport and on transonychial water loss (TOWL), and the magnitude of the voltages required for a practical use of the technique. Each volunteer participated in three experiments: passive control, 0.2 mA anodal transungual iontophoresis and 0.2 mA cathodal transungual iontophoresis. A commercial electrode on a skin site was used to complete the electrical circuit. The outward transungual extraction of sodium and chloride ions by passive diffusion and iontophoresis was quantified. Iontophoresis enhanced chloride and sodium transport ~ 8 and 27 fold respectively compared to passive diffusion. Sodium transport numbers were measured to be t Na + = 0.51 ± 0.11. TOWL was used as a potential marker of nail damage and hydration. Basal TOWL was measured before each experiment, and the return to baseline values was monitored for 1 h after the treatment (passive or iontophoresis application) was finished. TOWL was increased after both iontophoretic and passive experiments and typically returned to baseline values in 1 h post-treatment. The voltage of the nail-to-skin circuit was monitored during iontophoresis and compared to those observed in a skin-to-skin circuit. Nail-to-skin circuit voltages were generally ~ 50 V when the current was started and dropped fast to 20–30 V, a value comparable to that observed in the skin-to-skin circuit. On the whole, the clear enhancement of ionic transport observed, the feedback from volunteers, the small effects in TOWL, and the magnitude of voltages indicate that nail DC current iontophoresis is feasible and probably a safe technique.

Electric block current induced detachment from surgical stainless steel and decreased viability of Staphylococcus epidermidis

In vitro studies investigating the influence of electric DC current on bacterial detachment have demonstrated that continuous currents of only 25–125 μA stimulated staphylococcal strains to detach from surgical stainless steel. However, DC currents produce more power that has to be dissipated by the skin as compared to alternating currents. Also, an excess of ions on the steel can cause negative osteogenesis and fixation results. Therefore, it is the aim of this paper to examine whether detachment of Staphylococcus epidermidis from stainless steel surfaces in a parallel plate flow chamber can also be stimulated using electric block currents. Block currents of 15, 60 and 100 μA with different frequencies (0.1–2 Hz) and duty cycles (5–50%) were applied to induce bacterial detachment. Block currents of 100 μA cause detachment of about 76% of adhering staphylococci from stainless steel, whereas in addition the remaining bacteria are less viable, as determined by culturing the remaining bacteria on agar plates. Therewith, block current-induced detachment of adhering bacteria from stainless steel appears to be an equally promising method to prevent infection of orthopaedic fixation pins and screws than application of DC currents.

Reducing Mass-Transport Limitations by Application of Special Pulsed Current Modes

Current pulsing, unlike potential pulsing, is generally considered ineffective in enhancing mass transport. However, we show here, that by properly selecting the pulsed current parameters, the depletion of the reactant at the electrode during cathodic reduction, or its excess during anodic dissolution, can be reduced compared to the corresponding dc current application, while still passing the same amount of charge in an identical amount of time. The advantageous pulsed current modes include a sequence of decreasing current density amplitudes, or pulsing the current at the same amplitude, but with increasing relaxation intervals. By comparison, it is also shown that applying a sequence of constant-amplitude square current pulses at constant time intervals leads to an identical concentration profile as in dc. The application to the battery-charging process is briefly discussed.

POINT-CONTACT SPECTROSCOPY OF MAGNESIUM DIBORIDE WITH DIFFERENT COUNTER-ELECTRODES

We report on tunneling and Andreev-reflection conductance spectra of 39 K superconducting magnesium diboride, obtained with Pb and Au counter-electrodes. Two distinct steps at close to 2.7 and 7.1 meV appear in a low-resistance metallic-type Au–MgB 2 junction characteristic, whereas a tunneling-like spectrum measured for the same junction, annealed by the application of DC current, exhibits only a rounded contribution of the larger gap. Junctions with a superconducting lead counter-electrode pressed into a bulk MgB 2 sample reveal two conductance peaks that are interpreted as the result of the formation of a highly-transmitting break junctions inside the magnesium diboride ceramic. Our results strongly support the two-band model with two different gap values on quasi-two-dimensional σ (7.1 meV) and three-dimensional π (2.7 meV) Fermi surface sheets of MgB 2.

Break excitation alone does not explain the delay and amplitude of anodal current-induced vasodilatation in human skin.

In iontophoresis experiments, a 'non-specific' current-induced vasodilatation interferes with the effects of the diffused drugs. This current-induced vasodilatation is assumed to rely on an axon reflex due to excitation of cutaneous nociceptors and is weaker and delayed at the anode as compared to the cathode. We analysed whether these anodal specificities could result from a break excitation of nociceptors. Break excitation is the generation of action potentials at the end of a square anodal DC current application, which are generally weaker than those observed at the onset of a same application at the cathode. In eight healthy volunteers, we studied forearm cutaneous laser Doppler flow (LDF) responses to: (1) anodal and cathodal 100 microA current applications of 1, 2, 3, 4 or 5 min; (2) 100 microA anodal applications of 3 min with a progressive ending over 100 s (total charge 23 mC); these were compared to square-ended 100 microA anodal applications of the same total charge (23 mC) or duration (3 min); (3) a 4 min 100 microA anodal application with a 333 msec break at half time. Results (mean +/- S.D.) are expressed as percentage of heat-induced maximal vasodilatation (%MVD). Onset (T(vd)) and amplitude (LDF(peak)) of vasodilatation were determined. We observed that: T(vd) was linearly related to the duration of current application at the anode (slope = 1.01, r(2) = 0.99, P < 0.0001) but not at the cathode (slope = 0.03, r(2) = 0.02, n.s.). Progressive ending of anodal current did not decrease LDF(peak) (63.3 +/- 24.6 %MVD) as compared to square-ending of current application of the same duration (36.9 +/- 22.2 %MVD) or the same total charge (57.1 +/- 23.5 %MVD). A transient break of anodal current did not allow for the vasodilatation to develop until current was permanently stopped. We conclude that, during iontophoresis, anodal break excitation alone cannot account for the delay and amplitude of the vascular response.

Tumor compression due application of DC current

The aim of this paper is to evaluate the forces that appear in the tumor region when the DC current flows in it. The knowledge of the electromagnetic force distribution inside the region of study is very important because the DC current therapy (ECT) produces the destruction of tumor cells. When the DC current is applied the reduction of tumor size occurs. Additionally, the DC current flowing in the tumor promotes the micro-thromboses (desirable effect). The micro-thromboses consist of the blockade of arterial vessels that feed the malignant cells leading to regression of the tumor. So, one component responsible for these effects is the electromagnetic force distribution in the tumor area. The determination of these force distributions involves three steps of numerical evaluations: a) J/spl I.oarr/ determination, b) B/spl I.oarr/ determination and c) knowing (in the domain of study) the vectors J/spl I.oarr/ and B/spl I.oarr/ the vector F/spl I.oarr/ should be determined. Indeed, the knowledge of force distributions in the area of interest will allow a better understanding of the phenomena that occur in the cancerous cells when ECT is applied in human beings.

Electrochromic characteristics of liquid-crystal materials

The time dependence of optical density during a coloration and bleaching sequence has been investigated in the isotropic phase for several liquid-crystalline materials doped with a small amount of tetra-n-alkyl-ammonium iodide. As a result, a rate equation fitting experimental results obtained for low current densities has been derived: dOD/dt=αJ−κ(OD+OD0), where OD is the change in optical density of colored cells after the application of dc current, J is the applied current density, α is a coefficient related to the coloration rate, κ is a coefficient governing the bleaching rate, and OD0 is a constant for a given cell. Furthermore, the dependence of these coefficients upon electrolyte concentration, cell thickness, and cell temperature has been studied. The value of α is almost independent of device parameters, while κ is dependent upon the latter two parameters.