Pulse Reverse Current Research Articles

Effect of electrodeposition conditions and reinforcement content on microstructure and tribological properties of nickel composite coatings

In this work, pure nickel and nickel composite coatings (Ni–Al 2O 3, Ni–SiC, and Ni–ZrO 2) were deposited from Watts bath using direct current (DC), pulsed current (PC), and pulsed reverse current (PRC) electrodeposition conditions. Detailed investigations on the effect of deposition conditions on the evolution of surface microstructure, crystallographic micro-texture, microhardness, and sliding wear behavior of pure nickel and nickel composite coatings are presented. For all the coatings, the PC and PRC deposition conditions resulted in more random/weak crystallographic texture compared to DC deposition. The composite coatings deposited using PC and PRC deposition also exhibited significant improvement in microhardness and wear resistance due to enhanced reinforcement of nanoparticles in the coatings. Also, the effect of nanoparticle content of the electrolyte bath on the surface microstructure, tribological properties, and level of reinforcement in the Ni–Al 2O 3 composite coating is investigated. The reinforcement of nanoparticles in the Ni–Al 2O 3 composite coatings increased linearly with the amount of nanoparticle loading in the electrolyte bath. The microhardness and wear resistance of the Ni–Al 2O 3 composite coatings also improved with increasing Al 2O 3 content in the coatings.

High Anticorrosion Nano Zn-Fe Coatings by Pulse Electrodepositing

Nano Zn-Fe coatings in a chloride electrolyte with additives by reverse pulse current were obtained and the anticorrosion was investigated. The morghology and crystal size of Zn-Fe alloy depositions were measured by scanning electron microscope and atom force microscope. Coatings with 30 nm or so crystal size was obtained with mean current density 9.0 A•dm-2, duty cycle 60%, frequency 500 Hz and time of negative to positive 30 ms ∶8 ms. It was detected by X-ray diffraction that the pulse plated coatings of Zn–Fe were mixtures of two phases, one of them being the α-phase and the other pure zinc or the α-phase with a significantly lower proportion of Fe. The pulse plated Zn-Fe coatings’ corrosion resistance was greatly improved compared with Zn-Fe coatings by direct current according to Tafel tests, saline immersion and salt spray tests. The anticorrosion of Zn-Fe coatings with 30 nm crystal size was 2~3 times than that of normal Zn-Fe alloy deposits.

Effects of Pulse-Reverse Current on Purity of Deposit in Electrowinning of Cobalt

In order to improve the purity on deposit in cobalt electrowining, a fundamental study using Pulse- Reverse Current (PRC) was carried out. Based on a sulfate solution, Cu, Ni, and Fe as impurities were added during cobalt electrowinning. There were four reverse waveforms and frequency conditions from 1 Hz to 10 kHz, and the purity of each condition was compared with the Direct Current (DC) purity. From the results, it was found that the anodic potential induced by reverse current affects selective dissolution of impurities. In this work, the case of the highest reverse peak current density (Ir) with a short reverse time (tr) at 100 Hz showed a higher purity than that of the DC. This PRC condition also showed only a 4% low current efficiency comparable to the DC. We concluded that an optimized PRC for cobalt electrowinning could improve the purity with little loss of current efficiency.

The effect of pulse reversal on morphology of cobalt hard gold

The impact of pulsed reverse current on cobalt hard gold electrodeposition from a cyanide bath is presented. The reversed current results in a significant change in the morphology of electrodeposits, improvement of the overall current efficiency, and reduction of deposit porosity. With longer pulses, hemispherical surface features are generated, while larger grains result from shorter pulse widths. The porosity of the plated samples is found to decrease compared with results at the same time-average plating rate obtained from dc or on–off pulse plating.

Improved performance of GaN-based light-emitting diodes by using short-period superlattice structures

AbstractAn InGaN/GaN multiple-quantum-well (MQW) light-emitting diode (LED) with a ten-period i (undoped) -InGaN/p (Mg doped) -GaN (2.5 nm/5.0 nm) superlattice (SL) structure, was fabricated. This SL structure that can be regarded as a confinement layer of holes to enhance the hole injection efficiency is inserted between MQW and p-GaN layers. The studied LED device exhibits better current spreading performance and an improved quality, compared with a conventional one without SL structure. Due to the reduced contact resistance as well as more uniformity of carriers injection, the operation voltage at 20 mA is decreased from 3.32 to 3.14 V. A remarkably reduced reverse-biased leakage current (10−7–10−9 A) and higher endurance of the reverse current pulse are found. The measured output power and external quantum efficiency (EQE) of the studied LED are 13.6 mW and 24.8%, respectively. In addition, significant enhancement of 25.4% in output power as well as increment of 5% in EQE for the studied devices is observed, as the studied devices show superior current spreading ability and reduction in dislocations offered by the SL structure.

Hardness and Wear Resistance of Ni/Al2O3 Composite Coatings by Electrodeposition

Ni/Al2O3 composite coatings were prepared by direct current (DC), single pulse current (PC) and pulse reversal current (PRC), respectively. The hardness and wear resistance of the coatings were investigated and the morphology and elements distribution in cross-section were analyzed by the application of SEM/EDS, XRF and XRD equipped with stress measuring device. The results show that the hardness of the three kinds of coatings increase with increasing Al2O3 content. The coating prepared by PRC plating exhibits higher hardness and better wear resistance, while that of DC plating has lower hardness and poorer wear resistance. The higher hardness and better wear resistance of coating of PRC plating can be ascribed to fine microstructure and weaker stress between substrate and coatings.

An Experimental Study of Bipolar Pulse Electroforming Nickel

An experimental study of bipolar pulse electroforming nickel is presented in this paper. Based on the principles of electric double layer and double diffusing layer, the advantages of pulse electroforming over direct current electroforming, bipolar pulse electroforming over single pulse and pulse-reverse current were explained in the view of microcosmic. The influence of major technological parameters on the process of electroforming was investigated. The experimental results indicate that the the quality and precision of the electroformed coating, as well as the mechanical properties of electroformed parts, can be improved, with the bipolar pulse power.

Effects of anodic spark oxidation by pulse power on titanium substrates

AbstractThe characteristics of the oxide layer of titanium generated by anodic spark oxidation are affected significantly by the process variables. In this study, electrochemical treatments were performed while applying a direct current, a pulse current, and a reverse pulse current during anodic spark oxidation. A mixed solution of 0.015 M DL‐α‐GP (DL‐α‐glycerophosphate disodium salt) and 0.2 M CA (calcium acetate) was used as the electrolyte. The pore size generated after anodic spark oxidation was smallest in the group exposed to the reverse pulse current followed in order by the pulse current and direct current. Anatase was the major crystal phase of the TiO2 produced on the surfaces subjected to 280 V, and the rutile phase was additionally detected in the group subjected to 320 V. The crystals precipitated on the surface after the hydrothermal treatment were hydroxyapatite (HA) crystals that had a polygonal bar‐shaped needle structure. Good activity was observed in the 320‐V pulse treated group, in which very thin needle‐shaped crystals were observed after immersing the samples in Hanks' solution for 4 weeks. The cell viability was increased greatly by anodic spark oxidation, and the surface roughness was also increased. It is believed that the surface treated using a pulse current has excellent characteristics, making it suitable for applications in biomaterials. Copyright © 2010 John Wiley & Sons, Ltd.

Fast Switch-Off of High Voltage 4H–SiC npn BJTs from Deep Saturation Mode

In this paper, very fast switch-off of high voltage 4H–SiC npn Bipolar Junction Transistors (BJTs) driven in deep saturation regime is reported. It is shown that the switch-off time can be as short as 4 ns if a reverse base current pulse is applied that provides forced minority carrier sweep out from the base.

Characteristics of a GaN-Based Light-Emitting Diode With an Inserted p-GaN/i-InGaN Superlattice Structure

An interesting GaN-based light-emitting diode (LED) with a ten-period i (undoped)-InGaN/p (Mg doped)-GaN (2.5 nm/5 nm) superlattice (SL) structure, inserted between a multiple-quantum well (MQW) structure and a p-GaN layer, is fabricated and studied. This inserted SL can be regarded as a confinement layer of holes to enhance the hole injection efficiency. As compared with a conventional LED device without the SL structure, the studied LED exhibits better current spreading performance and an improved quality. The turn-on voltage, at 20 mA, is decreased from 3.32 to 3.14 V due to the reduced contact resistance as well as the more uniformity of carriers injection. A substantially reduced leakage current (10- 7 to 10- 9 A) and higher endurance of the reverse current pulse are found. The measured output power and external quantum efficiency (EQE) of the studied LED are 13.6 mW and 24.8%. In addition, as compared with the conventional LED without the SL structure, the significant enhancement of 25.4% in output power as well as the increment of 5% in EQE are observed due to the superior current spreading ability and reduction of dislocations offered by the SL structure.

Serpentine flux path for high torque MRF brakes in haptics applications

This research aimed to address two main goals in the development of a rotary magnetorheological fluid (MRF) brake: (1) design of a compact and powerful brake and (2) low friction sealing technique to reduce the off-state braking torque and prevent the fluid from leaking. Using magnetically conductive and non-conductive rings a serpentine flux path was developed to weave the magnetic flux through the MRF. Experimental results showed that, when compared to a commercial MRF brake, our 33% smaller prototype MRF brake could generate 2.7 times more torque (10.9 Nm). A ferro-fluidic sealing technique was developed that resulted in sealing in the fluid and decreased the off-state friction. Further reduction in the off-state torque was obtained by applying a reverse current pulse to collapse a residual magnetic field in the brake. A 1-DOF haptic interface employing the brake enabled crisp virtual wall collision and Coulomb friction simulations.

Fast turn-off of high voltage 4H–SiC npn BJTs from the saturation on-state regime

Fast turn-off of high-voltage (breakdown voltage ⩾ 3 kV) 4H–SiC npn bipolar junction transistors driven in a deeply saturated regime has been reported. In the conventional turn-off mode (base current break), the turn-off delay and current fall times are 80 ns and 100 ns, respectively. It is shown that these times can be made as short as 20 and 4 ns, respectively, if a reverse base current pulse of appropriate amplitude is applied to sweep out minority carriers from the base. The experimental values of delay and turn-off times well coincide with those calculated in terms of the charge control model.

Effect of electrodeposition parameters on the hydrogen permeation during Cu–Sn alloy electrodeposition

The Cu–Sn alloy coatings were synthesized on 27SiMn steel by direct current (DC), pulse current (PC) and pulse reverse current (PRC) electrodeposition techniques from pyrophosphate-based electrolyte. The hydrogen permeation behaviors during the electrodeposition by different techniques were investigated using Devanathan– Stachurski method. The results demonstrated that the hydrogen permeation amount of different electrodeposition techniques decreased in the order: DC > PC > PRC. Frequency and duty cycle have great effect on the sub-surface concentration C o of atomic hydrogen and hydrogen permeation amount. The minimum of hydrogen permeation amount was observed at the frequency of 1000 Hz or 2500 Hz and the duty cycle of 40%. It indicates that the amount of permeated hydrogen in the steel during deposition can be reduced due to the decrease of C o by PC and PRC methods.

On a GaN-Based Light-Emitting Diode With a p-GaN/i-InGaN Superlattice Structure

An interesting GaN-based light-emitting diode (LED) with a ten-period i-InGaN/p-GaN (5-nm/5-nm) superlattice (SL) structure, inserted between a multiple-quantum-well structure and a p-GaN layer, is fabricated and studied. This inserted SL can be regarded as a confinement layer of holes to enhance the hole injection efficiency. As compared with a conventional LED device without the SL structure, the studied LED exhibits better current-spreading performance and an improved quality. The turn-on voltage, at 20 mA, is decreased from 3.32 to 3.14 V due to the reduced contact resistance as well as the more uniformity of carrier injection. A substantially reduced leakage current (10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> A) and higher endurance of the reverse current pulse are found. As compared with the conventional LED without the SL structure, the significant enhancement of 25.4% in output power and the increment of 5% in external quantum efficiency are observed.

The influence of ultrasonic agitation on copper electroplating of blind-vias for SOI three-dimensional integration

Three-dimensional (3D) integration, which employs through-silicon-vias (TSVs) to electrically interconnect multiple-stacked chips, is a promising technology for significant reduction in interconnect delay and for hetero-integration of different technologies. To fabricate void-free TSVs, this paper presents a copper electroplating technique with the assistance of ultrasonic agitation to fill blind-vias, and discusses the influence of ultrasonic agitation on copper electroplating. Blind-vias with an aspect ratio of 3:1 are used for copper electroplating with both direct current (DC) and pulse-reverse current modes, combined with either ultrasonic agitation or mechanical agitation. Experimental results show that blind-vias with small aspect ratio can be completely filled using pulse-reverse current, regardless of the agitation methods. For DC, ultrasonic agitation is superior to mechanical agitation for copper electroplating in filling void-free vias. These results indicate that agitation, though is a secondary control factor to pulse-reverse current, can enhance mass transfer in blind-vias during copper electroplating and can improve the filling capability of copper electroplating.

Reverse Current Pulse Method To Restore Uniform Concentration Profiles in Ion-Selective Membranes. 2. Comparison of the Efficiency of the Different Protocols

The membrane potential of ion-selective electrodes is measured at zero current in traditional potentiometric analysis. Recently, pulsed potentiometric methods have gained importance. In pulsed potentiometric methods, the voltage measured at the end of a current pulse is usually the analytical signal. The applied current alters the concentration profiles inside the sensing membrane. For reproducible voltage measurements the original concentration profiles must be restored in the membrane between current pulses. The simplest restoration method is the zero-current relaxation. Unfortunately, the zero-current method is very slow, which limits the frequency of measurements. In analytical practice the controlled voltage restoration method is most commonly used, but the controlled voltage method has no adequate theoretical description. This paper presents a finite element model of the controlled voltage method to predict its efficiency. The model demonstrates for the first time that increasing membrane resistance decreases the efficiency of this restoration method. The model allows estimating the necessary restoration time for voltage errors below an acceptable threshold value and provides guidance for minimizing the voltage error. The efficiency of the controlled voltage method is compared to the reverse current pulse restoration method discussed in part 1 of this set of papers. It is found that the reverse current restoration method is simpler, requires shorter restoration times (i.e., it allows higher measurement frequency), and it has 4 and 10 times smaller voltage errors compared to the controlled voltage method. These theoretical results are confirmed experimentally. The only limitation of the reverse current pulse restoration method is that it cannot be used with membranes containing a background electrolyte (R(+)R(-)) but no excess lipophilic cation exchanger (R(-)). However, lipophilic cation exchanger can often be added to the membrane to reduce restoration times by allowing the reverse current pulse method to be used.

Reverse Current Pulse Method To Restore Uniform Concentration Profiles in Ion-Selective Membranes. 1. Galvanostatic Pulse Methods with Decreased Cycle Time

The applications of ion-selective electrodes (ISEs) have been broadened through the introduction of galvanostatic current pulse methods in potentiometric analysis. An important requirement in these applications is the restoration of the uniform equilibrium concentration profiles in the ISE membrane between each measurement. The simplest restoration method is zero-current relaxation, in which the membrane relaxes under open-circuit conditions in a diffusion-controlled process. This paper presents a novel restoration method using a reverse current pulse. An analytic model for this restoration method is derived to predict the concentration profiles inside ISE membranes following galvanostatic current pulses. This model allows the calculation of the voltage transients as the membrane voltage relaxes back toward its zero-current equilibrium value. The predicted concentration profiles and voltage transients are confirmed using spectroelectrochemical microscopy (SpECM). The reverse current restoration method described in this paper reduces the voltage drift and voltage error by 10-100 times compared to the zero-current restoration method. Therefore, this new method provides faster and more reproducible voltage measurements in most chronopotentiometric ISE applications, such as improving the detection limit and determining concentrations and diffusion coefficients of membrane species. One limitation of the reverse current restoration method is that it cannot be used in a few applications that require background electrolyte loaded membranes without excess of lipophilic cation exchanger.

Effects of different plating modes on microstructure and corrosion resistance of Zn–Ni alloy coatings

The aim of the work is to study the effects of different plating modes on the microstructure and corrosion resistance of Zn–Ni alloy coatings. Zn–Ni alloy coatings were deposited by direct current (DC), pulse current (PC) and pulse reverse current (PRC) methods, respectively. The surface morphology and the grain size were investigated by SEM and XRD. The corrosion resistance of the alloy coatings was evaluated in 3.5% NaCl solution by electrochemical impedance spectroscopy (EIS) technique and polarizing curves method. The results showed that the crystal grains of the alloy coatings prepared by DC, PC and PRC, respectively, became smaller and smaller in order, and the coating surface became compacter and smoother correspondingly. The alloy coatings were composed of a large number of γ-Zn–Ni alloy and a small quantity of η-Zn–Ni. The relative intensities corresponding to crystal face γ (4 1 1, 3 3 0) and η (1 1 2) of alloy coatings deposited by DC, PC and PRC, respectively, were decreased gradually, while the half width of peaks were increased, which illustrated that the crystal grains of the alloy coatings were fine. This was consistent with the surface morphology of the alloy coatings. The results of EIS and polarizing curve tests showed that the corrosion resistance of Zn–Ni alloy coatings deposited by PRC method was the best, and then by PC and DC in sequence. The corrosion resistance of the alloy coatings depended on the alloy structure and composition, the best corrosion resistance of the Zn–Ni alloy coatings deposited by PRC was attributed to its fining of the crystal grains and the dense structure.

A capacitor cell of a capacitive energy storage with a switch based on reverse switch-on dynistors

A capacitor cell of a capacitive energy storage designed for operating with an arc load is described. The cell that stores an energy of 64 kJ is based on a high-voltage (18 kV) capacitor and allows formation of current pulses with an amplitude of up to 60 kA. The discharge circuit of the cell contains a semiconductor switch in the form of an assembly of reverse switch-on dynistors (RSDs) connected in series, a crowbar diode switch, and a replaceable toroidal inductor. An assembly of protecting diodes connected in series to the RSD switch excludes the possibility of a flow of reverse-current pulses through dynistors. All elements of the cell are mounted on the capacitor and occupy a volume of 120 dm3.

Preparation and characterization of La-Co alloy nanowire arrays by electrodeposition in AAO template under nonaqueous system

La-Co alloy nanowires can be made in pulse reversal current(PRC) and direct current(DC) electrodepositions under nonaqueous system, with the porous anodic aluminum oxide(AAO) as template. This membrane is subject to the dual-oxidation (two-step) anodizing. Scanning electron microscope(SEM) examination shows that all of the nanowires have uniform diameter about 200 nm, and their diameters are determined by the pore diameter of applied AAO template. X-ray energy dispersion analysis indicates that the chemical composition of La and Co elements is very close to 1:2 in stoichiometry. X-ray diffraction pattern investigation demonstrates that La-Co nanowire is the face-centered cubic(FCC) LaCo 13.