Pulse Current Density Research Articles

Pulse-constructed energy–saving PbO2 electrode for copper electrowinning

Energy-saving PbO2 exhibit significant application potential in the non-ferrous metal electrowinning industry. By optimizing the deposition time, heteropolar spacing, nitric acid concentration, pulse current density and pulse frequency, the optimum conditions for deposition of PbO2 electrode were obtained. Meanwhile, the effects of electrodeposition parameters on the electrochemical performance, phase structure and morphology of β-PbO2 were systematically evaluated. The mechanism of action of pulse and direct current deposition was proposed. The simulated copper electrowinning experiment shows that an improved current efficiency (91.6%) was achieved and the low energy consumption (1855.1 kW⋅h/t) for copper production per ton was significantly reduced. Compared with the electrode prepared by direct current deposition, the current efficiency of copper is increased by 4.3% and the energy consumption is reduced by 198.6 kWh/t. Additionally, the PbO2 electrode produced by the optimized pulse deposition process exhibits excellent stability, which service-time is increased by approximately 99.4%. This research offers insights for developing energy-efficient and long-lived electrode materials.

Electrodeposition of Silicon in the Low-Temperature LiCl-KCl-CsCl-K2SiF6 Melt Under Direct and Pulse Current

In this work, the effect of electrolysis modes and their parameters on the morphology of the silicon deposits on glassy carbon were studied. In direct current mode it was found that an increase in current density and deposition time changes the morphology of the silicon from a coating to a deposit with a complex surface. Scanning electron microscopy showed that silicon films produced at low current densities and a short deposition time are represented by spherical particles with a diameter of less than 1 μm. The pulse current mode made it possible to increase the cathode density of the deposition current, and the pulse current density to an average of ≈250 mA cm−2 does not lead to the formation of a large amount of dendritic deposit. It was found that a low frequency makes it possible to obtain higher-quality silicon coatings, because when the frequency increases, the coating most often does not cover the entire electrode. The high value of the duty cycle, even at low pulse current densities, always leads to the formation of dendrites. An increase in the total deposition time also leads to an increase in the amount of deposit and the formation of dendrites.

Low-Temperature Annealing of Nanoscale Defects in Polycrystalline Graphite

Polycrystalline graphite contains multi-scale defects, which are difficult to anneal thermally because of the extremely high temperatures involved in the manufacturing process. In this study, we demonstrate annealing of nuclear graphite NBG-18 at temperatures below 28 °C, exploiting the electron wind force, a non-thermal stimulus. High current density pulses were passed through the specimens with a very low-duty cycle so that the electron momentum could mobilize the defects without heating the specimen. The effectiveness of this technique is presented with a significant decrease in electrical resistivity, defect counts from X-ray computed tomography, Raman spectroscopy, and nanoindentation-based mechanical characterization. Such multi-modal evidence highlights the feasibility of nanoscale defect control at temperatures about two orders of magnitude below the graphitization temperature.

Synergistic Thermal and Electron Wind Force-Assisted Annealing for Extremely High-Density Defect Mitigation.

This study investigates the effectiveness of combined thermal and athermal stimuli in mitigating the extremely high-density nature of dislocation networks in the form of low-angle grain boundaries in FeCrAl alloy. Electron wind force, generated from very low duty cycle and high current density pulses, was used as the athermal stimulus. The electron wind force stimulus alone was unable to remove the residual stress (80% low-angle grain boundaries) due to cold rolling to 25% thickness reduction. When the duty cycle was increased to allow average temperature of 100 °C, the specimen could be effectively annealed in 1 min at a current density of 3300 A/mm2. In comparison, conventional thermal annealing requires at least 750 °C and 1.5 h. For specimens with 50% thickness reduction (85% low-angle grain boundaries), the electron wind force was again unable to anneal the defects even at 3300 A/mm2 current density and average temperature of 100 °C. Intriguingly, allowing average concurrent temperature of 200 °C eliminated almost all the low-angle grain boundaries at a current density of 700 A/mm2, even lower than that required for the 25% thickness reduced specimens. Comprehensive electron and X-ray diffraction evidence show that alloys with extremely high defect density can be effectively annealed in less than a minute at approximately 200 °C, offering a substantial improvement over conventional high-temperature annealing.

Investigation of the Bonding Mechanism of Al Powder Particles through Pulse Current Sintering Technology

Compared with traditional powder metallurgy, pulse current sintering is an advanced powder-forming technology, but its bonding mechanism is still an open topic for debate. In this paper, pulse current sintering is used as the connection technology and millimeter-sized Al particles are used as the research object. In the whole sintering process, no pressure was loaded; the function of the pulse current was the only source of heat with which to achieve the bonding of Al particles. The bonding mechanism of pulse current sintering was investigated from the perspective of material connection behavior. The results show that the pulse current density of the particle surface reaches 3.48 × 105 A/m2 instantly, while the current density of the particle center is only 8187 A/m2 at the initial stage, which is the main difference between pulse current sintering and traditional powder metallurgy sintering. With the densification process, the current density and temperature distribution in the contact region as well as the center of Al particles contact region tend to be more consistent. Finally, dense interfacial bonding was obtained, and the contact region of Al particles also demonstrated a high hardness value of 0.6385 GPa and yield strength value of 212.83 MPa. The whole process can be considered as a comprehensive action of melting (evaporation), diffusion, and plastic deformation. Based on the above results, a new technology, named high-frequency pulse current sintering, was proposed.

Effect of pulse current density on creep ageing behavior of 2195 Al-Li alloy

Electrical pulse-assisted creep ageing forming can effectively improve the mechanical properties and forming efficiency of large aluminum components. However, it is difficult to achieve uniform and consistent current density at different positions in complex components. Thus, the creep behavior, mechanical properties, and microstructure evolution of 2195 Al-Li alloy under three pulse current densities (0A/mm2, 3A/mm2 and 8A/mm2) was systematically studied. The experimental results showed that the creep deformation increases with increasing current density during the 1st hour stage of electric pulse-assisted creep ageing process. However, the total creep strain of 8 h shows a trend of decreasing and then increasing. Low density pulsed currents (non-thermal effect) can promote the precipitation of the T1 phases and θ′ phases, and narrow the precipitates free zone compared to conventional creep aged sample (0A/mm2). High density (Both of non-thermal effect and Joule heating effect) pulsed currents can promote the precipitation of T1 phases, inhibit θ′ phases and form the precipitated phase penetrate the grain boundaries. A gratifying finding is that an increase in current density accelerates the aging hardening process, but the peak strength after creep ageing is the same for different current densities. This indicates that high pulse current density can improve creep ageing forming efficiency and ageing hardening process, and can use non-uniform current densities to solve the problem of significant differences in overall structural component formability while maintaining final performance consistency.

Study of the microstructure evolution of alloy structural steel and inhomogeneity effect of the microscale pulsed currents during current-assisted plane strain compressions by modeling a novel cellular automata method

The current-assisted forming process is considered to be a novel process that utilizes the electroplasticity effect to reduce the deformation resistance of difficult-to-deform metals and to refine the grain size while improving the mechanical properties of the part. However, the lack of understanding of the mechanisms by which pulsed current affects grain refinement still makes it difficult to experimentally develop analytical or empirical models of the relationship between grain size, pulse current parameters, and deformation amount. It will seriously hinder the further development and application of the current-assisted forming process. To reveal the mechanism of grain refinement coupling with electroplasticity, a series of Electron Back Scattering Diffraction observation tests were carried out after current-assisted plane strain compressions. The results show that the grain orientation spread value of the pulse current condition is lower than that of the non-current condition, while the refined grain area percentage is higher than that of the non-current condition. Based on the microstructure observation results, a cellular automata model for grain refinement is proposed. This consists of a dislocation density evolution, sub-grains generation, grain fragmentation, and a grain orientation rotation algorithm. To study the electroplasticity of the grain refinement process, the cellular automata model is also embedded with a finite difference numerical algorithm for solving the microscopic current density distribution of the model. The cellular automata model simulation results show that the error of grain size accuracy of this cellular automata model under non-current and pulse current conditions is 10.48% and 8.55%, respectively. It shows that the model can accurately characterize the grain refinement behavior of the current-assisted plane strain compression. The simulation results reveal the deep mechanism of pulsed current promotion on grain refinement, i.e., an inhomogeneous microstructure leads to uneven distribution of pulse current density. The inhomogeneous current distribution will further increase the grain refinement rate in the coarse-grained regions, thus increasing the proportion of the refined grain regions in the microstructure and leading to a relatively more homogeneous microstructure under pulse current conditions. The cellular automata model accurately reveals the mechanism of electroplasticity on the grain refinement. The model will serve as a crucial theoretical reference in designing current-assisted forming process routes to ensure excellent microstructure and properties in manufactured parts. It will enhance the widespread utilization of current-assisted forming process.

Plating Al coating on high-strength steel in chloroaluminate ionic liquid under pulse current modes

Aluminum coating is a potential candidate for cadmium coating replacement due to its excellent corrosion resistance and nontoxicity. Among the fabrication methods of Al coating, plating Al via ionic liquids has drawn major attention of researchers because of the superiority of controllability, stability and low energy consumption. However, the evolution rules of plating aluminum on high-strength steel via pulse current modes at room temperature requires deeper investigation. In this work, pulse current density and pulse duty factor are regulated to reveal the plating patterns of Al on 300M high-strength steel in AlCl3-EMIC (2:1 in mole) ionic liquid. It is found that higher current density can significantly facilitate the nucleation of Al grains and the compactness of morphology, while an enlarged pulse duty factor tends to result in more regular Al crystals. When the current density and the pulse duty factor are fixed at 20 mA cm−2 and 80 %, the densest and most uniform aluminum coating is obtained. The component of Al coating is verified to be pure Al crystals with good adhesion and the plating process achieves a high current efficiency of 97.27 %. Under the protection of Al coating, the impedance and galvanic corrosion current density of 300M steel substrate are optimized by two orders of magnitude, and the corrosion current density is markedly decreased from 5.58 μA cm−2 to 0.77 μA cm−2.

Improving soft X-ray imaging contrast uniformity of 50nm Au zone plate by optimizing pulse plating

The Fresnel zone plate plays a pivotal role in X-ray imaging systems, directly influencing the uniformity of imaging contrast. Achieving uniform imaging contrast imposes stringent requirements on the linewidth and height uniformity of the zone plate. The current mainstream method for zone plate fabrication involves utilizing electron beam lithography in conjunction with electroplating. However, in structures with large aspect ratios, precise deposition of gold to the bottom of the trench through electroplating becomes increasingly challenging to control. In this study, we employed a pulse plating process to enhance the uniformity of the plating height. Detailed investigations were conducted to analyze the effects of pulse current density, pulse duty cycle, and pulse frequency on plating height. Utilizing pulse plating, we successfully fabricated a zone plate with an outermost width of 50 nm and a thickness of approximately 245 nm. Structural analysis showed that the plating height uniformity is improved to better than 5%. The high uniformity imaging pattern was obtained by using the Siemens star test pattern at the soft x-ray imaging station at NSRL. The spatial resolution was down to 50 nm.

Synthesis of nanocrystalline nickel via pulsed current electrodeposition in additive-free deposition bath and comparison of nanoscale characterization

An experimental investigation on synthesis of nanocrystalline nickels by pulsed current electrodeposition has been carried out in an additive-free Watts bath employing nickel-sulphate solution with similar nickel ion concentrations. Aluminum was used as a substrate. It demonstrated the advantage of easier removal process of electrodeposited nanocrystalline nickel from its substrate. Whereas the use of high-purity nickel anode was intended to replace nickel ions, which decreased during electrodeposition. Different peak current densities of 450, 750 and 1000 mA/cm2 were applied. A pulsed current was set at a similar pulse pattern of on-time and off-time of 1 ms and 9 ms respectively. The shorter on-time demonstrated the ability to limit ion deposition, which was related to the formation of finer grains. The off-time arrangement was targeted to ensure that the ion mobility had completely stopped. Higher current density demonstrated a dominant impact on deposits, generating a higher nucleation rate that is related to depositing nanocrystalline nickel. A peak current density of 1000 mA/cm2 produced grain sizes in the nanoscale regime. Without any additional additive, nanocrystalline nickel was successfully yielded. Investigation of grain size obtained from the 1000 mA/cm2 has been conducted by extracting full width at half maximum peak intensity (FWHM) revealed from X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) exhibited consistent results of 22 nm and 25.4±3.4 nm, respectively. It is also evidence of the significant role of pulsed current density. In inclusion, nanocrystalline nickel can be synthesized in an electrodeposition bath without any addition of additives

Thermoelectric properties of Bi2Te3 films with low-angle grain boundaries formed through high pulse current density

Current applications of thermoelectric (TE) materials are limited by their low conversion efficiency. Interfacial engineering is a common way to improve TE properties. This study employed a pulsed electric field to tune the grain interfacial structure of Bi2Te3 films and thereby improve their power factor. The high-angle grain boundaries of the as-deposited films were transformed into low-angle grain boundaries (LAGBs) by the electrostatic force of a high pulse current density. The low interfacial energy of LAGBs maintains high carrier mobility while their reduced defects result in a low carrier concentration. These effects improve the Seebeck coefficient and conductivity simultaneously, with the power factor reaching 5394.77 μW·m−1·K−2 at 513 K. In addition, the compression stress generated by LAGBs enhances phonon scattering, creating a film with the highest power density yet reported (1.31 W·m−2). This provides a method for using PEF to improve the performance of TE materials.

Effect of reverse pulse current density on microstructure and properties of supercritical Ni-GQDs nanocomposite coatings

In this study, Ni-GQDs nanocomposite coatings were prepared by double-pulse electrodeposition under supercritical CO2 with graphene quantum dots (GQDs) as the second phase additive. The effects of supercritical CO2 conditions and reverse pulse current density on microstructure, crystal orientation, grain size, GQDs quality, mechanical properties, and corrosion resistance of Ni-GQDs nanocomposite coatings were investigated. The results show that when the reverse pulse current density is 0.8 A /dm2, the surface of Ni-GQDs-Ⅱ nanocomposite coating is compact and flat, GQDs is uniformly dispersed in the coating, and GQDs is closely bound to Ni grains. Compared with the coating prepared at normal temperature and pressure. The grain size of the Ni-GQDs-Ⅱ nanocomposite coating is 4.58 nm, and the grain size is reduced by 75.3 %. The quality of GQDs in the coating was improved. The coating hardness is 867.22 HV, which is significantly increased by 53.7 %. The roughness is 0.236 μm, which is significantly reduced by 37.2 %. The friction coefficient and volume wear were 0.262 and 3.395 × 107 μm3, respectively, which were significantly reduced by 27.4 % and 57.9 %. After electrochemical corrosion, the self-corrosion voltage of the coating was −139 mV, and the self-corrosion current density was 3.19 × 10−7 A/cm2. The self-corrosion voltage was significantly increased by 61.2 %, and the self-corrosion current density was significantly decreased by 71.2 %. The Rct value and Ndl value of the coating are 31594.53 Ω·cm2 and 0.862, respectively. Significantly increased by 226.2 % and 67.1 %, respectively. The coating has excellent mechanical properties and corrosion resistance.

Study on pulse current auxiliary heating process of submerged arc welding

During the welding process, temperature filed distribution of weldment is one of the key factors which influence welding quality. In order to improve the mechanical properties of welding joint, a technology for heating process of weldment using auxiliary pulse current was proposed in this article. Firstly, through metallographic experiment, strength experiment and hardness experiment, it was proved that the auxiliary pulse current not only can refine grain size but also improves the mechanical property of the welding joint. Then the paper used ANSYS and its ANSYS Parametric Design Language parametric design language to simulate the welding process with assistant pulse current, and the temperature field, the pulse current density distribution and the time of effective pulse current in the welded joint were obtained. Quantitative analyses were undertaken on the influence laws of auxiliary pulse current parameters on weld temperature field, auxiliary pulse current density distribution and the time of effective pulse current. A new parameter was defined as time-current density (the time integral of current density) to demonstrate the change rule of auxiliary pulse current density distribution with time. Finally, analyzing the reasons for raising the welding quality. There were two reasons for such phenomenon: one was auxiliary pulse current change the state of heat distribution in the weld seam area, the other was that the impulse oscillation of the auxiliary pulse influences the nucleation process of melting region.

Effect of High Current Density Pulses on Performance Enhancement of Optoelectronic Devices

Thermal annealing is commonly used in fabrication processing and/or performance enhancement of electronic and opto-electronic devices. In this study, we investigate an alternative approach, where high current density pulses are used instead of high temperature. The basic premise is that the electron wind force, resulting from the momentum loss of high-energy electrons at defect sites, is capable of mobilizing internal defects. The proposed technique is demonstrated on commercially available optoelectronic devices with two different initial conditions. The first study involved a thermally degraded edge-emitting laser diode. About 90% of the resulting increase in forward current was mitigated by the proposed annealing technique where very low duty cycle was used to suppress any temperature rise. The second study was more challenging, where a pristine vertical-cavity surface-emitting laser (VCSEL) was subjected to similar processing to see if the technique can enhance performance. Encouragingly, this treatment yielded a notable improvement of over 20% in the forward current. These findings underscore the potential of electropulsing as an efficient in-operando technique for damage recovery and performance enhancement in optoelectronic devices.

Study on wear resistance and toughness of calcium ion crosslinked cellulose nanofibers/multi-walled carbon nanotubes/hexagonal boron nitride hybrid reinforced Ni[sbnd]B composite coatings on N80 steel

This study developed a novel NiB/Ca-CNFs/MWCNTs/h-BN coating on N80 steel. The disadvantages of hexagonal boron nitride (h-BN) were improved by creatively combining multi-walled carbon nanotubes (MWCNTs), cellulose nanofibers (CNFs), and calcium ion cross-linking strategies. This led to the creation of Ca-CNFs/MWCNTs/h-BN hybrids, which were then doped into NiB coatings by varying pulse current densities. The results demonstrated that the surface morphology, mechanical properties, and toughness of the composite coating are all influenced by the Ca-CNFs/MWCNTs/h-BN doped at various current densities. Meanwhile, the NiB/Ca-CNFs/MWCNTs/h-BN (4 A/dm2) coating has the greatest microhardness (902.42 Hv) and the smallest friction coefficient (0.487) under reciprocating dry sliding friction conditions of Si3N4 friction balls. In addition, the results of nanoindentation and tensile tests show that the elastic modulus of NiB/Ca-CNFs/MWCNTs/h-BN (4 A/dm2) composite coating is 194.096 MPa and the tensile elongation is 12.2 %.

Zn–Cr pulse coatings for corrosion protection

ABSTRACT The influence of the Zn–Cr electrodeposition bath composition, cathode current density under direct current conditions, and the average pulse current density and the current density under pulse plating current conditions on the content of chromium in the obtained Zn–Cr coatings, the current efficiency and their corrosion properties were investigated. The obtained Zn–Cr coatings contained from about 0.01 wt-% to about 10 wt-%. The corrosion resistance largely depended on the chromium content of the coating, but also on the morphology and surface development. The best corrosion resistance was achieved for Zn–Cr alloy coatings obtained under impulse current conditions for average current densities 3 and 4 A dm−2, while cathodic peak current densities were 30 and 40 A dm−2.

New concept of two-cascade energy compression systems based on drift step recovery diodes

A new concept of effective high-voltage nanosecond pulse generators based on two compression cascades of drift step recovery diodes (DSRDs) is presented. The main advantage of the proposed approach arises from the decoupling of the operation cycles of DSRD cascades while using a single primary switch. This greatly improves the overall efficiency of the system. The first DSRD cascade operates with low pulse current densities. Its operation cycles can be extended resulting in an increase of the compression factor and pulse energy, whereas the loss level is kept at a minimum. The second DSRD cascade operates with high current densities, but the duration of its cycles can be chosen much shorter which ensures good efficiency too. Furthermore, an extension of the working cycle of the first DSRD cascade makes the requirement for the primary switch milder so that even relatively slow low-voltage switches can be employed.

Rapidly induced homogenization and microstructure control of Cu–15Ni–8Sn alloy by electropulsing treatment

The homogenization heat treatment is a key procedure to controlling the second phase, enhancing composition uniformity and workability of as-cast Cu–15Ni–8Sn alloy. Nonetheless, high annealing temperature and long holding time result in high energy consumption, high costs and severe oxidation. The effects of electropulsing treatment (EPT) and conventional homogenization treatment (CHT) on the microstructure and mechanical properties of Cu–15Ni–8Sn alloy by downward continuous casting were studied. The results showed that with increase of pulse current density, the treatment temperature of the alloy increased continuously. Subsequently, γ-(Cu, Ni)3Sn phase and lamellar (α+γ) phase underwent progressive spheroidizaiton and dissolution. Compared with CHT, EPT contributes to significant reductions in both treatment temperature (about 100 °C) and treatment time (1/34 of the CHT), the tensile strength decreased from 437 Mpa (as-cast alloy) to 380 MPa, while the elongation increased dramatically from 9.2 % to 41.6 %. Compared with being treated by CHT, the alloy treated by EPT performed excellent comprehensive mechanical properties. The extra free energy provided by EPT diminishes the thermodynamic energy barrier of γ phase dissolution and significantly accelerates atomic diffusion, which mainly contribute to rapid homogenization of Cu–15Ni–8Sn alloy by EPT at lower temperature. EPT can work as a novel homogenization heat treatment process for metallic materials, boasting advantages such as high efficiency, low energy consumption and low costs.

Optimization of process parameters for preparing the hydrophobic surface of aluminum alloy by laser-assisted electrochemical composite etching based on response surface method

To explore the influence of electrolyte concentration, single pulse energy, current density and scan times on the hydrophobic properties of laser-assisted electrochemical composite etching 2024 aluminum alloy surface, the experimental platform of laser-assisted electrochemical composite etching is built. Based on the results of the single-factor experiments, the response surface method (RSM) is chosen to optimize the process parameters. The optimum combination of process parameters is obtained, and the accuracy of the regression equation is verified by experiments. Through residual analysis, the established regression model fits well. By analysis of variance (ANOVA), the sequence of influence of the factors on apparent contact angle (from large to small) is single pulse energy, scan times, electrolyte concentration, and current density. With the maximum apparent contact angle as the goal, the combination of process parameters adjusted after optimization is: electrolyte concentration 2.0 mol/L, single pulse energy 20µJ, current density 18 mA, and scan times 15. Under these conditions, the experimental values of apparent contact angle is 157°, which is close to the predicted value (158°) by the models. The relative errors is 0.6%. It indicates that the regression model is accurate and reliable. This study shows that RSM is an effective method to optimize the process parameters and obtain the ideal experimental results.

Fabrication of Pb-Co-ZrO2 nanocomposite coatings and correlation of corrosion mechanisms with electronic work functions

It is still an urgent task to design metal coatings for the development of corrosion resistance. Herein, Pb-Co-ZrO2 coating is fabricated on the surface of aluminum plates via one-step pulsed electrodeposition for corrosion resistance. The pulse frequency, current density and duty cycle are 800 Hz, 15 mA cm−2 and 20 %, respectively. In this work, the concentration of ZrO2 nanoparticles in the bath is the main operating variable. We further explored the deposition mechanism of the nanocomposite coating and demonstrated its application potential in corrosion resistance. As expected, the corrosion resistance and mechanical properties of the coatings increased and then decreased with the increase of the concentration of ZrO2 nanoparticles in the plating solution. When the concentration of ZrO2 nanoparticles in the plating solution was 15 g L−1, the Pb-Co-ZrO2 nanocomposite coating exhibited excellent corrosion resistance in 3.5 wt% NaCl solution, with an impedance modulus value (5182 Ω cm2) that was eight times higher than that of the pure Pb coating (669 Ω cm2), possessed the highest corrosion potential (- 0.60 V) and the lowest corrosion current density (3.6 μA cm−2), while also exhibiting excellent mechanical properties. The mechanism of the improved corrosion performance of the Pb-Co-ZrO2 composite coatings was further explained using DFT calculations. The results show that the coupling between the interface of Pb-Co solid solution and ZrO2 nanoparticles effectively improves the overall electron figure of merit of the coatings and triggers an obvious electron localisation, which increases the energy required for the interfacial electrons to escape from the coating interface.