Application Of Pulsed Current Research Articles

Toughening mechanism of B4C/TiB2 ceramic materials by in situ reaction via spark plasma sintering

AbstractTo enhance the fracture toughness of B4C ceramics, B4C/TiB2 ceramics with excellent performance were prepared by using TiO2 as the addition item and using spark plasma sintering to introduce TiB2 based on in situ reaction, which was compared with ceramics directly introduced with TiB2, the impacts of TiO2 content, temperature and holding time on B4C/TiB2 ceramics were studied, and the toughening mechanism of B4C/TiB2 ceramics in situ reaction was discussed. The results showed that compared with the ceramics directly introduced with TiB2, B4C/TiB2 ceramics with reinforcement phase TiB2 introduced through in‐situ reaction were easier to obtain higher relative density and better properties. Due to the existence of a discharge effect and the application of pulse current, B4C/TiB2 ceramics with excellent comprehensive properties can be prepared at lower temperatures and short time. When 15 vol% TiO2 was added, the temperature was 1750°C and the holding time was 10 min, the comprehensive properties were better, and their relative density, Vickers hardness, flexural strength, and fracture toughness were 98.5%, 27.72 GPa, 474 MPa, and 5.08 MPa·m1/2, respectively. Toughening mechanisms such as crack deflection, crack branching, and crack bridging improved the fracture toughness.

Research on performance of new separated thermoelectric cooler at different pulse currents

This paper studies the performance of a novel split thermoelectric cooler under the different pulsed electrical currents. The investigation focuses on analyzing changes in the cold side temperature of thermoelectric cooler when subjected to different pulse forms. The three-dimensional heat transfer model established through COMSOL was used to investigate the new thermoelectric cooler. The study focused on analyzing the impacts of pulse amplitude, pulse period, pulse waveform, and heat dissipation conditions on the performance of split cooler. The results show that the cooling temperature of split component can be reduced by about 13 K at constant electrical current compared with the conventional component. The temperature of the separated component can be decreased by an additional 2–5 K through the application of pulsed current. The triangle pulse is the best choice for the split component under continuous pulse when the heat dissipation is insufficient. The split thermoelectric component can work more smoothly by using the slant drop triangle pulse compared with the optimized triangle pulse form. The performance of the split thermoelectric component is optimal under a square pulse when there is adequate heat dissipation.

A SiC Based Two-Stage Pulsed Power Converter System for Laser Diode Driving and Other Pulsed Current Applications

A SiC Based Two-Stage Pulsed Power Converter System for Laser Diode Driving and Other Pulsed Current Applications

In situ pulsed electrical biasing TEM observation of AA7075.

Electrically assisted heat treatment is the process of applying an electric current to a sample during heat treatment. Literature has generally shown there to be a difference in the resulting effects of direct current (DC) current and highly transient current (i.e. electropulsing). However, these differences are poorly characterized. In situ transmission electron microscopy (TEM) observation of an AA7075 sample while DC and pulsed current were passed through it was performed herein to explore the effects of an electric current on precipitate development. Numerical simulation results indicate that the thermal response of the samples was very rapid, causing the sample to reach steady-state temperatures almost instantly. There does not appear to be any significant difference between the results of pulsed current application and DC current. Additionally, the failure mechanism of an electrical biasing TEM sample is explored.

Effect of Process Parameters on Arc Shape, Macroscopic Features, and Microhardness in Pulsed GMA–Additive Manufacturing

Gas metal arc welding-based additive manufacturing (GMA–AM) is a promising, low-cost approach to fabricate large-scale and complex geometry components using layer-by-layer deposition of metals. However, the low forming accuracy of GMA–AM still limits its one-off industrial application due to the strong and nonlinear interactions between arc–droplet transfer and molten pool. To fully understand the influential mechanism of this inherent interaction in the GMA–AM process to precisely control the part accuracy, the arc–droplet transfer behavior in the GMA–AM process with different current waveforms was firstly studied experimentally. The phenomena of the arc swing and the differing droplet transfer with the increase in deposited height were interpreted. The thermal force status of the molten pool and its balance boundary conditions were also theoretically analyzed. Finally, the microstructure and the hardness of the AM parts with different cooling times were tested and analyzed. The experimental results demonstrate that using the spray droplet transfer mode can generate a stable AM process under direct current application conditions, but it easily ends the AM process at the third or fourth layer deposition owing to excessive heat input. A more highly accurate deposition morphology can be obtained in one droplet per pulse mode under pulsed current application conditions, which also indicates that the AM process with a constant current welding supply is stabler and easily produces better deposition than the process with a constant voltage welding supply. With the increase in cooling time, the microstructure evolved from fine ferrite to equiaxed ferrite and to columnar ferrite combined with acicular ferrite with a lower proportion of pearlite in the vertical direction of the part, and the average hardness changed to ~168 HV (bottom), ~175 HV (middle), and ~250 HV (top). The analysis indicates that the heat accumulation of the molten pool is a critical factor that affects the deposition accuracy. To this end, a novel strategy that uses the heat accumulation to compensate for the energy formed in the molten pool is proposed to further reduce the arc heat input and weaken the heat accumulation, and its feasibility is discussed.

Effect of Pulsed Current-Assisted Tension on the Mechanical Behavior and Local Strain of Nickel-Based Superalloy Sheet

Electrically assisted (EA) forming is a plastic forming technique under the coupling action of multiple energy fields, such as force field, temperature field, and electric field. It is suitable for the forming of difficult-to-deform materials such as nickel-based superalloys. In this paper, uniaxial tensile tests on nickel-based superalloy sheets were carried out using the pulsed current assisted with different parameters. The experimental results show that the flow stress of the material decreased with the increase in the current density under a high-frequency pulsed current, and the Joule heating effect explains the flow stress drop. In the pulsed current application process, the different types of Portevin-Le Chatelier phenomena appeared with the increase in the current density. The decrease in elongation assisted by the pulsed current was explained by analyzing the inhomogeneity of the maximum Joule heating temperature distribution. In addition, the digital image correlation (DIC) analysis was used to analyze the local strain behavior of the pulsed current-assisted tensile process. Under the application of a high-frequency pulse current, the specimen exerted an inhomogeneous temperature increase and local hot pressing stress, which resulted in the inhomogeneous distribution of the local strain.

Determining adhesion of critical interfaces in microelectronics – A reverse Finite Element Modelling approach based on nanoindentation

State-of-the-art microelectronic devices, especially power semiconductors, are usually exposed to harsh environmental conditions on the one hand, for example large temperature hubs, and to challenging application conditions on the other hand, such as pulsed current applications. Mechanical robustness and reliability have become more and more challenging in recent years. Along with a continuous shrinkage of dimensions, thin film materials are stacked and micro-structured for optimized performance of such devices. Major risks for device reliability can result from loss of adhesion at interfaces of these stacked thin films. Therefore, it is crucial for such devices to feature perfect initial adhesion of the said thin film layers, even after exposure to thermal treatment or in presence of intrinsic stress. In order to validate device robustness, the quality of interface adhesion between isolating and metallization layers should be carefully assessed. A particular focus is set on interfaces between the following, widely employed materials: Cu, Al, WTi, BPSG, SiN etc. Robustness by design at critical interfaces has relied more and more on advanced Finite Element Modelling (FEM) methods in recent years. This includes explicit modelling of adhesion and delamination. Accurate parameters that describe interfacial adhesion – critical adhesion energies in tensile and shear mode – need to be extracted by means of suitable experiments on tailored test vehicles. FEM is able in turn to verify the existing theoretical framework about extracting adhesion energies from experiments, given that the analytical models are often phenomenological and based on simplified assumptions. Experimentally, Nanoindentation on designed multi-layer thin film stacks has proven to be a suitable method to investigate inter-layer adhesion strength on test vehicle basis. We focused on layered stacks of tungsten‑titanium (WTi) and Boron-Phosphorous-Silicate Glass (BPSG) on Silicon substrates. The WTi layer exhibits compressive stress tailored by means of deposition. When an axis-symmetric conical or spherical indenter penetrates the WTi film, buckles around the indenter imprint arise upon loading and may propagate during unloading. Buckle geometry is measured by means of focused ion beam and Scanning Electron Microscopy. Afterwards the critical adhesion energies can be determined by existing analytical models. Combining experimental and simulation methods one may follow a Physics-of-Failure approach and assess the failure mechanisms related to thin film delamination and interface fracture. With experimental results on hand, we implemented an FE model of the same multi-layer system. Initiation and propagation of delamination was modeled by means of a Cohesive Zone Model (CZM) based on a cohesive surface contact approach. The model incorporates elastic-plastic deformation as well as intrinsic stresses of all layers, including the substrate. Following an inverse FEM approach, we reproduced the size of the delaminated area and load-displacement curves of the indenter by recursively readjusting Cohesive Zone parameters. The so-obtained adhesion parameters and modelling can be used elsewhere in delamination risk assessments of industrial semiconductor applications. This approach also gives insight into the accuracy of the formulae used for calculating the total energy release rate and extracting the further relevant parameters without the need to rely on phenomenological assumptions.

Effect of power supply type on the electroplastic effect

Abstract The electroplastic effect (EPE) encompasses the known reduction in flow stress and increase in ductility in a metal resulting from the application of an electric current concurrently with deformation, a phenomenon which cannot be accounted due solely to resistive heating. While several theories have been postulated, the mechanism responsible for the electroplastic effect is still in debate after nearly 60 years of scientific research. A significant amount of research has been conducted on the anomalous effects observed when performing research on the EPE. Particular behaviors which remain elusive are the transient effect of electric current application and the difference between constant and pulsed current applications. Throughout literature, the type of power supply used in electric current application appears to be ignorantly selected and output signals improperly or incompletely documented. It was found herein that the type of power supply used in electrically assisted tensile testing can have a significant effect on the resulting transient mechanical behavior for pulsed current testing within the parameters explored in this research.

An Extremely Low Ripple High Voltage Power Supply for Pulsed Current Applications

This article describes the development of an 18 kV, 30 kW power supply for a pulsed current load with the maximum current of 20 A and a di/dt equal to 100 A/μs. The achieved output ripple is less than 0.01%. In such a high level of precision, the most important issues are considerable difference between the instantaneous and average output powers, as well as insufficient reaction speed of the converter to the fast load change. Very low level of the voltage feedback and its sensitivity to the noise. The first issue necessitates a notable overdesign of the converter switches if the output voltage precision is dedicated to the converter. The second issue raises the problems relevant to observing the voltage ripple and providing it for the control loop. This article proposes, a fast and high current linear regulator developed based on the load current feedforwarding. Using this approach, the fast regulator compensates the voltage change caused by a high level of instantaneous power. The main converter maintains the average power. Thus, there is no need for converter overdesigning. Furthermore, the problems relevant to the high voltage feedback and providing it for the control loop are removed. The voltage feedback is solely served to correct the current loop probable error. Hence, the sensitivity of the control loop against the existing noise is minimized. Despite existing a 600 nF capacitor as the output capacitor, the output voltage drop is less than 0.01% in a wide range of the output current pulse up to 250 μs. The power supply is constructed and experimental results are provided to verify the mentioned specifications.

An Electrical Stimulator to Suppress the Nervous Pain in Diabetic Neuropathic Patients

Peripheral neuropathy is an acute disorder in diabetic patients who are suffering a very agonized pain in their peripheral nerves. Symptomatic relief can be achieved by some analgesic pain killers. One of the best approaches is using an electrical stimulation method where the sensory nerve fibers get excited by the application of pulsed currents at the site of pain. This could block the pain signals from reaching the brain, followed either by the pain gate theory or opioid mechanism. This study primarily focuses the feedback principle where the stimulus is given with respective to the patient’s skin intensity to avoid skin burning in therapy. The opioid mechanism has been proved scientifically that it provides long-lasting pain relief even after the stimulation. This paper documents the design and operation of feedback system which provide a constant output by varying the width of pulses. Thereby, the patient’s pain as well as the sufferings of skin reactions upon stimulus is reduced. As this electrical nerve stimulation strategy is a simple, safe, non-pharmacological, cost-effective it proves to be a better alternative for pain relief

Tailoring Color and Surface Morphology of Electrodeposited Chromium By Application of Pulsed Current

The electrodeposition of chromium layers for decorative purposes plays an important role in the surface finishing industry, especially for applications in sanitary, automotive, plating on plastics and similar fields. As the use of conventional hexavalent chromium based electrolytes is strongly restricted in several countries,1 the demand for alternative plating systems increased during the last years. The most promising alternative is the electrodeposition from trivalent chromium based electrolytes considering environmental safety, quality of the deposits and cost issues.2 Commercially applicable processes are already known since several decades.3 However, trivalent chromium based processes cannot fully meet the requirements on surface appearance of the layers.4 This is crucial for the above mentioned applications as slight differences in color can have a high impact on final implementation of the plated parts. In this work chromium layers plated from different electrolytes were characterized by colorimetry, SEM and AFM. A relation between optical appearance and surface morphology was found and supported by a model based on the theory of light scattering on rough surfaces.5 In case of chromium(III) sulfate based electrolytes, grain size and roughness increase with increasing layer thickness, leading to a color shift from blueish to yellowish. To achieve a blueish appearance while having sufficient resistance against corrosion and wear, a fine-grained surface structure has to be obtained at high layer thickness. By application of pulsed cathodic current, grain growth is suppressed and nucleation is re-initiated at each current pulse, giving a surface grain size of 60 to 100 nm. Up to a chromium thickness of 200 nm, the color value still in the blueish range (b* < 0 in the L*a*b* color system). However, special characteristics of chromium electrodeposition from trivalent solutions have to be considered for choosing suitable pulse parameters in large scale applications. European Chemicals Agency, Authorisation List, EC No. 215-607-8, 231-801-5, 231-889-5, 231-906-6, 232-140-5, 232-143-1, 234-190-3, 236-881-5. Z. X. Zeng, A. M. Liang, and J. Y. Zhang, Recent Pat. Mater. Sci., 2 (1), 50 (2009).S. L. Handy, C. F. Oduoza, and T. Pearson, Trans. IMF, 84 (6), 300 (2006).D. L. Snyder, Plat. Surf. Finish., 90 (11), 34 (2003).M. Leimbach, C. Tschaar, D. Zapf, M. Kurniawan, U. Schmidt, and A. Bund, J. Electrochem. Soc., 166 (6), D205 (2019).

Onset of Dendritic Li Electrodeposition: Experimental and Modeling Studies Highlighting the Critical Role of Li+ Transport within the SEI Layer

High-energy density batteries are essential for powering future electric vehicles. One major hurdle to the progress in developing rechargeable energy-dense Li-metal batteries is the dendritic electrodeposition of Li during the battery charging process. In this contribution, we report on our investigations of the onset time for dendritic growth during galvanostatic electrodeposition of Li metal. Using a combination of electrochemical and optical microscopy techniques, we observe that Li dendrites initiate at a time when the surface overpotential during galvanostatic electrodeposition reaches a local maximum value. This observation is explained using an analytical transport model. Within the framework of this model, the Li+ concentration within the solid electrolyte interphase (SEI) at the Li–SEI interface decreases gradually as the SEI becomes thicker over time. At the dendrite onset time (τonset), the Li+ concentration at the Li–SEI interface approaches zero. Due to such Li+ depletion, surface roughness on the Li electrode amplifies, eventually producing dendrites. Once dendrites form, they rupture the SEI, which then lowers the surface resistance for Li plating. Model predictions of how τonset varies with current density and electrode soak time are found to be in qualitative agreement with experimental observations. Support for this model is gained by the application of pulsed currents, which mitigate Li+ concentration depletion within the SEI, delaying or preventing the formation of dendrites. The effect of temperature on τonset is also investigated and discussed within the framework of the transport model. Figure 1

The comparative evaluation of AISI 316/A387-Gr.91 steels dissimilar weld metal produced by CCGTAW and PCGTAW processes

The mechanical properties (impact toughness and hardness profile) and the microstructure of dissimilar weld metal of AISI 316 and A387-Gr.91 steels produced by constant and pulsed currents GTAW were studied. The microstructural studies showed that the pulsed current application leads to finer and equiaxed dendrites in the weld metal central region, as well as to the expansion of this region. In addition, the pulsed current produces finer secondary phases with more uniform distribution. The chemical analysis of the dendritic and interdendritic zones revealed that the segregation of alloy elements takes place in the entire weld metals and that it is more intensive with the constant current. The segregation is recognized as the main agent in forming the secondary phases, such as MC carbides ((Nb, Ti) C) and intermetallic compounds. Moreover, the microstructure images and map analysis of the weld metal near the fusion line indicated that a filler-deficient zone, including beaches, peninsulas and islands with a chemical composition similar to the base metal is developed. It was disclosed that the zone scope is decreased by the pulsed current. It was observed that the use of the pulsed current increases the weld metal fracture toughness and hardness simultaneously.

Embedding of hybrid MWCNT-Al2O3 particles in Ni matrix: Structural, tribological and corrosion studies

Composite nickel coatings, were produced under direct (DC) and pulse current (PC) from a Watt's type bath, containing 0.5 g/L hybrid MWCNT-Al2O3, in presence and absence of additive Sodium Dodecyl Sulfate - SDS. Surface morphology, crystallographic orientation, wear resistance and corrosion resistance were studied. Micro-Raman measurements revealed that MWCNT-Al2O3 particles are distributed at the whole depth of the cross-section profile analysis. The application of pulse current, favored a random crystallographic orientation of Ni crystallites with reduced grain sizes in comparison with pure Ni. The evaluation of the tribological data demonstrated that the composite coatings produced under pulse conditions in presence of additive, exhibited lower coefficient of friction, higher resistance to dry sliding accompanied by the presence of increased amounts of nickel oxide in wear tracks compared to pure Ni coatings. The behavior of pure and composite coatings in corrosive environment was evaluated by electrochemical impedance spectroscopy. It was found that composite coatings attained their corrosion resistance characteristics for 60 h in 0.6 M NaCl solution. Differences between pure nickel and composite coatings were attributed mainly to morphological differences rather than differences on corrosion performance.

Current-induced viscoelastic topological unwinding of metastable skyrmion strings

In the MnSi bulk chiral magnet, magnetic skyrmion strings of 17 nm in diameter appear in the form of a lattice, penetrating the sample thickness, 10–1000 μm. Although such a bundle of skyrmion strings may exhibit complex soft-matter-like dynamics when starting to move under the influence of a random pinning potential, the details remain highly elusive. Here, we show that a metastable skyrmion-string lattice is subject to topological unwinding under the application of pulsed currents of 3–5 × 106 A m–2 rather than being transported, as evidenced by measurements of the topological Hall effect. The critical current density above which the topological unwinding occurs is larger for a shorter pulse width, reminiscent of the viscoelastic characteristics accompanying the pinning-creep transition observed in domain-wall motion. Numerical simulations reveal that current-induced depinning of already segmented skyrmion strings initiates the topological unwinding. Thus, the skyrmion-string length is an element to consider when studying current-induced motion.

Internal Hybrid Li-Ion Battery and Li-Ion Capacitor Energy Storage Cells

Lithium (Li)-ion battery (LIB) and electric double-layer capacitor (EDLC) are two widely used electrochemical energy storage devices. LIB is made with Li intercalated graphite anode and Li metal oxide cathode and EDLC is made with high surface activated carbon for both anode and cathode. To compare two energy storage devices, LIB has a higher specific energy (or energy density) than EDLC, but has low specific power (or power density) and poor cycle life than EDLC as shown in Fig. 1. In high energy and low power applications, the LIB is the best choice; in high power and long cycle applications, the EDLC is used; however, in many applications, the power requirement is not a constant but rather spans over a range of power levels. It has been demonstrated that when batteries and supercapacitors were externally connected to form a hybrid power source, the voltage drop during the pulsed current for the hybrid power source was less than that for the battery, and operating time of the hybrid power source was significantly extended [1,2]. However, because the maximum cell voltage of single cell EDLC is less than that of LIB; therefore, hybrid power sources could only be made with two separate battery and EDLC cells and electrically connect them with or without electric circuits. The Li-ion capacitor (LIC) is a new energy storage device which consists of an EDLC cathode and a LIB anode, between which the ions shuttle during charge and discharge processes. The LIC not only retained all the advantages of EDLC such as specific power >5 kW/kg and cycle life > 100,000 cycles; but also had higher specific energy of 15-30 Wh/kg and higher maximum cell voltage of 4.1 V than that of EDLC [3,4]. Because the potentials of anode and cathode as well as the maximum cell voltage of LIC is comparable to that of LIB, it allows the LIC and LIB to be assembled in one package as a monolithic LIB and LIC hybrid cell. Very recently, we have demonstrated a new hybrid energy storage device that combines the advantages of both the LIB and the LIC, thereby avoiding their inherent defects, while bridging the gap between the high energy densities offered by batteries and the high power densities seen in LIC as shown in Fig. 1. The energy density and power density of the hybrid cell can be designed to meet the requirements by a reasonable distribution of the ratio between LIB and LIC electrode materials in the internal hybrid cell. For example, in a LIB/LIC internal hybrid cell, made with a 20 wt.% LiFePO4 (LFP) and 80 wt.% activated carbon (AC) mixed cathode and a pre-lithiated hard carbon anode, the specific energy increased by 40% to compare with LIC. As can be seen in Fig. 2(a), the discharge profile can be divided into two parts: at cell voltage range of 2.2-3.0 V and 3.3-3.8 V, the capacity was contributed by capacity material, while at 3.0-3.3 V, it was contributed by battery material. It can also be seen from Fig. 2, that the capacity contribution by capacitance material was less sensitive than battery material when the discharge rate increased from 0.1C to 53C. Fig. 2(b) shows the charge-discharge voltage profiles measured at an interruption rate of 0.2C as a function of cycle number after the hybrid cell was cycled at 43C rate. It must be notified that cycle life of the hybrid energy storage cell was found to be prolonged significantly as shown in Fig. 2(c). After 20,000 cycles, the degradation of specific capacity for both capacitance and battery materials inside hybrid cell was less than 5%. As a comparison, the specific capacity of a battery cell using LFP cathode, as a control experiment, decreased by 40% after 2,000 cycles. Reference: [1] J.P. Zheng, S.P. Ding, and T.R. Jow, “Hybrid Power Sources for Pulse Current Applications”, IEEE Transactions on Aerospace and Electronic Systems, 37, 288 (2001). [2] D. Shin, Y. Kim, Y. Wang, N Chang, and M. Pedram, “Constant-current regulator-based battery-supercapacitor hybrid architecture for high-rate pulsed load applications”, J. Power Sources, 205, 516 (2012). [3] W.J. Cao and J.P. Zheng, “Li-ion Capacitors with Carbon Cathode and Hard Carbon/SLMP Anode Electrodes”, J. Power Sources, 213, 180 (2012). [4] W.J. Cao, J. Shih, J.P. Zheng, and T. Doung, “Development and characterization of Li-ion capacitor pouch cells”, J. Power Sources, 257, 388 (2014). Figure 1

GTA pulsed current welding of thin sheets of SS304 producing superior quality of joint at high welding speed

Thin sheets of austenitic stainless steel (SS304) are assembled using various pulse parameters of pulsed current gas tungsten arc welding. The sheets are joined with high welding speed for higher production rate, but the mean current is enhanced with higher welding speed for maintaining required heat input to get a sound joint. Application of pulsed current gas tungsten inert gas welding for joining of SS304 has been found advantageous in the form of production of weld joints with better mechanical and metallurgical characteristics. It has been observed that there can be elimination or lesser humping in weld joints. Undercut or dipped weld faces are also not found due to application of pulsed current. There is improvement of tensile strength and hardness by 12.5 and 12%, respectively. The enhanced tensile strength and hardness is justified through TEM micrograph showing presence of dislocation.

Effect of additives and current mode on zinc electrodeposition from deep eutectic ionic liquids

Zinc electrodeposition in ‘non-aqueous’ ionic liquids is recently of interest to avoid hydrogen discharge. This study aimed to demonstrate the effect of organic additives (acetonitrile and ethylenediamine) and current mode on the deposit morphology and grain size of zinc coatings electrodeposited from a deep eutectic ionic liquid based on choline chloride (ChCl) and urea. Cyclic voltammetry (CV) measurements were conducted and the resultant CV diagrams were precisely assessed to understand the effect of additives on the deposition mechanism. The electrodeposition current mode was altered from direct current to pulsed current to study its influence on the deposit morphology. The deposit morphologies and grain sizes were observed using a high-resolution field emission scanning electron microscopy. The results revealed that the deposit morphologies and grain sizes were influenced by the additives. Application of pulsed current was found to be more influential on the deposit morphology. Pulsed current produced smooth, uniform, and fine-grained Zn coats. Applications of additives and pulsed current modified markedly Zn electrodeposition from ionic liquids.

Electrochemically enhanced reduction of hexavalent chromium in contaminated clay: Kinetics, energy consumption, and application of pulse current

Electrochemically enhanced reduction of Cr(VI) in clay medium is a technique based on inputting extra energy into the clay to drive the favorable redox reaction. In this study, the reducing reagent Fe(II) was transported into Cr(VI) spiked kaolinite clay by direct current to investigate the dependency of reaction rate on energy consumption. A modified electrophoresis cell with platinum wires as working electrodes was used to run experiments. Results showed that the reduction rate of Cr(VI) was significantly increased by application of current with the pseudo-first-order rate constant kpse from 0.002min−1 at current density of 0mA/cm2 to 0.016min−1 at current density of 0.6mA/cm2, and the corresponding reduction efficiency after 60min experimental time was increased from 8.5% to 57.5%. Mass transport process of Fe(II) in clay pore fluid was determined as the rate controlling step. With the increasing rate of Cr(VI) reduction, both of the productive and non-productive energy consumption increased, from 0.53 and 0.15mWh at current density of 0.1mA/cm2 to 18.9 and 12.6mWh at current density of 0.6mA/cm2, respectively. The non-productive energy consumption was caused by the formation of [(Cr,Fe)(OH)3] precipitates. XRD analysis suggested that the [(Cr,Fe)(OH)3] formed at the clay surface and grew into the pore fluid. SEM–EDX results indicated that the overall Fe(III):Cr(III) ratio of the precipitates was approximately 1.26:1. Application of pulse current decreased the non-productive energy consumption by decreasing the polarization potential drop of each cycle. This effect was more significant in lower pulse frequency due to the better restoration of equilibrium state of clay medium during relaxation period.

Evaluation of the Current Modulation Effect on the Cathodic Efficacy during Copper Electroplating in Alkaline Medium

The main aim of this paper is to study copper ions electroplating, evaluating the cathodic current efficacy, from cyanide ion free alkaline baths, stabilized by different complexant agents for the Cu2+ions. The cathodic current efficacy was assessed through quartz microbalance measurements, employing different current modulations. Results revealed that the pulsed current application has great influence on the cathodic current efficacy during electroplating in the baths under study.