Effects Of Pulse Duty Cycle Research Articles

Effect of Pulse Parameters on Early Stage Nucleation Phenomena

Pulse electrodeposition has garnered significant attention from decades to control important parameters of the growing electrodeposits such as grain size, crystal orientation, and microhardness. Recently, pulse charging has become a major research focus due to its ability to suppress dendritic growth during the charging process for metal-anode based rechargeable batteries. In this work, we have comprehensively studied the effect of pulse duty cycle, D (D = tON/(tON+tOFF)) and frequency on the nucleation phenomena using an in-situ visualization technique (Figure 1). The nuclei density of copper electrodeposits on Indium Tin Oxide (ITO) coated glass substrate is evaluated microscopically and quantified using image processing. The pulse parameters are made equivalent to the corresponding DC voltage (VDC) by two possible ways, i) increasing the peak voltage (VPeak) based on the duty cycle applied (VPeak = VDC/D) , and ii) expanding the total deposition time, or in other words equating the cumulative reaction time (tON) in pulses to the total DC time (tDC = ∑tON). Interestingly, exactly opposite trends are observed for the two aforementioned methods. A sharp increase (∼75%) and decrease (∼80%) in nuclei density as compared to DC are observed while reducing the duty cycle till D = 1/4 for the two methods respectively. However, a decline in nuclei density is noticed while increasing in frequency in both methods. The associated pulse time scales, and the coalescence of the evolving nuclei due to merging of the diffusion zones surrounding a growing nucleus are likely to play the leading role behind this observation. The results add insights to the governing process, and will be useful in designing efficient pulse parameters to control dendritic growth. Figure 1

Effect of Pulse Duty Cycle and Oxidation Time on Microstructure and Properties of Micro-arc Oxidation Coatings on Ti6Al4V Alloy

Micro-arc oxidation (MAO) technology can in-suit generate coatings with high hardness and strong adhesion on the surface of titanium alloy, thereby greatly improve the application range of titanium alloy. The morphology and properties of coatings are controlled by changing electrical parameters such as duty cycle and oxidation time. This work mainly aims to study the influence of different duty cycles and oxidation times on MAO coatings microstructures and properties of Ti6Al4V alloy under the condition of constant voltage and pulse frequency. The scanning electron microscopy (SEM) and X-ray Diffractometer (XRD) were used to investigate into MAO coatings microstructure and phase composition. The roughness, porosity, thickness, and microhardness of MAO coatings were evaluated respectively by roughness tester, thickness gauge, and microhardness tester. The results show that surface morphology of the MAO coatings change from crater-like micropores to foam-like protrusions with the enhancement of duty cycle and oxidation time. When duty cycle is 50% and oxidation time is 30 min respectively, the ejection of the molten material made the MAO coating surface appear foam-like protrusions, and the surface morphology is seriously damaged. When the oxidation time and the duty cycle are 30 min and 10% respectively, the rutile phase intensity is the maximum, and further increasing the duty cycle will lead to a rutile phase decrease. In a limit range, the hardness rise with increase of oxidation time and duty cycle. The highest hardness is 668.85 HV.

Enhanced performance of electrodeposited Ni-SiC plating as an alternative to electroplated chromium deposits: the effect of pulse duty cycle

Ni-SiC composite coating was prepared by the electrodeposition under the pulse current as an alternative for the environment polluted and human cancerogenic hard chromium plating. The microstructure and tribological performance of the composite coating under different duty cycles were studied. The results showed that the mechanical performance of the Ni-SiC can be optimized by adjusting the pulse duty cycle. With the increase of the duty cycle, the grain size of the Ni matrix are refined and the friction coefficient of the coating are decreasing. Composite coating obtained with 80% duty cycle possesses the lowest wear volume during the friction and wear test. The effect of the duty cycle on the microstructure and tribological performance of the composite coating were discussed. Moreover, the co-deposition mechanism of Ni atoms and the SiC particles under the pulse current were discussed.

Fabrication of Ni–B/TiC–Y2O3 nanocomposites by one-step electrodeposition at different duty cycle and evaluation of structural, surface and performance as protective coating

A novel Ni–B/TiC–Y2O3 nanocomposites has been synthesized by one-step pulse electrodeposition at different duty cycle as protective coating. The effects of pulse duty cycle on its structural, surface, corrosion an wear behavior were evaluated. The coating exhibits compact and hill-valley like structure. The average roughness (Sa) was about 56–161 nm and duty cycle of 30% benefits low roughness and fine-grained structure. The crystallite size is 16–19 nm and slightly varied with process parameters. The coating exhibits the preferred orientation of Ni (111) texture. AFM and XPS were utilized to analyze the surface properties. Electrochemical impedance and wear studies illustrated that duty cycle of 30% was the optimal parameter for the best corrosion and wear resistance, exhibiting an excellent long-term performance stability in 3.5 wt% NaCl corrosive solution. This coating exhibits good potentiality for various industrial applications in aggressive medium.

Ultrasound-assisted pulse electrodeposition of cobalt films

Pulse electrodeposition of cobalt was conducted in a sodium saccharin contained sulfate bath under silent or insonated conditions. The effects of pulse duty cycle, pulse frequency and ultrasonic agitation on the crystallographic structure and surface morphology of cobalt deposits were studied. All deposits obtained have a hexagonal close-packed structure, with its basal plane preferentially aligned parallel to the substrate surface. With the increase in duty cycle, texture coefficient for (100) plane increased whether ultrasonic agitation was imposed or not, while the imposition of ultrasonic agitation clearly decreased the texture coefficient for (100) plane. A finer-grained and smoother cobalt electrodeposit was obtained at 62.5 Hz and 25% duty cycle under insonated condition. To understand the roles that these operating parameters played in the electrodeposition, chronopotentiometry and linear sweep voltammetry were used to record the cathodic potential in cobalt deposition and hydrogen evolution current, respectively, which were associated with the morphological and structural change of cobalt deposits. Transmission electron microscopy was also employed to investigate the microstructure and crystal defect of cobalt films. A high density of stacking faults was detected in the cobalt films by high-resolution transmission electron microscopy.

Investigation on the electrochemical machining of micro groove using masked porous cathode

Micro groove, as a typical surface texture, has played an important role in the development of many advanced fields. This paper introduced an electrochemical machining of micro groove using masked porous cathode. A porous metallic plate covered with a mask was prepared as the masked porous cathode. During machining, the masked porous cathode was covered on the workpiece, and the electrolyte could flow into the machining region through the porous structure in the cathode for machining. As the machining unit was closed, the distribution of electrical field was uniform on the machining surface, which could improve the machining accuracy. In addition, the masked porous mask had no damage during machining and could be reused, which improved the machining efficiency. With this method, multiphysics coupling model, including flow field model, electric current model, heat transfer model, reactant transport model, and moving mesh model, was built to investigate their influence on the machining process with different flow modes. The simulation and experiment results indicated that compared with other two flow modes, jet flow mode could provide a high electrolyte velocity in the machining region around the nozzle, and the mass transfer process was enhanced, which was helpful to improve the machining quality. The effect of pulse duty cycle was investigated, and the pulse duty cycle of 20% with the frequency of 2 kHz could further improve the mass transfer process and was preferred to generate micro groove with low standard deviation and roughness. In addition, with the applied voltage rising, the depth of micro groove increased, and increasing the nozzle reciprocating motion number could enhance the mass transfer process during machining, which further improved machining quality. Finally, with the optimized flow mode and machining parameters, a group of ten micro grooves were well generated by using a masked porous cathode with ten micro slits, and the width was about 330 μm with the depth of 45 μm.

Influence of duty cycle on behaviors: wear, corrosion and tribocorrosion resistance of Ni-P coatings

Ni-P coatings were prepared on carbon steel in ammonia-citrate bath by pulse electrodeposition. The effect of pulse duty cycle on the microstructure, wear, corrosion and tribocorrosion resistance of Ni-P coatings were investigated systematically. The results showed that pulse duty cycle has less effect on the microstructure of the Ni-P coatings. However, the Ni-P coating prepared under 50% duty cycle exhibited superior wear, corrosion and tribocorrosion resistance. In addition, the corrosion plays a leading role in tribocorrosion process.

Rapidly pulsed reductants for diesel NOx reduction with lean NOx traps: Effects of pulsing parameters on performance

The use of Rapidly Pulsed Reductants (RPR) provides a method for injecting hydrocarbons in rapid pulses ahead of a lean NOx trap (LNT) with the goal of achieving greater than 90% NOx conversion at temperatures as high as 600°C. This approach was recently discussed under the name Di-Air by Toyota. It may be useful for diesel vehicles with smaller engines that cannot conveniently accommodate urea SCR technology. A further goal of RPR is to reduce the fuel penalty associated with the fuel injections used to purge the LNT.The focus of this study was on understanding this approach in the exhaust temperature range of 450°C to 600°C. The impact of pulsing parameters, i.e., pulse frequency, pulse amplitude, and duty cycle (i.e., ratio of pulse-on/total-cycle-time) on RPR performance was investigated using ethylene injection into simulated exhaust with a research LNT catalyst over a wide range of conditions. A novel injection system was designed that allowed for the investigation of previously unexplored areas of high frequency (up to f=100Hz) and produced pulse durations as short as a millisecond. NOx storage capability was found to be essential for RPR operation. An optimal pulsing frequency was always found for a given set of flow conditions that produced a maximum NOx conversion while holding the fuel penalty (i.e., hydrocarbon dose) constant. The optimal pulsing frequency, usually on the order of 1Hz, was dependent on a number of parameters including the flow velocity, concentration of injected hydrocarbons, and operating temperature. The effects of pulse duty cycle and amplitude, which together determine the amount of injected reductant or the fuel penalty, were investigated separately. Regardless of pulsing frequency and duty cycle, pulses of injected hydrocarbon large enough in magnitude to generate a rich mixture were necessary during the pulse in order to achieve high NOx conversion. Lean or even stoichiometric pulses did not achieve significant NOx conversion. However, even with the rich pulses, the cycle-averaged air/fuel ratio remained net lean in this work.In the main temperature range of this study (450–600°C), where the NOx storage capacity of the LNT was very limited, RPR operation could be divided into two frequency regimes, one below and one above the optimum frequency. At injection frequencies below the optimum frequency, it was observed that the NOx conversion improved as the frequency increased. This was primarily because the duration of the lean period was decreasing, increasing the average NOx storage efficiency during the lean period while still maintaining sufficient durations of the rich period to adequately purge the LNT. At injection frequencies above the optimum frequency, reductant mixing and its parasitic consumption by the gas phase O2 resulted in inadequate purging of the LNT, causing the NOx conversion to drop from the maximum value. These competing factors led to the maximum NOx conversion observed during RPR operation for a LNT at temperatures as high as 600°C for a specified fuel penalty.

Effect of pulse duty cycle on mechanical properties and microstructure of nickel-graphene composite coating produced by pulse electrodeposition under supercritical carbon dioxide

Nickel (Ni) and nickel-graphene oxide (Ni-GO) composite coatings were produced by pulse electrodeposition technique under supercritical carbon dioxide (SC-CO2). The GO and resulting nanocomposites were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectra and zeta potential. It was found that GO was reduced to reduced graphene oxide (RGO) using this method. Effect of duty cycle on surface morphology, microstructure, phase structure, microhardness and wear resistance of the resulting coatings were compared and researched in detail. The results show that the Ni-GO composite coating electrodeposited under SC-CO2 fluid exhibits brighter surface appearance, lower surface roughness and smaller grain size. In addition, the preferred orientation plane of (200) for the coating is changed to be close-packed (111) plane for the addition of RGO. The microhardness of Ni-GO composite coating electrodeposited under SC-CO2 fluid reaches the maximum of 756.4HV0.2. Moreover, the wear tests show that the incorporations of RGO in the coating improve the wear resistance and friction reduction of the deposit.

Pulsed electrodeposition of Co–W amorphous and crystalline coatings

Replacement of hard chromium plating has been of particular interest to many industrial applications, including automotive, aircraft, and machinery parts that require high hardness and wear/corrosion resistance. Co–W alloy coatings, owing to their eco-friendly processing and high hardness/wear resistance, are promising for electrolytic chromium replacement. In the present study, pulsed electrodeposition of amorphous and crystalline Co–W coating is reported. Systematic investigations on the effect of pulse duty cycle and pulse frequency on development of surface microstructure, phases, composition, surface roughness, and micro-hardness are presented. Furthermore, detailed analysis of micro-/nano-mechanical (using ball-on-disc wear tester and nanoindentor) and corrosion (using potentiodynamic polarization method) behavior of optimized Co–W coatings is presented.

Comparative study on structure, corrosion and hardness of Zn–Ni alloy deposition on AISI 347 steel aircraft material

Zn–Ni alloys were electrodeposited on AISI 347 steel aircraft materials from various electrolytes under direct current (DCD) and pulsed electrodepositing (PED) techniques. The effects of pulse duty cycle on thickness, current efficiency and hardness of electrodeposits were studied. Alloy phases of the Zn–Ni were indexed by X-ray diffraction (XRD) techniques. Microstructural morphology, topography and elemental compositions were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray fluorescence spectroscopy (XRF). The corrosion resistance properties of electrodeposited Zn–Ni alloy in 3.5% NaCl aqueous solution obtained by DCD and PED were compared using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) technique. Elemental analysis showed that 88% of Zn and 12% of Ni obtained from electrolyte-4 by PED technique at 40% duty cycle for 50 Hz frequencies having better corrosion resistance than that of deposits obtained from other electrolytes.

Treatment of berberine hydrochloride wastewater by using pulse electro-coagulation process with Fe electrode

Pulse electro-coagulation (PE) technology was applied to the treatment of refractory berberine hydrochloride (BH) wastewater. It showed that with Fe electrode the removal efficiencies of pollutants were significantly higher than that with Al electrode. By using Fe electrode and simulated wastewater, the effects of pulse duty cycle, current density, pulse frequency, electrode distance and electrolysis time on the removal efficiencies of BH and COD were investigated. Under the optimal conditions of reaction time of 3.5 h, pulse duty cycle of 0.3, pulse frequency of 1.0 kHz, current density of 19.44 mA/cm 2, and electrode distance of 2.0 cm, the removal efficiencies of BH and COD reached 72.8% and 69.6%, respectively. The raw BH wastewater was then treated with PE process, and 90.1% BH and 62.6% COD could be removed. Finally, the energy costs of PE and traditional electro-coagulation (EC) were compared and it showed that PE saved 90% energy than EC.

Effects of pulse bias duty cycle on fullerenelike nanostructure and mechanical properties of hydrogenated carbon films prepared by plasma enhanced chemical vapor deposition method

Fullerenelike hydrogenated carbon films were produced by pulse bias-assisted rf inductively coupled plasma enhanced chemical vapor deposition (ICPECVD). The effects of pulse duty cycle on the microstructure and mechanical properties of the resultant films were investigated by means of high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, nanoindentation, and stress measurement. The low pulse duty cycle was found the key in the formation of fullerenelike structure in hydrogenated carbon films, and thus increased the hardness, elasticity, and internal stress of the films. The role of pulse duty cycle in evolution of fullerenelike structure was also discussed in terms of ion bombardment, hydrogen removal, and “annealing” effects.