Use Of Pulsed Current Research Articles

Pulse Electroplating of Gold-Nickel Alloys: Morphological and Aesthetic Improvement Compared to DC

The use of pulsed current is well known as a research tool to study the electrodeposition mechanism of metals, however, it was realized that this method could provide a means to improve the properties of deposits. Electrodeposition of gold or its alloys is not only used in the electronics industry due to its conductive and anti-corrosive properties, but also as a final layer due to its aesthetic properties. In this study we focused on a cyanide gold-nickel bath, among the most frequently used in the electroplating industry intended for the decorative sector. The use of modulated currents has proven to be an effective methodology to be able to control and improve the chemical and physical characteristics of metal deposits. Deposits obtained through pulsed currents have a smaller grain size and a more homogeneous surface, both at the level of thickness dispersion on the surface and at the roughness of the samples themselves. A direct consequence of the above results is the improvement of the aesthetic finish of the workpieces with an increase in brightness as well as anti-corrosive properties.

Electrodeposition of Calcium Phosphate Coatings on Metallic Substrates for Bone Implant Applications: A Review

This review summaries more than three decades of scientific knowledge on electrodeposition of calcium phosphate coatings. This low-temperature process aims to make the surface of metallic bone implants bioactive within a physiological environment. The first part of the review describes the reaction mechanisms that lead to the synthesis of a bioactive coating. Electrodeposition occurs in three consecutive steps that involve electrochemical reactions, pH modification, and precipitation of the calcium phosphate coating. However, the process also produces undesired dihydrogen bubbles during the deposition because of the reduction of water, the solvent of the electrolyte solution. To prevent the production of large amounts of dihydrogen bubbles, the current density value is limited during deposition. To circumvent this issue, the use of pulsed current has been proposed in recent years to replace the traditional direct current. Thanks to breaking times, dihydrogen bubbles can regularly escape from the surface of the implant, and the deposition of the calcium phosphate coating is less disturbed by the accumulation of bubbles. In addition, the pulsed current has a positive impact on the chemical composition, morphology, roughness, and mechanical properties of the electrodeposited calcium phosphate coating. Finally, the review describes one of the most interesting properties of electrodeposition, i.e., the possibility of adding ionic substituents to the calcium phosphate crystal lattice to improve the biological performance of the bone implant. Several cations and anions are reviewed from the scientific literature with a description of their biological impact on the physiological environment.

Improving the energy efficiency of an electrodialytic process to extract phosphorus from municipal solid waste digestate through different strategies

This work assesses the possibility of energy optimisation during the electrodialytic extraction of phosphorus from the municipal solid waste digestate. Strategies tested for energy optimisation consisted in (i) using a dual-stage extraction approach; (ii) replacement of continuous stirring by pulse stirring and; (iii) utilisation of pulse electric current as an alternative to a constant current. Experiments were carried out using different stirring profiles (continuous stirring, pulsed stirring, manual stirring and no stirring) and different profiles for generating the electric field (continuous current and pulsed current). Dual-stage approach decreased the energy consumption by 30%. Energy was mainly used in the stirring operation (80%). Applying this strategy caused a faster acidification of the waste suspension and reduced the time required for the extraction. As for the second strategy, use of pulse stirring, it is possible to save energy by operating the stirrer 25% of the time, without compromising the phosphorus extraction values, which are close to 90%. Corresponding energy savings reached 70%. The third strategy tested, use of pulse current, had as side-effect a significant decrease of the phosphorus extracted, so the implementation of pulse current is not recommended. Overall, the energy efficiency of the electrodialytic extraction of phosphorus can be improved by 80% through the use of the dual-stage approach and the use of stirring for 25% of the time. There is also a potential in further reducing the energy use by further improving the stirring system.

Positive Impact of Pulsed Electric Field on Lactic Acid Removal, Demineralization and Membrane Scaling during Acid Whey Electrodialysis.

The drying of acid whey is hindered by its high mineral and organic acid contents, and their removal is performed industrially through expensive and environmentally impacting serial processes. Previous works demonstrated the ability to remove these elements by electrodialysis alone but with a major concern—membrane scaling. In this study, two conditions of pulsed electric field (PEF) were tested and compared to conventional DC current condition to evaluate the potential of PEF to mitigate membrane scaling and to affect lactic acid and salt removals. The application of a PEF 25 s/25 s pulse/pause combination at an initial under-limiting current density allowed for decreasing the amount of scaling, the final system electrical resistance by 32%, and the relative energy consumption up to 33%. The use of pulsed current also enabled better lactic acid removal than the DC condition by 10% and 16% for PEF 50 s/10 s and 25 s/25 s, respectively. These results would be due to two mechanisms: (1) the mitigation of concentration polarization phenomenon and (2) the rinsing of the membranes during the pause periods. To the best of our knowledge, this was the first time that PEF current conditions were used on acid whey to both demineralize and deacidify it.

Influence of PC-GTAW Parameters on the Microstructural and Mechanical Properties of Thin AISI 1008 Steel Joints

Butt weld joints are prepared using pulse current gas tungsten arc welding out of thin sheets of AISI 1008 steel using various combinations of pulse parameters. During welding, the welding speed was kept high, but with the increase of welding speed the mean current was also increased to get the required weld joint at the constant heat input. The use of pulse current has led to improvement in mechanical and metallurgical properties of weld joints. It has resulted in less development of humping which is a common problem with high-speed welding. The undercut or dipped weld face is not observed severe. The tensile strength and hardness are enhanced by 12.5 and 12%. The increase of tensile strength and hardness is justified through TEM micrograph showing the presence of dislocation.

Chloride transport through cementitious membranes using pulsed current

Microstructural changes and chloride transport in cement pastes are studied under DC current and pulsed electric fields. Impedance spectroscopy and ultrasonic pulse velocity measurements have been employed for quasi-real time monitoring of changes in the cement paste microstructure. The results show that the electric resistivity and ultrasound velocity (measured at 500kHz) are modified during the migration experiments. At the end of test, mercury intrusion porosimetry reveals an important increase in the fraction of gel pores. The experimental results show conduction enhanced through gel pores. The use of pulsed current is presented as an alternative method to minimise the negative effects produced by DC current.

パルス電解法による硫酸塩浴からのＺｎ‐Ｃｒ合金電析

The electrodeposition of Zn-Cr alloys from sulfate solutions was conducted using rectangular pulsed current. Changes in the current efficiency and the Cr content in the deposits with varying values for the average current density showed similar results as seen in direct current plating. Cr in the deposits existed in both its metallic and trivalent states in the pulsed current plating, while no metallic Cr was observed in the deposits in direct current plating. Results thus indicated that the use of pulsed current increased the limiting current of Zn to attain the deposition potential of Cr. The superimposition of direct current on pulsed current allowed a significant increase in the content of metallic Cr in the deposits, suggesting that the superimposition of direct current prevented the reoxidation of Cr in the deposits during the off-time period of pulse plating. Varying the plating conditions resulted in the cathode being polarized to an extremely negative region where mass transport became predominant. At that point, the deposits contained a considerable amount of trivalent Cr, which was the product of hydrolysis resulting from the accelerated decomposition of water.

Effect of pulsed reverse current on the structure and hardness of copper deposits obtained from acidic electrolytes containing organic additives

The effect of pulsed reverse current on the grain size, surface topography and hardness of copper deposits from an acidic electrolyte has been studied using a cathodic pulse time of 10 ms, an anodic pulse time of 0.5 ms, an anodic/cathodic current density ratio of 3:1 and an average current density of 3 A dm −2. Using these fixed conditions, the grain size and hardness of deposits obtained with various organic additive combinations were compared with those obtained by the use of direct current. It was found that in an additive-free electrolyte, the use of pulsed current increased the grain size of the deposits by an order of magnitude and reduced the deposit hardness. The addition of polyether molecules to the electrolyte was found to have a gain-refining effect with both direct and pulsed reverse current although the grain size obtained with pulsed reverse current was more uniform than that obtained with direct current. The addition of sulphopropyl sulphides to an electrolyte containing polyethers was found to produce grain growth with direct current, but grain refinement with pulsed reverse current, thus suggesting a different adsorption mechanism. A correlation was found between deposit hardness and grain size in all cases.