Electrolytic Bath Research Articles

Main process parameters and covers characteristics as criteria for evaluating the effectiveness of the of anodic micro-arc oxidation

The article is devoted to the evaluation of the feasibility and efficiency of modernization of the microarc oxidation process (MAO) by changing the conditions and parameters of sparking, as well as the selection of criteria for assessing the quality and predicting the service properties of formed ceramic-like coatings. The predominant role in changing the nature of structure formation and in ensuring the predicted quality and properties of the oxidized alloy is played by the intensity of sparking, which occurs in the process of electric discharges migrating along the treated surface of the object immersed in the electrolyte. Intensity of sparking determines the conditions for obtaining equidistant coatings: the less stochastic the nature of sparking around the oxidized part is, the more evenly and rapidly the thickness of the formed coating increases and its density is higher. These considerations allowed us offering the option of upgrading method of the anode MAO (AMAO), wherein only the anodic component of the current, causing thereby obtaining thin coatings with extensive porosity by stabilizing the process of arcing through the use of the system of quasi cathodes in the electrolysis bath. In this study, we consider the possibility of controlling the parameters of coatings obtained by the AMDO method in its standard and upgraded versions, by fixing in real time the nature of the distribution of spark discharges, indirect evidence of which is the change in the current density over time and the uniformity of the thickness of the coatings created. Taking into account the influence of micro-arc oxidation on the structural and qualitative features of formed layers, it was assumed that the surface of the coating obtained by the modernized method should have a higher quality, one of the indicators of which is a more smooth and uniform relief. Thus, another criterion for the efficiency of the modernized process can serve as amplitude and step parameters of roughness, which, without allowing an objective assessment of the microprofile of the formed coating, can give more extensive information about the nature of the increase in its thickness and quality changes, determining the level of operational capabilities of metal objects with such a coating.

Bathless Inorganic Composite Nickel Plating: Dry‐Cell Stamping of Large Hygroscopic Phosphor Crystals

AbstractIn contrast to current composite‐metal electroplating, where objects are submerged into a liquid bath, a bathless aqueous inorganic electroplating method is investigated to increase composite loading and incorporation of large hygroscopic particles. This method can be applied as a stamping coating onto large or irregular conductive objects without the need for an electrolyte bath. Instead of stirring in solution, the composite particles are trapped in the electrolyte and forced to plate within the metal matrix. In this set‐up, a nickel salt mixture containing the composite is applied to the cathode and is separated from the anode with an ion‐permeable membrane. As a proof of concept, large noncharged fluorescent composite particles are electrochemically embedded via electrochemical reduction of nickel salts resulting in up to 80 ± 12% surface area coverage after controlling deposition parameters of current density and duration. Long persistent afterglow SrAl2O4:Eu2+, Dy3+ phosphor powder is chosen because of its large crystal size (87 ± 30 µm) and hygroscopic nature. The photoluminescent quantum yield is measured and compared to the composite coatings, which reaches up to 9.9 ± 0.8% after 18 h of coating. Film morphology, phosphor surface loading, and film thickness are characterized by optical microscopy.

Pulse electrodeposition and characterization of graphene oxide particle-reinforced Ni–W alloy matrix nanocomposite coatings

The structure and properties of pulse electrodeposited Ni–W alloy-based nanocomposite coatings, reinforced with varying amounts of graphene oxide (GO) particles, have been evaluated. An aqueous sulfate–citrate electrolytic bath with a suspension of GO particles was used for the deposition of Ni–W/GO composite coatings. Using X-ray diffraction, scanning and transmission electron microscopy with selected area electron diffraction, the effect of graphene oxide particles on microstructural characteristics of the nanocomposite coatings was examined with emphasis on the evolution of constituent phases, morphology, grain size (16–30 nm), and micro-strain. The GO particle reinforcement in the Ni–W alloy reduces the average matrix grain size and increases micro-strain in the alloy matrix. The presence of GO particles in the matrix of nanocomposite coatings is found to strongly influence both nanoindentation hardness and elastic modulus, obtained by analyzing the load–displacement curves, lower the friction coefficient, and enhance the corrosion resistance.

Investigation of the ignition phase in electrolytic plasma polishing under different starting conditions

Electrolytic plasma polishing is a hybrid process in which the electrolytic process is an assisting process for a plasma region, which subsequently cleans and polishes the surface of a workpiece. The basic process takes place in an electrolyte bath, where very different starting conditions can be met. The extreme cases are the ignition in the bath, the ignition during a rapid immersion phase and the ignition in a slow immersion phase. Characteristic of these individual cases are the extreme changes of the tool impedance in connection with the electrolyte. The paper shows how the current-voltage characteristic can be measured, without adjustment problems between the process energy source (PES) and the connection impedance. The individual phases of the ignition phase are explained on the basis of a phenomenological model and the changes in the model (equivalent circuit diagram) of the process are taken into account. From these findings, the conditions can be derived to the PES and energy consumption in the ignition phase can be minimized. The basic objective is also to convert the ignition phase into a stable polishing phase and to have as few re-ignition phases as possible during the polishing period. In particular, the boundary conditions for the Bath-PeP are defined, which allow for a fast polishing of the surface, without deteriorating the mechanical properties of the surface or changing the geometry of the functional surface. In contrast to electrolytic polishing, no edge rounding occurs if a correspondingly short processing time is maintained.

Development and characterization of Cu-Gr composite coatings by electro-co-deposition technique

Graphene nanoplatelets (Gr) are considered as promising reinforcing elements in the composite coatings owing to its exceptional mechanical, electrochemical, electrical, and thermal properties. In the present work, Cu-Gr composite coatings were deposited on stainless steel substrate from the electrolyte bath containing different concentrations of Gr using the electro-co-deposition technique. The microstructure and phases of the Cu-Gr composite coating were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Energy dispersive x-ray spectroscopy (EDS). Microhardness tester was employed to calculate the microhardness. The experimental results show that the surface morphology and microstructure of the Cu-Gr composite coatings are significantly affected by the reinforcement of Gr. The microhardness of the Cu-Gr (0.2 g/L) composite coating is enhanced by 21.42% compared to the pure Cu coating.

Mechanical and microstructural characterization nickel electroplated metal matrix composites

The current study chiefly depicts the fabrication and investigation of mechanical and microstructural properties of Al7SiMg/RHA metal matrix composites with a different weight percentage of reinforcement by employing stir casting technique. Nickel plating is electrodeposited on to the base alloy and metal matrix composites using a conventionally stirred electrolytic watts bath. The microstructure characterization of the composites and the nickel electrodeposition superficial morphology is inspected by employing scanning electron microscope, X-ray diffraction techniques. The prime mechanical properties like density, hardness, and tensile strength of the metal matrix composites were investigated for the base alloy and Al7SiMg/RHA metal matrix composites. Scratch test is performed for nickel plated specimens for determining the adhesion characteristics. Hardness and residual stresses for nickel plated specimens are studied and presented in this paper.

Random Sequential Simulation of the Resulting Surface Roughness in Plasma Electrolytic Polishing of Stainless Steel

Plasma electrolytic polishing (PeP) is an electrochemical method for surface treatment. Unlike electrochemical polishing, PeP requires higher voltage and uses environment friendly aqueous solutions of salts. This process can be realised by immersing a workpiece inside an electrolyte bath or by using an electrolyte jet (Jet-PeP process).In this work a new stochastic method for modelling the plasma electrolytic polishing process is presented. The model was developed to predict the possible achievable surface roughness based on the defined initial one after PeP and Jet-PeP processes. The model describes the workpiece surface and the plasma-gas layer in 2D. The method formulation is based on the assumption, that PeP can be described as an electrochemical process. The physical parameters of the plasma-gas layer were calculated based on the experimental data.To realise the surface roughness change during PeP process a random method for the generation of the initial rough surface and a random method for the removal process were developed. The rough surface generation is based on the random deposition method and the Monte Carlo method. Initial Ra roughness is given as an input parameter.The removal process is simulated using locally defined probability. This probability is based on the Poisson point process depending on the current density on the surface. The simulation model uses the finite difference method (FDM) for the calculation of the electric potential and electric field.In this work, the calculation of various surface roughness variables is implemented and the results of polishing simulation are discussed. It is shown that with the help of the developed stochastic method it is possible to simulate the surface roughness change during the PeP process.

Development of Nanostructured Ni–Fe Alloy Coatings; Characterisation and Corrosion Analysis

The present investigation deals with the electrofabrication of nanostructured Ni-Fe alloy coatings on a mild steel using sulfate bath. The electrolytic bath composition and the current density of the coatings were optimized. Composition analysis by energy dispersive X-ray spectroscopy revealed that the Ni–Fe alloy coatings are of anomalous type. Potentiodynamic polarization corrosion test and electrochemical impedance spectroscopy methods in 3.5% NaCl solution direct towards the lowest corrosion rate at 4 A dm–2. Hardness and roughness of the coatings were evaluated using Vickers hardness test and atomic force microscopy, respectively. The surface morphological analysis of the coatings was characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy. The phase structure, the texture coefficient, and the crystallite grain size of the coatings were calculated and studied using X-ray diffraction.

Manufacturing of High Quality Titanium Thin Foil by Electrodeposition Route

To challenge the significant reduction of manufacturing cost of Ti thin sheet or foil in the future, manufacturing of Ti foil by electrodeposition route was studied with emphasizing on factors affecting quality of the foil and separability from Mo cathode. Current density was one of the strong factors affecting soundness of deposited Ti foil and its separability from the cathode. Electrolyte bath temperature also affected soundness and separability of deposited Ti foil. Separability was closely related to interdiffusion distance of Ti and Mo, that is, shorter diffusion distance, which was brought by low temperature and low current density, led to good separability as well as good surface quality. By reflecting above knowledge, post card size Ti foil of around 0.1 mm in thickness was successfully obtained. It had good quality and could be separated from the cathode by hand. O and Fe contents were drastically decreased by this process.

Synthesis and Electrochemical Characterisation of Novel Hybrid Copper / Poly (diphenylamine) (PDPA) Nanocomposites

The Poly (diphenylamine) (PDPA) nanoparticles was synthesized by surfactant assisted dilute polymerization method and characterized by UV-Visible, FTIR and Cyclic Voltammetry techniques. The PDPA nanoparticles were then suspended in an acidified copper sulphate electrolytic bath to prepare Cu-PDPA nanocomposites by simple electrodeposition technique. The XRD analysis revealed that the crystallite structure of Cu-PDPA nanocomposites and pure copper coatings was crystalline fcc and the grain size was 32 nm for pure Cu and 27 nm for Cu-PDPA nanocomposites. This decrease in crystallite size of Cu-PDPA nanocomposites shows the inclusion of PDPA nanoparticles was uniformly distributed throughout the copper matrix. The microstructure of the Cu-PDPA nanocomposites was examined by SEM analysis shows cauliflower like crystallites with layer by layer outward growth compared to electrodeposited pure copper coatings. The Electrochemical AC impedance and Tafel polarization studies were performed for electrodeposited copper and Cu-PDPA nanocomposites in 3.5% NaCl solution. It revealed that the Cu-PDPA nanocomposite coatings were found to be more corrosion resistance than electrodeposited pure copper coating.

Morphology and corrosion properties of FeMn-Graphene oxide composite coatings

Morphology and corrosion properties of electrodeposited iron manganese-graphene oxide (FeMn-GO) composite coatings was investigated as a function of the GO content. The composite coatings exhibited uniform and compact morphology for lower concentrations of GO in the coating. For higher GO concentrations, agglomeration of GO in the electrolyte bath resulted in non-uniform coating morphology with large surface defects. The influence of GO concentration and coating morphology on the corrosion properties of the coatings was studied by Tafel polarization and electrochemical impedance spectroscopic (EIS) techniques. The impermeability of GO to the corrosive media enhanced the corrosion properties of the composite coatings, with respect to pristine FeMn coating, up to the optimum GO concentration, after which the corrosion resistance behaviour of the composite coatings degraded due to defects and micro-pores present on the surface of the coatings.

Preparation of AlN-Cu composite powders by electroless plating of controlled oxidized nitride particles to prevent degradation by hydrolysis

The present work describes the preparation of AlN-Cu composite powders by electroless plating. Initially, the hydrolysis reaction of the ceramic particles in the electroless solution was studied as a reference element for the design of a protective surface barrier that enabled the coating process, with no ceramic phase degradation. The metal source of the electrolytic bath was copper sulfate, with formaldehyde as the reducing agent, under alkaline conditions of pH 12. The microstructural characterization indicated the formation and growth of aluminum hydroxides from AlN particles, inhibiting the coating of Cu by increasing the OH− ions in the solution. As the exposure time increased, the ellipsoidal bayerite grew from AlN and transformed into prismatic particles of the thermodynamically more stable gibbsite phase. To prevent the degradation of AlN, a controlled oxidation stage was implemented to form a protective barrier of non-reactive alumina on the surface through thermal treatment in oxidizing atmospheres. An atmosphere of dry air was found to be more appropriate than pure oxygen for the formation of a continuous and dense layer of crack-free alumina on nitride surfaces, and a temperature of 1000 °C for 1 h enabled the formation of 3.9 by weight of α-Al2O3, capable of reducing the hydrolysis reaction of AlN. The process of autocatalytic deposition on the passivated particles, applied in three consecutive steps of metallization, led to AlN-Cu composite powders with 29 wt% Cu. Finally, the coated powders were treated in a hydrogen-reducing atmosphere at 400 °C to remove traces of the Al(OH)3 phase encountered, as well as to improve the adhesion of the nanostructured deposit of the cauliflower-like structure to the AlN surfaces, obtaining AlN-Cu composite powders suitable for the preparation of metal/ceramic composites.

Electrochemically driven multi-material 3D-printing

Major efforts for the advancement of additive manufacturing are lately focused on the development of multi-material 3D-printing (mMat-3DP) methods which can enable the fabrication of complete devices in a single printing process combining materials with different properties (structural, functional, conductive, etc.). Printing conductive (metal and non-metal) materials with low-energy-consuming and economical methods is of particular interest since it would facilitate the production of electrodes, catalytic surfaces and electronic circuitry in general for countless applications. In order to contribute to the future vision of mMat-3DP, we wish to show here an economical method to selectively deposit different conductive materials (metal and conductive polymer) by means of electrochemical driving forces. A custom-made electrochemical liquid dispenser with embedded electrodes is used to electrodeposit selectively a metal (Cu), a conductive polymer (polyaniline), or a combination of the two, with both precursors present simultaneously and conveniently in the common electrolytic bath. Combining the 3D-patterning ability of a desktop 3D-printer with a concurrent control of the electrochemical process, selective deposition is demonstrated over a conductive graphite foil used as the cathode. Printing and electrochemical parameters have been optimized using scanning electron microscopy and energy dispersive X-ray spectroscopy to characterize the printed structures. The electrochemical 3D-printing method, being inherently low-cost, scalable and compatible with electrode fabrication methods shall find a broad scope of applications.

Review—Electrolytic Metal Atoms Enabled Manufacturing of Nanostructured Sensor Electrodes

Sensing materials play a key role in the successful implementation of electrochemical sensors, and nanotechnology has emerged as an important and rapidly growing field for stimulating the innovation of high-performance sensors. The fabrication, characterization, and evaluation of the nanostructured electrodes are therefore a focus of this field. Compared to a variety of dry and wet technologies which have been extensively developed for this purpose, electrochemical methods are typically convenient, highly effective, and potentially low-cost for the production of different nanostructures. This minireview is designed to introduce a unique electrochemical method - electrolytic metal-atom enabled manufacturing (EM2) and its application in electrochemical sensors. The EM2 technique employs electrolytic metal atoms generated from their corresponding salt precursor as a tool to nanostructure a wide range of substrate electrodes used in electrochemical sensors, based on a one-pot electrochemical deposition and dissolution of the metal atoms in the same electrolyte bath. Briefly, the metal atoms are electrodeposited on a substrate electrode during the cathode reduction, and they are selectively removed from the substrate during the subsequent anode oxidation. Because of the interactions between the electrolytic metal atoms and the substrate atoms, the repetitive electrodeposition and dissolution of the former on the substrate enable the nanostructuration of the substrate, particularly within its surface layers. The nanostructured electrodes have demonstrated very attractive performance for the determination of numerous analytes, such as high sensitivity and selectivity, high interference tolerance, and low detection limits. However, the EM2 technique and the application of the resulting nanostructured electrodes in electrochemical sensors and beyond have still been very limitedly investigated. In order to bring the community from academic, industries, agencies, and customers together to develop the EM2 technique and advance electrochemical sensor systems, this minireview will introduce the thermodynamic and kinetic fundamentals of this technique, the characterization of resulting nanostructures, the analysis of their electrochemical behavior, and the implementation of this technique for the development of advanced sensor electrodes. Finally, an outlook with a focus on further research areas is provided.

Effect of Processing Temperature on the Morphology and Crystal Structure of Anodic TiO2 Nanotubes

In the present work, we have investigated the influence of temperature on the morphology of anodically produced self-organized titanium oxide nanotubes (TiNTs). TiNTs are synthesized by two-step anodization in ethylene glycol-based electrolytes containing ammonium fluoride and deionized water. Experiments are performed at constant anodization voltage of 50 V for 2 h. An investigation by the SEM images reveals that if the temperature is kept constant during the anodizing experiment, variation in the average tube diameter is significantly reduced. Degree of pore arrangement, pore size and oxide thickness increased with the increase in temperature as observed at a range of electrolyte temperatures fixed between 5°C and 40°C. However, if the temperature is not controlled during the anodization experiment, then due to the exothermic nature of the reactions to the formation of TiNTs, the temperature of the electrolyte continues to increase. This variation in electrolyte bath temperature introduces strong variations in tube diameter (10–160 nm) along the length of the tubes. Current profiles, recorded during the anodization experiments, predict the effect of constant and varying experimental temperatures as well. In both cases, XRD results show the complete anatase crystal structure of nanotubes upon annealing at 450°C. The present work highlights the importance of fixed processing temperature during the anodization experiments in order to develop an ordered array of nanotubes with a uniform tube diameter.

Simplified two-electrode electrochemical growth and characterization of Cd1−xZnxS thin films: Influence of electrolytic bath pH

Cd1−xZnxS thin films were prepared from an aqueous electrolytic solution using a simple low-cost two-electrode electrodeposition technique. Effect of pH on physico-chemical properties was studied at three different pH values of 1.8, 2.7 and 3.6. It was found as the pH is raised, intensity of the X-ray diffraction peaks of the films decreased gradually. Raman measurement also showed similar observation a decrease in intensity of peaks as pH is raised. Compositional characterization shows that more Zn is incorporated into the CdS lattice as pH increases and on the other hand deposition rate decreases due to formation of more OH− ions in the bath. SEM measurement reveals that the variation of pH significantly influences surface morphology of the films. The optical band gap ranges from 2.43 eV to 2.50 eV which indicate that, electrodeposited Cd1−xZnxS thin films can be used as good window/buffer layer for solar cell application in place of CdS.

Anodic oxidation of carbon fibers in alkaline and acidic electrolyte: Quantification of surface functional groups by gas-phase derivatization

Carbon fibers were anodically oxidized using two different electrolytes, i.e. an alkaline aqueous ammonium bicarbonate solution (pH ≈ 8) and an acidic dilute sulfuric acid solution (pH ≈ 2). Two different treatment modes were utilized: (1) a static, discontinuous anodic oxidation treatment of a spatially fixed fiber bundle and (2) a dynamic, continuous oxidation of a fiber tow, which was dragged through the electrolyte bath with constant speed. The resulting degree of oxidation of the carbon fiber surface was analyzed by x-ray photoelectron spectroscopy. By gas-phase derivatization of the fiber surfaces the concentrations of surface hydroxyl and carboxyl groups were quantified. Good agreement between the oxygen elemental concentration determined from the derivatized surface functionalities and that extracted from x-ray photoelectron spectroscopy elemental analysis demonstrates the reliability of the derivatization results. While both treatment modes result in the same oxidation, significant differences of the oxidation behavior exist for carbon fibers treated by the two different electrolytes. This is explained by a mechanism involving the effect of electrolyte salt ions.

Surface Protection of Carbon Steel with ZrO2 Composite Induced Zinc Based Electrolytic cell via Electrodeposition Technique

The effect of Zirconium dioxide (ZrO2) as additive to Zn-MgO electrolytic chemical bath coating by co-deposition on carbon steel was investigated. Weight loss was conducted on the electrodeposited mild steel and it was inspected. The anti corrosion properties were assessed by linear polarization procedure in 1 mole of HCl medium. From the results gotten, all deposited coatings displayed significant improvement. An amazing improvement was accomplished in every one of the coatings as against the as-received sample. Zn-MgO-ZrO2 (0.8V) with the best performing coating showing an upgrade indicates enhanced anti-wear and friction qualities displaying wear resistance improvement.

Synthesis and Characterization of Silver and Gold Nano-Structures on Chitosan-Porous Anodic Alumina Nano-Composite

This study was designed to probe the fabrication of unique silver and gold nano-structures engaging a self-designed chitosan-porous anodic alumina nano-composite as a template. Porous anodic alumina has been manufactured by di-step aluminum anodization in an oxalic acid electrolytic bath. The surface properties of porous anodic alumina were reinforced by chitosan neutralized in sodium hydroxide. Multifarious nano-morphologies of silver, as well as gold nanostructures, were observed. Furthermore, the long chitosan biopolymer chains were degraded by γ-irradiations and the same procedure was employed for modification of porous anodic alumina with γ-degraded chitosan. The morphologies of fabricated silver and gold nanostructures were investigated by scanning electron microscopy, while their composition was evaluated with the help of energy-dispersive X-ray spectroscopy. X-ray diffraction study exposed the face-centered cubic phase for both silver and gold nanostructures. Reflection mode UV-Vis spectroscopy was used to ascertain reflection grooves in the absorption range of silver and gold nanostructures respectively. The technique does not involve any harmful reagent and shows different selectivity than methods in general practice. The achieved results apprised that the fabricated nanostructures offer the advantages of biocompatibility and eco-friendliness for numerous biomedical uses.

Soft Sensors in the Primary Aluminum Production Process Based on Neural Networks Using Clustering Methods.

Primary aluminum production is an uninterrupted and complex process that must operate in a closed loop, hindering possibilities for experiments to improve production. In this sense, it is important to have ways to simulate this process computationally without acting directly on the plant, since such direct intervention could be dangerous, expensive, and time-consuming. This problem is addressed in this paper by combining real data, the artificial neural network technique, and clustering methods to create soft sensors to estimate the temperature, the aluminum fluoride percentage in the electrolytic bath, and the level of metal of aluminum reduction cells (pots). An innovative strategy is used to split the entire dataset by section and lifespan of pots with automatic clustering for soft sensors. The soft sensors created by this methodology have small estimation mean squared error with high generalization power. Results demonstrate the effectiveness and feasibility of the proposed approach to soft sensors in the aluminum industry that may improve process control and save resources.