Application of pulsating overpotential regime on the formation of copper deposits in the range of hydrogen co-deposition

Electrodeposition of copper by pulsating overpotential (PO) regime in the range of hydrogen co-deposition was examined by scanning electron microscopy. It was found that the increase of the pause-to-pulse ratio produced a strong effect on the morphology of electrodeposited copper. Honeycomb-like copper structures were formed with the pause-to-pulse ratios up to 5. Up to this value of the pause-to-pulse ratio, the diameter of the holes formed by attached hydrogen bubbles was decreasing, while their number was increasing by the application of PO regime. The compactness of the formed honeycomb-like structures was also increasing with the increasing pause duration. The increase of the pause-to-pulse ratio suppressed a coalescence of neighboring hydrogen bubbles. Copper dendrites in the interior of the holes and at their shoulders were formed with the higher pause-to-pulse ratios. The size of the formed dendrites, as well as their number, increased with the increasing pause duration. Depth of holes was decreasing with the increasing pause duration. The increased compactness of the obtained structures was explained by the use of a set of equations describing the effect of square-wave PO on electrodeposition process.     

Effect of parameters of square-wave pulsating current on copper electrodeposition in the hydrogen co-deposition range

Copper electrodeposition processes in the hydrogen co-deposition range by the pulsating current (PC) regime were examined by the determination of the average current efficiency of hydrogen evolution and by the scanning electron microscopic (SEM) analysis of the morphology of the formed deposits. The two sets of the square-wave PC of the same pause to pulse ratios, but with different duration of deposition pulses and pauses were analyzed. The one set of square-wave PC was with the constant pause duration and different deposition pulses. In the other set, the deposition pulse was constant while the pause duration was varied. The obtained results were compared with those obtained by electrodeposition at the constant overpotential from solutions of different CuSO₄ and H₂SO₄ concentrations. It was found that the effect of the increasing deposition pulse was equivalent to the decreasing CuSO₄ concentration, while the effect of the decreasing pause duration was equivalent to the increasing H₂SO₄ concentration. It is shown that it is possible to achieve a substitution of more solutions of different CuSO₄ and H₂SO₄ concentartions by the use of the only one solution if the appropriate PC parameters were applied, what can be of high technological significance.     

Morphology, internal structure and growth mechanism of electrodeposited Ni and Co powders

In this paper the morphology (SEM analysis), the internal structure (cross-section analysis) and the growth mechanism of Ni and Co powders electrodeposited from ammoniacal electrolyte are investigated. It is shown that morphology and the internal structure of those powders are quite different. For Ni powder, all particles are of the same morphology, cauliflower-like type. In the case of Co powder, generally two types of particles are detected: (1) dendrite particles and (2) different types of agglomerates, compact, spongy-like and ball-like ones. The growth mechanism for all agglomerates is based on the fact that with the time of growth the disperse (dendrite) agglomerate is branching in different directions and at the tip of each branch spherical diffusion takes over the planar one, providing conditions for the growth of compact deposit. After some time, these branches form compact deposit all over the agglomerate surface and the same agglomerate further grows as a compact one, until it falls off from the electrode surface. Characteristic of all agglomerates is the presence of deep cavities on their surface and the fern-like dendrites on the bottom for most of these cavities.     

Optimization of process of the honeycomb-like structure formation by the regime of reversing current (RC) in the second range

Journal of Solid State Electrochemistry - Formation of the honeycomb-like electrodes of copper by the regime of reversing current (RC) in the second range has been investigated. Morphological and...     

Control of the morphology of electrodeposited three-dimensional copper foam by tuning the pressure

Three-dimensional(3D) copper foams have been formed by electrodeposition at different nitrogen pressures and examined by scanning electron microscopy.The results indicate that an increase in system pressure leads to a decrease of the pore size of the copper foam due to the suppressed coalescence of hydrogen bubbles,while the thickness of the copper foam increases with decreasing pressure.Also,the walls around the pores on the copper foam consist of copper dendrites,and the copper dendrites are made up of copper grains with sizes less than 1 μm.The average sizes of the copper grains decrease with increasing system pressure.It has been demonstrated that copper foams with controllable 3D structure formed by electrodeposition at different pressures are comparable to those obtained by electrodeposition at normal pressure in the presence of specific additives.     

Electrocatalysis of the reduction of nitrate ion at cadmium electrodes by electrodeposited copper

The irreversible reduction of nitrate to nitrite at a cadmium electrode in slightly alkaline solution is electrocatalyzed by copper deposited on the electrode surface. Mass transport-limited currents were observed at a Cu—Cd disc electrode to rotational velocities of 1050 rad s^-1 (10000 rev. min^-1). Electron mugraphs revealed that the copper is plated as closely packed muspheres less than 1 μm in diameter.     

Mechanistic features of reduction of copper chromite and state of absorbed hydrogen in the structure of reduced copper chromite

The review discusses the experimental data on the unusual mechanism of the reduction of copper cations from the copper chromite, CuCr₂O₄, structure. Treatment of copper chromite in hydrogen at 180–370°C is not accompanied by water formation but leads to absorption of hydrogen by the oxide structure with simultaneous formation of metallic copper as small flat particles which are epitaxially bound to the oxide. This process is due to the redox reaction Cu²⁺ + H₂ → Cu⁰ + 2H⁺; the protons are stabilized in the oxide phase, which is confirmed by neutron diffraction studies. The reduced copper chromite which contains absorbed hydrogen in its oxidized state and the metallic copper particles epitaxially bound to the oxide phase structure exhibit catalytic activity in hydrogenation reactions.     

Morphology and internal structure of barium sulfate--derivation of a new growth mechanism

Particle formation is the decisive step to control crystal morphology. Besides the classical primary processes, nucleation and molecular growth, the particle size can also increase by aggregation. The special case of self-assembled aggregation leads to the formation of highly ordered particles which often possess a porous internal structure. In the experiments of these studies the particle formation of barium sulfate has been investigated. SEM analysis shows a large variety of growth forms including plate-like, star-like, and spherical particles, whereas TEM exposures reveal the porous internal structure at all investigated supersaturation levels. The pore size and the volume fraction can be influenced by changing the supersaturation ratio. By means of a fast sampling technique in combination with cryo-TEM analysis it has been shown that the particles at the early stages of growth shortly after the beginning of nucleation consist of many small nanocrystallites which have aggregated in a highly ordered manner. The diffraction pattern indicates many small-angle grain boundaries, whereas the particles at the end of the precipitation process are monocrystalline. This leads to the conclusion that barium sulfate grows according to a self-assembled aggregation mechanism followed by a fast recrystallization process.     

Effects of ultrasonic field on structure evolution of Ni film electrodeposited by bubble template method for hydrogen evolution electrocatalysis

Journal of Solid State Electrochemistry - Self-supporting porous Ni film with uniform honeycomb-like micropores and a thickness of up to 66 μm is electrodeposited by dynamic hydrogen...     

Morphology, structure, and magnetism of FeCo thin films electrodeposited on hydrogen-terminated Si(111) surfaces

In this work we describe the fabrication of FeCo alloy (less than 10 at% Co) thin films from aqueous ammonium sulfate solutions onto n-type Si(111) substrates using potentiostatic electrodeposition at room temperature. The incorporation of Co into the deposits tends to inhibit Fe silicide formation and to protect deposits against oxidation under air exposure. As the incorporation of Co was progressively increased, the sizes of nuclei consisting of FeCo alloy increased, leading to films with a highly oriented body-centered cubic structure with crystalline texture, where (110) planes remain preferentially oriented parallel to the film surface.     

Graphene CVD growth on copper and nickel: role of hydrogen in kinetics and structure

Understanding the chemical vapor deposition (CVD) kinetics of graphene growth is important for advancing graphene processing and achieving better control of graphene thickness and properties. In the perspective of improving large area graphene quality, we have investigated in real-time the CVD kinetics using CH(4)-H(2) precursors on both polycrystalline copper and nickel. We highlighted the role of hydrogen in differentiating the growth kinetics and thickness of graphene on copper and nickel. Specifically, the growth kinetics and mechanism is framed in the competitive dissociative chemisorption of H(2) and dehydrogenating chemisorption of CH(4), and in the competition of the in-diffusion of carbon and hydrogen, being hydrogen in-diffusion faster in copper than nickel, while carbon diffusion is faster in nickel than copper. It is shown that hydrogen acts as an inhibitor for the CH(4) dehydrogenation on copper, contributing to suppress deposition onto the copper substrate, and degrades quality of graphene. Additionally, the evidence of the role of hydrogen in forming C-H out of plane defects in CVD graphene on Cu is also provided. Conversely, resurfacing recombination of hydrogen aids CH(4) decomposition in the case of Ni. Understanding better and providing other elements to the kinetics of graphene growth is helpful to define the optimal CH(4)/H(2) ratio, which ultimately can contribute to improve graphene layer thickness uniformity even on polycrystalline substrates.     

Moderate-temperature reduction of copper chromite by hydrogen and hydrogen desorption from the surface of reduced chromite

The reduction of copper chromite CuCr₂O₄ by hydrogen at 300–573 K and a hydrogen pressure of 4×10⁴-8 × 10⁴ 10⁴ Pa and hydrogen desorption from the surface of a reduced sample are studied. The rate of copper chromite reduction becomes high at temperatures above 473 K. Hydrogen desorbs from the surface of metallic copper covering the surface of chromite during its reduction. The heat of hydrogen adsorption on the metallic copper is almost independent of the surface coverage, 70–80 kJ/mol.     

Electronic structure of the diaquabis(hydrogen malato) copper(II) crystal

Summary The electronic absorption and e.s.r. spectra of a crystal of the title compound [Cu(H₂O)₂ (C₄H₅O₅)₂] were recorded and experimental results are discussed quantitatively, using ligand field theory and the radial wave function of bound Cu^II. The electronic structure of the compound is consistent with its crystal structure.     

Effect of current density on the microstructure and morphology of the electrodeposited nickel coatings

The aim of this research work was to study the effect of deposition current density on microstructure and surface morphology of electrodeposited nickel coatings. For this purpose, nickel deposits have been synthesized by direct current from Watts bath without additive, to limit the incorporation of pollutants resulting from surface adsorption or electro-activity of these compounds. Nickel deposits have been investigated by scanning electron microscopy and X-ray diffraction. Cyclic voltammetry was also used to gain information on the general behavior of the deposition. The optimum conditions of deposition were established and the influence of current density on the grain size, surface morphology, and crystal orientation was determined.     

Amperometric determination of hydrogen peroxide in pickling baths for copper and copper alloys by flow injection analysis

The hydrogen peroxide is oxidized at + 1.5 V vs. SCE at a glassy carbon electrode of the wall-jet type. The samples are diluted about 100 times in a dispersion coil before entering the amperometric detector. The calibration curve is linear from 10^?4 to 1 M H₂O₂, when 5-μl samples are used. With 50-μl samples the detection limit decreases to 10^?6 M H₂O₂. Neither metal ions (Cu²⁺, Zn²⁺, Ni²⁺, Al³⁺) up to 0.5 M nor changes in the sulfuric acid concentration of the samples between 0.1 and 1 M interfere with the hydrogen peroxide determination. About 75 samples can be analyzed per hour.     

Determination of copper in niobium in the sub-ppm range by differential pulse anodic stripping voltammetry

Summary Low levels of copper in niobium may be determined rather rapidly and accurately by differential pulse anodic stripping voltammetry (DPASV). Three sigma detection limit of about 10 ppb can be achieved with a stripping time of 10 min. Wire, sheet and rod samples are dissolved by anodic oxidation in methanol and powder samples in a mixture of hydrofluoric acid and nitric acid. The methanolic solution is transferred into an aqueous one by the addition of an aqueous 1 M oxalic acid solution and by the evaporation of the methanol. The oxalic acid and oxalic acid + hydrofluoric acid solutions, respectively, are analysed by DPASV without any separation of the matrix. Only a few metals interfere with the copper signal when they are present in large excess, but these interferences can be overcome by changing the electrolyte, the solution or the pH. — This method can also be applied to the determination of copper in niobium salts that are soluble in oxalic acid or in hydrofluoric acid.

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Bestimmung von Kupfer in Niob im Sub-ppm-Bereich durch inverse differenzielle Pulspolarographie

Zusammenfassung Niedrige Gehalte an Kupfer in Niob können ziemlich schnell und genau mit Hilfe der inversen differenziellen Pulspolarographie bestimmt werden. Mit einer Anreicherungszeit von 10 min erreicht man eine Drei-Sigma-Nachweisgrenze von ungefähr 10 ppb. Draht-, Platten- und Stangenproben werden durch anodische Oxidation in Methanol und Pulverproben in einer Mischung aus Flußsäure und Salpetersäure gelöst. Die methanolische Lösung wird durch Zugabe von 1 M Oxalsäure und durch Verdampfen des Methanols in eine wäßrige Lösung überführt. Die oxalsaure Lösung ohne bzw. mit Flußsäure wird mit Hilfe der inversen differentiellen Pulspolarographie ohne Abtrennen der Matrix analysiert. Nur wenige Metalle stören die Kupferstufe, wenn sie in großem Überschuß zugegen sind. Man kann diese Störungen u.a. durch Änderung des Elektrolyten, durch Lösungswechsel oder pH-Änderung beseitigen. — Diese Analysenmethode kann auch bei der Bestimmung von Kupfer in Niobsalzen angewandt werden, die sich in Oxalsäure oder Flußsäure lösen.

Presented in part at the International Symposium on Microchemical Techniques, Davos, Switzerland, May 22–27, 1977     

The effects of the pause to pulse ratio in the regime of pulsating overpotential on the formation of honeycomb-like structures

The formation of honeycomb-like structures in the pulsating overpotential (PO) regime was examined by scanning electron microscopy (SEM). The honeycomb-like structures obtained with a square-wave PO of different pause to pulse ratios were compared to the one obtained in the constant potentiostatic regime. Increasing the pause to pulse ratio led to a decrease of the diameter of the holes formed by attached hydrogen bubbles, as well as to an increase in the number of holes formed at the surface area of copper electrodes. The size of the agglomerates of copper grains, of which the walls of the holes were constructed, was reduced with increasing duration of the pause. Also, the uniformity of the honeycomb-like structures was increased by application of the PO regime. It was shown that the effects attained by application of this regime were comparable with those obtained by electrodeposition in a constant potential regime with the addition of specific additives.     

Electrocatalytic properties of cobalt-molybdenum alloy deposits in the hydrogen evolution reaction

Electrocatalytic activity of cobalt-molybdenum deposits is studied in the hydrogen evolution reaction (HER) in an alkaline solution. The studied electrode materials were obtained electrochemically in the galvanostatic mode. It is shown that the rate of hydrogen evolution in 1 M NaOH at 293 K at the Co-Mo alloy is higher, as compared to pure cobalt deposits obtained in similar conditions, which is due both to the increase of the electrode true surface area and possibly to the electronic structure of the obtained alloys. It is established that the hydrogen reaction exchange current grows at the increase of molybdenum content in the electrode deposits in the range of 0–40 at %.     

In vivo iontophoretic delivery of calcium ions through guinea pig skin enhanced by direct and pulsating current

Studies were initiated to investigate the effect of the delivery mode of⁴⁵Ca ions through guinea pig skin in vivo. Direct current (DC), pulsating current (PC) and a Bernard current form, the “courtes periodes” current profile (CP) were applied with the same current density (0.16 mA/cm²) and for the same duration (30 minutes). The⁴⁵Ca ions were delivered from a Ca-bentonite patch radiolabeled with⁴⁵Ca (a natural mineral clay rich in calcium, 50 mgCa/g). The total quantity of applied bentonite was 1.5g×10 days=15g.⁴⁵Ca was counted in different biological samples of the animals. The delivery of⁴⁵Ca ions into the body (systemic effect) is the highest when CP current is applied (6.87±0.95·10⁻¹²g/samples). The local effect appears to be more effective in case of DC current mode (5.89±0.12·10⁻¹²g/0.5g bone). Total calcium measurements proved that the result of transdermal radiocalcium delivery is not only an ion exchange process at the surface of the bone but a deposition of calcium ions into the hydroxiapatite matrix (the net calcium introduction, which represent the difference between the total calcium into the treated bone and total calcium into untreated bone varied from 15.52±2.42·10⁻³g/0.5g bone to 44.30±3.50·10⁻³g/0.5g bone). The results suggest that iontophoresis could be used to accumulate calcium into different target tissues using the appropriate current system.