Electrocrystallization Process Research Articles

Electrochemical Behavior of Copper in the (NaCl-KCl-CuCl<sub>2</sub>) Molten Salt

2 system at 700°C. The results showed that so long as Cu appears or the electrodeposit process carries on, Cu++ can be reduced into Cu+; that the electrochemical reaction process of copper is a quasi-reversible process mix-controlled by ion copper diffusion rate and electron transport rate; that the electrochemical reaction mechanism is Cu++e-→Cu; that the electrocrystallization process of copper is an instantaneous hemispheroid three-dimensional nucleation process; that the Cu ion diffusion coefficient is 2.5×10-4cm2∙s-1 at experimental conditions.

Three-dimensional nucleation and growth under galvanostatic conditions

The nucleation and growth of new phase clusters have been studied under galvanostatic conditions. Time dependences of the overpotential, number, and size of clusters formed on the electrode have been calculated from a model of the electrocrystallization process.

Electrocrystallization mechanism of iron phosphate coatings onto mild steel electrode surfaces

Samples of mild steel AISI-SAE 1018, 1045 and 1080 were electrochemically phosphatised, both potentiodynamically and potentiostatically, in a concentrated H3PO4 aqueous solution. The conversion coating layers formed were characterised by means of scanning electron microscopy and energy-dispersive x-ray analysis. The kinetics and mechanisms of the electrocrystallization process of FePO4·2H2O(c) films were studied using the potential step technique. It was found that the mechanism governing the formation of FePO4·2H2O(c) anodic film was common for all the steel samples, namely, the overall electrodic process comprises four different simultaneous contributions to the overall current (j(t)). The individual contributions were: j ad(t), the current density contribution due to H3PO4 adsorption; j d(t), the current density involved during electrodissolution of iron of the steel electrode in the zones which were not covered yet by the FePO4·2H2O(c) film; j g(t), the current density contribution due to 2D nucleation and growth of an insoluble FePO4·2H2O(c) conducting adlayer; and j f(t), the current due to the growth of the passive layer induced by electrodissolution of iron metal and transport of the resulting Fe(II) ions through the FePO4·2H2O(c) film. However, each stage contributed to the overall process in a different manner, depending upon the carbon contents. The results from voltammetry indicated that it is possible to establish the potential at which the FePO4·2H2O(c) film begins to form and that this was also a function of the carbon contents.

Preparation, characterization, and electrochemical studies of sulfur-bearing nickel in an ammoniacal electrolyte: the influence of thiourea

Sulfur-bearing nickel was prepared by a direct electrodeposition in an ammoniacal Ni(II) electrolyte containing thiourea. This sulfur-bearing nickel showed an excellent dissolving activity when used as anodic materials in the traditional Watt bath. The influence of thiourea on the surface microstructure, crystallization texture, and electrocrystallization process of sulfur-bearing nickel were investigated by scanning electron microscopy, X-ray diffraction, and electrochemical techniques. The results show that the S element is uniformly distributed in the electrodeposited nickel. The prepared nickel samples present a blade shape microstructure, and the blade size decreases by the addition of thiourea. Sulfur-bearing nickel exhibits face-centered cubic structure and (111) preferred orientation, and the orientation distribution is strengthened with increased thiourea concentration. The nucleation parameters, such as N0, A, and J0, are obtained from the initial parts of the transients making use of Sharifker–Mostany theoretical model. Both the nucleation rate and the vertical growth rate are increased by the addition of thiourea, leading to finer grains and better dissolving activity.

Growth of single silver crystals during electrodeposition from a melt in the presence of an excess background electrolyte

The regularities of the initial stages of growth of silver nano- and microcrystals during electrodeposition from the AgNO3-KNO3-NaNO3 melt with an excess background electrolyte are studied. A model for the electrocrystallization process is proposed. Experimental and theoretical time dependences of the overpotential (supersaturation) and the crystal size are obtained. The applicability of this model is discussed. The main electrodeposition parameters are found to be the specific capacity of a double electrical layer, the equilibrium concentration of single adatoms at the electrode, and the diffusion coefficient of depositing ions in the melt.

Electrochemical production of ultrafine powders of copper

Investigation of different stages influence on the process of electrocrystallization is a very difficult experimental problem, and for the electrodeposition of copper has not yet received an unambiguous conclusion. The paper considers different approaches to the electrochemical production of ultrafine powders of copper and its comparative analysis has been done.

A new method for electrocrystallization of AgTCNQF4 and Ag2TCNQF4 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) in acetonitrile

Semiconducting AgTCNQF4 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) has been electrocrystallized from an acetonitrile (0.1 M Bu4NPF6) solution containing TCNQF4 and Ag(MeCN)4+. Reduction of TCNQF4 to the TCNQF41− anion, followed by reaction with Ag(MeCN)4+ forms crystalline AgTCNQF4 on the electrode surface. Electrochemical synthesis is simplified by the reduction of TCNQF4 prior to Ag(MeCN)4+ compared with the analogous reaction of the parent TCNQ to form AgTCNQ, where these two processes are coincident. Cyclic voltammetry and surface plasmon resonance studies reveal that the electrocrystallization process is slow on the voltammetric time scale (scan rate = 20 mV s−1) for AgTCNQF4, as it requires its solubility product to be exceeded. The solubility of AgTCNQF4 is higher in the presence of 0.1 M Bu4NPF6 supporting electrolyte than in pure solvent. Cyclic voltammetry illustrates a dependence of the reduction peak potential of Ag(MeCN)4+ to metallic Ag on the electrode material with the ease of reduction following the order Au < Pt < GC < ITO. Ultraviolet-visible, Fourier transform infrared, and Raman spectra confirmed the formation of reduced TCNQF41− and optical microscopy showed needle-shaped morphology for the electrocrystallized AgTCNQF4. AgTCNQF4 also can be formed by solid–solid transformation at a TCNQF4-modified electrode in contact with aqueous media containing Ag+ ions. Chemically and electrochemically synthesized AgTCNQF4 are spectroscopically identical. Electrocrystallization of Ag2TCNQF4 was also investigated; however, this was found to be thermodynamically unstable and readily decomposed to form AgTCNQF4 and metallic Ag, as does chemically synthesized Ag2TCNQF4.

Electrochemical behavior of silicon compound in LiF–NaF–KF–Na2SiF6 molten salt

The electrochemical reduction and nucleation process of Si4+ on an electrical steel electrode in the eutectic LiF–NaF–KF molten salt were investigated at 750 °C, by means of cyclic voltammetry and chronoamperometry technique. Silicon was electrodeposited on steel, and Fe3Si was formed by the diffusivity of silicon on the electrode surface. The electrochemical reduction of Si4+ process in single-step charge transfer and the cathode process was reversible. The electrocrystallization process of silicon is controlled by progressive three-dimensional mechanism. The diffusion coefficient was calculated to be 5.42 × 10−7 cm2/s by chronopotentiometry at experimental conditions.

Electrocrystallisation of cobalt, copper and cobalt–copper alloys on fluorine-doped tin oxide electrodes

In this work, a systemic study of the Co, Cu and Co–Cu electrocrystallisation process was performed on a fluorine doped tin oxide coated conducting glass substrate. This was carried out in a sulphate solution of Na2SO4+H3BO3 (pH 3·8) without complexing agent. The influence of applied potentials on the electrochemical nucleation and growth has been studied, using cyclic voltammetry and chronoamperometry techniques. The cyclic voltammetry results clearly show that the potential of Co–Cu dissolution and their positive shifts depend on the cathodic limit and reveal a variation in the deposit composition when switching potential is varied. A number of kinetics parameters have been estimated from the analysis of current transients on the basis of the Scharifker–Hills model for electrochemical nucleation and diffusion controlled growth. From the analysis of the experimental current transients, it has been found that the nucleation mechanism is instantaneous with a typical three-dimensional nucleation and growth process for Co, Cu and Co–Cu respectively. A strong dependence of the number of active sites N0 with applied potential is observed on the fluorine doped tin oxide surface.

Nucleation and growth of zinc on aluminum from acidic sulfate solution with [BMIM]HSO4 as additive

The nucleation and first stages of the growth of zinc on aluminum from acidic sulfate solution in the absence and presence of 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO4 as additive were investigated using cyclic voltammetry, chronoamperometric current–time transients, and scanning electron microscopy techniques. The dimensionless chronoamperometric current–time transients for the zinc electrodeposition on aluminum electrode from the solution free of [BMIM]HSO4 showed the zinc deposition can be interpreted by a model involving instantaneous nucleation with hemispherical diffusion controlled growth of nuclei. The addition of [BMIM]HSO4 induced a blocking effect on the zinc electrocrystallization process through its cathodic adsorption on the electrode surface. This effect led to increase the number density of active sites, decrease the nucleation and growth rate of these nuclei, and produce more leveled and fine-grained cathodic deposits without affecting the instantaneous nucleation mechanism. Surface morphology analysis revealed the crystal structure of the zinc deposits formed did not change by the adsorption of [BMIM]HSO4 at the first stages of deposition.

Study of the effect of new brightener on Zn–Ni alloy electrodeposition from acid sulphate bath

The electrodeposition of Zn–Ni alloy from acid sulphate bath was carried out in presence of a brightener, such as condensation product of vanillin and serine (VS). The cyclic voltammetry and chronoamperometry techniques were used to study the nucleation mechanism process, while polarization and electrochemical impedance spectroscopic (EIS) techniques for corrosion studies. The model of Scharifker and Hills was used to analyze the current transients and it revealed that Zn–Ni electrocrystallization process in presence of VS, under the studied conditions, is governed by progressive nucleation process. Corrosion studies showed that bright Zn–Ni alloy coatings exhibited higher corrosion resistant nature. The Zn–Ni layer obtained in presence of VS shows smooth morphology with smaller grain sizes and higher percentage of reflectance signals.

Study of the influence of sonication during the electrod­eposition of nickel matrix nanocomposite coatings on the protective properties

The interest in the electrocodeposition has been revived due the development of new nanotechnology methods for the production of nano-particles. The codeposition of nanoparticles might enhance the mechanical properties of composite deposits without penalizing the corrosion resistance and avoid the formation of an abrasive third body during the wear process. On the other hand, the volume fraction of codeposited nano-particles is generally low and usually inversely proportional to their size. Many efforts have been done in order to improve the codeposition rate of nanoparticles. Most of the research on nickel composites is focused on the electrodeposition process or on the mechanical and wear properties rather than on the corrosion resistance. In this work, the protective properties of nickel matrix nanocomposite coatings have been studied by means of potentiodynamic curves and electrochemical impedance spectroscopy. Two different nanopowders, i.e., silicon carbide and alumina, were added to a Watts type galvanic bath in order to deposit the nanocomposites coatings on steel substrate. Ultrasonic vibrations have been considered as new process parameter to improve the dispersion of the powder into both the plating bath and metal matrix coating and to substitute pitting control agents for the production of defect-free coatings. Unique, functional properties of composite coatings are derived not only from the presence of the particles dispersed in the bulk of the metallic matrix but also on the matrix microstructural changes induced by the interaction between particles and electrocrystallization process. It has been demonstrated that the codeposition of the silicon carbide particles induces an important microstructural refinement. On the contrary, the aluminum oxide powder is strongly agglomerated and only under ultrasonic vibrations can be dispersed. Ultrasounds have a positive effect not only in hindering the porosity but also in dispersing the ceramic powder and increasing the codeposition rate leading thus to the production of protective and very refined coatings. Moreover, the better dispersed powder induces an improvement also in the corrosion protection leading to the formation of a more stable and resistant passive nickel oxide.

Controlled potential electrodeposition of a microcrystalline thin film of the charge transfer material tetrathiafulvalene–polyoxometalate of approximate composition (TTF)5.3(Bu4N)0.7[P2W18O62]·3H2O

Electrocrystallisation provides a systematic approach to the preparation of tetrathiafulvalene (TTF)–polyoxometalate materials in the form of films having significant conductivity. In this study, a highly uniform microcrystalline thin film derived from TTF+ and the Dawson–Wells anion [α-P2W18O62]6− has been deposited onto glassy carbon, gold and indium tin oxide surfaces by controlled potential oxidative electrolysis of TTF in the presence of K6[P2W18O62] in acetonitrile (0.1 M [Bu4N][PF6]). Elemental analytical data are consistent with the formation of this conducting charge transfer salt having the approximate composition (TTF)5.3(Bu4N)0.7[P2W18O62]·3H2O. Spectroscopic data support this conclusion. Mechanistic aspects of the electrocrystallisation process have been monitored by cyclic voltammetry, electrochemical quartz crystal microbalance and chronoamperometric methods. A less crystalline form of this material with a slightly different composition also can be produced by bulk electrolysis of TTF to TTF+ followed by addition of K6[P2W18O62]. The conductivity of the film at room temperature is in the semiconducting range. The EPR spectra, together with the field strength and temperature dependence of the magnetic susceptibility, suggest that regions of film behave as a quasi one-dimensional system, with antiferromagnetic and spin-flop behaviour at low temperatures. The Raman spectra are consistent with an average TTF charge state of +1, while voltammetry confirms the presence of [P2W18O62]6−. The morphology and crystallinity of the electrocrystallised and chemically prepared materials were investigated by scanning electron microscopy and X-ray diffraction, respectively.

Anomalous Conductivity Behavior of AgI-Vycor7930 Nanocomposites

Using the electrocrystallization process, silver iodide particles were embedded into bulk Vycor7930 porous glass (VPG) to obtain ionic conductor composite. X-ray microdiffraction (μXRD) was carried out on the composite. AgI was found to be in its β-form with nanometric crystallite size. Microstructure has also been investigated by scanning electron microscopy (SEM). The ionic conductor was found to be embedded in the center of the VPG disk, into the 4 nm diameter pore network. Electron probe for micro analysis (EPMA) has shown the homogeneity of the silver iodide precipitate inside the VPG. Electrical conductivity was measured by complex impedance spectroscopy (CIS). A large hysteresis phenomenon in the conductivity versus temperature curve at a temperature close to the transition β ↔ α-AgI was observed. At low temperature, the conductivity of the composite was found to be higher than that of pure β-AgI by 1 order of magnitude.

Initial Electrodeposition Behavior of Amorphous Ni-P Alloys

The growth morphology and structure of deposits during the initial stages of amorphous Ni-P electrodeposition was studied using atomic force microscopy (AFM), X-ray diffraction (XRD) and transmission electron microscope (TEM). Combined electrochemical and surface analytical measurements showed that the electrocrystallization process follows a three-dimensional instantaneous nucleation and growth mechanism. The structure of the Ni-P deposits progressively changed from polycrystalline to amorphous state with increasing electroplating time. Additional electrodeposition was carried out on amorphous carbon film at potential -650mV (SCE) for 5s in the same bath for plating Ni-P alloy. It was confirmed that the formation of crystal Ni at initial stage of electroplating Ni-P amorphous alloy was not caused by the epitaxial relationship between the crystal Ni and the crystal substrate and there was a nucleation process in the electrodeposition of amorphous alloy.

Effect of sulfate ion adsorption on the rate of copper electrocrystallization on Ag(111) face

The process of copper electrocrystallization on the Ag(111) face was studied in acidic perchlorate-sulfate electrolytes. Enhanced rate of charge transfer in the course of nucleation and growth of epitaxial copper crystallites was observed in the solutions with additives of sulfate ion as a result of local electrostatic effects under specific adsorption of anions. Copper nucleation parameters were estimated in the framework of the diffusion models and atomistic theory of electrochemical nucleation.

Role of SPS in chloride ions and PEG additive system for copper electrocrystallisation

Cyclic voltammetry and chronoamperometry techniques were employed in the study of copper electrocrystallisation process on a glassy carbon electrode from acid sulphate electrolytes in the presence of bis(sodiumsulfopropyl) (SPS) and polyethylene glycol and Cl– ions (PEG–Cl––SPS). The role of SPS in the effect of PEG–Cl––SPS was investigated. It was found that SPS can weaken the strong suppression of PEG–Cl– for copper electrocrystallisation. This weakening was proportional to the SPS concentration. The increase in SPS concentration also resulted in the promotion of the nuclei number density. The nucleation mechanism depended on not only SPS concentration but also the potential applied in the presence of PEG–Cl––SPS. In the presence of PEG–Cl––SPS, instantaneous nucleation followed by three-dimensional growth (3DI) occurred at negative electrodeposition potentials, as in an additive free bath. However, progressive nucleation followed by three-dimensional growth (3DP) was found at less negative potentials.

Electrodeposition of hydroxyapatite coating on CoNiCrMo substrate in dilute solution

Abstract In the present work, calcium phosphate coatings on CoNiCrMo substrate were prepared by electrodeposition at different voltages (− 1.4,−1.6,−1.8,−2.0 and − 2.2 V versus Ag/AgCl) in the mixed solution of 0.6 mM Ca(NO 3 ) 2 ·4H 2 O and 0.36 mM NH 4 H 2 PO 4 at 80 °C. The electrocrystallization process of the moderate potential (− 1.8 V) was addressed. To investigate the role of pH on HA formation during electrodeposition, different kinds of uncharged substrates (including CoNiCrMo, non-conducting polyethylene, Ti substrate and glass) were placed close to the cathode separately in some of the electrodeposition experiments at − 1.8 V. Moreover, the effect of pH on saturation indexes with respect to hydroxyapatite, octacalcium phosphate and dicalcium dihydrogen phosphate of this dilute solution were calculated by a computer program PHREEQC. The results showed the moderate potential sample (− 1.8 V) exhibited a uniform coating consisted of fine crystallized hydroxyapatite with hexagonal prism shape. It was also found the local pH value plays a crucial role in the formation of HA during the electrodeposition.

Nickel and nickel-phosphorous matrix composite electrocoatings

Nickel and nickel-phosphorous matrix composite coatings reinforced by TiO 2, SiC and WC particles were produced under direct and pulse current conditions from an additive-free Watts' type bath. The influence of the variable electrolysis parameters (type of current, frequency of current pulses and current density) and the reinforcing particles properties (type, size and concentration in the bath) on the surface morphology and the structure of the deposits was examined. It is demonstrated that the embedding of ceramic particles modifies in various ways the nickel electrocrystallisation process. On the other hand, Ni-P amorphous matrix is not affected by the occlusion of the particles. Overall, the imposition of pulse current conditions leads to composite coatings with increased embedded percentage and more homogenous distribution of particles in the matrix than coatings produced under direct current regime.

Morphology and growth of electrodeposited cuprous oxide under different values of direct current density

The growth of Cu 2O thin films electrodeposited by a two-electrode system with acid and alkaline electrolytes under different values of direct current (DC) densities was investigated. The microstructure of Cu 2O thin films produced in the acid electrolyte changes from a ring shape to a cubic shape with increasing DC density, and the microstructure of Cu 2O thin films produced in the alkaline electrolyte has a typical pyramid shape. The X-ray diffraction results show that Cu 2O thin films can be electrodeposited over a larger current domain than those deposited by a three-electrode system. The growth of Cu 2O thin films is examined under this domain, and the electrocrystallization process of such films is discussed taking into consideration the effect of current density on nucleation, cluster growth, and crystal growth.