Some novel efforts to describe the nucleation and growth at electrodeposition

Some alternative ways are developed of looking at the model concepts on electrochemical nucleation. The article consists in several parts concerning several stages of the overall process of nucleation and growth: the statistical approach to nucleation kinetics, the kinetics of the initial stage of the nuclei growth, the growth of an individual cluster under combined charge transfer and diffusion control, nucleation rate and the overall number of clusters, the growth of an increasing number of clusters at overlapping of diffusionally depleted zones, and galvanostatic nucleation.     

Modeling a solid-phase electrochemical reaction of lithium intercalation in aluminum during a noninstantaneous nucleation of Β-LiAl

The interfacial surface area and the electrode surface coverage by a product during the nucleation and growth of a new phase are modeled numerically and calculated analytically for electrochemical intercalation of lithium in aluminum in the course of which intermetallic compound Β-LiAl forms. As opposed to the theoretical calculation, the model accounts for mutual influence of the new-phase nuclei on their distribution over the cathode surface under conditions of noninstantaneous nucleation. The ordering of such a distribution varies extremally (passes through a maximum) with increasing size of zones where the nucleation probability is low and which surround the nuclei. This makes the dependence of a maximum specific interfacial area on the zone radius extremal as well. The model may be applied for analyzing potentiostatic current transients during cathodic intercalation of lithium in aluminum from a LiClO₄ solution in propylene carbonate.     

AFM studies of metal deposition: instantaneous nucleation and the growth of cobalt nanoparticles on boron-doped diamond electrodes.

In situ atomic force microscopy (AFM) is used to study the growth of cobalt nuclei on a boron doped diamond electrode under potentiostatic control. The rate of growth of the nuclei at the electrode surface is monitored using AFM as a function of time at different deposition potentials. The nucleation of cobalt nuclei is found to be "instantaneous" and the growth of the nuclei is shown to be kinetically rather than diffusionally controlled over periods of tens and hundreds of seconds. At very short times (<10 seconds) the kinetics of nucleation are apparent.     

添加剂丙烯基硫脲对镍电沉积的影响研究

采用循环伏安、线性扫描和恒电位阶跃电化学方法结合扫描电镜研究了不同浓度的丙烯基硫脲(ATU)对NH₃-NH₄Cl-H₂O体系镍在玻碳电极上的电沉积过程的影响. 循环伏安测试、线性扫描以及恒电位暂态曲线一致表明ATU的加入对镍电沉积具有阻化作用,并且随着ATU浓度的增加其阻化作用增强;恒电位暂态曲线结果表明,镍的电结晶是按瞬时形核三维生长机理进行的,随外加电位负移,晶体向外生长速率增大;ATU的加入没有改变镍的形核方式,但形核数密度增大,并且减小晶体向外生长的速率;扫描电镜结果表明,ATU的加入可以细化晶粒,得到整平、致密的镍沉积层.     

Overlapping of Diffusion Zones during the Growth of Electrodeposited Crystal Nuclei

A new way of accounting for the overlapping of diffusion zones during growth of individual crystal nuclei is suggested. A generalized formula for the time dependence of the nuclei growth current, which including both the diffusion and the electrochemical parameters of the process, is derived.     

Time Dependence of Current during Potentiostatic Growth of Clusters in Diffusion Mode of Electrodeposition

The fundamentally new model describes the initial current transients during the growth of clusters in the diffusion mode after instantaneous nucleation. The specific feature of the model is that it is based on the initial hemispherical diffusion of ions from bulk solution to the surface of growing clusters rather than on the period of Cottrell current decay. The subsequent overlapping of diffusion zones is taken into account by multiplying the current by a factor smaller than unity. The factor is equal to the ratio of true diffusion volume to the “extended” volume, which is equal to the overall volume of all diffusion hemispheres ignoring their overlapping. The results calculated by the model appeared to be rather close to those obtained using the conventional Scharifker–Hills–Mostany model, and, thus, confirm the correctness of this model. In this connection, the reasons for its inconsistency with the experimental data on the number of growing clusters remain unclear.     

Formation of diffusion zones around growing clusters during electrocrystallization of metals

The problem of the radius of depleted-by-diffusion zones around the growing individual clusters during the electrocrystallization in the mode of diffusion kinetics is solved. It is shown that a decrease in the probability of nucleation in every prescribed instant of time depends on the diffusion coefficient, overpotential, and individual characteristics of deposited metal: a specific surface energy and molar volume.     

Early stages of mercury electrodeposition on HOPG

The electrodeposition of mercury on highly oriented pyrolytic graphite (HOPG) from nitrate solution was studied using cyclic voltammetry, potentiostatic current transients, and in situ scanning tunneling microscopy (STM), in order to correlate the results of the kinetic nucleation with the deposit morphology. At relatively low overpotentials, the mercury deposition can be described by a model involving progressive nucleation on active sites and diffusion-controlled 3D growth without overlapping of diffusion zones. The deposition was initiated on step edges and surface defects forming 3D islands following the Volmer–Weber mechanism. The small number of atoms in the critical nucleus (n_k=1), together with the linear log J vs. η dependence, indicated that the nucleation process can be described by the atomistic model.     

Early Stages of CeO2 Thin-film Nucleation and Growth with Photo Irradiation

In this paper, the early stages of nucleation and photoirradiation growth of CeO₂ thin films have been studied. Cyclic voltammetry, chronoamperometry and scanning electron microscopy were used to analyze the nucleation process of CeO₂ thin films deposited on the anode with photo irradiation. Experimental results show that the anodic deposition process with photo illumination is controlled by diffusion. Compared with the dark state, photo illumination mainly contributed to increase the current density of the three-dimensional nucleation process, because photo illumination is helpful to create active sites and accelerate the nucleation progress on the surface that a thin ceria film has been formed. Two-dimensional nucleation process mainly exists within the initial 2 s, and then only three-dimensional instantaneous nucleation process continues, which may be the main reason why the thickness of the CeO₂ film can continue to grow with photo illumination but not in the dark state. Increasing the deposition overpotential can promote two-dimensional nucleation and growth rate, whilst when the potential exceeds 0.65 V, three-dimensional current density decreases. The li-miting factor at that time may be the diffusion rate of cerium ions in the solution towards the electrode substrate.     

Incipient CdS thin film formation

The quality of a final thin film is essentially determined by the processes taking place at incipient CdS deposition, which in turn are strongly influenced by the physicochemical properties of the substrate and liquid in contact. SEM pictures of deposits formed through steady flow of a supersaturated (with respect to CdS) solution suggest that initially nuclei are continuously generated on the substrate and grow as discrete "surface" particles. With time, these particles tend to "coalesce" with neighboring ones, while new nuclei keep forming and growing, leading to the formation of a coherent film. There is evidence that similar growth patterns prevail in CdS deposition via the chemical bath deposition (CBD) process. Based on experimental observations, a simple model is developed, which is capable of predicting macroscopically determined film characteristics such as the temporal thickness evolution including the "induction period." Two cases of the growth pattern are examined theoretically; one based on instantaneous surface nucleation (due to its simplicity) and another with a constant surface nucleation rate, which appears to be closer to experimental observations.     

聚苯胺的成核及生长机理

本文通过恒电位阶跃法研究了聚苯胺在不同介质中的成核与膜的生长过程动力学。结果表明, 在硫酸介质中, 成核过程为扩散控制下的三维连续成核, 得到疏松、多孔的膜; 而在高氯酸介质中, 成核则是电化学动力学控制下的二维成核过程。在高电位时(E>1.02V, vs, SCE)为二维连续成核过程, 而在较低的电位时, 主要表现为二维瞬时成核, 膜层呈网状且致密。     

Influence of [BMIM]HSO4 on electrodeposition and corrosion behavior of Zn coatings from acidic sulfate bath

The effect of 1‐butyl‐3‐methylimidazolium hydrogen sulfate‐[BMIM]HSO₄ on the nucleation and growth of zinc from acidic sulfate bath was investigated at a glassy carbon (GC) electrode using cyclic voltammetry, chronoamperometric and scanning electron microscopy techniques. Dimensionless chronoamperometric current‐time transients for the electrodeposition of zinc on GC from the bath free of [BMIM]HSO₄ were in good accord with the theoretical transients for the limiting case of instantaneous three‐dimensional nucleation with diffusion‐controlled growth of the nuclei. The addition of [BMIM]HSO₄ was found to have a blocking effect on the electrodeposition of zinc and led to decrease of the nucleation and growth rate of nuclei. In addition, the instantaneous nucleation mechanism observed in the additive‐free bath was changed to a more progressive one when [BMIM]HSO₄ was present in the bath. Surface morphology analysis indicated that [BMIM]HSO₄ can induce the formation of finer grained deposits by the adsorption of additive in the first stages of deposition. The corrosion behavior of Q235 steel with coating by a thin layer of zinc in the absence and presence of [BMIM]HSO₄ was examined in 3.5% NaCl solution. The Zn coating obtained from the additive‐containing baths exhibited more excellent protection of the base metal in comparison to the additive‐free one. Copyright © 2012 John Wiley & Sons, Ltd.     

Modeling growth of organized nanoporous structures by anodic oxidation

Nanostructured porous oxides are produced by anodic dissolution of several metals. A scaling approach is introduced to explain pattern nucleation in an oxide layer, and a related microscopic model shows oxide growth with long nanopores. The scaling approach matches the time of ion transport across the thin oxide layer, which is related to metal corrosion, and the time of diffusion along the oxide/solution (OS) interface, which represents the extension of oxide dissolution. The selected pattern size is of order (dD(S)/v(O))(1/2), where d is the oxide thickness, v(O) is the migration velocity of oxygen ions across the oxide, and D(s) is the diffusion coefficient of H(+) ions along the oxide/solution interface. This result is consistent with available experimental data for those quantities, predicts the increase of pore size with the external voltage, and suggests the independence of pore size with the solution pH. Subsequently, we propose a microscopic model that expresses the main physicochemical processes as a set of characteristic lengths for diffusion and surface relaxation. It shows a randomly perturbed OS interface at short times, its evolution to pore nucleation and to stable growth of very long pores, in agreement with the mechanistic scenario suggested by two experimental groups. The decrease of the size of the walls between the pores with the interface tension is consistent with arguments for formation of titania nanotube arrays instead of nanopores. These models show that pattern nucleation and growth depend on matching a small number of physicochemical parameters, which is probably the reason for the production of nanostructured porous oxides from various materials under suitable electrochemical conditions.     

Na_5P_3O_(10)-Ca(OH)_2-CO_2-H_2O体系纳米CaCO_3的成核与生长

通过化学分析、SEM显微分析技术结合RosinRamiler概率统计理论从介观层次研究Na5P3O10CaOH2CO2H2O体系纳米CaCO3的合成反应及其成核和生长过程。结果表明Na5P3O10对CaOH2的碳化反应具有抑制作用。随着Na5P3O10的增加体系中CaCO3的成核速率B0逐渐增大。在Na5P3O10=0ppm时CaCO3结晶的生长由长程扩散和凝聚生长控制Na5P3O10=380.4760.9ppm时前期受短程扩散和界面反应控制、后期受长程扩散控制。Na5P3O10的存在抑制了纳米CaCO3的晶体生长。     

Liquid-liquid phase separation by nucleation and growth in solutions of poly(2,6 dimethyl-1,4 phenylene oxide) in toluene

In solutions of poly(2,6 dimethyl-1,4 phenylene oxide) in toluene, the nucleation of the newly formed phase during liquid-liquid phase separation takes place after induction periods which vary between several minutes (at temperatures close to the spinodal) and several hours (at temperatures close to the cloudpoint). The growth of the nuclei in the initial stages is diffusion controlled. The diffusion coefficients and the activation energy of diffusion were calculated. From these values, together with the calculated volume free energies and the experimental induction times, an estimate could be made of the size of a critical nucleus and of the surface free energy of the nuclei.     

玻碳电极上铜电沉积初期行为研究

运用循环伏安和计时安培法研究酸性镀铜溶液中硫酸和 2_巯基苯骈咪唑对铜电沉积初期行为的影响 .实验表明铜的电沉积经历了晶核形成过程 ,其电结晶按瞬时成核三维生长方式进行 ,硫酸对铜的电沉积具有加速作用 ,而 2_巯基苯骈咪唑对铜的电沉积起阻化作用 ,两者均不改变铜的电结晶机理     

Nucleation on active centers in confined volumes

Kinetic equations describing nucleation on active centers are solved numerically to determine the number of supercritical nuclei, nucleation rate, and the number density of nuclei for formation both of droplets from vapor and also crystalline phase from vapor, solution, and melt. Our approach follows standard nucleation model, when the exhaustion of active centers is taken into account via the boundary condition, and thus no additional equation (expressing exhaustion of active centers) is needed. Moreover, we have included into our model lowering of supersaturation of a mother phase as a consequence of the phase transition process within a confined volume. It is shown that the standard model of nucleation on active centers (Avrami approach) gives faster exhaustion of active centers as compared with our model in all systems under consideration. Nucleation rate (in difference to standard approach based on Avrami model) is equal to the time derivative of the total number of nuclei and reaches some maximum with time. At lower nucleation barrier (corresponding to higher initial supersaturation or lower wetting angle of nucleus on the surface of active center) the exhaustion of active centers is faster. Decrease in supersaturation of the mother phase is faster at higher number of active centers.     

Computer simulation of the kinetic behaviour of surface reactions driven by a linear potential sweep: Part III. Monolayer formation by a nucleation and growth mechanism

The kinetic behaviour of a surface process involving the deposition of a two-dimensional surface film by a nucleation and growth mechanism is treated for the case of linear potential sweep control. Features which distinguish nucleation and growth in monolayer formation from random electrodeposition (Langmuir case) treated in previous papers are emphasized. Two main mechanisms are considered: one where the growth occurs from a fixed surface density of nuclei and the other where growth occurs from a potential-dependent density of nuclei. Computer simulations and some analytical derivations of the kinetic behaviour for these two cases are made and the characteristic kinetic features of the process are deduced, enabling the latter to be distinguished in terms of experimentally accessible criteria. The extent of reversibility of the processes can be usefully expressed in terms of a limiting sweep-rate parameter, s₀, which is related to the rate constant for nucleation or the surface density of nuclei and the rate constant for growth.     

A new approach to nucleation of cavitation bubbles at chemically modified surfaces

Cavitation at the solid surface normally begins with nucleation, in which defects or assembled molecules located at a liquid-solid interface act as nucleation centers and are actively involved in the evolution of cavitation bubbles. Here, we propose a simple approach to evaluate the behavior of cavitation bubbles formed under high intensity ultrasound (20 kHz, 51.3 W cm(-2)) at solid surfaces, based on sonication of patterned substrates with a small roughness (less than 3 nm) and controllable surface energy. A mixture of octadecylphosphonic acid (ODTA) and octadecanethiol (ODT) was stamped on the Si wafer coated with different thicknesses of an aluminium layer (20-500 nm). We investigated the growth mechanism of cavitation bubble nuclei and the evolution of individual pits (defects) formed under sonication on the modified surface. A new activation behavior as a function of Al thickness, sonication time, ultrasonic power and temperature is reported. In this process cooperativity is introduced, as initially formed pits further reduce the energy to form bubbles. Furthermore, cavitation on the patterns is a controllable process, where up to 40-50 min of sonication time only the hydrophobic areas are active nucleation sites. This study provides a convincing proof of our theoretical approach on nucleation.     

Nucleation and growth of copper on glassy carbon: Studies in extended overpotential interval

The nucleation and growth of copper crystals on a glassy carbon electrode are investigated at different constant overpotentials. Current transients are recorded and the number of copper nuclei is microscopically registered. The experimental data for the growth current are interpreted according to the theories of progressive and instantaneous nucleation and information is obtained on the stationary nucleation rate, the saturation nucleus number density and the exchange current density at the crystals–solution interface boundary.