Three-dimensional Growth Mechanism Research Articles

Crystallization of CoWB ternary boride in nickel-based metallic glass

The crystallization kinetics of CoWB ternary boride were investigated through non-isothermal differential scanning calorimetry experiments, using a Ni-based metallic glass precursor as the starting material. The effects of isothermal heat treatment temperature on the phase evolutions were also systematically studied. The results showed that the melt crystallization and glass crystallization behaviors of the alloy differ from each other. The continuous heating transformation diagram plotted from non-isothermal analyses is consistent with the results of isothermal heat treatments. A broad ternary boride precipitation zone was demonstrated, involving the gradual precipitation of CoWB crystals. Avrami exponent values for the early crystallization stage showed that the crystallization mechanism of CoWB is governed by the interface-controlled three-dimensional growth mechanism, and nucleation rate is high. As the crystallization progresses, a diffusion-controlled growth occurs and the nucleation rate decreases. This study offers insights into the heat treatment of CoWB-reinforced nickel matrix nanocomposites, benefiting future research and industrial production processes.

Preparation of Cu nanolayers by magnetic field-assisted electrodeposition and research on the nucleation and growth mechanism

Electrodeposition technology is widely used in the surface treatment of copper foil, and the core of this technology is roughening and curing treatment. During the electrodeposition process, the deposited layers often exhibits some problems, such as coarse grain size, uneven thickness and difficult control of crystal morphology. The magnetohydrodynamic (MHD) effect of magnetic field can obviously control the electrodeposition of Cu and improve the micro-morphology and performance of deposited layers. In this paper, Linear Sweep Voltammetry (LSV), Cyclic Voltammetry (CV) and Chronocoulometry (CC) curves were adopted to investigate the electrochemical behavior of deposited Cu in ultra-high acidity sulfate systems under different magnetic field conditions. The nucleation and growth mechanism were discussed, and the micro-morphology of deposited layers was analyzed. The results show that the electrodeposition of Cu follows the three-dimensional (3D) growth mechanism of progressive nucleation and diffusion control under the static condition, and the deposits appear cylindrical shape formed by spherical agglomerated. The magnetic field significantly improves the mass transfer rate, and the deposited layers will be more uniform and dense, following 3D growth mechanism under the electrochemical control. With the increasing of magnetic field intensity, the nucleation mechanism gradually shifts from progressive to transient nucleation. At the early stage of nucleation, the high-intensity magnetic field can significantly increase the number of grains and refine them, obtaining uniform and dense deposited nanolayers.

Reutilization of Reclaimed Asphalt Binder via Co-Pyrolysis with Rice Husk: Thermal Degradation Behaviors and Kinetic Analysis.

Realizing the utilization of reclaimed asphalt binder (RAB) and rice husk (RH) to reduce environmental pollution and expand the reutilization technique of reclaimed asphalt pavement (RAP), co-pyrolysis of RAB with RH has great potential. In this study, the co-pyrolysis behaviors, gaseous products, and kinetics were evaluated using thermogravimetric analysis and Fourier transform infrared spectroscopy (TG-FTIR). The results showed that incorporating RH into RAB improved its pyrolysis characteristics. The interactions between RAB and RH showed initial inhibition followed by subsequent promotion. The primary gaseous products formed during co-pyrolysis were aliphatic hydrocarbons, water, and carbon dioxide, along with smaller amounts of aldehydes and alcohols originating from RH pyrolysis. All average activation energy values for the blends, determined through iso-conversional methods, decreased with RH addition. The combined kinetic analysis revealed two distinct mechanisms: (1) at the lower conversion range, the pyrolysis of the blend followed a random nucleation and three-dimensional growth mechanism, while (2) at the higher conversion range, the control mechanism transitioned into three-dimensional diffusion.

Anion-Regulated Hierarchical Self-Assembly and Chiral Induction of Metallo-Tetrahedra.

The precise control over hierarchical self-assembly of superstructures relying on the elaboration of multiple noncovalent interactions between basic building blocks is both elusive and highly desirable. We herein report a terpyridine-based metallo-cage T with a tetrahedral motif and utilized it as an efficient building block for the controlled hierarchical self-assembly of superstructures in response to different halide ions. Initially, the hierarchical superstructure of metallo-cage T adopted a hexagonal close-packed structure. By adding Cl- /Br- or I- , drastically different hierarchical superstructures with highly-tight hexagonal packing or graphite-like packing arrangements, respectively, have been achieved. These unusual halide-ion-triggered hierarchical structural changes resulted in quite distinct intermolecular channels, which provided new insights into the mechanism of three-dimensional supramolecular aggregation and crystal growth based on macromolecular construction. In addition, the chiral induction of the metallo-cage T can be realized with the addition of chiral anions, which stereoselectively generated either PPPP- or MMMM-type enantiomers.

Electrodeposition nanoarchitectonics of nickel cobalt phosphide films from methyltriphenylphosphonium bromide-ethylene glycol deep eutectic solvent for hydrogen evolution reaction

Active hydrogen evolution electrocatalysts based on earth-abundant elements are essential in the widespread application of water electrolyzers. Nickel cobalt phosphide films (Ni-Co-P) are electrodeposited on to carbon cloth substrates from a methyltriphenylphosphonium bromide-ethylene glycol deep eutectic solvent using the potentiostatic method. The formation of Ni-Co-P follows the diffusion-controlled three-dimensional instantaneous nucleation and growth mechanism, and the deposited Ni-Co-P have rough surface and contain abundant pores. The Ni-Co-P are active towards hydrogen evolution, and the most active film reaches 10 mA cm−2 current densities with an overpotential of 93 mV in 1 M KOH, and with the Tafel slope at 48 mV dec−1. The high electrocatalytic activity is originated from the enhanced intrinsic activity induced by the electron interaction that accelerates the hydrogen adsorption process (Volmer step) at the electrochemically active sites. The Ni-Co-P can stably catalyze the HER.

Selective Extraction of Silver and Palladium in Leachate Based on EDTA Complexation: Electrodeposition, Nucleation Mechanism, and Kinetic Analysis

The development of green recycling technology for precious metals such as Ag and Pd from secondary resources can prevent environmental pollution caused by improper disposal, and it can alleviate resource shortage and promote sustainable development. Ag and Pd often coexist in some solid waste. This study proposed the extraction of Ag and Pd stepwise from leachate through the green technology of potential-controlled electrodeposition, and the reduction potential difference of Ag and Pd in solution was increased based on EDTA (ethylenediaminetetraacetic acid) complexation. The electrochemical behavior of Ag+ and Pd2+ in solution was investigated. It was determined that the electrodeposition separation of Ag+ and Pd2+ can be achieved with a pH of 9 and an EDTA molar ratio of 1:1.5 in the solution. With sequential electrodeposition at 0 V and −0.7 V, 99.3% of Ag and 96.15% of Pd were recovered, respectively, and their purity was achieved 100%. Pd electrodeposition conformed to three-dimensional instantaneous nucleation and growth mechanism analyzed with the Scharifker–Hills model. Compared with the EDTA-free environment, the diffusion coefficient of ions reduced, and the activation energy of Ag and Pd reduction reaction increased in the EDTA environment. This study provides an environmentally friendly and efficient method for precious metal recovery from secondary resources.

Electrodeposited Cobalt Nanosheets on Smooth Silver as a Bifunctional Catalyst for OER and ORR: In Situ Structural and Catalytic Characterization.

Developing earth-abundant, cost-effective, and active bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is key to boosting sustainable energy systems such as electrolyzers and lithium-air batteries. However, the performance of promising cobalt-based materials is impaired by the external effects of binders and carbon additives as well as inhomogeneous electrode fabrication. In this work, binder- and carbon-free flower-like Co-decorated Ag catalytic nanosheets were in situ-synthesized via a simple electrodeposition approach. The morphology, composition, and structure of Co/Ag before and after OER were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Co/Ag thin film electrodes with various Co contents exhibited a bifunctional activity toward ORR and OER due to a synergistic effect. XPS analysis suggested the formation of Co3O4 as the main active species for OER. In particular, Co (83%)/Ag surface revealed a 60 mV lower ORR overpotential than a pure Ag surface and even lower than drop-casted Co3O4 nanoparticles on Ag surface. Only 1.5% peroxide was generated, suggesting a four-electron transfer ORR. In addition, the OER onset potential on Co/Ag is 60 mV less than Co3O4. Tafel slopes of 71 and 75 mV dec-1 were obtained for ORR and OER, respectively. Importantly, the three-dimensional (3D) growth mechanism of a cobalt layer (∼1 nm) on a well-defined atomic smooth Ag surface is unraveled by in situ electrochemical scanning tunneling microscopy (EC-STM). EC-STM suggests that Co prefers to nucleate at the step edges of Ag and grows in a 3D, forming nanoparticles, where the deposition/dissolution process of the Co adlayer on Ag is reversible. This investigation may provide insights into design strategies of efficient oxygen electrocatalysts.

New Frontiers in Electrodeposition for More Sustainable Electroplating Processes

Although technological and processing advancements occurred in the past forty years, industrial firms are still struggling to provide solutions to corrosion protection as well as reduction of toxic wastes. Specifically, large-scale industrialization of electroplating techniques will continue to be limited by strict environmental regulations. Moreover, price volatility of the highly demanding electroplated materials like gold, palladium, copper and nickel will heavily impact the market in the next years. In that respect, alloy plating offers better answers in terms of economic growth and environmental sustainability due to fine tuning composition, morphology and crystallinity [1]. The main categories of alloy compounds are presented and the most important properties for the manufacturing process discussed. Particular attention is devoted to advances in industrial quality control and viable solutions for the reduction of precious metal content in electroplated accessories as well as replacement of cyanide and nickel baths with non-toxic compounds, also considering the commercial needs of wear resistance and aesthetic characteristics of gloss.The electrodeposition of Cu-Sn alloys (bronze) has earned considerable interest thanks to the chemical-physical properties of this alloy, which make it a valid substitute for nickel in fashion industry. Generally, most of the bronze coatings are electroplated starting from baths containing cyanides, and the metal precursors are selected as cyanide compounds. Free cyanide is a well-known problem in the galvanic production cycle both in terms of toxicity for the workers as well as for the environment, and in terms of costs associated with its disposal. The aim of this study is to develop an electroplating bath totally cyanide-free, therefore formulated in an innovative way and which, in addition to being free from this dangerous species, has an eco-friendly support electrolyte. To achieve this goal, methanesulfonic acid (MSA) was chosen as electrolyte, which is biodegradable as part of the natural sulfur cycle. We've studied different formulations in terms of metal precursors, organic additives and their concentrations [2-3].The same cyanide issue is present also in for the electrodeposition of silver, for this reason the influence of polyethyleneimine (PEI) as additive for cyanide-free silver bath, in combination with 5,5-dimethylhydantoin (DMH) as complexing agent, was studied [4]. Chronoamperometry was used to investigate the electrodeposition mechanism, which is found to be a three-dimensional diffusion-controlled nucleation and growth mechanism, according to the Scharifker–Mostany’s model. Smoother, brighter and blue colored silver deposits are obtained in the presence of PEI in a Hull’s cell test, at low density current. Eventually, the influence of nitrate anion is also investigated. The presence of nitrate increases the range of current density allowing for an effective Ag deposition.We also investigated the use of modulated currents to increase the throwing power of electroplating, obtaining a more uniform deposition and reducing the amount of metals but maintaining the required characteristics. Pulsed current justifies its practical application mainly through its ability to influence the mechanisms of electrocrystallisation, which in turn control the mechanical and physical properties of the deposited metal. By simply adjusting the amplitude and length of the pulses, it is possible to control not only the composition and thickness, in atomic order, of the deposits, but to improve their characteristics such as grain size, porosity and homogeneity [5].The authors acknowledge Regione Toscana POR CreO FESR 2014-2020 – azione 1.1.5 sub-azione a1 – Bando 1 “Progetti Strategici di ricerca e sviluppo” which made possible the projects “A.C.A.L. 4.0” (CUP 3553.04032020.158000165_1385), “A.M.P.E.R.E.” (CUP 3553.04032020.158000223_1538) and “GoodGalv” (3647.04032020.157000060).

Thermal kinetics study on the conversion of β-MoO3 to α-MoO3; A molybdenite concentrate derivative as a catalyst

Herein, thermal decomposition kinetics of molybdic acid (MA) obtained from the leaching of molybdenite concentrate are extensively studied as a precursor for the preparation of molybdenum trioxide (MoO3). The thermal kinetics equation of the reaction suggests that the precursor (MA, H2MoO4.H2O) is converted to β-MoO3 and then to α-MoO3 due to the heating process, giving rise to a transformation temperature of 260-320°C, the average activation energy of about 26.53 ± 0.02 kJ/mol, and a pre-exponential factor of 107 1/min for the transformation of β-MoO3 to α-MoO3. Moreover, differential scanning calorimetry reveals that the volume diffusion mechanism controls the crystallization reaction, leading to the decomposition of MA. Our results indicate that Johnson-Mehl-Avrami (JMA) kinetics with nucleation and three-dimensional growth mechanism can model the experimental data with acceptable accuracy. The catalytic attributes of the stable β-MoO3/α-MoO3 compound provided an efficiency of over 89 % for the oxidation process of methanol to formaldehyde.

Differences in Electrodeposition of Cu Onto Au(111) from Deep Eutectic Solvents of Varying Composition

Recently, there has been an increasing interest in the electrodeposition of various metals from deep eutectic solvents (DESs) as an alternative to other non-aqueous electrolytes. Beneficial characteristics include low viscosity compared to ionic liquids, a broad electrochemical stability window, and the individual components can be purified separately.[1] DESs consist of two components, an organic (type III) or inorganic (type IV) salt and a hydrogen bond donor (HBD).[2,3] If mixed in their eutectic ratio, a liquid is typically formed at room temperature and the freezing-point depression is believed to result from strong interactions between salt and HBD. However, the effect of the different components on this phenomenon has not been studied in detail, yet.In this study, the impact of various HBDs on the thermal properties is investigated as a function of their molar ratio in relation to the salt. Phase diagrams of DESs types III and IV are generated by differential scanning calorimetry (DSC), and subsequently, the eutectic composition and temperature of the respective mixtures are determined. As copper electrodeposition onto Au(111) single crystal electrodes has already been subject of numerous studies,[4,5] in this work it has been chosen as reference system to investigate the electrochemical characteristics of DESs by cyclic voltammetry, chronoamperometry, and electrochemical quartz crystal microbalance (EQCM). The impact of the salt, the HBD, and their molar ratio on Cu underpotential and bulk deposition and dissolution behavior are studied. We find that these reactions cannot be associated with the freezing-point depression of the DESs, but are instead strongly dependent on the electrolyte composition.The mechanism of Cu electrodeposition from chloride- and nitrate-containing DESs type III in combination with Cu+ and Cu2+ salts is affected by the high concentration of ions. Regardless of whether ethylene glycol or trifluoroacetamide is used as HBD, both Cu+ and Cu2+ species are easily reduced and deposited. The two-electron reduction prevails with presence of ethylene glycol and higher salt content. In all media studied, deposition follows a nucleation and three-dimensional growth mechanism controlled by diffusion. The diffusion rate of the Cu species is strongly related to the molar ratio of salt and HBD.DESs type IV exhibit a different behavior during electrodeposition and dissolution that is attributed to the HBD containing various functional groups. The HBD also influences the morphology of Cu deposits, as studied by atomic force microscopy (AFM). The crucial role of the anion is demonstrated in the examples of triflate and nitrate.

Cyanide-free silver electrodeposition with polyethyleneimine and 5,5-dimethylhydantoin as organic additives for an environmentally friendly formulation

The influence of polyethyleneimine (PEI) as additive for cyanide-free silver bath, in combination with 5,5-dimethylhydantoin (DMH) as complexing agent, is studied. Cyclic voltammetry (CV) measurements are used to characterize the electrochemical behaviour of the Ag/DMH complex. The Ag electrodeposition from the cyanide-free silver-plating bath is analysed by CVs and the process is optimized varying the PEI concentration. Chronoamperometry is then used to investigate the electrodeposition mechanism, which is found to be a three-dimensional diffusion-controlled nucleation and growth mechanism, according to the Scharifker–Mostany’s model. Smoother, brighter and blue coloured silver deposits are obtained in the presence of PEI in a Hull’s cell test, at low density current. Eventually, the influence of nitrate anion is also investigated. The presence of nitrate increases the range of current density allowing for an effective Ag deposition.

Nucleation and growth mechanism of Cu-Zn/AgNPs composite coatings at different concentrations of silver nanoparticles (AgNPs) in solution

Atomic force microscopy (AFM), X-ray Diffraction (XRD), and electrochemical techniques (voltammetry and chronoamperometry) were used to evaluate the influence of the concentration of silver nanoparticles (AgNPs) on the electrodeposition and nucleation mode of Cu-Zn/AgNPs composite coatings. The voltammetry analysis display three reduction processes during the formation of the Cu-Zn/AgNPs metal composite. The first process (peakPCI) appears in the potential range of -0.5 to -1.2 V vs. saturated calomel electrode (SCE) and corresponds to the reduction of Cu(II) to Cu(0). The second and the third processes, peak PCII and PCIII, respectively are located in the range of -1.4 to -1.6 V vs. SCE and are associated with the deposition of various crystalline phases of the Cu-Zn alloy. The potential of the PCI peak is shifted in the negative direction by increasing the concentration of AgNPs in the electrolytic solution. This effect is related to the adsorption of AgNPs on the substrate surface. From the chronoamperometry study, it was possible to disclose a process of nucleation and growth of phases in the potential region where the peak PCI is formed. This nucleation process may be explained in terms of a combination of an adsorption process and a diffusion-controlled three-dimensional crystal nucleation and growth mechanism (3D−dc(PcI)). In the potential range where the PCII and PCIII peaks appear, a second nucleation process take place. This nucleation process involves three mechanisms: an adsorption process and two three-dimensional (3D) mechanisms of the kinetics of nucleation and diffusion-controlled growth of bimetallic phases (3Ddc−bimetal) that correspond to the nucleation of various phases of the alloys. On the other hand, a decrease in the nucleation kinetics parameters (density of active sites formed (N0) and the nucleation rate (A)) is observed with the increasing concentration of the AgNPs in the electrolytic solution. XRD analysis confirmed the formation of various crystalline structures of the Cu-Zn alloy at -1.50 V vs. SCE. Furthermore, AFM showed that the morphology and size of the formed metal clusters strongly depend on the content of the AgNPs in the bath.

Targeted recovery of Ag-Pd alloy from polymetallic electronic waste leaching solution via green electrodeposition technology and its mechanism

Electronic waste (e-waste), as hazardous waste, is a promising secondary resource of precious metals. The extraction of precious metals from e-waste has great environmental and economic benefits. Most of the existing methods have high energy consumption, environmental pollution or low recovery efficiencies. This study proposed the application of green electrodeposition technology to realize targeted recovery of Ag-Pd alloy from Ni, Cu, Ag, Pd, Bi polymetallic e-waste leaching solution. Linear sweep voltammetry was conducted to determine the feasibility of targeted extraction. The high purity of Ag-Pd alloy was realized by controlling the potential. The recovery efficiencies of Ag and Pd were 97.72% and 98.05% after 5 h in 0.5 mol/L HNO3 with applied potential of 0.35 V. The results indicated the formation of monophase Ag-Pd alloy. Besides, the effect of acidity and potential on the particle size of alloy was analyzed. Chronoamperometric method was applied to study the electrodeposition mechanism. The Ag-Pd electrodeposition followed three-dimensional instantaneous nucleation and growth mechanism analyzed with Scharifker-Hills model, thus producing a solid solution. The nucleation site increased with the overpotential. This study provides a novel, efficient and green approach for the targeted recovery of Ag and Pd from the complex multi-metal system of e-waste.

Nucleation and growth mechanisms of an electrodeposited Ni–Se–Cu coating on nickel foam

Electrocatalysts for water splitting have been widely explored among recent years. In this study, nickel–selenium–copper (Ni–Se–Cu) coating was synthesized on nickel foam through potentiostatic electrodeposition. The electrochemical kinetics and nucleation mechanisms of the deposition were investigated, and the diffusion coefficient D from different deposition potentials and temperatures was calculated. Results reveal that the electrodeposition of Ni–Se–Cu follows an instantaneous nucleation and diffusion-controlled three-dimensional (3D) growth mechanism. Deposition potential and bath temperature slightly effect the nucleation mechanism of electrodeposition. The apparent activation energy Ea of the hydrogen evolution reaction (HER) in 1.0 M KOH electrolyte of Ni–Se–Cu is 21.1 kJ·mol−1, which is lower than that of Ni–Se (37.7 kJ·mol−1). The majority phase formed by nickel and selenium is Ni3Se2, and a Ni(Cu) solid solution forms after the incorporation of Cu atoms into a Ni lattice.

Thermal decomposition kinetics analysis of the oil sludge using model-based method and model-free method

Oil sludge (OS) is one of the main waste in the petrochemical industry, and serious consequences can result from the improper disposal of this waste. Pyrolysis is an effective method to dispose of OS and to recover the high heating value combustibles from it. The pyrolysis of three OS samples was carried out in a nitrogen atmosphere at heating rates of 5°C/min, 10°C/min, and 20°C/min, respectively. The TG-DTG/DSC-DDSC curves show that the thermal decomposition of OS has been divided into 5 stages, and each stage has unique thermal decomposition characteristics. Two model-free methods were used to calculate the apparent activation energy at a conversion rate from 0.05 to 0.95, and based on 10 solid-state mechanisms of thermal decomposition, the model-based method was used to fit the thermal decomposition mechanisms exposed to the three heating rates. The results show that the high heating rate is beneficial for the pyrolysis of OS. The apparent activation energy varies irregularly with the conversion rate, and the apparent activation energy error calculated by the FWO method is smaller. For the three samples, OS-1, OS-2 and OS-3, the average apparent activation energies calculated by the FWO method are 40.39kJ/mol, 38.01kJ/mol, and 85.53kJ/mol, respectively. The mechanism function of OS thermal decomposition changed, and the process of thermal decomposition should be described by a three-step thermal decomposition model. During 140.48–331.88°C, the fitting correlation coefficients of the two-dimensional phase interfacial reaction mechanism under the three heating rates were all above 0.99. During 400.00–556.57°C, the fitting result of the three-dimensional nucleation and growth mechanism is better than fitting results of other models. During 583.82–676.60°C, the two-dimensional diffusion mechanism has a good fitting regression. Significantly, model-based method and model-free method provide effective and reliable thermal decomposition kinetics parameters and models as a theoretical support for optimization of OS industrial pyrolysis and treatment of OS.

Observing the three-dimensional terephthalic acid supramolecular growth mechanism on a stearic acid buffer layer by molecular simulation methods.

The terephthalic acid (TPA) supramolecular growth mechanisms on the stearic acid (STA) buffer layer, such as the phase separation and layer-by-layer (LBL) mechanisms, were considered by molecular simulations. The electrostatic surface potential (ESP) charges obtained by the semi-empirical ab initio package VAMP with PM6 were used with the Dreiding force field. The stochastic tunneling-basin hopping-discrete molecular dynamics method (STUN-BH-DMD) was first used to construct the most stable STA buffer layers (STA100, STA120, and STA140) on graphene. At STA100 and STA120, the STA molecule stacking along their long axis is the major mechanism to obtain the stable STA buffer layer. At STA140, the hydrogen bond network between the terminal COOH groups of STA molecules makes the STA buffer layer the most stable, leading to a higher disintegration temperature among all STA coverages. In the early growth of the TPA supramolecule, TPA molecules were first adsorbed by the holes between STA piles. At STA100 and STA120, the subsequent TPA molecules were adsorbed by the TPA molecules within the holes, leading to the phase separation growth. At STA140, the TPA supramolecule tends to grow by the LBL mechanism.

Electrochemical behavior and electrodeposition of Ni-Co alloy from choline chloride-ethylene glycol deep eutectic solvent

In this work, nickel-cobalt (Ni-Co) alloy was prepared in choline chloride-ethylene glycol deep eutectic solvent by deposition. Metal ion complex structure and stability were studied using UV–Vis. The electrochemical behavior in different metal salts was studied by voltammetry (CV) and chronoamperometry (CA). The corrosion resistance was studied using potentiodynamic polarisation and electrochemical impedance (EIS). Surface and phase composition of Ni-Co alloy coatings were characterized by scanning electron microscopy (SEM/EDS) and X-ray diffraction (XRD). The results from the voltammetry showed that the reduction peak appear among −0.6 V ∼ −1.13 V, which belonged to Ni-Co codeposition. The reduction of Ni-Co alloy in the CE was an irreversible process under diffusion control. Chronoamperometric results indicated that the electrodeposition of Ni-Co on a glassy carbon electrode followed the mechanism of instantaneous nucleation and three-dimensional growth. The results of microstructure and phase composition showed that the control of deposition potential could effectively control the microstructure and Co content of Ni-Co alloy. Nano crystal structure could be obtained with a grain size in the range of 3.1–4.0 nm. Comparison in the corrosion behaviour of the coatings showed that the change of Co content had an effect on the corrosion resistance of Ni-Co alloy.

RESPONSE TO ASCORBIC ACID ON POLYPYRROLE FILM MODIFIED BY COPPER PARTICLES

In this work, a modified electrode of copper-polypyrrole (Cu-PPy) is elaborated by charging the polymer matrix by Cu particles. The response to ascorbic acid (AA) of this material was tested. The results show good performances. The results indicated a sensitive oxidation peak current of AA on the modified electrode. The success of this application led us to study the nucleation mechanism of copper on the PPy surface which permits to obtain this response. Nucleation and growth of electrodeposited copper onto PPy substrate have been studied in an aqueous solution of 0.01[Formula: see text]M CuCl2 and 1[Formula: see text]M KCl by means of electrochemical methods: cyclic voltammetry, chronoamperometry, and using atomic force microscopy (AFM). The model described by Scharifker and Hills was used to analyze current-time transients. According to this model, the nucleation and growth kinetics at the initial stages of deposition process involve an instantaneous nucleation followed by three-dimensional (3D) growth mechanism.

Isothermal Crystallization Kinetics Study of Fully Aliphatic PA6 Copolyamides: Effect of Novel Long-Chain Polyamide Salt as a Comonomer.

N1, N6-bis (4-aminobutyl) adipamide (BABA) diamine and sebacic acid (SA), also called BABA/SA polyamide salt, were used in a typical melt polymerization processes of polyamide 6 (PA6) to form a series of PA6-BABA/SA copolyamides. The effects of BABA/SA on the isothermal crystallization kinetics of PA6-BABA/SA were studied for the first time. An isothermal crystallization analysis demonstrates that the PA6-BABA/SA matrix provided a higher crystallization rate and shorter half-crystallization time than virgin PA6 did. The degree of crystallization of the PA6-BABA/SA30 matrix was also the lowest among all of the samples considered herein. This result is attributed to the high nucleation efficacy of a small amount of BABA/SA in the crystallization of PA6. Values of the Avrami exponent (n) from 1.84 to 3.91 were observed for all of the polyamide samples, suggesting that the crystallization was involved via a two- to three-dimensional growth mechanism. These findings deepen our understanding of the structure–property relationship of PA6-BABA/SA copolyamides, favoring their practical application.

Radial Growth Evolution of InGaAs/InP Multi-Quantum-Well Nanowires Grown by Selective-Area Metal Organic Vapor-Phase Epitaxy.

III-V semiconductor multi-quantum-well nanowires (MQW NWs) via selective-area epitaxy (SAE) is of great importance for the development of nanoscale light-emitting devices for applications such as optical communication, silicon photonics, and quantum computing. To achieve highly efficient light-emitting devices, not only the high-quality materials but also a deep understanding of their growth mechanisms and material properties (structural, optical, and electrical) are extremely critical. In particular, the three-dimensional growth mechanism of MQWs embedded in a NW structure by SAE is expected to be different from that of those grown in a planar structure or with a catalyst and has not yet been thoroughly investigated. In this work, we reveal a distinctive radial growth evolution of InGaAs/InP MQW NWs grown by the SAE metal organic vapor-phase epitaxy (MOVPE) technique. We observe the formation of zinc blende (ZB) QW discs induced by the axial InGaAs QW growth on the wurtzite (WZ) base-InP NW and propose it as the key factor driving the overall structure of radial growth. The role of the ZB-to-WZ change in the driving of the overall growth evolution is supported by a growth formalism, taking into account the formation-energy difference between different facets. Despite a polytypic crystal structure with mixed ZB and WZ phases across the MQW region, the NWs exhibit high uniformity and desirable QW spatial layout with bright room-temperature photoluminescence at an optical communication wavelength of ∼1.3 μm, which is promising for the future development of high-efficiency light-emitting devices.