ZnMn alloys obtained using pulse, reverse and superimposed current modulations

Zinc-manganese alloys were electrodeposited using pulse techniques: pulse, pulse reverse and superimposed pulse. The alloys obtained under each condition were characterized by their composition, thickness, morphology and structure. Results indicate that, in the same interval of average current densities, all methods led to similar or higher manganese contents than those obtained using direct current (dc), but current efficiencies were lower. In general, all pulse methods improved the thickness and composition uniformity of the alloys, particularly, when pulse reverse plating was used. However, current efficiencies with this method were so low that the process would be uneconomical. With pulse and superimposed pulse techniques uniform and compact alloys were obtained, the latter method with current efficiencies that were slightly higher than the former. Moreover, the structure of the alloys obtained with the pulse techniques was simpler than that observed with dc plating and monophasic alloys could be obtained in a wide interval of conditions.     

Cathodic inhibition and anomalous electrodeposition of Zn-Co alloys

The electrodeposition of Zn-Co alloys from chloride electrolytes was studied on steel substrate. Electrodeposition of Zn-Co alloys is usually divided into two potential regions, i.e. normal (positive to Zn deposition potential versus SCE) and anomalous (negative to ). In order to elucidate the deposition mechanism a complementary approach was used based on the combination of various electrochemical techniques. The morphology of the deposits and elemental composition analysis were determined by using SEM/EDX. It was found that the presence of Zn²⁺ in electrolyte inhibited Co²⁺ and H⁺ reductions in normal region. A critical potential was also noticed in the so-called normal deposition range above which a Co-enriched phase of Co-Zn alloy was favored and below that a severe mitigation to deposition occurred that was considered due to underpotential deposition (UPD) of Zn on the substrate and on active Co sites at either nucleation or growth stage. Beyond the deposition is considered anomalous due to the fact that Zn deposits preferentially compared to the more noble Co. This anomalism was explained by the faster deposition kinetics of Zn as compared to Co on steel and could be overcome by either increasing the Co²⁺/Zn²⁺ ratios in the electrolyte or by carrying out the deposition at higher temperature.     

碱性锌钴合金电镀工艺

介绍碱性无氰锌钴合金电镀工艺、镀层和镀液性能及槽液维护控制。镀层耐蚀性高,镀液稳定性好,是理想的锌合金镀层。     

汽车用锌-钴合金的制备及其耐蚀性的研究

在汽车用软钢上电沉积制备锌-钴合金,并研究了沉积电位对锌-钴合金的成分、厚度及耐蚀性的影响。研究表明:锌-钴合金的电沉积过程属于异常共沉积。钴的电沉积属于扩散控制,沉积电位越负,锌-钴合金中钴的质量分数越低。在-1.8V下制备的锌-钴合金表面致密,具有优异的耐蚀性,其中钴的质量分数为12.5%。     

Electrodeposition of cobalt-nickel alloys from ammoniacal single-complex baths

The electrodeposition of cobalt-nickel alloys has been studied from ammoniacal single-complex baths containing 5–50 CoSo₄·7H₂O, 5–50 NiCl₂·46H₂O, 20–50 g dm^?3 (NH₄)₂SO₄ and 250–350 cm³ dm^?3 NH₄OH (20.5% solution). The effects of the plating current density and the concentrations of the bath constituents on the cathodic polarisation, current efficiency and composition of the alloy were investigated. A wide range of alloy compositions with a current efficiency of 60–80% could be obtained from the main baths examined. The alloy plating system interchanged between the normal and the anomalous types depending upon the plating current density and the concentration of NH⁺₄ ion in the bath. Electron microscopic and X-ray diffraction studies proved that the structure of the electrodeposited alloy was controlled by the alloy composition.     

Electrodeposition of Ni-Mo alloys with pulse reverse potentials

With the aim of improving the protective properties of Ni-Mo alloy layers, pulse reverse electro-deposition has been investigated. The anodic pulses were applied in the potential range where hydrogen desorption and oxidation occur. The alloy composition was shown to depend on the pulse parameters, especially on the anodic pulse duration. For long anodic pulses a preferential dissolution of molybdenum in the electrodeposited alloy occurs, while bulk Ni-Mo alloys do not undergo any dissolution. For anodic pulses longer than a certain threshold the electrocrystallization process becomes blocked. The morphology and microstructure of the layers are mainly determined by the molybdenum content rather than by the pulse parameters.     

Electrodeposition of amorphous/nanocrystalline and polycrystalline Ni-Mo alloys from pyrophosphate baths

Pyrophosphate plating bath was found to be a good alternative to citrate bath for deposition of Ni-Mo amorphous alloys. The addition of wetting agents such as 2-butyne-1,4-diol and rokafenol N-10 to the pyrophosphate bath resulted in the removal of bumps, spheres and cracks from the Ni-Mo alloy surface. The plated alloy layers adhered well to Cu-Zn brass and steel, were of thickness from a fraction to tens of micrometers and the molybdenum content was independent of the distance from the support. An increase in the concentration of the molybdate ion in the bath leads to an increase in the amount of Mo in the alloys up to 33-35 at.% and to a decrease in the deposition rate. These changes and the influence of pH are discussed in the paper. The atom arrangement in the alloys changes from (2 2 0) preferred for pure-nickel deposition to (1 1 1) for content of Mo higher than 15 at.%. For 20 and more at.% of Mo the structure of the alloy is amorphous like. An analysis of SEM and STM micrographs obtained indicates that contrary to the Ni-W alloy the “amorphous” phase is made of circa 10-50 nm in diameter objects and not by long needles perpendicular to the substrate.     

Electrodeposition and characterization of Cu-Ni-Zn and Cu-Ni-Cd alloys

The electrodeposition of ternary Cu-Ni-Zn and Cu-Ni-Cd alloys was investigated in acidic sulphate electrolytes. The influence of Zn²⁺ and Cd²⁺ ions concentrations as well as the effect of current density on the surface appearance and the deposits’ composition was examined. Sodium dithiolate (NaS)₂CC(CN)₂·3H₂O was used as surface active substance (SAS), and the effect of the SAS on the alloys composition and surface morphology was also investigated. No significant effect of SAS on the alloy composition, however, apparently effect on the deposits surface morphology was observed. It was also noticed that on increasing Zn²⁺ (or Cd²⁺) concentration in the bath, a depletion in the nickel content in the deposit occurred. Deposits obtained were characterized from the structural and morphological points of view. It was found that the structure and morphology of the deposited alloys are mainly controlled by both the applied current densities and the bath composition.     

Electrochemical study on the inhibitory effect of the underpotential deposition of zinc on Zn-Co alloy electrodeposition

Zn-Co alloy electrodeposition from chloride baths containing different Zn²⁺/Co²⁺ ratios was investigated by cyclic voltammetry and anodic linear sweep voltammetry using a Pt electrode. The peaks were attributed by means of EDX analysis, SEM and TEM observations performed on some alloys potentiostatically deposited. In the range of potential where zinc deposits underpotential, cyclic voltammetry showed a complex cathodic peak with one maximum and two shoulders, correlated with the deposition of different cobalt rich alloys. Up to four anodic peaks, two correlated with zinc oxidation from η and γ phases and two correlated with oxidation of solid solutions of zinc in cobalt, were observed. ALSV and TEM indicated that the remarkable increase in Zn content of the alloy, which occurs with a strong inhibition of the process at potentials more negative than that of the cathodic peak and more positive than the bulk deposition potential of zinc, is due to the deposition of γ phase. No inhibition of the alloy deposition process was observed with very low concentrations of zinc (<0.015 M) in the bath containing 0.19 M Co²⁺.     

Electrodeposition of silane films on aluminum alloys for corrosion protection

In this paper, three types of protective silane films, methyltrimethoxysilane (MTMS), vinyltrimethoxysilane (VTMS) and dodecyltrimethoxysilane (DTMS) were prepared on aluminum alloys AA 2024-T3 by electrodeposition technique. The Reflection-Absorption Fourier Transform IR (FTRA-IR) measurements showed that, the silane films were successfully deposited through chemical bonding between silane agents and Al alloys. Electrochemical impedance spectroscopy (EIS) tests indicated that in comparison with those by conventional “dip-coating” method, silane films electrochemically prepared at cathodic potentials exhibited obviously higher corrosion resistances. “Critical potential” was all observed for each silane system. Silane films prepared at this potential performed the highest corrosion resistance. The scanning electron microscopy (SEM) images indicated a potential dependence of surface morphology of silane films. The highest compactness was obtained at the “critical potential”. Due to the presence of long hydrophobic dodecyl chain in bone structure, DTMS films displayed the highest barrier properties.     

Electrodeposition of Co-Cu-Zn/Cu multilayers: influence of anomalous codeposition on the formation of ternary multilayers

Electrodeposited Co-Cu-Zn/Cu multilayers have been prepared with various control modes. It was found in all cases that the Zn content of the magnetic layer is higher than that in the corresponding dc-plated sample. The data of the composition analysis were elucidated by the assumption of anomalous codeposition of Zn and Co. When the less noble layer is deposited, a Zn-rich zone is produced first, then it is covered with a Co-rich layer. If exchange reaction was allowed during the pulse-plating, Co dissolved selectively while the Zn content of the Co-rich layer remained unchanged. The relative resistance of Zn against the exchange reaction is due to the limited accessibility of the Zn-rich zone of the sample rather than electrochemical reasons. The structure of the deposit was analyzed by X-ray diffraction (XRD). It was revealed that Zn incorporation leads to strongly textured deposits with (1 1 1) orientation. The Zn atoms also enlarge the lattice distances of all phases formed. The incorporation of Zn into the magnetic layer of the multilayers decreases the magnetoresistance of the samples.     

Pulsed electrodeposition of bismuth telluride films: Influence of pulse parameters over nucleation and morphology

Pulsed electrodeposition methods were applied to the preparation of bismuth telluride films. Over the potential ranges from −170 mV to −600 mV, the formation of Bi₂Te₃ nuclei proceeded through a three-dimensional instantaneous nucleation mode. The nuclei densities for several values of potential were ranged between ∼10⁶ nuclei cm⁻² and ∼10⁸ nuclei cm⁻². For a pulsed galvanostatic electroplating, the best covering percentage and a stoichiometry close to the desired Bi₂Te₃ were obtained with the parameters t_on, t_off and J_c, respectively, equal to 10 ms, 1000 ms and −100 mA cm⁻².     

Pulse plating of Ni-Mo alloys from Ni-rich electrolytes

Pulse plating of Ni-Mo alloys from nickel-rich electrolytes was studied with an inversed rotating disk electrode. The deposit composition and the current efficiency were measured as a function of pulse variables (pulse period, duty cycle) and mass transport parameters (electrode rotation speed, molybdate concentration). At sufficiently short pulse periods, the Mo content of the pulse plated alloys was higher than in dc plating. Experiments using a rotating electrochemical quartz crystal microbalance and Auger electron spectroscopy showed that under the conditions of the experiments no significant corrosion reaction takes place during the pulse off-time. A simplified non-steady state diffusion model can explain the observed enhancement in Mo content and correctly predict the influence of pulse plating variables on deposit composition.     

Electrodeposition of rhenium-nickel alloys from aqueous solutions

Rhenium-nickel alloys were deposited on copper substrates in a small three-electrode cell, under galvanostatic conditions. The bath solution consisted of ammonium perrhenate, citric acid and nickel sulfamate. The effects of bath composition and deposition time were studied. The Faradaic efficiency (FE) and partial deposition current densities were calculated based on mass gain and elemental analysis using energy dispersive spectroscopy. The surface morphology was characterized by scanning electron microscopy. The thickness of the coating was measured on metallographic cross-sections. The results are discussed with emphasis on routes to increase the Faradaic efficiency and rhenium content in the coating. A plausible mechanism for the electrodeposition of rhenium-nickel alloys is presented.     

机械法兰盘合金钢基材电镀锌-钴合金镀层

法兰盘作为轴与轴之间相互连接的零件在机械领域应用非常广泛。在法兰盘用16Mn钢板上制备了锌-钴合金镀层,并研究了硫酸钴的质量浓度对锌-钴合金镀层的沉积速率、成分、硬度、耐蚀性及表面形貌的影响。结果表明:钴的电沉积过程属于扩散控制。适当地增加硫酸钴的质量浓度,有利于增大沉积速率并提高锌-钴合金镀层中钴的质量分数,从而提高锌-钴合金镀层的耐蚀性。当硫酸钴的质量浓度大于15 g/L时,剧烈的析氢反应使得锌-钴合金镀层的致密性下降,从而导致其性能明显降低。     

脉冲电沉积RE-Ni-W-B复合镀层的研究

研究了脉冲频率和占空比对电沉积RE-Ni-W-B复合镀层硬度及沉积速率的影响,以及热处理温度对复合镀层硬度、磨损率及抗高温氧化性的影响.结果表明,当脉冲频率(f)和占空比(r)控制在1000 Hz和3∶1时,复合镀层硬度最高,厚度最大,分别为636 HV和0.0281 mm.使用脉冲电流,并在镀液中添加稀土元素,能有效降低镀层中镍含量,提高钨含量,降低复合镀层表面的裂痕.脉冲电沉积复合镀层的硬度均高于直流电镀复合镀层,磨损率均低于直流镀层.当热处理温度低于400°C时,热处理温度升高,复合镀层硬度增加,在400°C时,硬度最高,磨损率最低;高于400°C后,两种复合镀层的硬度又开始下降,磨损率上升.直流及脉冲复合镀层在600°C以下氧化增重都较小,600°C以后氧化增重明显增加.     

Electrodeposition of zinc-cobalt alloy from a complexing alkaline glycinate bath

The influence of cobalt on the electrodeposition of zinc onto AISI 1018 steel was studied in weakly alkaline glycine solutions. Thermodynamic calculations were performed to construct predominance-zone diagrams to identify the stability of the zinc and cobalt glycine complexes, and experimental studies of electrochemical behavior and deposit properties were conducted. When zinc is present, cobalt deposition shifts to more negative potentials, producing ZnCo alloys. Two main reduction steps were observed for electrodeposition from the ZnCo bath: the first at low potentials was due to ZnCo electrodeposition. In the second, at more negative potentials, cobalt content in the deposit increased forming a range of intermediate phases, and the hydrogen-evolution reaction became significant. The presence of Co(II) in the bath modified the morphology of the deposits as well as reducing the faradaic metal-deposition efficiency. ZnCo-deposit morphology was modified by the applied current density as well as the metal composition of the coating. X-ray diffraction studies revealed that cobalt oxide or hydroxide is formed during ZnCo electrodeposition, indicating that an elevation of the interfacial pH plays a role in the alloy deposition process.     

Synthesis and characterization of nickel tungsten alloys by electrodeposition

The objective of the current work was to study in detail the effect of bath chemistry, additives and operating conditions on the chemical composition, microstructure and properties of Ni-W alloys deposited from citrate-containing baths, in the absence of ammonia or ammonium salts, on stationary working electrodes. The morphology of the deposits was studied by scanning electron microscopy (SEM) as well as atomic force microscopy (AFM), and the approximate composition by energy dispersive spectroscopy (EDS). Metallographic cross-sections were also analyzed, and micro-hardness tests conducted. The results are discussed in detail with emphasis on routes to increase the tungsten content and deposit thickness, while reducing the extent of cracking.     

Multicriteria optimization of mechanical and morphological properties of chromium electrodeposits under reverse pulse plating

In this work, a central composite design experiment was performed to estimate the effect of the electroplating parameters (temperature of electrolyte, cathodic and anodic pulse current densities, and cathodic and anodic pulse lengths,) on four properties of hard chromium electrodeposits. The studied responses were the hardness (Hv), the roughness quantified by the two criteria R_a (nm) and R (μm)), and the specific abrasive energy, E_s (μJ μm⁻³). Analysis of the responses using optimal path technique did not lead to a common set of experimental conditions which fulfilled the required properties. Thus, the desirability function approach has been employed in order to find the best compromise between the different experimental responses. The optimal conditions are: electrolyte temperature: 49.9 °C; cathodic pulse current density: 42.0 A dm⁻²; anodic pulse current density: 51.5 A dm⁻², cathodic pulse length: 6.23 s and anodic pulse length: 28.5 ms. Under these conditions, the estimated response values are 738 Hv, 262 nm, 2.61 μm and 0.027 μJ μm⁻³ for hardness, R_a, R and specific abrasive energy respectively, validated experimentally. The resultant coating, examined by AFM, exhibits a nodular fine-grained morphology.     

Electrodeposition of AuCo alloys and multilayers

AuCo alloys and Au/Co multilayers have been fabricated by electrodeposition from non cyanide-containing electrolytes. The effect of pH and citric acid concentration on the deposit composition and current efficiency was investigated. Results showed that a lower citric acid concentration (0.47 m) at pH 6.15 was favored for multilayered Au/Co deposits with disparate compositions in each layer. An increase in the citric acid concentration or pH requires a larger applied current density to achieve the same cobalt concentration, and results in a drop of current efficiency.