Effect of plating mode, thiourea and chloride on the morphology of copper deposits produced in acidic sulphate solutions

The influence of plating mode, chloride and thiourea (TU) on morphology of copper deposits has been studied. All experiments were conducted on disc electrodes rotating at 500 rpm and an average current density of 4 A dm⁻² to produce 10 μm thick deposits. In additive-free solutions, the use of pulsed current (PC) improved deposit morphology and brightness over DC plating. In the presence of thiourea (no Cl⁻), the deposits obtained by DC and PC plating were similar under most plating conditions. The presence of thiourea generally improved deposit quality over that obtained in additive-free solutions, but caused the formation of microscopic nodules and the deposits to appear slightly cloudy, resulting in lower reflectances than that of a polished uncoated copper surface. The addition of Cl⁻ to thiourea-containing solutions strongly influenced deposit morphology at both microscopic and macroscopic scales depending on chloride concentration and pulse conditions. It prevented nodule formation and created microscopically bright and reflective deposits, but caused extreme macroscopic roughness. Nevertheless, PC plating at 50 Hz in solutions containing appropriate amounts of thiourea and Cl⁻ was found to yield macroscopically and microscopically smooth deposits with reflectance similar to that of a polished uncoated copper substrate.     

电沉积纳米晶镍-铁-铬合金

采用直流和脉冲电沉积方式从三价铬的氯化物镀液中沉积出镍-铁-铬纳米合金镀层，利用扫描电镜分析镀层形貌及晶粒尺寸，研究了沉积速率，电流效率，三价铬浓度及pH值随沉积时间的变化关系，结果表明，脉冲电沉积所得镀层的结构和性能均优于直流电沉积，这是由于脉冲电沉积存在断电时间，使得电极表面扩散层中金属离子的浓度得到及时恢复。     

脉冲无氰镀银及镀层抗变色性能的研究

采用赫尔槽试验筛选出一种阴离子表面活性剂及含氮杂环化合物作为脉;中无氰镀银的添加剂,并初步确定了无氰镀银的工艺条件及脉冲条件一通过正交试验进一步化化脉冲条件及镀银添加剂含量分别为：脉宽1ms、占空比10％、平均电流密度0．6A／dm^2、阴离子表面活性剂及含氮杂环化合物含量分别为12mg/L、110mg/L测定了该镀银层的耐蚀性、抗变色性能及与基体的结合力,并用扫描电镜对其微观形貌进行了观察。结果表明,脉冲无氰镀银层的抗变色性能优于直流无氰镀银层;光亮镍打底后再脉冲无氰镀银,可获得更加光亮、结晶细致的镀银层,且抗变色性能及耐蚀性均增强.     

Electrodeposition of zinc-nickel alloy coatings: influence of a phenolic derivative

The electroplating of Zn–Ni alloy films from a chloride bath has been studied under different plating conditions, both in the absence and presence of a phenolic derivative. Under the conditions examined, the electrodeposition of the alloys belonged to the anomalous type. The morphology and composition of the deposits varied with current density, temperature, bath composition and additive concentration. The results show that the additive modifies the structure and surface topography of the deposits to a large extent and produces smoother deposits. The corrosion resistance of the alloys has been analyzed by means of salt-spray tests.     

Electrodeposition of high Mo content amorphous/nanocrystalline Ni–Mo alloys using 1-ethyl-3-methyl-imidazolium chloride ionic liquid as an additive

In the following research, adherent, compact and bright Ni–Mo alloy has been electrodeposited on mild steel in the presence of ionic liquid additive 1-ethyl-3-methyl-imidazolium chloride in ammonia citrate solution using pulse plating technique. The textural components of the coatings were evaluated employing X-ray diffraction (XRD) method. Microstructure, morphology and chemical composition of the coatings were studied using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. The results revealed that in the presence of ionic liquid at pH of 8.5, Ni–Mo films containing more than 49 wt.% Mo have been carried out whilst no proper deposits have been conducted in additive free solution at the same condition. SEM micrographs showed different morphology of Ni–Mo deposits in the presence of ionic liquid additive. Also XRD patterns represented that present conditions lead to amorphous/nanocrystalline Ni–Mo coatings. Temperature and pH were varied for studying their effects on Ni–Mo characteristics. Moreover the effect of substrate preparation on morphology of coatings was also investigated.     

Zinc electrowinning from acidic sulphate solutions Part II: Effects of triethylbenzylammonium chloride

The effects of triethylbenzylammonium chloride (TEBACl) on the electrowinning of zinc from acidic sulfate solutions have been studied in the presence and absence of antimony(iii). The factors considered included the current efficiency (CE), power consumption, polarisation behaviour, and the crystallographic orientations and surface morphology of the deposits. Compared with the traditional industrial additive, glue, the addition of TEBACl increased CE, reduced power consumption and improved the surface morphology. Maximum CE and minimum power consumption were obtained at 2mgdm–3 TEBACl and 0.01mgdm–3 Sb(iii). The exchange current density, Tafel slope and transfer coefficient were determined to elucidate the nature of the electrode reactions involved.     

Influence of pulse plating parameters on the synthesis and preferred orientation of nanocrystalline zinc from zinc sulfate electrolytes

The influence of pulse electrodeposition parameters (current on-time T_on, current off-time T_off, and pulse current density J_p) was investigated on the surface morphology and grain size of zinc electrodeposited from a sulfate bath containing polyacrylamide and thiourea additives. The grain size and surface morphology of zinc deposits were studied by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM), and the preferred orientation of the deposits was studied by X-ray diffraction. At constant current off-time and pulse current density, the grain size decreased asymptotically with increasing current on-time. In contrast, increase in the current off-time at constant current on-time and pulse current density resulted in grain growth. A progressive decrease of the grain size was observed with increasing pulse current density at constant current on-time and off-time. Nanocrystalline zinc with an average grain size of 38 nm was obtained at a pulse current density of 1200 mA/cm². The crystallographic orientations developed were correlated with the change in the cathodic overpotential, the angle between the preferred oriented plane and the lowest energy of formation plane (0 0 0 2), and the pulse electrodeposition parameters.     

Hardening effect induced by incorporation of SiC particles in nickel electrodeposits

Pure Ni and nickel matrix composite electrocoatings containing micron- and nano-SiC particles (1 μm and 20 nm respectively) were produced under direct and pulse current conditions from an additive-free Watts type bath. The effect of the particle size, codeposition percentage of SiC and type of imposed current on the microhardness as well as on the microstructure of the electrodeposits were investigated. Ni/SiC composite deposits prepared under either direct or pulse current conditions exhibited a considerable strengthening effect with respect to pure Ni coatings. The improved hardness of composite coatings was associated to specific structural modifications of Ni crystallites provoked by the adsorption of H⁺ on the surface of SiC particles, thus leading to a (211) texture mode of Ni crystal growth. Pulse electrodeposition significantly improved the hardness of the Ni/SiC composite coatings, especially at low duty cycles, in which grain refinement and higher SiC incorporation (vol. %) was achieved. The enhanced hardness of Ni/nano-SiC deposits, as compared to Ni/micron-SiC composites, was attributed to the increasing values of the number density of embedded SiC particles in the nickel matrix with decreasing particle size. In addition, the observed hardening effects of the SiC particles might be associated to the different embedding mechanisms of the particles, which could be characterized as inter-crystalline for micron-SiC and partially intra-crystalline for nano-SiC particles.     

Electrodeposited Palladium Nanoflowers for Electrocatalytic Applications

Palladium was electrodeposited on an electrochemically activated carbon black substrate using potentiostatic technique, with and without the addition of polyethylene glycol (PEG‐6000) as an additive. Scanning electron micrographs showed change in morphology of Pd from spherical to flower, with increasing additive concentration. As an electrocatalyst for oxygen reduction reaction (ORR), formic acid oxidation and CO stripping, Pd nanoflowers displayed three‐ to fourfold increase in electrocatalytic activity in comparison to the spherical Pd deposits in terms of electrochemical surface area (ESA) and mass specific current density. X‐ray diffraction (XRD) patterns showed, the introduction of additive with varying concentration effect the direction of Pd growth thereby changing the morphology from spherical to flower. The result demonstrates an increase in efficiency of Pd utilization achieved with the addition of PEG during electrodeposition, which could also be applicable to other precious metal electrocatalysts. A scheme for the change in Pd morphology during electrodeposition with additive is also proposed.     

The effects of pulse plating variables on morphology and corrosion behavior of Zn–Fe alloy coatings

Considerable researches have been focused on zinc–iron (Zn–Fe) alloy coatings due to their superior characteristics among zinc alloy electrodeposits in recent years. The corrosion behavior of these coatings depends on the phase structure and morphology of the Zn–Fe deposits. In this work the effects of pulse plating variables such as current density, off-time, frequency and pulse modes on the morphology and phase structure of Zn–Fe deposits was studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometry (EDS) analysis. The corrosion behavior of these coatings was measured by means of polarization curves and Neutral salt spray tests. It was shown that pulse reverse coatings exhibit excellent resistance to corrosion in comparison with normal pulse and direct current conditions.     

添加剂对喷射电沉积纳米晶Co-Ni合金的影响

在氯化镍-硫酸钴体系电解液中采用添加剂喷射电沉积纳米晶Co-Ni合金,测定了其阴极极化曲线.研究了添加剂对阴极过电位、电流效率、镀层中Co含量、镀层的相结构、晶粒尺寸、表面形貌及显微硬度、软磁性能等影响.结果表明:添加剂增加了极化作用,影响了Co、Ni电沉积的动力学过程.当添加剂为2.5g/L时,与未加添加剂相比较,阴极过电位从3.594V增大到4.755 V,电流效率和沉积层中Co含量变化不大,但沉积层晶粒尺寸从12.8 nm明显降低到5.5 nm,维氏硬度从423升高到511,同时Co-Ni合金的软磁性能得以提高.     

Electrodeposited Pt for cost-efficient and flexible dye-sensitized solar cells

Pt electrodes were prepared by direct and pulse current electrodeposition for use as counter electrodes in dye-sensitized solar cells. Scanning electron microscope and transmission electron microscope images confirmed the formation of uniform Pt nanoclusters of ∼40 nm composed of 3 nm nanoparticles, when the pulse current electrodeposition method was used, as opposed to the dendritic growth of Pt by the results from direct current electrodeposition. By applying pulse electrodeposited Pt which has a 1.86 times higher surface area compared to direct current electrodeposited Pt, short-circuit current and conversion efficiency were increased from 10.34 to 14.11 mA/cm² and from 3.68 to 5.03%, respectively. In addition, a flexible solar cell with a pulse current electrodeposited Pt counter electrode with a conversion efficiency of 0.86% was demonstrated.     

复合添加剂对次磷酸钠化学镀铜的影响

在以次磷酸钠为还原剂的化学镀铜体系中,考察了2,2'-联吡啶/亚铁氰化钾复合添加剂对化学镀铜的影响。采用电化学方法分析了无添加剂、单一添加剂和复合添加剂对次磷酸钠氧化电势和电流的影响,结果表明,2,2'-联吡啶、亚铁氰化钾和2,2'-联吡啶/亚铁氰化钾复合添加剂均使次磷酸钠氧化电势增加,氧化电流减小。扫描电子显微镜(SEM)、能量色散谱(EDS)、X射线衍射(XRD)、四探针测试法(SZT-90)检测结果显示:较之单一添加剂,10 mg/L 2,2'-联吡啶/4 mg/L亚铁氰化钾复合添加剂所得铜镀层纯度更高〔w(Cu)=96.27%〕,外观更加光亮、致密和均匀,铜层表面平均电阻率也降低至0.022 9μΩ.m。     

Pulse current electrodeposition and corrosion properties of Ni–W alloy coatings

Ni–W alloy coatings were prepared on a mild steel substrate by means of pulse current (PC) and compared to the coatings electrodeposited by direct current (DC). In particular the study dealt with the influence of the frequency using pulse current on the surface morphology while maintaining a constant duty cycle. A constant charge for DC and PC electrodeposition of Ni–W alloy coatings was used. The morphology of the coatings was explored by scanning electron microscopy and the composition of the coatings was analysed by X-ray powder diffraction and energy dispersive X-ray analysis. Corrosion resistance of Ni–W alloy coatings was investigated by potentiodynamic polarization in a chloride medium. The corrosion products were analysed by Raman spectroscopy. It was found that the temperature of the electrolysis affects current efficiency of the DC and PC electrodeposition. The frequency of pulse electrodeposition alters the morphology of the Ni–W alloy coatings. There was evidence of the positive influence of increased tungstate concentration in the electrolyte on corrosion resistance of the Ni–W alloy coatings.     

直流和脉冲Ni-ZrO2纳米复合电铸层显微硬度的研究

利用SEM分析了纯镍电铸层,以及用直流和脉冲工艺所制备纳米复合电铸层的表面形貌,分别研究了影响直流和脉冲纳米复合电铸层显微硬度的各种因素,同时对纳米复合电铸层的强化机理进行了探讨.结果表明,纳米复合电铸层的表面形貌不同于纯镍电铸层,并且其显微硬度得到明显提高.纳米复合电铸层的强化机理主要是细晶强化机制、弥散强化机制和高密度位错强化机制.     

Application of constant current pulse to suppress bubble incorporation and control deposit morphology during aqueous electrophoretic deposition (EPD)

Electrophoretic deposition (EPD) from aqueous suspension generally forms deposits containing enormous pores because of evolution of hydrogen gas at cathode and oxygen at anode due to electrolysis of water on application of DC electric field. We have demonstrated through this investigation on aqueous EPD of alumina suspension as an example that application of pulsed DC instead of the conventionally used continuous DC is a convenient and effective way to control and suppress the amount of bubble incorporation in the deposit. Bubble-free deposits of reasonable yield were obtained at suitable pulse widths and/or duty cycle. The deposit yield and bubble incorporation decreased progressively with decrease in the pulse width and duty cycle of the applied pulse current. A characteristic deposition window was found in the current vs. pulse width plot within which smooth and bubble-free deposits are obtained. The window is wider at low-applied currents compared to that at higher currents implying that it is easier to control the pulsed EPD at lower applied currents. No deposition occurred below the window whereas deposits with incorporated bubbles formed above the window. Possible mechanisms involved in pulsed EPD have been advocated on the basis of amount of hydrogen evolved/pulse due to the electrolysis of water. The discrete amount of H₂ evolved/pulse was higher for larger pulse widths leading to incorporation of more bubbles and vice versa. This was verified by monitoring the gain in weight of palladium (Pd) electrode used as cathode for electrolysis experiment since it is known to absorb hydrogen.     

Effects of some additives on the corrosion behaviour and preferred orientations of zinc obtained by continuous current deposition

The effect of thiourea, urea and guanidin on zinc deposits obtained from chloride baths under continuous current conditions are described and discussed. The corrosion behaviour of the deposits was investigated in an aerated 3.5% NaCl solution; anodic polarization curves, polarization resistance (R _p) measurements and weight-loss studies were performed. The corrosion resistance of zinc deposits improved in the presence of urea. The deposit morphology was analyzed using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. The preferred crystallographic orientations of zinc deposits (112) do not change in the presence of urea and guanidin except for an increase in the peak intensity of the (112) plane. In the presence of thiourea, zinc deposits crystallise in two textures; (100) and (110). The influence of each additive and the difference between additives on the zinc deposits are also discussed.     

Magnetic properties of nanocrystalline iron group thin film alloys electrodeposited from sulfate and chloride baths

Systematic studies of iron group binary (NiCo and CoFe) and ternary (CoNiFe) thin film alloys relating their magnetic properties with film composition, grain size and the corresponding crystal structure were investigated. Anions influence current efficiencies, magnetic properties, surface morphology and phases of electrodeposited films. Higher current efficiencies in chloride baths compared to sulfate baths were observed for CoFe, NiCo and CoNiFe alloys. The higher deposition current efficiencies in chloride baths were attributed to a catalytic effect. Anion types in CoFe and CoNiFe thin film alloys influenced the microstructures and the resulting magnetic properties (coercivity and squareness). The microstructures of NiCo alloys depend on the deposit Co contents rather than anion types. The surface morphologies of CoFe, NiCo and CoNiFe thin films were independent of anion types. CoFe deposits exhibited relatively smooth surface morphology and turned into fine crystallites with increasing solution Fe⁺² concentration. NiCo deposits showed very smooth surface morphology. CoNiFe deposits had the surface morphology of polyhedral crystallites. The deposit Fe content in CoFe electrodeposits linearly increased with increasing solution Fe⁺² concentration for both chloride and sulfate baths. Similar linear behavior of deposit Co contents was observed in NiCo electrodeposits.     

Optimization of pulsed electrodeposition of aluminum from AlCl3-1-ethyl-3-methylimidazolium chloride ionic liquid

In this study, Al was electrodeposited on a platinum substrate at room temperature from an ionic liquid bath of EMIC containing AlCl₃ using potentiostatic polarization (PP), galvanostatic polarization (GP), monopolar current pulse polarization (MCP) and bipolar current pulse polarization (BCP). Transition of current or potential during galvanostatic or pulse polarization revealed that the initial stage of the deposition process was controlled by a nucleation process depending on the polarization condition. For example, the average size of Al deposits decreased with increasing current density in the case of GP. FE-SEM observation showed that dense and compact Al deposits with a smooth surface were obtained by the current pulse method. Roughness factor evaluated from electrochemical impedance measurement confirmed the smooth surface of these deposits. Adhesion strength of Al deposits was greatly improved using BCP in which an anodic pulse was combined with a cathodic pulse for electrodeposition. In this study, the optimal parameters for BCP were found to be I_C = −16.0 mA cm⁻², I_A = 1.0 mA cm⁻², r_C (duty ratio) = 0.5, and f = 2 Hz. The mechanisms of electrodeposition by these three methods are discussed.     

Direct and pulse current electrodeposition of Ni–W–TiO2 nanocomposite coatings

Ni–W–TiO₂ nanocomposite coatings have been obtained on mild steel surface by direct current (DC) and pulse current (PC) electrodeposition from Watts bath containing an ammonical citrate complexing agent. The morphology of the coatings was explored by scanning electron microscopy (SEM), atomic force microscopy (AFM) and the composition of the electrodeposits was analyzed by energy dispersive X-ray analysis (EDX). Surface morphology studies revealed that Ni–W alloy surface was covered by long needle like crystals and Ni–W–TiO₂ composite coatings with smaller spherical sized grains. The coated surface contained 25.55% W and 5.55% Ti. XRD studies revealed that (111) plane was predominant in both Ni–W alloy deposits and Ni–W–TiO₂ composite coatings. The patterns of the electrodeposits confirmed only fcc frame work structure. Microhardness values increased with TiO₂ addition in the alloy. The corrosion resistance of Ni–W alloy deposit and TiO₂ incorporated coatings was evaluated by Potentiodynamic polarization studies in 3.5% NaCl solutions. Corrosion current densities decreased with TiO₂ inclusion in the alloy deposit. Electrochemical impedance studies revealed that the charge transfer resistance increased with TiO₂ inclusion in the alloy deposits while the double layer capacitance decreased. The PC composites coatings offer uniform surface, high microhardness and enhanced corrosion resistance than DC composites coatings.