A Study on Zinc-Iron Alloy Electrodeposition from a Chloride-Electrolyte

The electrodeposition of zinc-iron alloys from a chloride-based electrolyte has been studied using electrochemical polarisation techniques, Ager Electron Spectroscopy (AES), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDXA) and Computer Assisted Pulse Plating (CAPP).

A change in the electrodeposition mechanism from equilibrium codeposition to anomalous codeposition with a change in cathodic current density has been observed.

Zn-Fe alloys with compositions ranging from less than 5 wt-% to more than 75 wt-% Fe have been electrodeposited from a single electrolyte, making this system ideal for production of compositional modulated alloy (CMA) electrodeposits. Chloride content, pH and agitation of the electrolyte have been observed to have a strong influence on the reaction at the cathode surface, just as the use of pulse reversal current during electrodeposition.

A theory on the electrodeposition mechanism, accounting for the above observations, is presented.     

Ni-Co alloy coatings obtained from methanesulfonate electrolytes

It is found that codeposition of nickel and cobalt with alloy formation from methanesulfonate electrolyte occurs with predominant cobalt deposition. The crystalline alloy structure is considerably distorted as compared to pure alloy-forming metals. It is shown that a significant effect on the structure and properties of nickel-cobalt deposits is produced, apart from the alloy composition, by the current density of coating deposition. Comparison of dependences of the alloy composition on current density for methanesulfonate and sulfate electrolytes indicates a smaller change in the content of components in deposits obtained from methanesulfonate electrolyte. The observed small deviations from the constant value of the composition of the Ni-Co alloy deposited from methanesulfonate electrolyte in the current density range of 1–7 A/dm² together with large microhardness values characteristic for these coatings point to extensive prospects of application of methanesulfonate electrolytes for deposition of nickel-cobalt alloys.     

The Electrodeposition of Cobalt–Chromium Alloys from Sulfate–Oxalate Solutions

The kinetics of separate and concurrent discharge of cobalt and chromium ions from sulfate–oxalate solutions is studied. Cobalt–chromium alloys with the cobalt content of 4 to 94% and carbon content of 1 to 4% are obtained. At a concurrent discharge of chromium and cobalt ions, the deposition potential of chromium is shifted by 150 to 200 mV in the positive direction. The shift depends on the current density and cannot be accounted for by the energy of mixing of the components. The alloying of chromium with cobalt decreases the overpotential of the hydrogen discharge. The codeposition with chromium did not decelerate the reduction of cobalt ions in contrast to the electrodeposition of nickel. The main reasons for the difference between the effect the alloying with chromium produces on the electrochemical reduction of nickel and cobalt, which are similar in their properties, are considered.     

Gel-chromatographic separation of boron-gluconate electrolyte for obtaining nanocrystalline Co–W coatings: Composition and electrochemical activity of components. Part II. Electrochemical activity of separation products and their role in the process of manufacturing the alloy

Study of the electrochemical activity of fractions of boron-gluconate electrolyte used for the manufacturing of nanocrystalline Co–W coatings (the fractioning is performed based on the different molecular weights of the solution components) shows that the electrodeposition results in the formation of an alloy with a very low concentration of tungsten (~1% at.) only from the fractions with a high molecular weight. Electrodeposition from the low-molecular fraction that contains chloride, boron-gluconate, and wolframate ions with cobalt inclusions is not observed. The obtained results are found to be described correctly by the Podlaha–Landolt model of the induced codeposition of iron-group metals with refractory metals.     

n 型 Bi-Te-Se 温差电材料溶液体系的电沉积过程研究

目的研究硫酸体系中元素铋、碲和硒的电沉积行为,为电沉积制备n型Bi2Te3-ySey温差电材料提供理论参考。方法采用电化学循环伏安测试技术,对硫酸溶液体系中铋、碲、硒三种元素的电沉积及不同元素间的共沉积过程进行研究。结果纯铋硫酸溶液体系中,Bi3+还原成单质铋的电化学反应是分步进行的,游离态和络合态的铋离子先后发生还原反应。纯碲硫酸溶液体系中,HTe O2+以吸附态和游离态两种形式先后发生还原反应。纯硒硫酸溶液体系中,溶液中的H2Se O3也通过分步还原反应生成硒单质。在Bi-Te-Se三元硫酸溶液体系中,Bi3+的浓度和基材对电沉积过程有显著影响,Bi-Te-Se化合物对电沉积过程具有促进作用。结论在Bi-Te-Se三元硫酸溶液体系中,Se,Te和Bi元素可依次在阴极表面发生还原反应而实现共沉积,从而制备出n型Bi-Te-Se温差电材料。     

Positron annihilation in Ni-B and Ni-P alloys prepared by catalytic chemical reduction of nickel ions by borohydride, dimethylamino borane, and hypophosphite

Positron-annihilation technique was used to determine the Fermi energy and the concentration of trapping centers in nickel alloys (with various contents of phosphorus and boron) prepared by catalytic chemical reduction of nickel ions. It has been established that for Ni-B alloys there is observed a charge transfer from nickel to boron. In Ni-P alloys, the Fermi energy increases with increasing phosphorus concentration in the alloy. The introduction of phosphorus or boron into nickel increases the concentration of trapping centers for positrons.     

Influence of bath concentration and pH on electrodeposition process of ternary Zn-Ni-Mo alloy coatings

The influence of bath pH and also citrate and molybdate concentration, on the electrodeposition process of ternary Zn-Ni-Mo alloy coatings has been examined. The occurrence of the particular forms of the metal-citrate complexes in the electrolytes was analysed using UV-VIS spectroscopy and on the basis of the stability constants of the complexes. In the solutions with lower pH (4·5 and 5·7), in which free metal ions and ZnHCit^? and NiHCit^? complexes predominate, anomalous codeposition of nickel with zinc took place. In electrolytes with higher pH, containing excess of citrate, in which all the metal ions occur in the form of citrate complexes, and about 20% of the Zn²⁺ and Ni²⁺ ions form a ZnNiCit₂^4? mixed complex, the codeposition changes from anomalous to normal. The percentage of Mo in the alloy increases with the increase in concentration of uncomplexed MoO₄^2? ions in the solution. Alloys with much higher Mo content may be obtained from the bath in which preferential deposition of nickel (normal codeposition) takes place.     

Annual Report of the Council

The anodic behaviour of nickel has been studied in chloride solutions containing various concentrations of thiourea, thioacetamide and thiosemicarbazide and it has been shown that the activation overpotential is a minimum at a critical concentration of the organic compound. In the case of thiourea the same critical concentration appears to have the maximum effect in lowering cathode polarization during electrodeposition of nickel. The results have been interpreted in terms of the actual and relative concentrations of the sulphur compound and its decomposition products (the sulphide and bisulphide ions). The sulphur anions are considered to facilitate egress of nickel ions, whereas the undecomposed sulphur compounds inhibit dissolution, presumably by forming a chemisorbed layer. The nature of the corroded surface of the nickel has been studied by electron microscopy and it has been shown that the presence of the sulphur compounds modifies the characteristic hemispherical shape of pits which occur in chloride solutions.     

Kinetics of the Codischarge of Nickel and Chromium Ions from Oxalate–Sulfate Solutions into an Alloy

The kinetics of individual and concurrent discharge of nickel and chromium ions from oxalate–sulfate solutions is studied. At a high cathodic potential (–1.2 V), the process of nickel deposition is sharply decelerated due to the surface passivation of the cathode with nickel oxides and the adsorption of organic products. During the coreduction of the ions with the formation of an alloy, the discharge rate of nickel ions is sharply decreased and the deposition of chromium is accelerated, compared to the electrodeposition of individual metals. The phenomenon observed is accounted for by a sharp decrease in the rate constant of the electrochemical reaction of nickel discharge on the surface of an alloy.     

Electrochemical Doping of Zinc Coatings with Chromium and Nickel Coatings with Phosphorus

The electrochemical doping of coatings with metals and nonmetals is discussed. Using the examples of the electrodeposition of zinc–chromium and nickel–phosphorus coatings, it has been shown that the presence of donors of the electrodeposited coating components in the inner sphere of a heteronuclear or heteroligand complex contributes to their coreduction and the formation of an alloy. The composition, morphology, and properties of the coatings have been characterized. It has been shown that the corrosion resistance of the zinc–chromium coatings is two times higher than that of the zinc coatings. After storage, the nickel–phosphorus coatings preserve their solderability with low-temperature solders.     

Electrodeposition of lead–tin alloy from methanesulphonate bath containing organic surfactants

The article discusses the process of electrodeposition of lead-tin alloy (tin content in the deposit up to 10–12 wt %) from methanesulfonate electrolytes. A composition was proposed of organic additives to the electrolyte providing attainment of high quality microcrystalline coatings with the alloy of predetermined composition at relatively low content of Sn²⁺ in the solution. It has been shown that the tin content in the deposit increases at an increase in current density and decrease in the electrolyte temperature. For production of anti-frictional Pb-Sn alloys with the tin content of about 10% the electrolysis should be performed at a current density of about 4 A/dm² and the temperature not exceeding 25°C. The effect of a decrease in the discharge rate of the Sn²⁺ ions into the alloy at deposition from electrolyte without organic additives was discovered, that is stipulated by deceleration of crystallization stage of tin on foreign substrate. When the alloy is deposited from electrolyte containing a composition of organic additives, the effect of super-polarization of discharge of Sn²⁺ ions is reduced.     

A Rotating Ring-Disc Electrode Study of Zinc Electrodeposition from Zincate Solutions

The electrodeposition of zinc on iron/steel and the simultaneous evolution of hydrogen have been investigated using a rotating ring-disc electrode technique.

The effects of the hydrodynamic conditions, the concentration of ZnO and NaOH as well as the addition of commercially available organic additives were evaluated. The data were supplemented with the investigations of hydrogen permeation performed by the Devanathan-Stachurski bipolar electrode method.

It was found that the additives inhibited the electrodeposition of Zn and stimulated the hydrogen evolution from the cathode to the electrolyte. The hydrogen permeation in the iron substrate was suppressed in the presence of the additives in the electrolyte.     

影响共电沉积过程中纳米Cr、Al粒子复合量因素初探

在Ni与纳米Cr粒子或Al粒子共电沉积过程中,发现Ni镀层复合纳米Al粒子要比复合纳米Cr粒子容易.电化学测试表明:两种粒子在镀液中阴极极化行为不同,加入纳米Cr粒子后,极化曲线正向偏移,阴极极化降低.而加入纳米Al粒子后,极化曲线负向偏移,阴极极化增大.进一步用HREM对镀层中纳米粒子进行原子尺度观测,发现两者表面皆存在几个纳米厚的氧化膜层,提出了纳米粒子表面氧化膜半导体类型不同而引起粒子在镀液中吸附阳离子能力的强弱不同,是影响纳米粒子复合量的重要因素.     

涡轮叶片气膜冷却孔电解加工气液两相流场特性分析

以高温镍基合金Inconel718为基材进行气膜冷却孔电解加工基础试验,在电解加工过程中,阴极反应界面析出氢气,导致电解液的电导率不再是一个常数,从而影响冷却孔的加工成型精度。结合前期基础试验,建立冷却孔电解加工流道二维模型,基于COMSOL Multiphysics软件对冷却孔端面间隙内气液两相流场进行仿真,研究加工电压、电解液入口压力及管电极进给速度对氢气析出量的影响,并定性地分析电解加工过程中气泡率与电导率之间的关系。由仿真结果可知:氢气的体积分数随加工电压和电极进给速度的增大而增大,随电解液入口压力的增大而减小,且氢气体积分数越大,电解液的电导率越小。     

Electrodeposition of composite Fe–TiO<Subscript>2</Subscript> coatings from methanesulfonate electrolyte

The process of electrodeposition of an iron–titania composite electrochemical coating from methanesulfonate electrolyte is studied. TiO₂ Degussa P 25 nanopowder (a mixture of crystalline modifications of rutile and anatase, with the latter prevailing) is used for preparation of suspension electrolyte. The dispersed phase content in the composition coating increases at a decrease in current density and increase in TiO₂ in the suspension. It is shown that kinetics of codeposition is adequately described by the improved Guglielmi model. It is shown that inclusion of TiO₂ particles into an iron matrix results in an increase in microhardness of the coating due to dispersion strengthening. Fe–TiO₂ (anatase+rutile) coatings manifest photocatalytic activity with respect to the reaction of destruction of the methyl orange dye in aqueous solutions under exposure to UV radiation, and this activity is higher than in the case of similar coatings containing TiO₂–rutile particles.     

Electrocatalytic activity and electrochemical hydrogen storage of Ni-La alloy prepared by electrodeposition from aqueous electrolyte

Ni-La alloy coating was prepared by electrodeposition. The effect of cathodic current density on the La content of the alloy coatings was discussed. It is found that the content of La in the alloy increases with increasing the cathodic current density. The microstructures and codeposition mechanism of Ni-La alloy coatings were investigated by means of X-ray diffraction (XRD) and cyclic voltammetry (CV). The results demonstrate that the Ni-La alloy is FCC and codeposited by the induced mechanism. The hydrogen evolution reaction (HER) on the electrodeposited Ni-La alloy electrodes in alkaline solution was evaluated by Tafel polarization curves. It is found that La-Ni alloy coating exhibites much higher exchange current density for HER than pure Ni electrode, and that the exchange current density increases with increasing the La content of alloys. The good electrocatalytic activity for HER of this Ni-La alloy is attributed to the synergism of the electronic structure of La and Ni. The electrodeposited La-Ni alloys have a certain dectrochemical hydrogen storage capacity of 34- 143 mAh/g, which increases with increasing the La content of alloys.     

Electrodeposition of Amorphous Iron-Nickel-Phosphorus Alloy Coatings

The effects of plating parameters on the composition and structure of electrodeposited Fe-Ni-P alloys have been studied. A sulfate electrolyte containing sodium hypophosphite with an acetate buffer was used. Deposits were plated onto both planar and rotating cylinder electrodes. Alloy deposits that were amorphous over a wide range of iron:nickel ratios were achieved. The anomalous deposition typical of Ni-Fe alloy plating was not observed in these studies where phosphorus was codedeposited. The deposit composition was dependent on both the plating bath composition and current density.     

Laser-enhanced electrodeposition of nickel coatings

Optimal conditions for a laser-enhanced electrodeposition of nickel coatings have been specified. Comparative results of structure and mechanical properties of electrically deposited nickel coatings produced by a laser-enhanced galvanostatic method and without laser emission were analysed. It was found that laser medium wave IR radiation has a local thermal effect on the process of electrodeposition and stimulates formation of a nickel coating structure which is of a more equilibrium state, less defective and has reduced internal stress in the area of local laser heating. Studies of plating rate showed a 1.4 times increase for nickel coatings in conditions of laser-enhanced electrodeposition due to reduction of common cathode overpotentional and increase of cathode metal efficiency, that involves generation of a more coarse microcrystal structure. Results of studies of the laser radiation effect on structure and properties of nickel coatings show potential for increased adhesion of electrodeposited coatings with a copper substrate.     

Role of additives in electroless copper plating using hypophosphite as reducing agent

In electroless copper plating baths using hypophosphite as the reducing agent, nickel ions was used to catalyze hypophosphite oxidation. However, the color of the copper deposits was dark or brown and the electrical resistivity was much higher than that obtained from formaldehyde baths. Polyethylene glycol (PEG) and K₄Fe(CN)₆ were used to improve the microstructure and properties of copper deposits obtained from electroless copper plating bath using hypophosphite as the reducing agent. The effects of PEG concentration on the deposition rate, the microstructure, morphology and electrical resistivity of the copper deposits, and the electrochemical reactions of hypophosphite (oxidation) and cupric ion (reduction) were investigated. The traces of hydrogen escaping from the deposits surface disappeared and the color of the copper deposits changed from dark-brown to dark red when the PEG concentration was 1.67 × 10^− 5 M or more. The deposition rate increased and the electrical resistivity of the copper deposits decreased slightly with the addition of PEG to the plating solution. The electrical resistivity of copper deposits decreased to 2.85 μΩ cm with 1.67 × 10^− 5 M PEG and 4.70 × 10^− 6 M K₄Fe(CN)₆ in the bath. Larger grain size and higher (220) plane orientation were obtained with the increase of PEG concentration in the bath. The electrochemical current–voltage results showed that PEG accelerated the catalytic oxidation of hypophosphite at active nickel sites and had little effect on the reduction reaction of cupric ions on the deposit surface by adsorption on the electrode.     

Electrodeposition and properties of an iron-tungsten alloy

Iron-tungsten alloys were obtained from citrate electrolytes. The relation between Fe(II) and Fe(III), which permits maintaining the stability of an electrolyte as well as obtaining high-quality deposits for a long time, is revealed. The results of investigations show that the discharge of iron ions takes place from the three valent ions. It is found that the concentration of sodium tungstate in the electrolyte contributes to the codeposition of tungsten, increasing its ratio in the alloy. It is established that the current efficiency and composition of iron-tungsten coatings depend on the current density and the conditions of electrolysis. The microhardness of iron-tungsten deposits increases with an increase in the deposition temperature and depends on the tungsten content in the alloy. Investigations with an electron microscope have shown that, on the alloy surface, superficial inhomogeneous films with the content of tungsten and oxygen different from that in the deposit are formed. The obtained alloys have concentration and structure inhomogeneities.