Zinc-nickel alloy electrodeposition from uncomplexed acid bath

Zinc-nickel alloys, as protective coatings, are well known and a new citrate bath has been investigated. It was observed that boric acid favoured nickel deposition playing the dual role of specific adsorption and catalysis. The voltammetric behaviour of the alloy deposition in the presence of boric acid is described. The effect of Ni/Zn ratio, and potential scan range on the cathodic and anodic portions of the voltammograms are discussed. The presence of two cathodic peaks at high Ni/Zn ratios, which disappeared at lower ratios was identified.     

柠檬酸根对镍钛合金表面电沉积羟基磷灰石涂层的影响

在含有0.042 mol/L Ca2+、0.025 mol/L H,PO-4及2.5×10-4mol/L柠檬酸根的电解液中进行阴极电沉积,成功地在NiTi合金表面制备了羟基磷灰石(HA)涂层.在电沉积之前,用5 mol/LNaOH对NiTi合金进行碱热预处理,可在其表面形成一层纳米针状氧化物.与不加柠檬酸根的电解液相比...     

硫酸盐-柠檬酸盐体系锌锰合金电镀液稳定性的研究

锌锰合金镀液存在电流效率低,镀液稳定性差等缺点,选择硫酸盐－柠檬酸盐体系锌锰合金镀液,研究了阳极,二价锰离子以及连续作用等因素对镀液稳定性的影响,结果表明：采用不锈钢阳极和阴离子膜可提高镀液稳定性,防止二价被氧化,加入氢氧化可消除因补充锌锰离子而积累的硫酸根离子。     

Corrosion behavior of 2024 aluminum alloy anodized in presence of permanganate and phosphate ions

In this article, the effects of two inorganic corrosion inhibitors, permanganate and phosphate anions, on morphology, composition, thickness, and corrosion resistance of the anodic film formed on 2024 aluminum alloy in sulfuric acid were investigated. Surface morphology of the oxide films were studied by field emission scanning electron microscopy. Electrochemical impedance spectroscopy and potentiodynamic polarization tests were conducted to assess the corrosion resistance of the coatings. These analyses showed that the presence of the mentioned inhibitors changed the coating morphology, especially in the case of phosphate ions. Corrosion results indicated that using inhibitors during the anodizing process increased the corrosion resistance of the anodized samples. The increases were approximately 81% and 97% for 0.05 M of permanganate and phosphate ions, respectively, compared with the anodized coatings in the absence of additives. An increase in the inhibitor concentration results in better corrosion resistance of the aluminum anodic layer.     

Mechanism of nickel-molybdenum alloy electrodeposition in citrate electrolytes

The kinetics of the induced codischarge of Mo with Ni in citrate-ammonia electrolytes was investigated by means of polarization and a.c. impedance measurements. Three potential ranges were considered. At low polarization, hydrogen evolution resulting from citrate reduction is the main reaction. The impedance plots exhibit a large capacitive loop with a small high frequency inflection characteristic of the development of a porous layer and a low frequency inductive feature. At intermediate polarization, the partial currents for Ni and Mo discharge increase in the same proportion; the hydrogen evolution is first constant and then rapidly decreases. Then a large low-frequency capacitive feature is observed on the impedance plots, whose size decreases with increasing polarization. At still higher polarization, the Mo discharge becomes increasingly controlled by diffusion which generates an additional capacitive loop. A reaction scheme is proposed which accounts for the polarization data and the major impedance features.     

Precipitation of calcium carbonate in the presence of citrate and EDTA

The influence of process conditions such as feed rate, calcium/carbonate ratio, pH, complexing agents [ethylenediaminetetraacetic acid (EDTA), citrate (CIT)] and their concentration on the average particle size and shape of precipitated calcium carbonate was studied. The precipitation was performed in a semi-batch operated agitated vessel at constant pH by adding sodium hydrogen carbonate to a solution containing calcium chloride. In the absence of a complexing agent, agglomerates of needle-shaped crystals, probably aragonite, are obtained. Increasing feed time and the calcium/carbonate ratio increases the average particle size, whereas the opposite effect is observed for increasing pH. The observations can be related to the level of supersaturation. In the presence of complexing agents and at a concentration ratio of calcium vs. a complexing agent of 6, differently shaped and smaller particles were obtained. Furthermore, the effect of the other parameters on particle size becomes much weaker in the presence of complexing agents. In the presence of EDTA mostly spherical particles were obtained, and in the presence of citrate mainly rhombic particles corresponding to calcite were obtained. The effect on particle shape and size is attributed to interactions of the complexing agents with the faces of the crystalline calcium carbonate.     

Electrocatalytic deposition of polypyrrole in the presence of bromide

Bromide ions (typicallyc=1 mM) are oxidized in acetonitrile electrolytes at platinum anodes in two steps, well separated by about 300 mV, leading to tribromoanions1 and to bromine2, respectively. These basic electrochemical reactions interfere quite differently with pyrrole3, typicallyc=0.1-0.01 M, added to the system.1 oxidizes3 to bromopyrroles, indicated by an amplification of the limiting current density of the first wave by a factor of three. No polypyrrole is deposited. In the course of the second wave,2 oxidizes3 to the radical cation4. The rate determining step in the formation of polypyrrole is a dimerization of4 moieties, and the strong electrostatic shielding effect via complexation of1 with4 leads to a catalytic enhancement of the polymerization rate by more than a factor of 10 with respect to conventional systems. Regeneration of1 in the course of these processes gives a large current amplification in the second wave. The overall reaction leads to polypyrrole, which forms an electrode coating. The material has improved properties, for example electronic conductivities above 100 S cm^–1. The current efficiency is nearly 100%, but only if the convection is weak. This negative stirring effect is discussed in detail.     

Tuning the size of gold nanoparticles in the citrate reduction by chloride ions

A new approach was developed to control the size of gold nanoparticles in citrate reduction by altering the concentration of chloride ions. The size of the as-prepared gold nanoparticles could be tuned in the range 19-47 nm at a specific molar ratio of citrate and tetrachloroauric acid (5:1) by simply changing the concentration of chloride ions from 0 to 20 mM. UV-visible spectra and TEM observations showed that the increased size of the gold particles was primarily related to the promoted aggregation of the primary gold particles. The aggregation was attributed to their decreased surface charge as the chloride ion concentration in the reaction solutions increased. This approach could also be extended to other reaction systems, for example, the size of gold nanoparticles prepared by NaBH(4) reduction increased from 3 to 12 nm as the chloride ion concentration was increased from 0 to 20 mM.     

Electrochemical behavior of dopamine in the presence of citrate: Reaction mechanism

The electrochemical behavior at a mercury electrode of dopamine (DA) in the presence of citrate was investigated in aqueous solution, using cyclic voltammetry and alternating current polarography. The influence of the composition of the supporting electrolyte, citrate concentration and pH was evaluated. At potentials more positive than 250 mV DA and Hg are oxidized yielding, in the presence of citrate, dopaminoquinone (DQ) and Hg(II). Hg(II) reacts with the DA forming DQ, leucodopaminochrome (LDC) and dopaminochrome (DC). DQ undergoes further reduction at 200 mV. Citrate, in the form of Cit³⁻, stabilizes the DC formed and this new electroactive compound suffers further reduction at −250 mV. This reaction pathway inhibits the formation of polymerized films on the surface of solid state electrodes and allows the determination of DA using the mercury electrode.     

碱性锌酸盐型锌镍合金生产工艺研究进展

碱性锌酸盐型锌镍合金因其优异的综合性能已成为业界的研究热点,综述了近年来的工艺进展。碱性锌酸盐型镀液体系通常以NiSO_4、ZnO等做主盐,强碱(NaOH)作导电盐,具有分散能力好、易钝化处理、对设备腐蚀小等优点,但也存在镀液电流效率低,过程控制参数多,生产废水难处理等缺点。今后研究的核心问题在于寻找更好的镀液配方,开发更优异的络合剂及添加剂种类,从而保证镀件稳定光亮的同时,降低生产成本及废液处理难度。     

化学镀钴-镍-磷合金镀层沉积速度的探讨

化学镀钴－镍－磷合金镀层具有良好的磁学性能,正日益受到人们的青睐。由于沉积速度往往对镀层性能产生很大影响,在此重点了影响化学镀钴－镍－磷合金镀层沉积速度的各因素。结果表明,提高镀液中金属离子总浓度及镍盐所占的比例,在ＰＨ为８￣１０范围内加入适量的稳定剂及采用活性强的基材有利于化学镀钴－镍－磷合金镀层沉积速度的提高。     

Underpotential deposition of Tl on Ag in the presence of bromide ions – Estimation of specific capacitance for design of electrochemical supercapacitors

The analysis of underpotential deposition (UPD)-based systems for the development of electrochemical supercapacitors is investigated employing the UPD of Tl on Ag in the presence of bromide ions, as an illustrative example. The specific capacitance is estimated with the help of multi-cycle voltammograms, galvanostatic charge/discharge experiments and impedance spectroscopy. The equivalent circuit for the system is constructed and the parameters are deduced from the simulation. The deduced magnitude of ∼10² F g⁻¹ in conjunction with the satisfactory number of charge/discharge cycles obtained from galvanostatic experiments indicate the feasibility of these systems as supercapacitors.     

变形锌合金在柠檬酸盐镀镍液中的腐蚀行为

利用动电位极化曲线和电化学阻抗谱研究了变形锌合金在柠檬酸盐电镀镍溶液中的腐蚀行为,通过场发射扫描电镜(SEM–EDS)表征了腐蚀表面形貌和成分。结果表明,锌合金在镀液中呈活性溶解状态,柠檬酸钠对锌合金有缓蚀作用;提高镀液温度不仅加剧锌合金腐蚀,还会加快镍置换反应发生。     

Electrolytic deposition of oxide films in the presence of hydrogen peroxide

Cathodic electrosynthesis of TiO₂, Nb₂O₅, PZT, composite RuO₂–TiO₂ and Al₂O₃–TiO₂ films and powders was performed. In the proposed approach, TiO₂, Nb₂O₅, PZT film formation on platinized silicon or/and Pt substrates was achieved via peroxoprecursors. Obtained deposits were characterized by XRD, SEM, Auger and SIMS methods. The crystallization behaviour of the deposits has been studied. Possible cathodic reactions which underlie the deposition process and the role of hydrogen peroxide are discussed. ©     

Crystallization of ferrisilicate molecular sieve in the presence of fluoride ions

The ferrisilicate molecular sieve analogue of the ZSM-5 was prepared from the weak alkaline medium (pH 8) in the presence of F^- ions, which was confirmed by IR, X-ray powder diffraction, EPR.and²⁹Si MAS NMR studies. The addition of F^- ion in the preparation of metallosilicate molecular sieves could reduced the pH value of the reaction mixture, and prevent from the precipitation of metal ions which are sparingly soluble in strong alkaline media.     

锌镍合金镀层的耐蚀性能研究

在低碳钢表面电镀锌镍合金薄膜.考查了pH值、电流密度和镀液温度等因素对镀层质量的影响.采用XRD与SEM研究镀层的结构和形貌.选择3.5%NaCl溶液作为腐蚀介质,用稳态法研究了镀层的耐蚀性能,得出了较有价值的结论.     

化学镀镍铜磷三元合金沉积工艺的研究

为提高化学镀镍的硬度、耐磨及耐蚀性,以拓宽在电子工业中应用,采用在化学镀镍磷合金液中添加适量的铜离子制得镍铜磷三元合金。研究了镍离子与铜离子浓度比、次磷酸钠含量、沉积温度对合金镀层沉积速率的影响,利用Ｓ－５７０扫描电镜和Ｈ－８００透电镀观察了镀层表面形貌和显微组织,通过硝酸腐蚀试验比较了镍磷合金与镍铜镀层的耐蚀性。结果表明,铜的共沉积能明显提高镍磷合金的耐蚀性。     

Markov chain model of electrochemical alloy deposition

A new model of the electrochemical alloy deposition has been developed. It is based on the application of the finite Markov chain theory and is called the Markov chain model. The first analytical relationship between the alloy composition (ratio of mol fractions x_A/x_B and the metal ion concentrations in the electrolyte (mol fraction X_A and X_B can be deduced from the model.

     

Stability of an electrolytic alloy deposition process

The stability of electrolytic brass deposition in a continuous flow stirred tank electrolyser is studied via Liapunov functions based on an empirical model of the deposition process.Nomenclature A, B Quantities defined by Equation 8 - C ₁ Concentration of copper:C ₁ ^* , steady state;C _1i, inlet concentration - C ₂ Concentration of zinc:C ₂ ^* , steady state;C _2i, inlet concentration - F Faraday's constant - f _CN Free cyanide content - g(x, t) Perturbation vector - i Cathode current density - I _j Current carried by the j-th component (j=1, copper; j=2, zinc) - m ₁,m ₂ Maximum magnitude ofx ₁ andx ₂ - m _t Mass of brass deposited on the cathode - M Malkin bound for the partial derivatives of the Liapunov function - M ₁ Molar mass of copper - M ₂ Molar mass of zinc - P Symmetric positive definite matrix - q Inlet flow rate of electrolyte - R Relative amount of copper in the bath (%) - t Time - T Reactor temperature - V _r Reactor volume - W ₁,W ₂,W ₃ Positive definite functions (Malkin's theory) - x State vector - x ₁ Dimensionless copper concentration - x ₂ Dimensionless zinc concentration - y Relative amount of copper in the brass deposit - z Valency - ² Liapunov parameter - Bound for the state vector - ₁, ₂ Malkin bounds - _j Time-decay parameter - ₁, ₂ Liapunov parameters (nonautonomous system) - Time-decaying perturbation function (vector) - Dimensionless time     

LaCl3在柠檬酸体系电沉积锡-镍-铁三元合金中的应用

通过赫尔槽试验、极化曲线以及镀液和镀层性能的测定,探讨了LaCl<,3>对柠檬酸体系中电沉积锡-镍-铁三元合金的影响.结果表明,LaCl<,3>的加入能增大光亮电流密度范围和阴极极化作用,提高镀液分散能力,降低镀层孔隙率,镀层中Ni质量分数从3.45%提高到5.95%,其耐蚀性提高了约一倍.