STUDY OF THE INFLUENCE OF pH ON THE ELECTROCRYSTALLIZATION OF ZINC

1. IntroductionElectrodeposition ofalloys is w idely used in the production of new m aterials possessing specificchem ical,physicalproperties,such asnanocrystalline m agnetic thin film sand functionalm ultilayers[1-5].In com parison to otherdeposition tec…     

氨络合物体系电积锌的阴极过程

采用CHI650电化学工作站测定了在锌氨络合物体系中锌电沉积的稳态阴极极化曲线及电流-时间暂态曲线.结果表明:锌的阴极电结晶过程是以瞬时成核方式进行的,随外加电位负移,晶体的向外生长速率增大;添加剂的加入不会改变锌阴极电沉积的成核方式,但将大大减小晶体的向外生长速率.通过对不同NH3浓度下测得的阴极极化曲线的分析,可获得各条件下的平衡电位,以及阴极过程动力学参数(交换电流密度J°、传递系数α),进而推导出溶液中存在的主要离子为Zn(NH3)2 4,在阴极直接放电的络离子为Zn(NH3)22 .     

Steel cathodic protection afforded by zinc, aluminium and zinc/aluminium alloy coatings in the atmosphere

Zinc has traditionally been the metallic material most widely used to protect steel against atmospheric corrosion due to its ability to afford cathodic protection to steel in all types of natural atmospheres. In recent decades, aluminium and zinc/aluminium alloy coatings have been used instead of zinc in certain atmospheric applications. Although these coatings present some advantages over zinc, they are not able to cathodically protect steel substrates in all types of natural atmospheres. The present paper assesses the cathodic protection afforded by Al (flame spraying), Al/13 Si (hot dipping), 55Al/Zn (hot dipping), Zn/15Al (flame spraying), Zn/5Al (hot dipping), Zn (hot dipping), Zn (discontinuous hot dipping) and Zn (electroplating). Aluminium and aluminium-rich alloy coatings (55%Al/Zn) provide cathodic protection to the steel substrate only in atmospheres that are highly contaminated with chloride ions (>100 mg Cl⁻ m⁻² day⁻¹) where these coatings become active.     

Electrochemical behavior of electroplated Zn-P alloy

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Impact of zinc ion addition on corrosion of EH40 steel in natural seawater

Zinc ion is a common heavy metal in marine pollution, but its impact on corrosion of steels without passive films in natural seawater is far from being investigated. In this study, the impact of zinc ion addition (1.5 and 15 mmol/L) on corrosion of EH40 steel commonly utilized for building ships and offshore platforms was studied by numerous methods and technologies. It was found that EH40 steel corrosion was inhibited with the addition of zinc ion, and corrosion inhibition efficiency increased with the concentration added. The deposited ZnO and Zn(OH)₂ on the steel surface was believed to hamper electron transfer, thus inhibiting corrosion. Meanwhile, the bactericidal zinc ion and ZnO mitigated the activity of microorganisms in biofilms to reduce the damage caused by microbiologically influenced corrosion. But pitting corrosion was enhanced with a high concentration of zinc ion added due to the inhomogeneity of ZnO layers.     

热镀锌层上磷酸锌转化膜的生长与耐蚀性

热镀锌钢板在pH3.0、45℃的磷酸锌溶液中磷化2～600s,用扫描电镜、能谱仪和X射线衍射仪分析磷化膜的组织形貌和成分,并探讨膜层的生长行为。结果表明:磷酸锌晶体在锌晶粒内及晶界处均可成核,开始是以接近平行的片状生长,并逐渐向多方向生长成扇骨状的晶片。随着磷酸锌晶体的成核和生长,磷化膜的覆盖率增加,但晶体之间的孔隙难以完全消除;长大的磷酸锌晶片容易折断脱落,导致磷化后期膜层的质量增量减小;磷化膜主要由Zn3(PO4)2.4H2O组成。热镀锌钢板经磷化处理后,耐蚀性显著提高,磷化膜的耐蚀性随磷化时间和膜层覆盖率的增加而提高。     

ELECTROCHEMICAL NOISE ANALYSIS OF THE INFLUENCE OF THE Zn^2＋ IONS CONCENTRATION ON ZINC ELECTROPLATING

The influence of the concentration of Zn^2 ions on zinc electroplating process was investigated by means of electrochemical noise (EN) and cyclic voltammetry methods in conjunction with the scanning electron microscopy (SEM) technique. It was found that the EN generated during the electroplating of dentritic or large polymeric zinc deposit has large potential oscillation amplitude and positive potential drift while the compact zinc deposit possesses small noise amplitude and little potential drift. With the change of rate determining step from diffusion-control through mixed-contro! to activation-control, the maximum relative energy obtained from wavelet analysis defined from the region with larger scales to those with smaller scales, and the EDP (relative energy distribution plot) can be us, as “fingerprints” of EN to characterize the electroplating process and the deposit structure. The results also showed that electrochemical noise technique can give more information about the electrodeposit structure than other normal electrochemical measurements, such as linear potential sweep method and cyclic voltammetry, technique.     

氯化胆碱-尿素低共熔溶剂中锌的电沉积研究

目的研究锌在氯化胆碱-尿素低共熔溶剂(ChCl-Urea DES)中的电化学行为、电结晶机理、电沉积历程和耐蚀性。方法采用循环伏安(CV)和计时电流技术(CA),研究了锌在玻碳电极上的电化学行为和电结晶机理。采用扫描电子显微镜(SEM)和X射线衍射技术(XRD)对锌镀层的微观形貌和物相组成进行了表征。采用动电位极化曲线和电化学阻抗谱,对比研究了ChCl-Urea DES和水溶液中锌镀层的耐蚀性。结果CV测试表明,在Zn(Ⅱ)的氧化还原过程中仅出现了一对氧化还原峰,这说明Zn(Ⅱ)在ChCl-Urea DES中为一步还原及氧化,且还原峰电位为?1.207 V(vs.Ag)。不同扫描速度下的CV曲线表明,还原峰和氧化峰的峰值电位Ep和峰值电流I_p均随扫描速率v的变化而有规律的偏移,这符合不可逆电极反应的特征。对I_p和v^1/2的关系进行了线性拟合,发现I_p与v^1/2之间符合线性关系,故可认为Zn(Ⅱ)的还原反应是受扩散控制的,进一步计算出扩散系数DZn(Ⅱ)为6.67×10^?8cm²/s。在–1.141~–1.147 V下测定CA曲线,通过对比拟合CA曲线和理论曲线发现,Zn(Ⅱ)在ChCl-Urea DES中的形核方式不符合三维瞬时成核和三维连续成核,是一种具有两种形核方式特征的混合形核。SEM结果表明,不同沉积时间下锌镀层的微观形貌相差较大。随着沉积时间的增加,锌晶粒由细小、粒径均一的颗粒逐渐变化成大小颗粒交叠存在的六方形立体结构,然后又变成线状或棒状的结构,最终转变为六方形的片状晶粒。XRD表明,锌镀层由六方晶相的多晶锌构成。动电位极化曲线测试和电化学阻抗图谱表明,在没有任何添加剂的情况下,ChCl-Urea DES可获得与水溶液中耐蚀性相当的锌镀层,且ChCl-Urea DES中锌镀层的沉积速率略高于水溶液。结论Zn(Ⅱ)在ChCl-Urea DES中的电沉积过程是受扩散控制的不可逆电极过程,形核方式不符合三维瞬时成核和三维连续成核,是一种具有两种形核方式特征的混合形核。锌镀层是由六方晶相的多晶锌构成的。在ChCl-Urea DES中可获得与水溶液中耐蚀性相当的锌镀层,且沉积速率略高于水溶液。     

2024铝合金浸锌工艺研究

试验研究了浸锌工艺及溶液组成对2024铝合金基体浸锌层及电镀镍层外观和结合力的影响,优化了浸锌液的组成及工艺条件.发现良好的浸锌层是提高镀层与基体结合力的关键.     

STUDY THE INFLUENCE OF H3BO3 ON THE ZINC ELECTROPLATING USING ELECTROCHEMICAL NOISE TECHNIQUE

The influence of H3BO3 on the zinc electroplating was studied using electrochemical noise technique, cyclic voltammetry and steady-state polarization method. The results showed that,under the experimental conditions, the deposition of zinc followed the mechanism of two-dimensional nucleation and subsequent grain growth. The addition of H3BO3 into the electroplating solution prominently changes the nucleation and growth kinetics of zinc deposits, which is directly related to the features of electrocrystallization noise and the corresponding structure of the electrodeposits. The results also shown that the electrochemical noise (EN) technique can give more information about the electrodeposits structure and electroplating mechanism than other normal electrochemical measurements can give, such as steady-state polarization method and cyclic voltammetry technique.     

The temperature-dependence of the SO2-induced atmospheric corrosion of zinc; a laboratory study

The SO₂-induced atmospheric corrosion of zinc was studied at 4, 14, 22 and 30 °C and 95% RH. Each sample was exposed individually to synthetic atmospheres with careful control of SO₂ concentration (107 and 500 ppb), relative humidity and flow conditions. The initial reaction between SO₂ and zinc was studied in a time-resolved manner. Two-week exposures were performed to measure the corrosion rate and study the formation of corrosion products. Corrosion products were analysed by X-ray powder diffraction and ion chromatography. The corrosion rate was inversely dependent on temperature, the maximum rate being found at the lowest temperature. SO₂ deposition showed a similar trend with the highest deposition rate at 4 °C. At low temperature a thick film of ZnSO₄(aq) formed on the metal surface, whereas zinc hydroxysulphate (ZnSO₄ · 3Zn(OH)₂ · 4H₂O(s)) was the main corrosion product at 22 and 30 °C. The inverse temperature-dependence of the corrosion rate of zinc is proposed to be connected to the formation of sparingly soluble zinc hydroxy sulphate which slows down the deposition of SO₂ on the surface.     

Passivity and passivity breakdown of zinc anode in alkaline medium

The electrochemical behaviour of zinc in NaOH solutions has been investigated by using potentiodynamic technique and complemented by X-ray analysis. The E/i curves exhibit active, passive and transpassive regions prior to oxygen evolution. The active region displays two anodic peaks. The passivity is due to the Formation of a compact Zn(OH)₂ film on the anode surface. The transpassive region is assigned to the electroformation of ZnO₂. The reverse sweep shows an activation anodic peak and one catholic peak prior to hydrogen evolution. The influence of increasing additives of NaCl, NaBr and Nal on the anodic behaviour of zinc in NaOH solutions has been studied. The halides stimulate the active dissolution of zinc and tend to break down the passive film, leading to pitting corrosion. The aggressiveness of the halide anions towards the stability of the passive film decreases in the order: I^? > Br^? > Cl^?. The susceptibility of zinc anode to pitting corrosion enhances with increasing the halide ion concentration but decreases with increasing both the alkali concentration and the sweep rate.     

Effect of citrate additive on the electrodeposition and corrosion behaviour of Zn–Co alloy

The electrodeposition of Zn–15Co alloy on a stainless steel substrate from a citrate bath has been investigated as a function of pH and citrate concentration in the electroplating bath. UV–vis results and speciation diagrams of zinc and cobalt in aqueous citrate solution were used to select deposition baths with different dominant Zn–Co citrate complexes. Voltammetry and potentiostatic methods were used to study the codeposition mechanism. The corrosion behaviour of electrodeposits of Zn–15Co alloys was studied by means of electrochemical experiments in a solution of 3.5% NaCl using potentiodynamic polarisation and open circuit potential. The results showed that the corrosion resistance of the deposits was highly influenced by the presence of citrate in the electroplating bath.     

Aspects of galvanic action of zinc rich paints

The cathodic protection effect of zinc in zinc pigmented coatings can be clearly recognized above a certain pigment concentration. According to the results obtained during potentiostatic polarization experiments such an effect can be expected above 90% Zn. This effect will still be present after 30 days in sodium chloride solution, provided the original concentration is 93%, while the protective effect is lossed after this time in the case of 91% Zn. The potentiostatic methods are clearly superiour to a resistance method used preferentially and can be recommended for formulation of coating materials and for testing such coating materials and coatings.     

改性甲壳胺添加剂在钠盐镀锌中的应用

利用赫尔槽和金相观察观测等方法,对镀液性能和镀层性能进行了研究,探讨了改性甲壳胺分子对钠盐镀 影响,结果发现改性甲壳胺可作为钠盐镀锌的一种添加剂,其镀液及镀层性能优于裳睡的硫脲及氯锌１号镀液 。     

次氧化锌中砷的物相及砷的浸出(英文)

研究烟化炉次氧化锌中砷的物相类型。结果表明:按砷的物相可将次氧化锌分为3种类型。在一型次氧化锌中砷以As2O3形态存在,而在二型和三型次氧化锌中砷分别以亚砷酸锌(Zn(AsO2)2)和砷酸铅(Pb(As2O6),Pb4As2O9)形态存在。在热力学分析基础上,对二型次氧化锌进行浸出脱砷。结果表明:采用30g/LNaOH溶液,在液固比3、温度20°C的条件下,砷的浸出率在1h内可达到65%～70%,而铅、锌的损失均小于1%。     

Dissolution mechanism of solid nickel in liquid zinc saturated with Fe

The dissolution behavior of solid nickel in static liquid zinc saturated with Fe at 723 K was studied. The results show that when immersing solid Ni in liquid Zn saturated with Fe, the intermetallic compound layers consisted of γ and δ phases are formed on nickel substrate, which is the same as that in liquid pure zinc. However, some F2 particles are formed in the liquid near the solid/liquid interface. These Г2 particles can easily heterogeneously nucleate on （particles and grow fast. The dissolution process is governed by diffusion of nickel atom across a concentration boundary layer in liquid Zn saturated with Fe, and is different from a mixed control mechanism of nickel in liquid pure zinc. The participation of Г2 particles makes the dissolution of solid Ni in the liquid accelerated.     

Free-Cyanide Synthesis and Characterization of Cu–Zn Alloy by an Electrodeposition-Annealing Route

Substitution of cyanide in electroplating is a current challenge. We present an alternative method aiming to reduce the toxicity and the cost of electroplating of Cu–Zn alloy (usually prepared from cyanide baths) while maintaining the decorative qualities and anticorrosive properties of the coating. For this purpose, Cu–Zn alloys were obtained in two steps from non-cyanide electrolytes. First, a copper layer electrodeposited onto a nickel under-layer, followed by a thin layer of zinc from three different simple non-cyanide zinc baths. The Zn/Cu/Ni sandwich system was then subjected to heat treatment at a temperature of 400°C, to ensure the diffusion of zinc into the copper layer to give the desired Cu–Zn alloy structure. The synthesized films were characterized by using X-ray diffraction XRD, scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS). XRD demonstrated that the electrodeposited films are crystalline and present the Cu_0.7Zn_0.3 phase with preferential (111) orientation. An analysis of XRD patterns revealed that after heat treatment, the Cu–Zn alloys were composed of a predominating α-phase structure. The morphology and composition of the coatings depends on the zinc plating bath type. After annealing, well defined pseudospherical Cu–Zn grains were formed covering the entire substrate surface. The EDS analysis indicated the formation of Cu_0.7Zn_0.3 brass alloys. The results showed the feasibility of this low-cost new route for the preparation of good quality Cu–Zn alloys from cyanide-free electrolytes.     

Effect of zinc immersion pretreatment on the electro-deposition of Ni onto AZ91D magnesium alloy

The effect of zinc immersion pretreatment on the quality and properties of Ni deposited layer on the AZ91D Mg alloy has been studied. The evolution of surface morphology, composition and microstructure of the AZ91D Mg alloy in the process of pretreatment was characterized by scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX) and X-ray diffraction (XRD). The results showed that the activation step results in the deposition of some composite membranes consisted of fluoride and phosphate or pyrophosphate formed preferentially in the α phase region of the Mg alloy surface, while zinc immersion leads to the deposition of a network-like Zn layer formed preferentially in the β phase region of the Mg alloy surface. Cyclic voltammogram, dynamic potential scanning polarization technique and chronopotentionmetry measurements showed that the deposited Zn layer can markedly improve the anti-corrosion ability of the Mg alloy substrate in the Ni-plating solution and improve the nucleation and growth of Ni onto the surface of the Mg alloy substrate. With the proper Zn immersion pretreatment, a compact Ni layer can be electro-deposited on the magnesium alloy. The deposited Ni layer shows good adhesion to the Mg alloy substrate. The Mg alloy specimens after deposition of Ni have good anti-corrosion properties in a neutral 3.5 wt.% NaCl solution.     

Electrochemical aspects of deposition and characterisation of zinc coating produced in presence of 1,2-diaminopropane in sulphate bath

Abstract

The effect of 1,2-diaminopropane addition on zinc electrodeposition was studied using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Adding 1,2-diaminopropane into the electrodeposition bath increased the zinc ion discharge potential. Analysis of chronoamperograms in the absence and presence of 1,2-diaminopropane indicated that the progressive nucleation is predominant in both cases. Scanning electron microscopy analysis showed that the zinc coating obtained in the presence of 1,2-diaminopropane is more homogenous in appearance and lower in crystallite size. By inhibiting the growth of (00·2) planes, 1,2-diaminopropane also affected the texture of the zinc deposit. Potentiodynamic polarisation readings in deaerated 5%NaCl solution indicated that the corrosion resistance of the zinc deposit is slightly improved in the presence of 1,2-diaminopropane in the bath.