Electroplating and characterization of Zn-Ni, Zn-Co and Zn-Ni-Co alloys

Zn-Ni, Zn-Co and Zn-Ni-Co coatings were electrodeposited on mild steel from an acidic chloride bath containing p-aminobenzenesulphonic acid (SA) and gelatin. These additives changed the phase content in the coatings, most likely as a result of their adsorption at the surface of the cathode. The effect of gelatin was more pronounced than that of SA. The Faradaic efficiency was higher than 90%. As the current density was increased or the bath temperature was decreased, the concentration of the nobler metal in the coating increased. Both concentrations of Ni and Co in the ternary alloy increased as the applied current density was increased. Nickel and cobalt were found to have a synergistic catalytic effect. The thickness of all coatings increased as the applied current density was increased. The hardness increased with current density to a peak value, and then decreased. The rate of Zn deposition was heavily influenced by mass-transport limitation at high applied current densities, while the rates of Ni and Co deposition were not. The anomalous codeposition was explained by the great difference between the exchange current densities of Zn and the iron-group metal. Potentiodynamic polarization scans and electrochemical impedance spectroscopy showed that the corrosion resistance of the ternary Zn-Ni-Co alloy coatings was approximately 10 times higher than that of Zn-Ni and 7 times higher than that of Zn-Co. The improved corrosion resistance of the ternary alloy was attributed to its surface chemistry, phase content, texture, and surface morphology. The ternary Zn-Ni-Co coating may thus replace the conventional Zn-Ni and Zn-Co coatings in a variety of applications.     

Effect of electrodeposition conditions on the composition, microstructure, and corrosion resistance of Zn-Ni alloy coatings

The formation, composition, and structure of electrodeposited zinc-nickel alloys were investigated. It has been shown that both anomalous and normal codeposition of zinc and nickel can be realized by changing the bath composition and deposition conditions, with the nickel content in the resultant deposit being varied in a wide range (from 2 to 90 at.%). It has been also shown that the ammonical diphosphate electrolyte allows deposition of Zn-Ni coatings with a homogeneous phase structure (Ni₅Zn₂₁ and Ni₃Zn₂₂ intermetallides, a solid solution of Zn in Ni, or a solid solution of Ni in Ni₅Zn₂₁), whereas the weak acid chloride electrolyte produces two-phase coatings consisting of Ni₅Zn₂₁ with the admixture of polycrystalline Zn or Ni. The Zn-Ni coating with a nickel content of 19 at.% consisting of Ni₅Zn₂₁ intermetallic phase exhibits the highest corrosion resistance.     

电沉积Fe-Cr合金研究

三价铬盐的二甲基酰胺（ＤＭＦ）水溶液体系电沉积Ｆe-Cr合金,可获得含Ｃr12%-65%(质量分数）的光亮合金镀层,研究了阴极电流密度,镀液pH值,三价铬盐浓度对镀层分的影响及合金层耐腐蚀性能。     

Influence of Zn-Ni alloy electrodeposition techniques on the coating corrosion behaviour in chloride solution

The aim of this research work is to optimize the plating conditions during electrodeposition of Zn-Ni alloys. Electrodeposits of Zn-Ni alloys have been synthesized from sulphate bath using cyclic voltammetry and chronopotentiometry techniques under different conditions. X-ray diffraction measurements reveal that the alloys consisted of <gamma>-Ni₅Zn₂₁ and pure zinc phases. The composition and morphology of the deposits have been also studied and discussed. The surface analyses indicate that the deposition took place with the formation of Zn-Ni alloy coatings, containing at least 10 wt.% Ni. In order to obtain better barrier properties and corrosion resistance, coated steel samples have been immersed in 3% NaCl solution and studied using potentiodynamic stripping and electrochemical impedance spectroscopy. The process of dezincification is reduced when the coated steel is electroplated by chronopotentiometry (5 mA and 10 mA). In addition, these samples exhibit an improved morphology and fine grain size as compared with deposits electroplated by cyclic voltammetry.     

Electrodeposition of Corrosion Resistant Zinc Powder

ＥｌｅｃｔｒｏｄｅｐｏｓｉｔｉｏｎｏｆＣｏｒｒｏｓｉｏｎＲｅｓｉｓｔａｎｔＺｉｎｃＰｏｗｄｅｒＬｉＱｉｎｇｗｅｎ,ＬｉｕＲｕｉｑｕａｎａｎｄＸｉａＸｉ（李清文）（刘瑞泉）（夏熙）ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒｙ,ＸｉｎｊｉａｎｇＵｎｉｖｅ...     

The Influence of Bath Components on Deposit and Operational Characteristics in Hard Acid Gold Plating Solutions

This paper describes the influence of bath components, such as buffers, chelates, base metals and organic additives on bath operation and deposits obtained from hard acid gold baths. It also describes the interrelationships between these components.

Buffers are primarily used for pH control of the solution in use, since pH influences the effect of chelates and brighteners.

Chelates can be used to complex out contaminants. They are also used to control effective base metal concentrations as part of the brightener system.

Organic additives, used separately and in conjunction with base metal brighteners, can enhance bright plating ranges and change deposit distribution characteristics.     

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.     

Corrosion Resistance and Durability of Superhydrophobic Coating on AZ31 Mg Alloy via One-Step Electrodeposition

To enhance durability and adhesion of superhydrophobic surface,an integrated superhydrophobic calcium myristate(Ca[CH_3(CH_2)_(12)COO]_2) coating with excellent corrosion resistance was fabricated on AZ31 magnesium(Mg) alloy via one-step electrodeposition process.Field-emission scanning electron microscopy,Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy as well as X-ray diff raction were employed to investigate the surface characteristics(morphology,composition and structure) of the coatings.Hydrophobicity of the coating was evaluated by means of contact and sliding angles.Additionally,potentiodynamic polarization,electrochemical impedance spectroscopy and hydrogen evolution tests were conducted to characterize the corrosion resistance.Results indicated that the coating exhibited super-hydrophobicity with large static water contact angle(CA) and small sliding angle of 155.2°± 1.5° and 6.0°± 0.5°,respectively,owing to spherical rough structure and low surface energy(7.01 mJ m~(-2)).The average hydrogen evolution rate(HER_a) and corrosion current density(i_(corr)) of the coated sample were 5.3 μL cm~(-2)h~(-1) and 5.60 × 10~(-9)A cm~(-2),about one and four orders of magnitude lower than that of AZ31 substrate,respectively,implying the excellent corrosion resistance.The CA of the coating remained 155.6°± 0.9° after soaking for 13 days,showing the super-hydrophobicity and stability of the coating.Simultaneously,the large critical load(5004 mN) for the coating designated the outstanding adhesion to the substrate by nano-scratch test.     

锌镍合金的异常共沉积与正常共沉积的转变

讨论了在电镀锌镍(Zn-Ni)合金过程中由异常共沉积转变为正常共沉积的条件及原因.提出了温度和镀液的组成与转变电流密度的关系以及阴极电位对合金镀层成分的影响.     

稀土对硫酸盐体系电沉积Zn-Fe合金阴极极化的影响

为了深入地探讨Zn-Fe合金镀层的电沉积机理,实验在了三电极体系下,采用动电位法测定硫酸盐体系电沉积Zn-Fe合金镀层的阴极极化曲线,探讨了该合金镀层的电沉积机理,以及镀液成分和稀土盐的加入对电沉积阴极极化的影响.通过实验发现,Zn-Fe合金镀层的沉积属于异常共沉积,结果表明镀液中加入稀土盐Ce2(SO4)3后,对Zn-Fe合金镀层电沉积的阴极极化行为有较大影响.     

Electrodeposition and properties of Zn–Ni–CNT composite coatings

Zn–Ni–CNT composite coatings were prepared by electrodeposition from a sulphate bath. The effect of CNTs on the corrosion behavior, wear resistance and hardness of the composite coatings was investigated. Their corrosion properties were evaluated by polarization, impedance, weight loss and salt spray tests. The CNT particles inclusion improved the corrosion resistance, hardness and wear resistance of the coating. The grain size of the composite coating was smaller than that of a pure Zn–Ni coating with the same Zn/Ni ratio. Scanning electron microscope images and X-ray diffraction patterns of coating revealed its fine-grain nature.     

掺杂钨丝电沉积铬的工艺研究

为了研究掺杂钨丝（真空镀铬加热元件）表面电解沉积一定厚度（≥100μm）金属铬的工艺,详细考察了不同温度、电流密度、沉积时间等对镀层的影响,并对镀层进行了性能测试。结果表明,最佳工艺条件为：铬酐150—180μg／L,硫酸1．5～1．8g/L,稀土（La^3＋）添加剂0．5-1．5#L,温度为55℃,电流密度为8～10A／dm^2,电镀时间3h。此工艺条件下所得镀层光亮,色泽好,厚度可达100μm,且镀层耐蚀性好,结合力高。     

Electrodeposition of Zn-Co and Zn-Co-Fe alloys from acidic chloride electrolytes

The electrodeposition operating conditions for Zn-Co and Zn-Co-Fe alloys from chloride baths were studied. The electrodeposition was performed on a high strength steel substrate, under galvanostatic conditions, for a range of current densities at varying Co²⁺ and Fe²⁺ bath concentrations and at different temperatures. A transition current density was noticed above which a transition from normal to anomalous deposition took place. Below the transition current density electrodeposition of alloys with a higher amount of Co was obtained. Above the transition current density (i.e. in the anomalous range), both Zn-Co and Zn-Co-Fe alloys were deposited with a Co content lower than the composition reference line. This transition current density that resulted in normal to anomalous deposition was attributed to the shift in cathodic potential or polarization. However, it was found that under certain conditions the transition occurred from very high wt.% Co to almost equal to the amount of Co in the electrolyte. The increase of Fe²⁺ ions in the electrolyte assisted in increasing the Co content and decreasing the Zn content in the deposits. In addition, the increase of Fe²⁺ resulted in shifting the transition current density to a lower value. However, the cathodic current efficiency decreased with the addition of Fe²⁺ ions in the electrolyte.     

电沉积Ni-Mo-P合金镀层的组织结构与耐蚀性

用扫描电镜、透射电镜和失重法研究了电沉积Ni-Mo-P合金镀层的表面形貌、组织结构和耐蚀性能。结果表明，Ni-Mo-P合金的非晶态镀层，经过不同温度热处理后，镀层结构以非晶态→混晶态→结晶态的顺序变化，镀层的硬度和耐蚀性也因此发生了相应的变化。     

Electrodeposition of cerium (III)-modified bis-[triethoxysilypropyl]tetra-sulphide films on AA2024-T3 (aluminum alloy) for corrosion protection

The doping of rare earth salts, like Ce(III), has shown to enhance the corrosion performance of silane films due to their self-healing behaviors. In the present paper, the Ce(III)-doped bis-[triethoxysilypropyl]tetrasulphide (BTESPT) films with higher corrosion resistance were prepared by electro-assisted technique. The films were investigated using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), water contact angle measurements and Fourier transform reflection absorption IR (FTRA-IR). The results showed that both the cathodic deposition and cerium-doping can promote the formation of thicker and compacter silane films and enhance their protectiveness in the early stage of immersion in the corrosive media. However, it seems that the Ce(III)-doped BTESPT films prepared by electrodeposition lose their self-healing abilities after long-term immersion. The reason is still unclear, but might be attributed to the precipitation of Ce(III) oxides or hydroxides during the electrodeposition of doped silane films.     

Electrodeposition of cerium oxide films and composites

Nanostructured CeO₂ films were prepared by cathodic electrolytic deposition (ELD) and electrophoretic deposition (EPD). Benzoic acid has been utilized for the dispersion and charging of CeO₂ nanoparticles for EPD. The kinetics of ELD and EPD was investigated. Electrodeposition method has been developed for the deposition of poly(2-vinylpyridine) (PVP) films. The thickness of the films was varied in the range of 0.1-3 μm. The deposition mechanism was based on the pH increase in the cathodic reactions, electrophoresis of the protonated PVP macromolecules, neutralization of their charge and film formation at the cathode surface. The deposition yield was studied by the quartz crystal microbalance method. Two electrochemical strategies were developed for the fabrication of composite PVP-CeO₂ films, which were based on the electrodeposition of PVP and ELD or EPD of CeO₂. The composite films were studied by electron microscopy, X-ray diffraction, thermogravimetric and differential thermal analysis. The CeO₂ content in the composite films was varied by the variation of bath composition. The deposition methods allowed the fabrication of crack-free PVP-CeO₂ films, which provided corrosion protection of stainless steel substrates in aqueous NaCl solutions.     

Electrodeposition of sol–gel films on Al for corrosion protection

Sol–gel films were electrodeposited on aluminum electrodes following the methodology we have developed and is based on applying negative potentials. This increases the pH at the surface, causing acceleration of the polymerization. Our process follows the “two step method”, in which the monomer is first hydrolyzed in acidic solution (pH 4) and only then the negative potential is applied, which consumes protons and releases hydroxyl ions, thus enhancing the condensation.Films made of different monomers, i.e., tetraethoxysilane (TEOS), methyl trimethoxysilane and phenyl trimethoxysilane (PTMOS), were prepared, characterized and examined for their corrosion inhibition properties. Potentiodynamic polarization, electrochemical impedance spectroscopy, optical and scanning electron microscopy as well as atomic force microscopy have been used as a means of film characterization. Hydrophobic and steric silanes, such as PTMOS showed a considerable corrosion inhibition capacity as compared to the capacity exhibited by less hydrophobic and steric derivatives such as TEOS. The difference between the conventional dip-coating method and the electrodeposition approach for depositing sol–gel films was also examined, indicating a clear advantage of the latter.     

稀土铈对锌-铁合金镀层耐蚀性的影响

研究了铈盐对电沉积锌-铁合金镀层耐蚀性的影响,通过失重法、浸泡实验、电化学腐蚀参数的测量,得出在镀液中添加一定量的铈盐能显著改善镀层的耐蚀性能.扫描电镜测定镀层表面形貌的结果表明,定量铈盐参与下,可获得更加致密的镀层,这正是提高镀层耐蚀性的原因.     

The Influence of Ultrasonic Frequency on the Properties of Ni-Co Coatings Prepared by Ultrasound-assisted Electrodeposition

In this paper, Ni-Co coatings were electrodeposited onto carbon steel substrates with the aid of ultrasonic agitation. The coatings were analyzed by energy dispersive X-ray analysis （EDX）, X-ray diffraction analysis （XRD） and scanning electron microscopy （SEM）. The effects of the ultrasonic frequency on the roughness, hardness and corrosion resistance of the Ni-Co coatings were also investigated. The results indicated that the increase of the ultrasonic frequency from 20 to 120 kHz reduced the Ni content and the grain size of Ni-Co coatings. Moreover, the phase structure of the electrodeposited coatings was influenced by the ultrasonic frequency. Under 55 kHz ultrasonic agitation, the Ni-Co coating was single fcc phase and showed the finest roughness and the strongest corrosion resistance in 5 wt.% NaCl solution at the ambient temperature. Under ultrasonic agitation with frequency of 90 kHz, the coating was a mixture of fcc and hcp structure and showed the maximal hardness of about 420 HV. Therefore, ultrasonic agitation helped decrease the roughness, and enhance hardness and corrosion resistance of Ni-Co coatings.