Deposition of protective-decorative coatings onto aluminum alloys

Technique for deposition of a nickel coating onto various aluminum alloys was developed. This coating can be used both independently and as a sublayer under multilayer coatings and, in particular, under those of nickel, tin–bismuth, lustrous nickel, and lustrous chromium. The technique includes anodization, chemical treatment, and electrodeposition of nickel in a special solution. The working modes of the anodization electrolyte were chosen and the necessity for a preliminary chemical treatment of the oxide film being formed was substantiated. A composition of the acid electrolyte for the subsequent nickel plating was developed with buffer and improving additives. The thus deposited electroplated nickel coatings exhibit a high adhesion to the aluminum base without additional thermal treatment. This makes it possible not only to reduce the technological time for deposition of the subsequent multilayer coatings, but also to fully automate the whole process.     

Properties of composite nickel-cobalt-aluminum oxide coating deposited from chloride electrolyte

Effect of the cathodic current density, pH value, electrolyte temperature, and concentration of aluminum oxide introduced into the electrolyte on the wear, microhardness, and internal stresses in nickel-cobalt-aluminum oxide composite electrolytic coatings was studied. It is shown that the coatings under consideration can be used instead of chromium coatings.     

Electrodeposited paint-and-varnish nickel–polymer coatings

Specific features of preparation of paint-and-varnish nickel–polymer coatings by joint cathodic electrodeposition of an amine-containing oligomeric electrolyte and nickel were studied. The coatings obtained exhibit layer-by-layer heterogeneity, with the lowest layer constituted by an intermetallic compound of nickel with iron. The coatings are characterized by higher degree of cross-linking compared to the polymer coatings without nickel. A paint-and-varnish formulation based on a nickel–polymer film-forming agent was developed for electrodeposition of corrosion- and wear-resistant coatings.     

镍铝介金属镀膜之抗坑蚀行为

采用3种原子百分比Ni52Al48,Ni60Al40及Ni70Al30成分的靶材以阴极电弧放电离子被覆技术制备不同组成的Ni＿Al薄膜于AISI1045中碳钢基材表面上,并观察镀膜微结构与成分随靶材成分的变化,评估应用Ni＿Al于抗坑蚀功能方面的可行性.研究结果显示:使用上述3种靶材所获致的镀膜组成依次为Ni62Al38,Ni63Al37及Ni69Al31,镀膜镍含量随靶材镍含量增加而增加.3种镀膜的相组成均以Ni3Al为主,从富镍Ni70Al30靶材所得的镀膜尚含有部分镍相.镀膜具有极强的附着性并反映在镀膜的抗坑蚀性上.在纯水中,所有的Ni＿Al镀膜试片均能提高中碳钢基材的抗坑蚀性,约达10倍.在3.5wt%盐水与3.5wt%盐酸中亦分别有两倍以上的效果.而在这3种测试环境中,3种镀膜试片的坑蚀损失差别均不明显,无法判断镀膜组成对抗坑蚀性的影响.从动电位极化曲线可以看出,镀膜试片均能大幅提高基材在盐酸与盐水溶液中的抗蚀性,然而因坑蚀破坏而形成的孔洞会由于孔蚀而导致腐蚀加剧,造成镀膜试片在腐蚀溶液中之抗坑蚀效果低于电化学量测时所预期的保护效果.     

Possibility of raising the deposition rate of nickel coatings from a chloride electrolyte

Conditions under which nickel coatings can be deposited from a chloride electrolyte at a high rate were studied. The mechanism of this process was suggested and experimentally confirmed. The mass-transfer rate of nickel-containing particles was determined by chronopotentiometry, with temperature raised from 20 to 50°C. The dependence of pH_s on the current density was determined. Physicochemical parameters of the coatings (microhardness, internal stresses, porosity, luster, and adhesion) were measured.     

Kinetics of electrodeposition of Ni–ZrO<Subscript>2</Subscript> nanocomposite coatings from methanesulfonate electrolytes

Regularities of incorporation of zirconia nanoparticles into a nickel matrix in the course of electrodeposition of Ni–ZrO₂ coatings from methanesulfonate electrolyte are established. The content of the dispersed phase in coatings grows at an increase in its concentration in electrolyte. Moreover, nanocomposites containing a greater amount of zirconia are deposited from the methanesulfonate electrolyte as compared to sulfate electrolyte. This is explained by the greater partial concentration of ZrO₂ in the solution due to enhanced aggregative stability of the dispersed phase in methanesulfonate electrolyte. The mechanism of formation of the composite coating is considered that is based on the concept of particle incorporation into the metal matrix due to the different rates of metal electrodeposition on the electrode surface free of nonmetallic particles and on the electrode surface conditionally occupied by them. A physically substantiated mathematical model is suggested that describes the kinetics of formation of the composite coating that agrees well with the experimental data.     

Aluminum electrodeposition from a non-aqueous electrolyte—a combined computational and experimental study

Electrodeposition of aluminum (Al) from an organic non-aqueous electrolyte of ethylbenzene containing aluminum bromide is demonstrated. It is offered as a simple method for the preparation of Al coatings. This work employs distinct electrochemical techniques and explores the effects of the experimental parameters on the kinetics of the process and the quality of the final coatings. The process presented here enables deposition of pure and crystalline Al at room temperature and facilitates the production of uniform Al coatings on various metallic substrates. Morphological studies establish that the growth of Al deposits follows an island mode, and thus, the most noteworthy effect of the substrate over the morphology of the deposits originates from its impact over the nucleation stage, and the density of islands. This study is complemented by theoretical modeling for the adsorption of Al atoms at the different surfaces. Corrosion evaluation determines the dissolution mechanisms of each of the studied substrates in the examined electrolyte. These findings further corroborate the claim that this electrolyte enables the reversible electrodeposition of Al.

     

Ni–Mo alloy nanostructures as cathodic materials for hydrogen evolution reaction during seawater electrolysis

In the case of hydrogen production involving seawater electrolysis, one of the main targets is to develop more active cathodic materials, to optimize the efficiency of hydrogen evolution reaction (HER) and, by doing so, enhance the overall energy efficiency of electrolysis. Thus, to develop suitable HER electrocatalysts either an increase of the electrode active surface area or a design of a material having high intrinsic catalytic activity should be taken into consideration, both of them decreasing the HER overpotential. In the present work, various Ni–Mo alloy nanostructures (10–40 wt% Mo) have been prepared involving electrochemical deposition from aqueous and deep eutectic solvent (DES)-based electrolytes as potential cathodic materials suitable for hydrogen evolution reaction during water electrolysis. The electrocatalytic activity of the obtained layers has been investigated using real seawater electrolyte. The determined Tafel slopes suggested that the electrodeposited Ni–Mo alloy coatings follow an HER mechanism controlled by the Volmer reaction step. The EIS results indicated that the use of choline chloride-based ionic liquids as electrolytes facilitated Ni–Mo alloy coatings showing a significant increase in surface roughness. Studies of the intrinsic activity showed that the main contribution towards the apparent activity comes from the increase of the real surface area, although a slight increase of the intrinsic electrocatalytic activity in the case of Ni–Mo alloy coatings electrodeposited on Ni foam was also noticed. These results showed that Ni–Mo alloy coatings electrodeposited from the novel electrolytes based on choline chloride–urea–citric acid ternary mixtures associated with a porous substrate may represent a promising technological approach to build cathodic materials suitable for seawater electrolysis.     

Anodic oxidation of complex shaped items of aluminum and aluminum alloys with subsequent electrodeposition of copper coatings

It was shown that the method of anodization of aluminum and aluminum alloys can be applied for subsequent plating of highly adherent copper coating instead of the known zincate treatment with additional annealing. Fluorine-containing additives in anodizing electrolyte were proposed as activator of oxide film. The parameters of the anodic film (thickness, porosity, and microroughness) were calculated. The plated quality copper coatings have high adhesion to the aluminum support, and no additional heat treatment is required. This considerably reduces the processing time for deposition of multilayer coatings and decreases the material costs.     

Behavior of aluminum in its anodic oxidation in aqueous solutions of acids and their salts

Influence exerted by the nature and concentration of an electrolyte and by the electrolysis temperature on the process of anodic oxidation of aluminum in aqueous solutions was studied. It was shown that two modifications of aluminum hydroxide are formed as electrolysis products. Making higher the electrolyte concentration and raising the process temperature results in that the fraction of boehmite aluminum hydroxide in the product increases and that of bayerite aluminum hydroxide decreases. A scheme by which aluminum is anodically oxidized in aqueous solutions is suggested.     

Effect of Sonochemical Treatment Modes on the Electrodeposition of Cu–Sn Alloy from Oxalic Acid Electrolyte

Methods of scanning electron microscopy, potentiodynamic polarization, and X-ray diffraction analysis were used to study the kinetic features of the electrodeposition process of the copper–tin alloy from an oxalic acid electrolyte and analyze the structure, composition, and luster of coatings formed under sonochemical treatment conditions at varied power of the ultrasonic field and current load. The ultrasonic treatment with power of 8–40 W dm^–3 makes it possible to 2–8 times intensify the cathodic process and obtain coatings containing 10–15 wt % tin with luster of 20–40%. The specific content of tin in a coating being formed is nearly independent of the ultrasound power and grows with increasing the cathodic current density.     

The role of migration mass transfer in the electrodeposition of nickel from sulfate-chloride and chloride solutions containing succinic acid

The electrodeposition of nickel from 0.5 M sulfate-succinate-chloride (I) and 0.3 and 0.5 M chloride-cuccinate (II) solutions at a temperature of 50°C is studied. It is found that, depending on the pH₀ of solution and the concentration of succinic acid and nickel, the maximum cathodic current density for producing high-quality nickel deposits is to 35 A/dm² in electrolytes I and to 60 A/dm² in electrolytes II. This corresponds to the metal deposition rates to 23 and 48 A/dm², respectively. It is shown experimentally that high buffer properties of solutions (succinate buffer) are one of the reasons for high permissible current densities of nickel electrodeposition. The computer-calculated data showed that the intensification of nickel electrodeposition is caused also by the acceleration of mass transfer due to the presence of a considerable fraction of nickel in the form of positively charged complexes and a high concentration of components stabilizing pH_S in the near-cathode layer.     

钙作为合金元素对铝在碱溶液中的缓蚀作用及其与酒石酸盐的协同效应

通过集气法、极化曲线和电化学阻抗谱研究了在铝中添加合金元素钙对其在碱 溶液中的缓蚀作用及其与酒石酸盐的协同效应。实验结果表明，铝电极的腐蚀速率 随钙含量的增加而减小。溶液中不含酒石酸盐时，钙对电极反应的阴极过程有显著 的抑制作用，对阳极过程作用不明显；而当溶液中含有酒石酸盐时，阴极过程和阳 极过程均被显著抑制。阻抗谱的解析结果还表明，钙离子或酒石酸钙络离子是通过 减小反应物在活性位上的反应速率而起缓蚀作用的，它们可能属于界面型缓蚀剂而 非成相型缓蚀剂。     

Electrodeposition and physicomechanical properties of coatings and foil of copper reinforced with nanosize aluminum oxide

Method of electrosynthesis of composite coatings and foil composed of copper reinforced with nanosize aluminum oxide is described. A method for chemical dispersion of aluminum oxide by the top-down principle and an electrolyte composition are suggested, which provide synthesis of composite materials with varied content of the modifying phase. The results of mechanical tests indicate that the plasticity, strength, and a number of other physicomechanical properties of thus synthesized composite materials are improved.     

Formation and Properties of Nickel–Phosphorus–Graphite Composite Coatings in Autocatalytic Deposition

It is shown that nickel–phosphorus–graphite composite coatings can be deposited by the autocatalytic deposition method. The optimal concentration of graphite and the duration of ultrasonic treatment of a graphite suspension in solution for deposition of composite coatings based on the nickel–phosphorus alloy were determined. The influence exerted by thermal treatment parameters on the properties of the deposits was examined. The optimal process conditions are suggested.     

电沉积Ni-PSZ梯度镀层过程中阴极电流效率的研究

采用动电位扫描,电化学交流阻抗及扫描电子显微镜研究电沉积Ｎｉ－ＰＳＺ梯度镀层过程中阴极电流效率的变化规律及其机理．结果表明,Ｎｉ－ＰＳＺ复合镀层对氢的析出反应具有催化作用,在镀液中加入ＰＳＺ微粒后,能增大镍还原过电位,降低氢析出过电位,从而不断降低电沉积梯度镀层过程中的阴极电流效率．在电沉积Ｎｉ的过程中,有中间吸附相Ｎｉ＋ａｄｓ生成,ＰＳＺ微粒的加入能优先催化Ｈａｄｓ,加速氢气析出     

Formation of porous ceramic supports for catalysts by microarc oxidation

Microarc oxidation of aluminum in borate and silicate-alkaline electrolytes in order to form porous ceramic coatings that can be used as catalyst supports was subjected to an integrated study. The advantages of the technological modes of microarc oxidation of aluminum were analyzed. A catalytically active nickel oxide was deposited into pores of a ceramic coating.     

Formation of Protective Coatings on Graphite by a Microspark Oxidation Method

Models, mechanisms, and criteria of formation of protective coatings on graphite by a microspark oxidation method (MSO) are considered. It is established that a prerequisite for the graphite MSO is the deposition of a barrier film of a valve metal oxide at the graphite surface. Optimum regimes of the graphite MSO in aqueous solutions of sodium aluminate are determined. Protective coatings on graphite comprising α-phase aluminum oxide are obtained. It is concluded that the graphite MSO should be viewed as a version of MSO of metals, which involves the electrochemical deposition (at high voltages that cause the anode to microspark) of oxide films consisting of electrolyte components on graphite, as opposed to a version of MSO of metals, which involves the formation of an anodic film consisting of electrolyte components and the intrinsic oxide.     

X-ray photoelectron spectroscopic studies of electrode surfaces using a new controlled transfer technique: Part I. Description of apparatus and preliminary studies

The design and use of an apparatus suitable for the controlled transfer of an electrode from an electrolyte solution to a high vacuum spectrometer chamber is described. Preliminary experiments with a nickel electrode illustrate the ability to transfer a non-noble metal without oxidation of the surface. Polarisation of a stainless steel electrode at progressively more cathodic potentials shows the gradual reduction of the oxide film present on the ‘as received’ material.