Influence of copper on chromate conversion coating of aluminium alloys

Abstract

The formation of chromate/fluoride conversion coatings is investigated for binary Al–2·3 at.-%Cu alloy and AA 2014-T6 aluminium alloy in order to determine the influences of copper on coating development. Copper is shown to cause detachment of the coating layer after a particular time of coating. The time of detachment is reduced with increase in the concentration of copper in solid solution in the various alloy regions. Therefore, a thicker layer of coating material can develop on the copper depleted matrix regions of AA 2014-T6 alloy compared with that on the copper rich intermetallic particles. The detachment occurs following enrichment of copper in the alloy during the initial stages of formation of the coating, with the main layer of hydrated chromia detaching from close to the alloy surface. Following detachment, subsequent thickening of the coating is restricted. It is suggested that this behaviour is related to the incorporation of nanoparticles of copper into the coating.     

Effect of water on the electrodeposition of copper on nickel in deep eutectic solvents

ABSTRACT

Most studies of metal electrodeposition in ionic liquids dry the electrolyte thoroughly, as water is thought to be detrimental. In some cases, water has a beneficial effect on deposit morphology. The electrodeposition of copper has been studied in 1ChCl: 2EG-water mixtures. It is shown here that the presence of water increases the apparent brightness of the deposit due to changes in the electrodeposit surface feature size, up to a water content of approximately 20 wt-%. This study characterises speciation and mass transport in solution, and shows that diffusion can be controlled independently of speciation. It is shown that there is an optimal water content, which is thought to originate from formation of a bi-continuous micro-emulsion phase in DES-water mixtures. Additionally, the copper species remains in a predominantly ionic medium at low water content but moves to an aqueous environment when water is the main component.     

Mechanical properties and substructure of metals

The effect of the angle of misorientation of substructural elements, structure reversibility during plastic deformation, and the formation of microcracks on the surface of and within a metal on its mechanical properties are examined. It is shown that it is possible to define a degree of degradation (damage) of a metal using the true stress-residual strain diagram.Institute of Machinery Science. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 12–17, October, 1994.     

Physicochemical model of detonation synthesis of nanoparticles from metal carboxylates

We have shown previously that when metal carboxylates are subjected to a shock-wave action, diamond nanoparticles and nanoparticles of metals (Ag, Bi, Co, Fe, Pb) are formed and their characteristic size is about 30–200 Å. The metal nanoparticles formed are covered by an amorphous-carbon layer up to 20 Å thick. In this work we put forward a physicochemical model of the formation of diamond and metal nanoparticles from metal carboxylates upon shock-wave action. The energy released upon detonation inside the precursor is lower than in regions not occupied by the stearates. The characteristic time of temperature equalization has been estimated to be on the order of ～10^?3 s, which is greater by a factor of ～10³ than the characteristic reaction time. Due to the adiabatic nature of the processes occurring, the typical temperature of a “particle” will be lower than the temperature of the surrounding medium. In the framework of the model suggested, it has been assumed that the growth of metal clusters should occur by the diffusion mechanism; i.e., the “building material” is supplied through diffusion. The calculation using our previous experimental data on the reaction time and average size of metal particles has shown that the diffusion properties of the medium in which the metal nanoparticles are formed are close to those of the liquid state of the substance. The temperature and pressure under detonation conditions markedly exceed the analogous parameters characteristic of experiments on the thermodestruction of metal carboxylates. The small time of existence of the reaction mixture is compensated by the high mobility and concentration of reagents.     

中空二氧化硅微球包覆2-巯基苯并噻唑自修复涂层防腐性能

涂层技术广泛应用于金属设备腐蚀防护，而针对传统涂层服役过程中的微损伤难以及时探测并修复，导致损伤后涂层防腐性能失效、金属腐蚀进程加速等问题。开发一种中空介孔SiO₂微球包覆2-巯基苯并噻唑的自修复涂层，并对涂层的自修复性能进行全面表征测试。将包覆2-巯基苯并噻唑的SiO₂微球作为填料，添加到无溶剂环氧树脂涂层中制备自修复涂层，在质量分数为3.5%的NaCl溶液中探查受损涂层在铜基体表面的自修复过程。采用多种测试表征方法测试SiO₂微球包覆2-巯基苯并噻唑的可行性，对涂层的自修复机理进行深入分析，综合评价自修复涂层的防腐性能。采用溶胶-凝胶法对SiO₂微球进行制备，制备的SiO₂微球具有中空结构，微球直径约为623nm。通过XDR、FTIR与TG等测试表征技术验证SiO₂微球实现对2-巯基苯并噻唑的包覆，且负载量良好；通过EIS阻抗测试对自修复涂层的修复性能进行测试，经对照实验测试自修复涂层具有较为良好的防腐性能，并在6d时防腐性能达到最大；通过SEM、ED...     

The Growth Habit of Electrodeposited Copper

By plating under base reproduction conditions in an acidified copper sulphate solution, the growth processes occurring at polycrystalline cathodes have been studied and compared with those at single crystal cathodes. It has been found that the surface topography of the deposit formed on any one grain of the polycrystalline aggregate is identical to that of a deposit, grown under similar conditions, on a single crystal of the same orientation. The growth habit is in each case related to the atomic configuration of the initial cathode surface. The thickness of the deposit formed on electropolished polycrystalline strip has been found to vary from grain to grain. This may be explained in terms of electrochemical anisotropy. It has been found that the growth habit of thick deposits (10 microns) formed on deeply etched surfaces is similar to that on electropolished surfaces. Mechanical polishing of the basis metal causes the development of a polycrystalline, textured deposit, although some base influence can be detected even through very thick deposits (40 microns). Under certain conditions, deposits of the base-reproduction type can be obtained from cyanide copper solutions. Such deposits develop well-defined surface structures, with large, regular features and highly reflecting facets.     

Process of faceting in nanoparticles of FCC metals: Results of simulation by the molecular-dynamics method

The process of formation of facets (faceting) in Ni, Al, and Au nanoparticles has been investigated by the molecular-dynamics method. It has been established that the surface of nanoparticles of fcc metals with attainment of a low-energy habit can be transformed via correlated displacements of atomic groups of the facet in the octahedral plane. It has been shown that such a process is similar to the surface diffusion of atomic n-mers with the activation energy depending on the facet size, and for particles with a diameter d < 3.0 nm the correlated displacement of atomic layers proves to be the dominant mechanism of faceting.     

Discussion of Annual Conference Papers

The surface texture of the underlying metal has been shown to influence the type of crack pattern produced in the chromium overlay although the chromium was deposited from the same microcracked solution. Zoned crack patterns were found to be characteristic of bright unpolished copper or nickel surfaces but were not observed in chromium deposited on polished undercoats. Cracks were preferentially orientated at right angles to the polishing direction on soft undercoats such as copper and silver. Cracking, even on a macro scale, did not take place so readily on matt surfaces. The surface texture of the undercoat has also been shown to influence the internal stress in the chromium layer. When a step occurred in the curves relating instantaneous stress and chromium thickness, this was indicative of the point at which microcracking took place. Compressive stresses were observed in thin chromium deposits plated from the microcracked, crack-free and bright chromium solutions on to nickel undercoats. These initial compressive stresses could be accounted for on the basis of hydrogen adsorption by the surface of the underlying metal.     

Surface residual stresses in multipass welds produced using low transformation temperature filler alloys

Tensile residual stresses at the surface of welded components are known to compromise fatigue resistance through the accelerated initiation of microcracks, especially at the weld toe. Inducement of compression in these regions is a common technique employed to enhance fatigue performance. Transformation plasticity has been established as a viable method to generate such compressive residual stresses in steel welds and exploits the phase transformation in welding filler alloys that transform at low temperature to compensate for accumulated thermal contraction strains. Neutron and X-ray diffraction have been used to determine the stress profiles that exist across the surface of plates welded with low transformation temperature welding alloys, with a particular focus on the stress at the weld toe. For the first time, near surface neutron diffraction data have shown the extent of local stress variation at the critical, fusion boundary location. Compression was evident for the three measurement orientations at the fusion boundaries. Compressive longitudinal residual stresses and tensile transverse stresses were measured in the weld metal.     

纳米加工液对金属表面的润滑与修复

兼具润滑与表面修复功能的纳米粒子已开始应用于金属加工液中并受到了国内外学者的广泛关注。与传统加工液不同,将纳米粒子均匀分散到水性或油性基液中制备的纳米加工液除了具有润滑冷却、减摩抗磨作用外,其表面修复功能更加值得关注,在提高金属加工表面质量方面具有较高的应用前景。虽然纳米加工液具有诸多优势,但其分散稳定性、润滑机理及其表面修复功能仍是纳米润滑领域的研究热点问题。主要针对近年来纳米粒子的润滑机理与其表面修复作用的微观本质等一系列问题的研究与发展进行阐述。从纳米粒子的选择与分散出发,讨论了添加表面活性剂和对纳米粒子进行表面改性这两种提高纳米粒子分散稳定性的主要方法。重点论述了滚珠轴承效应、薄膜润滑机制、自修复功能和微量磨削作用这四种被广泛认同的纳米润滑机理,依据前人的研究结果,归纳这四种润滑机理的理论模型、适用情况及其相互间的配合关系。此外,从纳米粒子的润滑机理出发,探索其表面修复作用,对金属表面的物理吸附膜、化学反应膜及沉积自修复膜进行判别与比较,分析其表面修复作用的微观本质。     

A Study of Benzotriazole as an Addition Agent for Acid Copper Sulphate Solutions

During a study of addition agents for acid copper sulphate solution, it has been shown that benzotriazole forms an insoluble cuprous complex which codeposits with the copper^1a A method has been devised for dissolving the deposit and separating the addition agent and it has been deffionstrated that benzotriazole can be recovered from the electrodeposit in the undecomposed form.² Since benzotriazole can be separated and estimated with accuracy, it provides a compound which is eminently suitable for studying addition agent action during electrodeposition. Polarization studies have shown that benzotriazole markedly increases the activation overpotential of the cathode η_A—mainly by decreasing the active area of the surface by film formation—and it is possible to detect 10^?7 M benzotriazole from its effect on the cathode overpotential. Additions of 0·012 g/1 benzotriazole give very fine grained deposits of copper and prevent epitaxy, while higher concentrations (0·12 g/1) result in fully-bright deposits with a banded structure. The effect of plating variables on the amount of benzotriazole included in copper deposits has been studied as a necessary prerequisite for suggesting a mechanism of addition agent action which, in this particular system, has been based on the formation of metal complexes.     

Thermal stability of structure in small gold clusters

Limits of thermal stability of the original fcc phase in gold clusters up to 3.5 nm in diameter have been studied. The simulation carried out by the molecular-dynamics method using a modified TB-SMA tight-binding potential has shown that in small Au clusters under the effect of the temperature factor there occurs a transition from the original fcc phase to other structural modifications, including those with a pentagonal symmetry. As the size of gold nanoparticles increases, the polytypic-transition temperature shifts toward the melting temperature of the cluster. The results obtained are compared with the data for copper and nickel nanoparticles with similar sizes. It has been shown that, in the case of nickel and copper clusters, it is the transition from the fcc phase into structures with a pentagonal symmetry, which are not found in the bulk state, that is the governing factor; the gold clusters demonstrate a much more intricate behavior.     

Influence of copper on quality of hot strips by EAF-CSP process

Electron microscopy and X-ray Energy Dispersive Spectroscopy (XEDS) study on influence of Cu on low carbon hot strips produced by CSP (Compact Strip Production) process has been carried out. The results indicated that copper segregation and enrichment at interfacial layer between oxidized surface and steel matrix is the key factor, which results in microcracks and edge flaws on the strips. The primary considerations to prevent detrimental effects from Cu include controlling copper content in proper level, higher soaking temperature and non-oxidizable atmosphere during soaking. Copper sulfide precipitates with nanometers in size were observed, they may be beneficial to the properties of CSP products, and influence of Cu on quality of CSP hot strips is discussed.     

A Study on Thermal Conductivity and Stability of Nanofluids Containing Chemically Synthesized Nanoparticles for Advanced Thermal Applications

This study presents easy methods of synthesizing silver (Ag) and copper (Cu) nanoparticles through chemical route in an aqueous medium under atmospheric condition at ambient temperature. The synthesized nanoparticles have been characterized with different techniques, such as x-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, high-resolution transmission electron microscopy, UV–visible spectroscopy and dynamic light scattering measurements. Experimental observations have revealed the absence of any metal oxide layer around the nanoparticles which are found to remain stable under ambient conditions. The featured properties, such as narrow size distribution, stability, make these nanoparticles potential candidates for the synthesis of effective nanofluids. The nanofluids have been prepared by dispersing the nanoparticles synthesized through chemical route in a suitable base fluid. The thermal conductivity of nanofluids with different nanoparticles loading has been measured by transient hot-wire method, and the results have shown that the increasing trend of enhancement in thermal conductivity with respect to nanoparticles concentration is attainable only when the nanoparticles concentration is below some limiting value depending on the type of nanofluid. Beyond this limiting value of loading, the thermal conductivity of the nanofluid decreases due to pronounced agglomeration effect. The measurements of thermal conductivity of nanofluids over varying temperatures for a given volume fraction loading of nanoparticles have shown that the thermal conductivity increases markedly with the increase in temperature. Hence, nanofluids are likely to be much more promising at high-temperature applications.     

Nanocomposites of polyaniline,its derivatives and platinum prepared using aqueous Pt sol

Polyaniline (PANI), poly(o-methoxyaniline) (POMA) and poly(o-toluidine) (POT) have been used as matrices for incorporation of Pt nanoparticles from the previously prepared aqueous Pt sol. Polymer–Pt nanocomposites thus obtained have been characterized by X-ray diffraction, transmission electron microscopy and IR spectroscopy. It has been revealed that metal nanoparticles (predominantly of sizes in the range between 2 and 4 nm) have been present in all the composites. It can be postulated that the polymers prevent Pt nanoparticles from agglomeration, i.e. act as their stabilizers. As has been found, charge transfer interactions between polymer chains and Pt nanoparticles are responsible for this stabilization. Among the polymers studied, POT shows the weakest stabilizing effect.Catalytic isopropyl alcohol conversion has shown that PANI–Pt nanocomposite obtained using aqueous Pt sol exhibits strong redox properties. Its overall catalytic activity is ca. three times higher than that of PANI–Pt composite containing larger Pt particles. This is connected with better dispersion of Pt particles in the composite prepared using aqueous Pt sol.     

Tribological properties and lubricating mechanisms of Cu nanoparticles in lubricant

Wear and friction properties of surface modified Cu nanoparticles as 50CC oil additive were studied. The effect of temperature on tribological properties of Cu nanoparticles was investigated on a four-ball tester. The morphologies, typical element distribution and chemical states of the worn surfaces were characterized by SEM, EDS and XPS, respectively. In order to further investigate the tribological mechanism of Cu nanoparticles, a nano-indentation tester was utilized to measure the micro mechanical properties of the worn surface. The results indicate that the higher the oil temperature applied, the better the tribological properties of Cu nanoparticles are. It can be inferred that a thin copper protective film with lower elastic modulus and hardness is formed on the worn surface, which results in the good tribological performances ofCu nanoparticles, especially when the oil temperature is higher.     

Negative effective refractive index of metallic nanoparticles in disordered nanocomposites

An effective-medium theory is suggested, which is used to study optical properties of disordered metallodielectric nanocomposites. Expressions for the effective fields and effective parameters of nanoparticles with allowance for the electrodynamic interaction of nanoparticles have been obtained. It has been shown that the polarizing mutual influence of the structure elements of a system can give rise to regions with negative effective refractive index in the spectrum of individual particles. A model of a «left-handed» based on a field manipulation of the polarizability of nanoclusters different from the previously studied material manipulation has been put forward.     

铜/银合金纳米粒子的制备及表征

研究了铜/银合金纳米粒子的制备方法,用抗坏血酸做还原剂,制备了粒径小的纳米铜粉。由于纳米铜粉的稳定性差,易氧化,为了提高其稳定性,在制备的纳米铜粉中加了少量的Ag+,在纳米铜粉表面还原制备出银纳米层覆盖于在铜上。所制备的纳米铜/银合金纳米粒子稳定性好,具有纳米粒子的效应,有望应用于印制电路的制造。该制备方法可以减少传统印制电路板制作方法的工序,节约资源,且减少对环境的污染。     

Nature of Chromium on Passivated Tinplate

Abstract

Samples of tinplate passivated by a cathodic dichromate treatment have been analysed by photo-electron spectroscopy to determine the nature of the chromium on the surface. This has confirmed the presence of chromium metal which appears to be present in discrete regions rather than as a continuous film. The entire surface composed of exposed tin and regions of chromium metal is shown to be covered with trivalent chromium compounds. The X-ray Photoelectron Spectroscopy results are consistent with other models postulated from anodic polarisation work which suggests that a Cr(OH)₃ overlayer is present with some Cr₂O₃ underneath formed by air oxidation of chromium metal.     

纯镁微弧氧化-壳聚糖/海藻酸钠载铜复合膜层制备及抑菌性

目的采用多种表面技术复合在纯镁表面制备了功能性生物复合膜层,以调控医用纯镁降解速度,赋予纯镁内固定材料的抑菌性和生物活性。方法分别通过纯镁微弧氧化,电镀壳聚糖、海藻酸钠,化学镀铜等方法,制作不同复合膜层,分别为纯镁微弧氧化膜层(A组)、纯镁微弧氧化-壳聚糖复合膜层(B组)、纯镁微弧氧化-壳聚糖/海藻酸钠复合膜层(C组)、纯镁微弧氧化-壳聚糖/海藻酸钠/壳聚糖复合膜层(D组)和纯镁微弧氧化-壳聚糖/海藻酸钠载铜复合膜层(E组)。采用扫描电子显微镜分析膜层的微观形貌,测定润湿角,将材料与大肠杆菌共同培养,计算抑菌率。结果 A组表面有很多微孔和少量微裂纹,B组表面的微孔和微裂纹减少,C组的微孔和裂纹基本消失,D组和E组表面的微孔裂纹消失并出现微网状结构。A组和E组为亲水性膜层,C组为疏水性膜层,B组和D组的膜层接近疏水性。A组抑菌率最低,B、C、D组的逐渐增高,分别为26%、30%、61%,E组的抑菌率高达88%。结论纯镁微弧氧化-壳聚糖/海藻酸钠载铜复合膜层有封孔和愈合裂纹的作用,具有较好的抑菌性。