Prevention of zinc corrosion in oxygenated 0.5 M NaCl by treatment in a cerium(III) nitrate solution and modification with sodium hexadecanoate

A self-assembled monolayer (SAM) of hexadecanoate ion (C₁₆A⁻) was prepared on a zinc electrode covered with a layer of hydrated cerium(III) oxide Ce₂O₃. The protection of zinc against corrosion was examined for the electrode coated with the Ce₂O₃ layer and the C₁₆A⁻ SAM in an oxygenated 0.5 M NaCl solution. A more positive open-circuit potential of the coated electrode was maintained during immersion in the solution for 4 h than that of the uncoated one and polarization curves showed marked suppression of the anodic process, implying that the layer modified with the SAM acted as a passive film. The protective efficiency of the modified layer was extremely high, more than 99%. The zinc surface coated with the Ce₂O₃ layer and the C₁₆A⁻ SAM was characterized by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement with a drop of water.     

Effect of plating time for electroless nickel coating on rebar surface: An option for application in concrete structure

The ternary Ni-P-Fe alloy coating was developed by an electroless process using a citrate bath. During the steel sample dip in bath, Fe will first get dissolved from the rebar surface and would subsequently get introduced in the bath as Fe²⁺. This, in turn, would activate the surface and Ni, P and Fe are co-deposited on the activated rebar surface. The first deposition layer would act as catalyst for subsequent metal deposition. The coating was characterised using SEM, EDS and XRD techniques. The bath pH was found to play a strong role on process kinetics as well as composition of the coating but not on coating structure. The weight percentage of Ni, P and Fe in the coating was found to have a relationship with the bath pH. The Tafel and salt spray test were conducted to find out corrosion resistance performance of the coatings. Electrochemical behavior of the coated rebars in simulated concrete environment was influenced by the pH of the concrete pore solution and the ‘P’ content in the coating. Corrosion potential and the corrosion rate of the coating increased with increase in ‘P’ content in the coating and pH of the pore solution, whereas the resistance against chloride attack of the coating increased with increase in ‘P’ content. The marginal drop in the bond strength of the coated rebar with the concrete structure may be due to the higher ‘P’ content which is expected to provide improved surface smoothness.     

Prevention of liquid metal embrittlement cracks in resistance spot welds by adaption of electrode geometry

ABSTRACT

Advanced high strength steels are usually coated by a zinc layer for an increased resistance against corrosion. During the resistance spot welding of zinc coated steel grades, liquid metal embrittlement (LME) may occur. As a result, cracking inside and around the spot weld indentation is observable. The extent of LME cracks is influenced by a variety of different factors. In this study, the impact of the used electrode geometry is investigated over a stepwise varied weld time. A spot welding finite element simulation is used to analyse and explain the observed effects. Results show significant differences especially for highly increased weld times. Based on identical overall dimensions, electrode geometries with a larger working plane allow for longer weld times, while still preventing LME within the investigated material and maintaining accessibility.     

Self-healing protective films prepared on zinc by treatments with cerium(III) nitrate and sodium phosphate

Chromate-free, self-healing protective films were prepared on a surface of zinc electrode previously treated in a solution of cerium(III) nitrate Ce(NO₃)₃ by coverage of the surface with a layer of sodium phosphate Na₃PO₄. The self-healing ability of the film was examined by polarization measurements of the electrode after scratching the surface with a knife-edge crosswise and immersed in an aerated 0.5 M NaCl solution for many hours and by observation of pit formation at the scratches. A thin film containing 0.0552 mg/cm² of Na₃PO₄·12H₂O prepared on the electrode previously treated in 1×10⁻³ M Ce(NO₃)₃ at 30 °C for 30 min and dried at 90 °C for 23 h was highly self-healing and protective against corrosion of zinc in 0.5 M NaCl at the scratches. No pit was detected at the scratches on the electrode coated with this film after immersion for 72 h.     

Optical and transmission electron microscopical study of the evolution of surface layer on recycled aluminium along the rolling mills

A deformed near-surface region, also referred as ‘surface layer’, is always present on rolled aluminium alloy sheets. This paper studies in detail the evolution of the surface layer along the production line on a ‘recycled’ commercial alloy (AA5050). A microscopic investigation of a step-by-step formation of the surface layer has been carried out in the roll-bite. The effect of thermo-mechanical processing on the microscopic and optical characteristics of the surface layer has been studied. The distribution of the alloying elements within the surface layer has been investigated along the production line. The importance of the Total Reflectance (TR) method has been demonstrated for accurate estimation of the average thickness of the surface layer. Based on these results, a correlation has been drawn between the microscopic characteristics of the surface layer and the TR profile which in turn shows that the TR can be used in lieu of TEM for estimation of the surface layer thickness at different production stages.     

Kinetics of atmospheric corrosion of mild steel, zinc, galvanized iron and aluminium at 10 exposure stations in India

As a part of updating Corrosion Map of India project, atmospheric corrosion behaviour of commercially available engineering materials such as mild steel, galvanized iron, zinc and aluminium metals was studied in marine, industrial, urban, and rural environments by weight loss method at 10 exposure stations in India over a period of 5 years. The results of these studies demonstrated that galvanized iron, zinc and aluminium metals were several times more durable than mild steel. Compared to galvanized iron and zinc, aluminium provided superior protection in industrial and marine environment except at Mormugao Port Trust (MPT). It also offered much better resistance to corrosion in rural environments. At certain places, galvanized iron proved to be more durable than aluminium. The results obeyed well with the empirical kinetics equation of the form C = Ktⁿ, where K and C are the corrosion losses in μm after 1 and ‘t’ years of the exposure, respectively, and ‘n’ is a constant. Based on ‘n’ values, the corrosion mechanisms of these metals are predicted. The corrosion products formed on the metal samples in Chennai marine atmosphere were identified by X-ray diffraction analysis.     

Responsive behaviour of galvanic anodes in concrete and the basis for its utilisation

In this study, a unique concrete specimen was used to analyse the response of embedded sacrificial zinc and steel anodes to rainfall and fluctuations in temperature. Current from the zinc and steel anodes increased when the environment was aggressive, showing that the required protection current depends on the present level of corrosion risk. A basis for using the ‘responsive behaviour’ of galvanic anodes is provided by the protective effects of pit re-alkalisation and pH maintenance. By contrast, protection based on achieving adequate polarisation inhibits the use of responsive behaviour and galvanic anodes might only deliver adequate polarisation in aggressive environments.     

Self-healing mechanism of a protective film prepared on a Ce(NO3)3-pretreated zinc electrode by modification with Zn(NO3)2 and Na3PO4

Self-healing mechanism of a protective film against corrosion of zinc at scratches in an aerated 0.5 M NaCl solution was investigated by polarization measurements, X-ray photoelectron spectroscopy (XPS) and electron-probe microanalysis (EPMA). The film was prepared on a zinc electrode by treatment in a Ce(NO₃)₃ solution and addition of aqueous solutions containing 9.98 or 19.9 μg/cm² of Zn(NO₃)₂ · 6H₂O and 55.2 μg/cm² of Na₃PO₄ · 12H₂O. After the coated electrode was scratched with a knife-edge crosswise and immersed in the NaCl solution for many hours, polarization measurements, observation of pit formation at the scratches, XPS and EPMA were carried out. This film was remarkably protective and self-healing against zinc corrosion on the scratched electrode. The cathodic and anodic processes of zinc corrosion were markedly suppressed by coverage of the surface except for scratches with a thin Ce₂O₃ layer containing a small amount of Ce⁴⁺ and the surface of scratches with a layer composed of Zn₃(PO₄)₂ · 4H₂O, Zn(OH)₂ and ZnO mostly.     

An optimized multilayer structure of CdS layer for CdTe solar cells application

CdS layers grown by ‘dry’ (close space sublimation) and ‘wet’ (chemical bath deposition) methods are deposited and analyzed. CdS prepared with close space sublimation (CSS) has better crystal quality, electrical and optical properties than that prepared with chemical bath deposition (CBD). The performance of CdTe solar cell based on the CSS CdS layer has higher efficiency than that based on CBD CdS layer. However, the CSS CdS suffers from the pinholes. And consequently it is necessary to prepare a 150 nm thin film for CdTe/CdS solar cell. To improve the performance of CdS/CdTe solar cells, a thin multilayer structure of CdS layer (∼80 nm) is applied, which is composed of a bottom layer (CSS CdS) and a top layer (CBD CdS). That bi-layer film can allow more photons to pass through it and significantly improve the short circuit current of the CdS/CdTe solar cells.     

Correlation of interfacial electrode potential and corrosion resistance of plasma polymer coated galvanized steel. Part 1: Ultra-thin plasma polymer films of varying thickness

Ultra-thin SiO₂-like plasma polymer films were deposited on zinc coated steel. Such films led to a strong inhibition of cathodic and anodic electrochemical reactions and a negative shift in the electrode potential. When the SiO₂-like films are additionally coated with a few micron thick organic film, the resulting interface electrode potential is further shifted cathodically down to −0.8 V_SHE as measured by means of a scanning Kelvin probe. This interface potential is about the same as the free corrosion potential of zinc in a chloride containing electrolyte. Accordingly, the interface proved to be extremely resistant to cathodic de-adhesion processes.     

Microstructure and residual stress improvement in wire and arc additively manufactured parts through high-pressure rolling

Parts manufactured by Wire and Arc Additive Manufacture (WAAM) can have significant residual stress and distortion, as well as large grain sizes. To overcome these problems, each layer on a linearly deposited steel WAAM part was rolled with either a ‘profiled’ roller, which had a similar shape to the deposited layer, or a ‘slotted’ roller, in which a groove prevented lateral deformation. Both rollers reduced the distortion and surface roughness, but the slotted roller proved more effective – eliminating the distortion. The residual stresses in the rolled WAAM parts were measured and were lower than those in the unrolled control specimen – particularly adjacent to the baseplate. Rolling also induced additional grain refinement when the rolled material was reheated during the subsequent deposition pass. The application of rolling may be a key technology for enabling implementation of WAAM on large-scale structures.     

不同形状钨粉化学镀铜的研究

通过化学镀法制备铜包钨复合粉末,研究不规则形状的钨粉以及经等离子球化处理的球形钨粉的化学镀铜。结果表明,对于颗粒形貌不规则棱角分明的破碎钨粉,经化学镀包覆后粉末没有明显的棱角,表面粗糙。而经等离子球化处理后球形度较高的球形粉,颗粒表面存在缺陷,化学镀后粉末的球形度没有明显的变化,化学镀层在其表面沉积均匀,且钨粉表面质量得到改善,不存在表面缺陷。化学镀后复合粉末在600℃下进行氢气退火处理后,镀层上的粗糙的表面变得平滑,镀层中的空隙明显减少,形成了一层均匀致密的铜层包覆在钨颗粒表面。     

Improvement in the self-healing ability of a protective film consisting of hydrated cerium(III) oxide and sodium phosphate layers on zinc

A self-healing protective film prepared on a zinc electrode by previous treatment in a Ce(NO₃)₃ solution and coverage with a Na₃PO₄ layer was improved by the addition of Zn(NO₃)₂. The protective and self-healing abilities of the films against corrosion of zinc in an aerated 0.5 M NaCl solution were examined by polarization measurements and observation of pit-like anodic dissolution feature (plf) and pit formation after the electrode was scratched with a knife-edge crosswise and immersed in the solution for many hours. The film prepared on the pretreated electrode coated with 9.98 or 19.9 μg/cm² of Zn(NO₃)₂ · 6H₂O and 55.2 μg/cm² of Na₃PO₄ · 12H₂O was significantly protective and self-healing against zinc corrosion on the scratched electrode. The protective efficiency of the film was more than 96% in the region of the immersion time between 72 and 360 h. No plf was observed at the scratches after immersion for 120 h. Results of Fourier transform infrared reflection and X-ray photoelectron spectroscopies revealed that the film was composed of Na₃PO₄, Zn₃(PO₄)₂ and Ce₂O₃ layers.     

Application of electrophoretic deposition for inner surface coating of porous ceramic tubes

The direct coating of a nano-porous alumina layer on the inner surface of micro-porous alumina tubes was performed by electrophoretic deposition (EPD). A thin layer of polypyrrole (Ppy) was synthesized on the inside wall of the porous tubes by the chemical polymerization of pyrrole (Py) to give the wall electric conduction for the EPD electrode. The bimodal suspension of alumina powders with 0.6 μm and 30 nm average particle sizes was selected to control the nano-porous structure. The thickness of the coating layer was controlled by altering the applied voltage and deposition time. The interfacial connection of the coated layer and the substrate was observed by SEM before and after sintering. The pore size of the coated layer was characterized by its pore size distribution.     

Arc weldability of zinc coated steel sheets

Summary

CO₂ arc fillet welding of lap joints in zinc coated steel sheets and Zn-Fe coated steel sheets produced from base metals with a different surface roughness is performed to clarify the relationship between the properties of zinc coating layers and the factors affecting the generation of pits and blowholes during arc fillet welding of lap joints in zinc coated steel sheets. The results show that the generation of pits and blowholes is sharply reduced with a decreasing Fe content in the zinc coating layer and the decreasing surface roughness of the base metal. A reduction in the Fe content of the zinc coating layer decreases the melting point of the zinc coating layer, causing the zinc coating layer to melt faster and enabling the molten zinc to escape faster from the molten pool. A reduction in the surface roughness of the base metal increases the mobility of the molten zinc on its surface near the molten pool. When zinc coated steel sheets with a zinc coating weight of 40 g/m² produced from smooth surface base metal (Ra = 0.1 μm) were welded at a welding speed of 1.0 m/min, the generation of pits and blowholes was strongly suppressed to the same level as found during corresponding welding of cold-rolled steel sheets.     

NaCl-KCl共熔盐中Zn2+的电化学还原机理(英文)

为了开发高效、环境友好型冶金粉尘中锌回收技术,提出一种将选择性氯化和熔盐电解相结合的工艺。首先,通过热力学论证上述处理工艺的理论可行性。然后,采用多种暂态电化学测试方法研究973K时NaCl-KCl共熔盐中Zn²⁺在钨电极上的电化学行为。结果表明,Zn²⁺的还原过程是一步转移2个电子的反应,起始还原电位为-0.74 V(vs Ag/AgCl);且为受扩散控制的准可逆过程,计算得到Zn²⁺的扩散系数为10^-5cm²/s数量级。最后,在NaCl-KCl-ZnCl₂熔盐中于-1.6 V (vs Ag/AgCl)进行恒电位电解,电解9.5 h、后获得银白色类球状金属颗粒,经分析证实为金属Zn。本研究表明,在NaCl-KCl共熔盐中直接电解ZnCl₂提取金属锌是可行的,为冶金粉尘中锌的高效回收提供了有益的理论参考。     

Mechanistic changes in cut-edge corrosion induced by variation of organic coating porosity

The scanning vibrating electrode technique (SVET) has been used to investigate the mechanism of corrosion occurring at exposed metallic cut edges of galvanised steel materials coated with identical thickness organic polymeric layers. Organically coated galvanised steel samples have been prepared by application of a 30 μm polyester coating to both sides of a pre-treated hot dip zinc (99.85%) aluminium (0.15%) galvanised steel substrate. In separate samples the coatings were applied to both sides simultaneously and then cured or applied sequentially to each side curing after each application. Electrical impedance spectroscopy (EIS) was used to probe the porosity of the resulting organic coatings. This revealed that simultaneous coating application and curing resulted in both polymer layers showing EIS pore resistance of 0.6 MΩ whereas sequential coating resulted in one side showing a pore resistance of 0.6 MΩ and the other showing a capacitive EIS response with no measurable porosity. When the metallic cut edges of organically coated steel materials, coated with symmetric thicknesses of organic layers of identical pore resistance, are exposed to 5% NaCl the SVET iso-current contour maps show that both zinc layers behaving as local anodes. In addition, there is significant sample passivation in the 24 h exposure period. In the samples coated with materials of identical thicknesses but different porosity, the SVET iso-current contour maps show anodic activity focussed beneath the organic coating with the capacitive EIS signature. The greater porosity of the coating on the opposite side of the exposed cut edge enables oxygen transport to the delaminating surface and this forces anodic activity onto the other zinc layer.     

联氨液相还原制备镍包钨复合粉末

在含有悬浮细颗粒钨粉的氯化镍溶液中，采用联氨液相还原对镍包钨复合粉末的制备进行了研究，探讨了工艺条件对镍沉积速率及复合粉末性能的影响。结果表明，在合适的工艺条件下，联氨液相还原是制得成分均匀、分散性好的镍包钨复合粉末的简单有效而又成本低廉的方法。     

Investigation on wear behaviour of cryogenically treated TiAlN coated tungsten carbide inserts in turning

Cryogenic treatment has been ascribed as a way of improving the cutting life of tungsten carbide turning inserts. Most of the research conducted till date has not reported any effort to excavate the effect of cryogenic treatment on the performance of coated tungsten carbide inserts in terms of adhesion strength of coatings deposited on tungsten carbide substrate. In order to understand the effect of cryogenic treatment on the adhesion strength of coatings, a comparative investigation of the wear behaviour and machining performance of cryogenically treated coated tungsten carbide inserts in orthogonal turning has been carried out in this study. The commercially available TiAlN coated square shaped tungsten carbide inserts (P25) were procured and subjected to cryogenic treatment at two levels −110 °C (shallow treatment) and −196 °C (deep treatment) of temperature independently. The criterion selected for determining the turning performance was based on the maximum flank wear (0.6 mm) as recommended in ISO 3685-1993. The results showed that shallow cryogenically treated coated tungsten carbide inserts performed significantly better as compared with deep cryogenically treated and untreated inserts. Major outcome of the present study includes a substantial decrease in tool life of deep cryogenically treated inserts as compared to untreated inserts indicating the destructive effect of deep cryogenic temperature (−196 °C) on TiAlN coated inserts which is further supported by VDI-3198 indentation test.