Electrochemical study of corrosion behavior of graphene coatings on copper and aluminum in a chloride solution

Electrochemical characteristics and corrosion behavior of graphene coatings on Cu and Al in a 0.1 M NaCl solution were investigated. The graphene coatings were deposited on a Cu surface by chemical vapor deposition. Multiple graphene layers were then mechanically transferred from the growth substrate, Cu, onto Al surface by a transfer technique. The corrosion stability of graphene coatings was determined by electrochemical impedance spectroscopy and open circuit potential, while the corrosion rate was evaluated using potentiodynamic sweep measurements. Surface morphologies of the graphene coatings were analyzed by scanning electron microscopy and energy dispersive spectroscopy. Obtained results indicate that Cu coated with graphene grown using chemical vapor deposition shows corrosion-inhibiting properties in 0.1 M NaCl. On the other hand, Al coated with a multilayer graphene film mechanically transferred from the Cu surface exhibits electrochemical characteristics similar to an Al oxide on bare Al. Better protective properties of graphene coating on Cu compared to the graphene coating on Al were observed, probably due to the breakage of Al oxide film, causing the corrosion of Al to proceed rapidly in the presence of chloride electrolyte.     

二氧化钛光触媒在金属镀膜与金属防护技术中的应用第三部分光触媒的金属涂饰与腐蚀防护

分别介绍了金属表面二氧化钛光触媒涂层的自清洁原理和光半导体光触媒的防腐蚀原理。比较了含与不含光触媒涂层的不锈钢基体在不同pH的氯化钠溶液中的腐蚀电位。指出使水接触角趋于零而产生超亲水性是光触媒涂层具有自清洁功能的原因;吸收紫外光释放电子给金属,从而降低金属的腐蚀电位,是其具有防腐性能的实质;在基体与光触媒涂层间设置中间层可以避免基体被光触媒氧化;采用WO3与TiO2复合可以使光触媒涂层在无光或夜间继续发挥其防腐蚀功能。     

PVD Coating of Mg–AZ31 by Thin Layer of Al and Al–Si

Although magnesium alloys have the advantage of high specific strength, they have poor atmospheric corrosion resistance. An important method of improving the corrosion resistance is by applying a coating layer. In this work, the physical vapor deposition (PVD) technique is used for coating a magnesium (Mg) AZ31 sheet substrate with a thin layer of high purity aluminum (Al) and Al–12.6% Si. Aluminum is expected to be suitable as a coating layer on Mg sheets, due to its corrosion resistance and its formability. Before coating, the substrate was subjected to several consecutive surface preparations, including sand-blasting, mechanical grinding, mirror-like polishing, ultrasonic etching, and finally ion etching by magnetron sputtering (MS). PVD coating was conducted using a PVD machine with max electron beam power and voltage of 100 kW and 40 kV, respectively. This was either with or without plasma activation, and with variable substrate speeds ranging between 10 and 70 mm/s. During MS ion etching and coating, the substrate temperature increased. The substrate temperature increased with the application of plasma activation and with lower substrate speeds. The coating-layer thickness varied inversely with substrate speed. A thinner coat with finer morphology was obtained in the case of plasma activation. Other results included coating layer characteristics, diffusion between the AZ 31 substrate and the Al coating layer, adhesion of the coating layer to the substrate, and corrosion resistance by a humidity test.     

The effect of silane layer drying temperature on epoxy coating adhesion on silane-pretreated aluminum substrate

In this study, 3-glycidoxypropiltrimethoxysilane was used as an adhesion promoter to enhance the adhesion strength of epoxy coating on an aluminum (Al) substrate. Silane layer drying temperature was investigated as a factor that has an influence on the adhesion of polymeric coating on metal substrate and also on its performance in wet and corrosive environments. FTIR tests were carried out to study Al/silane interactions. Drying the silane layer at high temperatures formed a condensed siloxane layer that improved the bonding strength as well as the performance of the protective coating in corrosive environments. The highest dry and wet pull-off strengths were obtained at drying temperatures of 100 and 125°C, respectively.     

非铁基体上的化学镀镍

综述了近十年来非铁基体上的化学镀镍基合金技术的发展状况,特别是轻金属铝、镁、钛及其合金的化学镀镍前处理技术,还涉及塑料件前处理技术,发现前处理技术已发展到了不仅仅考虑镀层与基体结合力的问题,还考虑到工件在浸入镀液时表面pH值的瞬间变化,以及不同的前处理方式对化学镀镍起始层结构的影响和前处理液的带入对镀液性能的影响。还讨论了非铁基体化学镀镍液的合理组成,展现出该技术的最新发展成就。     

Improving the adhesive,mechanical, tribological properties and corrosion resistance of reactive sputtered tantalum oxide coating on Ti6Al4V alloy via introducing multiple interlayers

Tantalum oxide film has become an investigation focus for surface modification materials in the biomedical field owing to its outstanding biocompatibility, anti-corrosion, and anti-wear performances. However, tantalum oxide films exhibit poor adhesion because of the mismatch between the properties of the film and the substrate. In this study, a novel multilayer tantalum oxide coating of Ta_mO_n/Ta_mO_n-TiO₂/TiO₂/Ti (code M-Ta_mO_n) was deposited on Ti6Al4V by magnetron sputtering with Ta_mO_n single-layer coating as control. The purpose of this work is to evaluate the influence of the introduced Ta_mO_n-TiO₂/TiO₂/Ti multi-interlayer on the microstructure, adhesive, mechanical, and anti-corrosion properties of reactive sputtered tantalum oxide coatings. The outcomes show that the Ta_mO_n-TiO₂/TiO₂/Ti intermediate layer improves the bonding strength between the Ta_mO_n layer and Ti6Al4V matrix from 17.83 N to over 50 N and enables the Ta_mO_n coating to have an increased H/E and H³/E² ratio, decreased friction coefficient and wear rate, raised potential, and reduced corrosion current density. The improved properties of the multilayer system are attributed to the positive effects of the inserted multiple interlayers in reducing the residual stress in the coating, coupling the mechanical performance between the layer and the substrate, blocking the continuous growth of penetrating defects in a film with columnar structure. These experimental results provide a workable route for improving the properties of the tantalum oxide coating on Ti6Al4V alloy for medical applications.     

Adhesion enhancement of diamond coating on minor Al-modified copper substrate

We report on the enhanced interfacial adhesion of diamond coating on copper substrate modified by a small fraction of Al. For pure copper substrate, the diamond coating formed tends to crack and delaminate, primarily caused by a slight accumulation of detrimental graphite intermediate layer and thermal stress induced by mismatch of the coefficients of thermal expansion. Additions of 1 and 3 at.% Al to the copper substrate gradually decrease the intermediate graphitic phase. At the higher Al concentration, an aluminium oxide forms at the coating–substrate interface, and graphitic/amorphous carbon is completely inhibited, leading to significantly enhanced interfacial adhesion of diamond coating. The electron structure of copper is not observed to significantly alter on this Cu–Al dilute alloy. The alumina barrier layer preferentially formed on copper surface is believed to play a key role in preventing graphitization and adhesion enhancement.     

Micro-arc oxidation of bioceramic coatings containing eggshell-derived hydroxyapatite on titanium substrate

In the present study eggshells-derived hydroxyapatite (EHA) coatings were successfully produced on Ti6Al4V substrates using micro-arc oxidation process (MAO) at various concentrations of EHA (i.e. 1, 1.5 and 2 g/L) in an electrolyte consisting of tri-sodium orthophosphate. The attributes of the coatings were determine by X-ray diffraction, attenuated total reflectance-fourier transform infrared spectroscopy, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The adhesion strength was evaluated using micro scratch tester, while the corrosion behavior of the MAO-coated substrates in phosphate buffer solution was determined by an electrochemical method. The results showed that as the EHA concentration increased, this was accompanied by a reduction in the porosity due to the formation of a dense and thick coating layer. This has also resulted in an increased in the surface roughness and degree of crsytallinity of the HA phase. The MAO-coated substrate prepared with 1.5 g/L EHA concentration exhibited a well-formed coating layer with improved adhesive strength and excellent corrosion resistance. The mechanism of EHA-coating formation as well as the enhanced corrosion resistance of the coated substrates were discussed. This research shows the viability of using calcium-rich waste eggshells to produce phase pure HA suitable for coating on Ti6Al4V substrate using MAO method.     

激光重熔NiCrAlY涂层研究

采用空气等离子喷涂技术(APS)将NiCrAlY粉末作为粘结层材料喷涂在IN718镍基合金上,再用5 kW CO2连续激光器对其进行激光重熔处理,利用扫描电镜(SEM)、能谱分析(EDX)和X射线衍射(XRD)等手段对等离子喷涂层和激光重熔层的微观组织与成分进行了比较分析.结果表明:应用优化激光重熔工艺进行重熔后,涂层...     

Preparation and corrosion resistance of a self-sealing hydroxyapatite- MgO coating on magnesium alloy by microarc oxidation

An ideal self-sealing hydroxyapatite (HA)-MgO coating was designed on an AZ31 Mg alloy by one-step microarc oxidation (MAO) with the addition of HA nanoparticles into a base electrolyte. The formation mechanism of the self-sealing HA-MAO coating was discussed. The effect of the nano-HA addition on the corrosion resistance of the MAO coating was evaluated by corrosion tests in Hank's solution. The results show that HA nanoparticles inertly incorporated into the MAO coating during the process of coating growth. HA and MgO were the main constituents of the HA-MAO coating. The HA nanoparticles were absent in the inner barrier layer but concentrated in the outer porous layer. In addition, HA nanoparticles accumulated much more inside coating defects than in the other zones, which resulted in the nearly ideal sealing of micropores on the coating surface. By forming a denser and more stable outer layer, the incorporation of HA nanoparticles greatly enhanced the anti-corrosion properties of the MAO coating.     

钢包复合反射绝热层的试验

基于微纳米传热学理论,研制开发了钢包包壳内表面 (1) 氧乙炔火焰热喷涂纳米Al2O3涂层,(2) 复合反射绝热板,(3) 喷/抹涂绝热防护层,取得了钢包外壁温度下降78~140℃以上、减小钢水温降、提高内衬温度等效果.     

Polypyrrole films modified with graphite layer on mild steel

Electrochemically synthesized polypyrrole coating was modified with very thin graphite layer and top coated with another polypyrrole film. The corrosion behaviour of this coating has been investigated in aqueous sodium chloride solution. The synthesis of polypyrrole coatings was carried out by cyclic voltammetry technique, from aqueous oxalic acid solution. Electrochemical impedance spectroscopy and potentiodynamic measurements were used for corrosion tests. The cyclic voltammograms obtained in oxalic acid solution and the polarisation curves obtained in sodium chloride solution showed that the stability of coating was improved significantly by graphite layer. The impedance spectra also showed that the corrosion process was controlled by the diffusion rate along the coating, even after 96 h immersion period. The Warburg coefficient values were calculated and used to evaluate the barrier property of coating with time. It was shown that the water up taking process was slowed down by the hydrophobic nature of the graphite layer sandwiched between the two polypyrrole films.     

PDA包覆铝粉及其在HTPB中的分散稳定性

通过原位多巴胺(DA)聚合法在铝粉表面包覆聚多巴胺(PDA),制备了Al@PDA复合颗粒;采用SEM表征不同DA质量浓度下Al@PDA的表面形貌。用XRD测试铝粉包覆前后的晶型;采用XPS分析Al@PDA的表面元素组成;通过沉降法研究了铝粉和Al@PDA在HTPB中的分散稳定性;通过制备固化胶并切片取样观察固体颗粒在HTPB中的分散情况。结果表明,当DA质量浓度为3.5g/L时对铝粉的包覆效果最好,在铝粉表面形成牢固的PDA薄膜;包覆前后Al的晶型没有改变;XPS在Al@PDA表面检测到的C-OH、C=O组分和π-π共轭结构证实了PDA包覆层的存在。沉降24h后Al-HTPB体系出现分层,而Al@PDA-HTPB体系仍然颜色均一,表明Al@PDA在HTPB中的分散稳定性明显优于原料铝粉。     

Influence of a hard transition layer on the microstructure and properties of diamond-like carbon/hydroxyapatite composite coating prepared by magnetron sputtering

The nanostructured diamond-like carbon/hydroxyapatite composite coating (DLC/HA) was deposited using magnetron sputtering technique with a densely packed columnar cross-sectional structure and a uniform granular surface morphology. After heat treatment, the amorphous structure of the coating was transformed into a crystal structure. Nanohardness and scratch tests results demonstrated the DLC transition layer significantly enhanced the nanohardness of Ti6Al4V substrates from 4.8 GPa to 10.4 GPa, and increased critical load from 16.6 N (pure HA layer) to 26.5 N (DLC layer) without obvious brittle fracture, flaking and delamination. Electrochemical and immersion tests results demonstrated that DLC/HA composite coatings with a dense gradient transition interlayer had better corrosion resistance and could prevent harmful metal ions being released into the SBF solution more effectively than single HA coatings. Furthermore, active Ca²⁺ ions can be rapidly released from the coating surface during initial immersion in the SBF solution, and facilitated the formation of bone-like apatite.     

Structures and tribological performances of PEEK (poly-ether-ether-ketone)-based coatings designed for tribological application

Driven by economical and ecological reasons, thermoplastic-based coatings become a potential solution for anti-wear purpose. Two coating design concepts, flame spraying and printing PEEK (poly-ether-ether-ketone)-based coatings on Al substrate, were introduced in this paper. An amorphous PEEK coating was obtained by these two techniques. After being annealed, the coating presents a semi-crystalline structure. The friction and wear behaviors of PEEK-based coatings were investigated by means of ball-on-disc tests. The results show that PEEK coatings exhibit an excellent tribological performance with a relatively low coefficient of friction and wear rate. The semi-crystalline PEEK coating exhibits a lower friction coefficient and wear rate than the amorphous one. The additions of micron-sized particles such as SiC and graphite in PEEK coating can improve significantly the coating wear resistance.     

A study of the deactivation and service life of Ir oxide anodes supported on Al substrates

The deactivation of Ir oxides supported on Al substrates has been studied in 0.5 M H₂SO₄. Their electrochemical behaviour and service life was also compared to IrO₂ electrodes, similarly prepared, supported on Ti. The Ir oxides were prepared by thermal decomposition of an Ir salt precursor solution. The service life and other oxide properties were found to be influenced by different factors used for preparation of the Ir oxide electrodes, for example, the temperature used for the decomposition process and the solution used to etch the Al substrate. In contrast to the IrO₂ anodes supported on Ti, the service lives of the IrO₂ anodes supported on Al were found to be very short. The deactivation of the latter anodes appears to be related to poor adhesion between the Ir oxide and the Al substrate. However, it was found that the service life of IrO₂ anodes supported on Al is increased when a layer consisting of iridium is electrochemically deposited onto the Al substrate prior to the thermal formation of the IrO₂.     

Plasma electrolytic fluorination on Al alloys: Coating growth and plasma discharge behavior

The plasma electrolytic fluorination (PEF) process was conducted on 6061 Al alloy in the NH4F-EG non-aqueous electrolyte at room temperature. The microstructure and composition of the resultant coating were characterized by SEM, EDS, XRD and XPS. Also the coating growth and plasma discharge behavior were investigated by means of a well-designed jig, digital camera and OES, in order to understand the process characteristics. Results showed that the coating was dominantly composed of AlF₃, and characterized by a flake-like microstructure accompanying with some micro-pores and numerous micro-cracks. The internal of the coating was porous with a compact barrier layer near the substrate/coating interface. The fluorination of the substrate contributed the inward growth of the coating. PEF discharge sparks were characterized by tiny size and weak intensity during the whole process, of which the plasma electron temperature was about (3510 ± 110) K. Also, the discharge behavior and coating growth mechanism of the PEF process on Al alloy were discussed.     

Preparation and properties of wear-resistant carbonized-ceramic composite coating on pure aluminum surface

In this paper, a new composite coating was prepared on the surface of pure aluminum (Al) by combining the micro-arc oxidation (MAO) technology with the polyethylene glycol (PEG 400) carbonization technology. The composite coating and the single MAO coating were observed by a scanning electron microscope, and an energy-dispersive spectrometer, finding that the single MAO coating surface with volcano-like pores and microcracks, was covered by the carbonized layer of the composite coating where the overall coating thickness was around 19.5 µm, including 17.5 µm of inner MAO coating. The material properties of the composite coating were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The wear resistance of the composite coating was tested under dry friction conditions, finding that the wear width on the composite coating surface was 909.6 µm only, which was around 55.7%, 50.4%, and 58.2% of those for pure Al substrate, single carbonized coating, and single MAO coating, respectively. Then the comprehensive wear resistance of the composite coating was explored under different sliding speeds and lubrication mediums. Finally, the wear-resisting mechanism of the composite coating was discussed, concluding that the composite coating could effectively reduce adhesive wear and abrasive wear of the Al substrate.     

Corrosion protection properties of polypyrrole electropolymerized onto steel in the presence of salicylate

The corrosion performance of a polypyrrole coating constituted by hollow rectangular microtubes was monitored in chloride solutions using open circuit potential measurements, potentiostatic polarization and electrochemical impedance spectroscopy. The coating was electrosynthesized onto 316 L stainless steel from a salicylate solution and it provided a very good corrosion resistance to the substrate. It was found that polypyrrole films with granular morphology electrodeposited from a salicylate solution with lower concentration behave better in terms of protective behavior. In order to improve the corrosion protection imparted by the polypyrrole coating formed by the microtubes a system of two layers was electrodeposited, the first one consisted of polypyrrole with a granular morphology and the second one, on the top, was constituted by the microtubes. This bilayered system exhibited an excellent protective behavior during considerably long immersion time.     

Facile construction of silica-based surface coating onto polypropylene microporous film through dopamine-assisted hydrolysis of tetraethoxysilane

Surface modification with silica-based coating is widely used to attain high performance and construct special functions for thin films. In this paper, dopamine (DA) and tetraethoxysilane (TEOS) were used as initial building blocks to construct a biomimetic hydrophilic and mechanical robust silica-based coating onto polypropylene (PP) microporous film. It was found that the final DA/TEOS coating can be steadily immobilized onto PP film and greatly improve the hydrophilic property of PP film as evidenced by the decreased contact angle. Furthermore, the coating structures were comparatively investigated through one-step synthesis and two-step synthesis of DA and TEOS with a fixed ratio. Interestingly, the one-step synthesized coating possesses a loosely-packed layer with dispersed SiO₂ nanoparticles within polydopamine matrix while the two-step synthesized coating shows a high loading of SiO₂ nanoparticles. As a result, the two-step approach leads to a continuous SiO₂ layer with abundant hydroxyl groups, indicating a better lyophilic property and depressed thermal shrinkage. In addition, the concentric SiO₂ layer results in a significant increase of the tensile strength of PP films.