Electrochemical study of modified non-functional bis-silane layers on Al alloy 2024-T3

In the last few years great efforts have been made in order to find and to develop environmentally friendly substitutes for Cr⁶⁺ pre-treatments applied on aluminium alloys used in the aircraft industry. Among the potential substitutes, silane layers have attracted considerable interest from researchers and from the industry. The present work investigates the anti-corrosion behaviour of (bis-1, 2-(triethoxysilyl) ethane (BTSE)) silane layers modified with Ce ions and/or silica nanoparticles applied on Al alloy 2024-T3 substrates. The corrosion behaviour was investigated in 0.1 M NaCl solution via d.c. polarization and electrochemical impedance spectroscopy (EIS). Contact angle measurements and XPS were used to assess information on the chemistry of the silane pre-treated surfaces. The results have shown that the introduction of additives improves the corrosion protection properties of the silane layer.     

Synthetic Effect of Cr and Mo Elements on Microstructure and Properties of Laser Cladding NiCrxMoy Alloy Coatings

NiCr_xMo_y (x = 1, 1.5; y = 0, 0.1, 0.3) alloy coatings were prepared on the Q235 substrate by laser cladding under the protection of argon. The phase composition, microstructure, corrosion behavior, and mechanical properties of the NiCr_xMo_y alloy coatings were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electrochemical tests, X-ray photoelectron spectroscopy, microhardness, and nanoindentation tests. As the Cr content increased, the phase composition of the coatings changed from a single face-centered cubic (FCC) structure to a dual-phase structure coexisting with body-centered cubic (BCC) and FCC structures, while the addition of Mo promoted the precipitation of σ phase. The appearance of a homogeneous dual-phase structure and some amount of σ phase played a positive role in the corrosion resistance of NiCr_xMo_y coatings. Cr³⁺ ions and Mo⁶⁺ ions in the passive film enhanced the stability of the coatings. The nanoindentation tests showed that the nanohardness (6.71 GPa) and elastic modulus (184.40 GPa) of BCC phase were higher than those of the FCC phase (5.19 GPa and 155.26 GPa, respectively). Overall, the BCC phase and σ phase improved the mechanical properties of the coatings.     

碳钢超声磷化及在模拟干热岩地热水中的耐蚀性能

采用环境友好的硫酸羟胺为主要促进剂,避免使用强氧化性物质,并以超声处理来改进磷化工艺。通过动电位极化曲线方法研究了超声、促进剂、pH值和磷化时间对磷化膜耐蚀性能的影响。结果表明,超声处理能够细化磷化颗粒,提高其耐蚀性能。pH值和磷化时间显著影响磷化膜的耐蚀性,需保持在较优的范围。采用电化学阻抗谱研究了优化工艺得到的磷化膜在模拟干热岩地热水中的耐蚀性,发现其电荷转移电阻由碳钢的1.44×10³ Ωcm²增加到3.39×10⁶ Ωcm²。     

Corrosion monitoring of galvanised coatings through electrochemical impedance spectroscopy

In this work, corrosion of industrial galvanised coatings is monitored through potentiodynamic and electrochemical impedance spectroscopy (EIS) methods and supported by real-time immersion tests. For such purpose, the corrosion behaviour is studied in different media (NaCl, NaOH and rain water), at different concentrations and varying immersion times. The results show that EIS allows to establish the interfacial reactions and the dissolution mechanisms occurring in three corrosive media, hence to foresee the protection conferred by these coatings. The impedance diagrams of the coated steel do not provide information on the slowest reactions, which only occur in natural rain water. Finally, each Zn/medium interface is characterised by a specific equivalent circuit giving a similar impedance response.     

Electrodeposition of hydroxyapatite–silver–chitosan nanocomposite coatings

Hydroxyapatite (HA)–Ag–chitosan nanocomposite coatings were electrochemically deposited on various conductive substrates and studied using X-ray diffraction analysis, thermogravimetric and differential thermal analysis, energy dispersive X-ray spectroscopy, scanning and transmission electron microscopy. It was shown that the coating composition can be varied by the variation of AgNO₃ or HA concentration in the solutions used for electrodeposition. Nanocomposite coatings were deposited as HA–Ag–chitosan monolayers or multilayers containing individual HA–chitosan and Ag–chitosan layers. The coating thickness was varied in the range of 0−20 µm by the variation of deposition time for individual layers and by the variation of the number of different layers. Inductively coupled plasma optical emission spectroscopy studies showed that the Ag⁺ release rate from the Ag–chitosan layer can be reduced in the layered structure using a HA–chitosan layer. The obtained results can be used for the development of biocompatible antimicrobial coatings with controlled Ag⁺ release rate. Electrochemical impedance spectroscopy and potentiodynamic polarization studies showed that the multilayer coatings provide corrosion protection of the stainless steel substrates in Ringer's physiological solutions.     

15 Jahre deutsche Korrosionforschung im Forschungsprogramm Korrosion der Deutschen Bundesrepublik — Teil II

15 Years of German corrosion research in the research programme corrosion of the Federal Republic of Germany — Part II The second part of this report (Pt. I se WuK 24 [1973] 6; 525–535) deals in particular with the possibilities of corrosion protection, and in particular inhibitors, electrochemical methods (cathodic protection), electrolytically deposited metal coatings (including the feasibility of influencing their properties by galvanizing conditons), sprayed and vacuum deposited coatings non-metallic inorganic coatings (passivating layers such as anodizing etc., as well as their preparation mechanisms) and organic coatings. A concluding part deals with test methods, on the one hand methods to test the corrosion behaviour of materials in various media and under various conditions on the other hand methods to test the efficiency of various corrosion protection methods. 434 ref.     

装载缓蚀剂的蒙脱土对环氧涂层耐蚀性能的研究

将不同比例的装载缓蚀剂蒙脱土和环氧树脂混合制备出纳米复合环氧涂层。根据电化学阻抗谱 (EIS) 和盐雾实验对涂层的耐蚀性进行表征。结果表明,3%装载蒙脱土环氧涂层的水扩散系数为9.89×10^-11 cm²/s,孔隙率为2.22×10^-8,整个浸泡过程中阻抗值在10⁹ Ωcm²以上,表现出最佳的耐蚀性。     

Glass-like CexOy sol–gel coatings for corrosion protection of aluminium and magnesium alloys

This work reports the preparation of glass-like, environmentally-friendly, cerium-based coatings for active corrosion protection of aluminium and magnesium alloys. It describes the production of cerium sol–gel sols from cerium nitrate and their deposition by immersion and automatic spray onto aluminium and magnesium alloys to produce uniform coatings with amorphous (glass-like) structures (Ce_xO_y). The coatings have been characterised by profilometry, scanning electron microscopy (SEM), spectral ellipsometry and UV–visible, in order to analyse the structure and density of the glass-like cerium coatings as well as their redox ratio Ce⁴⁺/Ce³⁺ as a function of pH and sintering temperature. Finally, electrochemical measurements (EIS) and standard corrosion tests (neutral salt spray, filiform corrosion, immersion–emersion test and adhesion on embossing and T-bend test) have been performed to study the corrosion behaviour of the cerium glass-like coatings on aluminium and magnesium alloys. EIS measurements confirm the healing or blocking of the defects by the corrosion inhibiting species. Excellent corrosion protection is provided by cerium glass-like coatings, satisfying the most demanding industrial requirements.     

Protection of silver surfaces against tarnishing by means of alumina/titania-nanolayers

Tarnishing of Ag is due to the fact that the surface layer containing sulfides is not protective at all as, for instance, the oxide layers which are formed on stainless steel.Transparent ceramic coatings obtained by physical vapor deposition (PVD) intended as corrosion barriers, were studied in the past but their intrinsic defectiveness (residual porosity of the order of 1%) has been the major obstacle in order to guarantee a long-lasting protection. Therefore, organic varnishes are currently employed as protection.Recent nanotechnologies like Atomic Layer Deposition (ALD) are suitable to deposit single molecular layers which, by growing sequentially, turn out to be almost free of defects, displaying therefore a remarkable corrosion protection.In this work, Ag surfaces were coated with ALD alumina/titania nanolayers. Their microstructure and composition were studied with scanning electron microscopy (SEM) and glow discharge optical emission spectroscopy (GDOES) depth profiling. An evaluation of the corrosion behavior of the coatings was made through tarnishing tests and it was shown that the protection given by the ALD layers is at least 10 times superior to conventional organic varnishes. Such result is supported by electrochemical impedance spectroscopy (EIS), which indicates that the initial porosity of the ALD layers is of the order of 0.003%. It was also possible to follow as a function of time, the evolution of the electrical parameters characteristic of the protection system without damaging seriously the structure of the protecting layer.     

P/B对水性聚氨酯防腐蚀涂料性能影响研究

以水性聚氨酯为基料,加入颜填料和助剂合成水性防腐蚀涂料。改变涂料配方中颜填料和基料的质量比(P/B),在不锈钢板上制得涂层样品,通过极化曲线和电化学阻抗测试,讨论P/B对涂层腐蚀性能的影响,试验结果表明,涂料配方中P/B=0.8和1.5时涂层综合性能较好。     

Substitution of hexavalent chromate conversion treatment with a plasma electrolytic oxidation process to improve the corrosion properties of ion vapour deposited AlMg coatings

In this paper plasma electrolytic oxidation (PEO) is examined as a potentially beneficial post-deposition treatment for Al-5 wt.%Mg coatings deposited onto Ti alloy substrates using Ion Vapour Deposition (IVD), with a view to replacing toxic hexavalent chromate conversion treatments and at the same time enhancing the barrier protection properties of such IVD coatings. The aqueous corrosion behaviour of PEO layers formed on IVD coatings was evaluated by means of potentiodynamic polarisation scans, open circuit potential measurements and electrochemical impedance spectroscopy. Normally, IVD aluminium-based coatings require a post-coat shot peening treatment to densify the coating structure; however it was found that PEO layers could be formed successfully on as-deposited IVD coatings deposited onto Ti alloy substrates, providing a cost effective process to improve corrosion behaviour. PEO treatment provides unique improvements in the corrosion resistance of IVD coatings; the PEO layer possesses effective anticorrosion properties in aqueous environments containing Cl⁻ ions. A more positive corrosion potential, lower corrosion current and increased polarisation resistance were recorded for PEO layers, compared to traditional chromate conversion treatments.     

新型医用Ti-24Nb-4Zr-8Sn合金在Hanks溶液中的电化学腐蚀行为研究

采用极化曲线分析、电化学阻抗谱（EIS）测试和浸泡实验的方法,并结合XPS,XRD和SEM等分析手段对新型医用Ti-24Nb-4Zr-8Sn合金在37℃的Hanks人工模拟体液中的电化学腐蚀行为进行了研究,并与纯Ti和Ti-6Al-4V合金进行了比较.结果表明:在37℃的Hanks溶液中,Ti-24Nb-4Zr-8Sn合金的腐蚀电流密度与纯Ti相等,并且钝化性能优于纯Ti和Ti-6Al-4V,这与其钝化膜中存在大量的Nb₂O₅密切相关;EIS结果显示,Ti-24Nb-4Zr-8Sn合金表面形成内层致密而外层疏松的双层钝化膜结构,致密层特性对材料的耐蚀性能起到决定性作用;随着浸泡时间的延长,致密内层的电阻大幅度提高,Ti-24Nb-4Zr-8Sn合金的耐蚀性能增强,同时疏松外层中的微缺陷发展成为宏观裂纹,造成疏松外层整体脱落.     

有机涂层防护性能的电化学研究进展

曝晒、盐雾、浸泡、干湿循环、老化等传统的有机涂层防护性能研究方法,因测试周期长,测试结果多为定性分析,不能使涂层材料进行快速检验而投入评估使用.正是由于传统测试方法存在许多局限性,故综述了稳态电化学测试方法和暂态电化学测试方法这两种新技术在有机涂层防护性能中的应用与进展.介绍了动电位极化曲线法、极化电阻法等稳态电化学测试方法,这类方法主要反映涂层的极化电阻和腐蚀速度,并且方法简单,可直接分析实验数据,被广泛应用于有机涂层的失效分析中.而暂态电化学测试方法主要包括电化学阻抗法(EIS)、局部阻抗法(LEIS)、扫描Kelvin探针法(SKP)及电化学噪声(EN)等,主要用于研究涂层防护机制和局部缺陷.目前,在有机涂层防护性能和机理研究中,应用最多的是电化学交流阻抗法.丝束电极法(WBE)、扫描电化学显微镜(SECM)以及原子力显微镜(AFM)用于研究金属/涂层界面物理化学变化规律.阐述了上述方法在涂层防护研究中的应用成果及其优势和不足,指出对于深层次的涂层防护研究,需要应用多种测试手段,从不同的角度和方面综合分析,全面评估涂层的使用寿命.     

Novel anti-corrosion nano-sized vanadia-based thin films prepared by sol–gel method for aluminum alloys

Chromate conversion coatings have been widely applied for the corrosion protection of aluminum alloys. However, the waste containing Cr6+ has many limitations due to the environmental consideration and health hazards. Vanadates are among the proposed alternatives to chromating. Series of specimens were prepared under the following conditions: (a) as polished, (b) directly treated with vanadia, (c) etched, (d) oxide thickened, and (e) etching followed by oxide thickening. After surface preparation, the specimens were dipped in vanadia solution prepared via sol gel method. Electrochemical impedance spectroscopy (EIS) and polarization measurements have been used to evaluate the coating performance in 3.5% NaCl. The optimum conditions under which vanadia treatments can provide good corrosion protection to the aluminum substrate were determined. The surface morphologies of the treated samples were investigated using SEM and EDS. Optical microscope was also used to investigate the occurrence of pitting corrosion. The surface preparation prior to vanadia treatment was found to have a marked effect on the corrosion protection of AA6061 T6. Generally, vanadia treatments improve the corrosion resistance due to formation of highly protective vanadium oxides. According to the EIS and polarization measurements, a combination between etching and oxide thickening prior to vanadia treatment plays an important role on the corrosion protection mechanism.     

Optimization of deposition conditions for development of high corrosion resistant Zn-Fe multilayer coatings

Composition modulated multilayer alloy (CMMA) coating of Zn-Fe was developed galvanostatically on mild steel through single bath technique (SBT), using thiamine hydrochloride as additive. Electrodeposits with different coating matrices were developed, using square current pulses. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods were used to assess the corrosion performance of the coatings. The cyclic cathode current densities (CCCDs) and number of layers were optimized, for highest corrosion resistance. Experimental results showed that CMMA Zn-Fe coating, developed at 2.0-4.0 A/dm², having 300 layers is ∼30 times higher corrosion resistant than corresponding monolithic alloy of same thickness. The corrosion resistance increased with number of layers up to a certain number of layers; and then decreased. The better corrosion resistance was attributed to the dielectric barrier at the interface, evidenced by dielectric spectroscopy. The formation of multilayer and corrosion mechanism was analyzed using scanning electron microscopy (SEM).     

海洋环境中芽孢杆菌对聚氨酯清漆涂层分解的影响

采用电化学技术、扫描电镜和红外光谱等多种方法研究了海洋环境中芽孢杆菌对聚氨酯清漆涂层分解作用以及对腐蚀行为的影响.结果 表明,在浸泡时间为1h时,芽孢杆菌并没有对聚氨酯清漆涂层产生明显的降解作用.随着浸泡时间的延长,在含有芽孢杆菌的海水中的涂层耐蚀性明显小于在无菌海水中涂层的耐蚀性,表明芽孢杆菌能导致涂层的降解.浸泡初...     

Steel cathodic protection afforded by zinc, aluminium and zinc/aluminium alloy coatings in the atmosphere

Zinc has traditionally been the metallic material most widely used to protect steel against atmospheric corrosion due to its ability to afford cathodic protection to steel in all types of natural atmospheres. In recent decades, aluminium and zinc/aluminium alloy coatings have been used instead of zinc in certain atmospheric applications. Although these coatings present some advantages over zinc, they are not able to cathodically protect steel substrates in all types of natural atmospheres. The present paper assesses the cathodic protection afforded by Al (flame spraying), Al/13 Si (hot dipping), 55Al/Zn (hot dipping), Zn/15Al (flame spraying), Zn/5Al (hot dipping), Zn (hot dipping), Zn (discontinuous hot dipping) and Zn (electroplating). Aluminium and aluminium-rich alloy coatings (55%Al/Zn) provide cathodic protection to the steel substrate only in atmospheres that are highly contaminated with chloride ions (>100 mg Cl⁻ m⁻² day⁻¹) where these coatings become active.     

Corrosion behaviour of HVOF-sprayed Co–Cr–W–C coating in NaCl solution

Stellite 6 (Co–Cr–W–C) coating was deposited on carbon steel substrate by high-velocity oxyfuel spraying. The electrochemical corrosion behaviour of the coatings was investigated in 3.5% NaCl solutions at 25°C by means of polarisation studies and electrochemical impedance spectroscopy (EIS) measurements. The immersion time before corrosion tests was 0.5 and 24?h. The results showed that the corrosion rate of the coatings was lower than that of the steel substrate by one order of magnitude. An active–passive behaviour was observed during anodic polarisation of the coatings at both immersion times. The degree of substrate attack after polarisation tests of coated samples was not considerable. EIS measurement showed that two-time constants were observed in Nyquist plots of the coatings.     

O3/Cl-复合大气环境中Q235B钢的腐蚀演化特性

采用干/湿交替的实验方法模拟大气腐蚀过程。运用X射线衍射、电化学阻抗谱以及极化曲线等手段，研究了O₃/Cl^-复合大气环境中Q235B钢的腐蚀演化特性。结果表明，O₃和Cl^-的协同作用对Q235B钢的腐蚀有明显的促进作用，其腐蚀速率随着模拟环境中Cl^-含量的增加而增大。腐蚀演化特性方面，Q235B钢在腐蚀的初期阶段腐蚀速率最大，中期阶段腐蚀速率迅速下降，而到后期阶段腐蚀速率又有所提高。相比于不含O₃的大气环境，当Cl^-浓度较低时，O₃和Cl^-对Q235B钢腐蚀产物组份的影响并不明显。而当Cl^-浓度较高时，O₃和Cl^-能明显促进β-FeOOH的生成而抑制α-FeOOH和γ-FeOOH的生成。这说明O₃/Cl^-复合大气环境能促进Q235B钢的大气腐蚀与锈层相组分变化密切相关。