Emeraldine base as corrosion protective layer on aluminium alloy AA5182, effect of the surface microstructure

AA5182 aluminium alloy cold rolled samples were coated by thin films of emeraldine base (EB) obtained from a 5% solution in N-methylpyrrolidinone. Accelerated corrosion tests prove this coating very effective for corrosion protection of aluminium alloys in neutral environment. This study underlines the prominent role of surface cathodic intermetallic particles in pit initiation and coating break down in enhanced corrosion conditions and suggest that, beside the EB barrier properties, the enhanced corrosion resistance observed on the EB coated samples could partly arise from two other mains factors:

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a weak redox activity of the polymer which passivate the metal,

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a proton involving self-healing process taking place at the polymer-metal interface, which contributes to delay local acidification in first steps of corrosion on EB coated aluminium surfaces.

     

Role of dissolved oxygen diffusion in coating defect protection by emeraldine base

The corrosion protection of emeraldine base (EB) on mild steel in the artificial defect exposed to 1 wt% NaCl solution was studied using in situ optical microscope and scanning electron microscopy (SEM). The EB coating displayed good corrosion protection on the exposed bare steel, which was difficult to understand by traditional anodic protection mechanism or inhibitory protection mechanism, or cathodic protection mechanism, since steel usually cannot be passivated in brine, and EB coating cannot release inhibitory anions to protect exposed bare steel, and further, the galvanic coupling measurement demonstrates that EB cannot provide cathodic protection to exposed bare steel. The importance of dissolved oxygen diffusion caused by EB in corrosion protection was disclosed in this paper, a related protection model was therefore proposed, which was qualitatively verified by corresponding electrochemical measurements.     

The effect of epoxy coating containing emeraldine base and hydrofluoric acid doped polyaniline on the corrosion protection of AZ91D magnesium alloy

Corrosion protection of epoxy coatings containing emeraldine base polyaniline (PANI) or hydrofluoric acid doped PANI on AZ91D magnesium alloy were studied by EIS and Pull-Off Adhesion Test. The results indicated that the addition of emeraldine base PANI or hydrofluoric acid doped PANI could improve the corrosion resistance of epoxy coating. The epoxy coating containing hydrofluoric acid doped PANI had the best performance of the corrosion protection among three systems under investigation. The corrosion product film was analyzed by XPS indicating that PANI changed the chemical structure of the corrosion film. The protective mechanism imparted by PANI was discussed.     

A study on mechanism of corrosion protection of polyaniline coating and its failure

Polyaniline (PANI) coatings were electrochemically deposited on substrates of stainless steel and platinum in solutions of 0.2 M H₂SO₄ and 0.1 M aniline by cyclic voltammetry. The corrosion protection of the PANI coatings and their failure were investigated in 0.2 M H₂SO₄ solution. It was observed that the corrosion protection ability of the coating to steel substrate was increased with the increase of the coating thickness. The corrosion protection ability was mainly attributed to the passivating effect of PANI due to its oxidizing ability in its emeraldine state. During its operation, the PANI coating in emeraldine state tended to gradually lose its corrosion protection ability. This gradual failure of the PANI coating, but faster than expected, was confirmed to be related to a gradual reduction of the emeraldine PANI and a gradually increased resistance between the PANI coating and the stainless steel substrate. These findings lead to a new mechanism for the corrosion protection of PANI coating and its failure.     

Electrochemical impedance spectroscopy investigation of chlorinated rubber‐based coatings containing polyaniline as anticorrosion agent

Corrosion protection of mild steel by a newly developed chlorinated rubber (CR)‐based coating system containing the inherently conductive polymer polyaniline (PAni) as an anticorrosion agent was studied. The synthesis of PAni and preparation of CR‐based paint containing this polymer are described herein. The corrosion behavior of mild steel samples coated with a CR resin, CR/PAni‐EB (emeraldine base), CR/PAni‐ES (emeraldine salt), and CR/DBSA‐doped PAni were investigated in 3.5% NaCl solution. For this purpose, electrochemical impedance spectroscopy and corrosion potential versus time measurements were utilized. It was found that the addition of the two forms of PAni, doped and undoped, to the CR resin increased its corrosion protection efficiency.     

Polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene) as additives of organic coatings to prevent corrosion

The aim of this work is to compare the protection against corrosion imparted by different conducting polymers when these materials are used as anticorrosive additives in the formulation of conventional epoxy paints. Specifically, the polymers employed as anticorrosive additives are polyaniline emeraldine salt, polyaniline emeraldine base, polyaniline emeraldine salt composite with carbon black, polypyrrole composite with carbon black and poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonate). Initially, the structural, thermal and mechanical properties of the unmodified epoxy paint as well as the modified coatings, obtained by the addition of 0.3 wt.% of conducting polymers, have been characterized. After this, controlled accelerated corrosion assays in an aggressive solution medium were developed using coated steel panels. Results indicate that the protection against corrosion imparted by the formulations modified by the addition of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonate), polyaniline emeraldine salt and, especially, polyaniline emeraldine base is significantly higher than that of the unmodified paint. In contrast, the use of conducting polymer composite with carbon black reduces the efficacy of the coating. Results indicate that some conducting polymer compositions should be considered as a suitable alternative to replace inorganic anticorrosive pigments currently used in paint formulations.     

Long-term anticorrosion behaviour of polyaniline on mild Steel

Anticorrosion performances of polyaniline emeraldine base/epoxy resin (EB/ER) coating on mild steel in 3.5% NaCl solutions of various pH values were investigated by electrochemical impedance spectroscopy (EIS) for 150 days. In neutral solution (pH 6.1), EB/ER coating offered very efficient corrosion protection with respect to pure ER coating, especially when EB content was 5-10%. The impedance at 0.1 Hz of the coating increased in the first 1-40 immersion days and then remained constant above 10⁹ Ω·cm² until 150 days, which in combination with the observation of a Fe₂O₃/Fe₃O₄ passive film formed on steel confirmed that the protection of EB was mainly anodic. In acidic or basic solution (pH 1 or 13), EB/ER coating also performed much better than pure ER coating. However, these media weakened the corrosion resistance due to breakdown of the passive film or deterioration of the ER binder.     

The correlation between molecular structure and tendency to maintain or to destroy iron passivity in aqueous solution—II. Activation effectiveness of anions present together with a corrosion inhibitor and/or an oxidant

The relative tendency of 11 anions to destroy iron passivity has been assessed from open circuit potential measurements and/or from corrosion tests with 11 corrosion inhibitors and 4 oxidants.Sulphide, EDTA (sodium salt at pH 7) and sulphate were usually the most effective, and trifluoroacetate the least effective activators with dissolved air as oxidant. Chloride was the most effective in systems, giving higher redox potentials than that produced by dissolved air. Monatomic anions gave an approximate correlation between charge density and activation effectiveness. That sodium EDTA is an activator and strongly bound metal-EDTA complexes are inhibitors appears to be in accordance with the electrostatic hypothesis.There is some support for the electrostatic hypothesis of passivity stabilisation, but complicating factors intervene. The results indicate that these include hydrogen bonding, and the attraction between activator anions and other solution species, both of which tend to prevent adsorption of the anion at the metal-oxide interface.     

Electrochemical behavior of mild steel coated by polyaniline doped with organic sulfonic acids

A comparison of electrochemical behavior was made of coatings of pure undoped PANI cast from solution and this coating after doping as a film on the substrate. These were also compared to coatings of pure PANI/sulfonic acids adducts formed from the outset in the doped state through casting from xylene or chloroform solutions. The results obtained allowed to assume that the formation of protective iron oxide layers occurs mainly during the coating of pure undoped PANI (emeraldine base). During the doping stage a modification of these layers obviously proceeds leading to a change of the corrosion currents of the whole coating system. As a consequence, the formation of pure doped PANI coatings by casting doped PANI from solutions cannot give as good of results as does the two stage process.     

本征态聚苯胺的防腐性能

研究了分散的颗粒状本征态聚苯胺(EB)对冷轧钢(CRS)的腐蚀防护作用，在去离子水或NaCl溶液的作用下，EB颗粒可在CRS表面形成一层致密的氧化物钝化层，该氧化物层使CRS的腐蚀电位升高了200mV，并显著降低了腐蚀电流密度．在3．0mass％NaCl溶液中，单独的EB膜稳定性较差，不能提供有效的防腐性能，分散在环氧树脂中的EB保持了EB的氧化-还原特性，这种涂层材料能使CRS钝化，具有极好的稳定性，因而可提供极好的防腐性能．EB的存在使环氧树脂涂层的阻隔作用下降，因此需要涂敷较好阻隔作用的面漆．在含有EB的环氧树脂涂层上涂覆具有良好阻隔作用的面漆，可显著提高其防腐性能．     

铁质文物腐蚀防护技术研究进展

中国是有着五千年灿烂文化的文明古国和文化遗产大国。文物保护是中华儿女传承古老文明的历史责任。铁质文物在中国拥有漫长的历史，但由于铁作为金属的活泼性较强，易腐蚀，现存的铁质文物面临保存现状差且防护难度大的严峻挑战，因此如何对铁质文物进行系统性防护成为研究工作的重点。鉴于目前铁质文物腐蚀防护技术受到国内学者和文物界越来越多的关注，基于大量的文献调研和长期对国内外腐蚀防护技术研究动态的跟踪，对铁质文物腐蚀防护技术的研究进展进行了总结。首先，结合铁质文物具体保护实例简介了铁质文物的腐蚀机理。其次，讨论了铁质文物传统的腐蚀防护技术，主要包括除锈技术、脱盐技术、缓蚀技术和封护技术。除锈技术主要分为物理除锈技术和化学除锈技术，对比了两者的技术优势和劣势，重点阐述了激光清洗的作用机理以及除锈效果;脱盐技术的方法众多，主要通过实例介绍了索氏提取法和碱性溶液浸泡法的脱盐机理;缓蚀技术的核心为缓蚀剂，阐述了多种缓蚀剂对不同铁质文物的缓蚀效果;封护技术主要介绍了微晶石蜡、丙烯酸树脂和氟碳涂料3种材料在铁质文物上的应用。随着材料科学的发展，在铁质文物表面制备防护性涂层可实现对基体的有效保护，但由于金属涂层制备技术多以激光束、等离子束、电子束等高能量密度束为热源，导致涂层制备过程热输入过大，对铁质文物基体的损伤较大。根据铁质文物的防护性要求——“不改变文物原状”与“最小干预”原则，介绍了一种基于低温环境下将微米级金属粉末或复合粉末加速至超音速状态并沉积于基体材料表面形成涂层的新型表面防护技术——冷喷涂技术，重点介绍了几种不同金属基材料在铁碳合金表面形成涂层的实际性能，主要表现为显微组织均匀致密，且与基体之间形成了较好的界面结合，有望应用于铁质文物的修复与防护领域。最后，指出了铁质文物腐蚀防护研究进展尚存的关键问题，并对铁质文物腐蚀防护技术的发展前景进行了展望，为文物保护工作者的研究实践提供新思路。     

Corrosion protection with polyaniline and polypyrrole as anticorrosive additives for epoxy paint

Accelerated immersion tests have been carried out in the laboratory to investigate the performance of polyaniline emeraldine salt and polypyrrole composite with carbon black as additives of an epoxy paint coating. The steel panels coated with paint modified with polyaniline emeraldine salt presented the best protection after 720 h of exposure in 3.5% NaCl solution. The results indicated that this conducting polymer might works as both corrosion inhibitor and adhesion promoter. The protective mechanism imparted by conducting polymers is also discussed.     

Corrosion inhibition of aluminum alloy in chloride mediums by undoped and doped forms of polyaniline

Corrosion inhibition of Al 3003 alloy by pure undoped PANI (emeraldine base) and PANI doped with p-toluene-sulfonic, camphorsulfonic and dodecylbenzenesulfonic acids was investigated. Corrosion resisting properties of PANI coatings with an artificially created hole defect were evaluated by electrochemical impedance spectroscopy (EIS) in aqueous 3.5% NaCl and 0.1 N HCl solutions. The highest corrosion inhibition factor was obtained for undoped PANI being equal to 12 and 4.4 in neutral and acidic media, respectively. The results indicated that corrosion protection of the bare aluminum alloy surface resulting from a defect of the PANI coating is in line with an increase of the thickness of the oxide layer protecting the aluminum alloy surface. The efficiency of corrosion protection of mild steel and aluminum alloy by polyaniline coatings was compared.     

The development of the corrosion resistance of an Fe-Zn alloy coating on the basis of the behaviour of the corrosion product

Nickel was selected as an additional element to improve the corrosion resistance of an Fe-Zn alloy coating, from two values of the corrosion current and from the compactness of the adherent corrosion layer determined on a zinc specimen in NaCl solution containing iron and other metallic ions. About 1 wt% Ni added to the Fe-Zn alloy coating had an effect on the electrodepositing process of zinc crystals which thereby inhibited powdering of coating layer, and enhanced the corrosion resistance of the coating.     

A magnetic susceptibility study of emeraldine base polyaniline

Paramagnetic spins are found even in carefully synthesized samples of emeraldine base polyaniline. We report here magnetic susceptibility data up to a temperature of 475 K on a number of emeraldine base samples that were synthesized at different oxidant to monomer ratios. All the samples, although electrically insulating, show the presence of Pauli-like susceptibility. A simple albeit physically realistic model involving spin-pairs is shown to lead to such a dependence on temperature. The analysis of the data indicates that polarons in emeraldine base are created in pairs and that the intra-pair interactions encompass a broad distribution of antiferromagnetic exchange couplings.     

电弧喷涂Al-Zn-Si-RE合金涂层在3.5%NaCl溶液中的电化学腐蚀行为(英文)

采用电弧喷涂方法在低碳钢表面获得高铝含量的Al-Zn-Si-RE涂层。通过测量Al-Zn-Si-RE涂层在3.5%NaCl溶液中的动电位极化曲线,腐蚀电位-时间曲线和电化学阻抗谱,系统地研究涂层的电化学腐蚀行为。通过将测量电化学阻抗谱拟合成等效电路图,研究涂层在3.5%NaCl溶液中浸泡不同时间的阻抗行为。结果表明:Al-Zn-Si-RE涂层与Zn-15Al涂层具有相似的极化行为,阳极极化曲线均无钝化特征,仅呈现出活性溶解,但其腐蚀性能优于Zn-15Al涂层。Al-Zn-Si-RE涂层可以给钢基体提供有效的牺牲阳极保护作用,且牺牲阳极保护作用在涂层腐蚀过程中占主导地位。此外,腐蚀电位-时间曲线和电化学阻抗谱结果表明:在浸泡过程中存在点蚀-溶解-再沉积、活化溶解、阴极保护、腐蚀产物引起的物理屏蔽和涂层失效五个腐蚀阶段。     

Corrosion resistance of nanostructured magnesium hydroxide coating on magnesium alloy AZ31: influence of EDTA

A hexagonal nanosheet Mg(OH)_2 coating was prepared through a one-step hydrothermal method using LiOH solution as mineralizer and then modified by ethylenediaminetetraacetic acid(EDTA) to minimize the rapid corrosion of AZ31 Mg alloy.The performance of the coating was evaluated using electrochemical technique,hydrogen evolution measurements, nanoscratch test,Fourier-transform infrared spectroscopy(FTIR), X-ray diffraction(XRD) patterns and field-emission scanning electron microscopy(FESEM).The results suggested that the corrosion rate of bare AZ31 Mg alloys was significantly reduced by one and two orders of magnitude through the protection from Mg(OH)_2 coating and modification with EDTA(i.e., EDTA-Mg(OH)_2 coating), respectively.FESEM micrographs indicated that the modification in EDTA elicits to the formation of an EDTA-Mg(OH)_2 composite with a thickness as twice as that of as-prepared Mg(OH)_2 coating.Nanoscratch tests revealed strong adhesion between the composite or Mg(OH)_2 coating and the substrate.The study of formation and corrosion mechanisms of the coatings manifested that Mg(OH)_2 was first formed near the intermetallic compound AlMn particles and gradually covered the entire surface, wherein the AlMn particles played an important role in the coating growth process.And it also proved that EDTA accelerated the formation of Mg(OH)_2.     

Electropolymerization of PANI coating in nitric acid for corrosion protection of 430 SS

A smooth and adherent polyaniline (PANI) coating was electropolymerized in HNO₃ solution by cyclic voltammetry in order to protect the ferritic and economic 430 stainless steel (SS) from corrosion. The corrosion resistance was evaluated in 3.5 wt.% NaCl solution by anodic polarization, potentiodynamic polarization, and electrochemical impedance spectroscopy. The PANI coating shifts the corrosion potential of SS to the passive region and provides a strong and steady corrosion resistance. A low growth rate leads to a compact PANI coating that acts as a good physical barrier. However, the strong corrosion inhibition is mainly attributed to the dense oxide layers formed by the catalytic effect of PANI at the polymer/metal interface. The composition of the oxide layers was analyzed via depth profiling using X-ray photoelectron spectroscopy alternating with sputtering. Compared with layers formed on uncoated SS, the iron and chromium oxide layers under the PANI are thinner and denser, absorbing less oxygen, and providing a stronger corrosion inhibition.     

The synergistic effect of anions and the ammonium cation on the inhibition of iron corrosion in acid solution

The synergistic effect of various anions and the tetra-n-butylammonium cation on the inhibition of iron corrosion in 1 M HClO₄ and their joint adsorption on iron were studied by using an impedance and a polarization technique. Surface coverage obtained from double layer capacitance showed joint adsorption of the anion and cation on the iron surface. Assuming competitive adsorption of these ions at the interface, the synergism of corrosion inhibition and joint adsorption were estimated using a parameter calculated from the inhibition efficiencies and the surface coverages of the anion and/or cation. The synergistic effect was shown for all of the anions and cation examined.     

Microstructure and corrosion resistance of simultaneous Al-Fe coating on copper by pack cementation

Simultaneous Al-Fe coatings on copper were prepared by pack cementation to investigate the microstructure and corrosion resistance. The cross-section of prepared specimen was analyzed by scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). Then the cross-section of specimen corroded by solution of ferric chloride in ethanol was evaluated using SEM and X-ray diffraction (XRD). The coating consists of an intermetallic layer and an interdiffusion layer, and the thickness of coating layer increases parabolically with holding temperatures from 730 °C to 900 °C. The aluminum content in the coating varies between 7.65 and 4.0% from the surface to the inside layer while the iron content varies between 2 and 0.5%. The coating layer is composed of а-Cu/Al solid solution with a small amount of iron. Alumina formed on the surface of the coating layer during corrosion provides very good protection for the coating layer in the corrosive atmosphere and enhances the corrosion resistance of the coating.