Anticorrosion organic coating with layered double hydroxide loaded with corrosion inhibitor of tungstate

Mg–Al layered double hydroxides, loaded with tungstate anions, were synthesized via the co-precipitation method. The obtained compounds were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), inductively coupled plasma (ICP), and transmission electron microscopy (TEM), respectively. The ICP results demonstrated the partial anion-exchange process, involving the release of tungstate anions from layered double hydroxide by the chloride anions. Polarization measurements showed that the filtrate as electrolyte possessed a low corrosion current density value of 3.042 μA/cm². The electrochemical impedance spectroscopy (EIS) exhibited that the coating could effectively protect the alloy from corrosion. The function of the layered double hydroxide loaded with tungstate doped in organic coating was also discussed.     

The effect of mixture of mercaptobenzimidazole and zinc phosphate on the corrosion protection of epoxy/polyamide coating

The protective performance of solvent-borne epoxy/polyamide coatings formulated with zinc phosphate anticorrosion pigment was improved through the addition of 2-mercaptobenzimidazole as an organic corrosion inhibitor. In addition to determining the optimum percentage of mercaptobenzimidazole, the electrochemical impedance spectroscopy data could show the influence of inhibitor concentration on the epoxy behavior within 35 days of immersion in 3.5 wt% NaCl solution. The improved corrosion protection and adhesion strength in the presence of the pigment and inhibitor were connected to the deposition of a protective layer at the coating/substrate interface which might limit active zones for electrochemical reactions. The precipitation was confirmed using electrochemical impedance spectroscopy, polarization curves and SEM/EDX surface analysis.     

The influence of pH on corrosion inhibitor selection for 2024-T3 aluminium alloy assessed by high-throughput multielectrode and potentiodynamic testing

This paper complements our recently published work on the development of a high-throughput scanning technique for corrosion inhibitors named multielectrode. The multielectrode set-up, fully described in the previous work, combines nine pairs of different metals in a single multi-metal electrode configuration. In the working procedure a fixed potential is applied between identical metallic electrodes while immersed in an inhibitor solution, without the use of a reference electrode. The current flowing between the electrodes is measured and the combined electrochemical response of the anodic and cathodic reactions, with and without inhibitor, is then characterized. The methodology allows approximately 30 electrochemical experiments to be performed per hour, the rapid identification of inhibitors able to protect different metals, and the rapid detection of the optimal inhibitor concentration.The present work evaluates the influence of solution pH on the anticorrosion performance of three different inhibitors (CeCl₃, Ce(dbp)₃ and K₂Cr₂O₇) on 2024-T3 aluminium alloy (AA2024-T3) by means of conventional potentiodynamic polarization analysis and the multielectrode technique reported previously. The usefulness of the high-throughput multielectrode technique to detect the influence of the solution pH on the anticorrosive performance of different inhibitors has been studied and its correlation with traditional potentiodynamic polarization testing evaluated. The possible reasons for non-correlation between techniques are studied, and those considered important, highlighted. The combined dependence of corrosion inhibition on factors including pH, inhibitor type, and metal cross-contamination was also investigated showing that the multielectrode is a robust technique to detect efficiency changes due to pH variations.     

A study of the corrosion resistance of a waterborne acrylic coating modified with nano-sized titanium dioxide

The incorporation of nano-sized inorganic pigment particles into organic coatings may offer the potential for improving many of their properties, including corrosion resistance, at relatively low loadings. In the present research, titanium dioxide with a crystallite size of 5-10 nm was added to a waterborne organic primer formulation at loadings from 0.1 to 5% (w/w) and applied to hot-dip galvanized steel (HDG) panels. The corrosion resistance of the modified coatings was measured by neutral salt spray corrosion testing and electrochemical impedance spectroscopy (EIS), with an unpigmented film tested for comparison. 3% (w/w) TiO₂ appeared to produce an optimum improvement in the corrosion resistance.     

Mercapto functional azole compounds as organic corrosion inhibitors in a polyester-melamine coating

The corrosion inhibition of two mercapto functional azole compounds including 2-mercaptobenzimidazole (MBI) and 2-mercaptobenzoxazole (MBO) for mild steel in 1 M NaCl solution was studied by electrochemical impedance spectroscopy (EIS), then their impact on the protective performance of a polyester-melamine coating was evaluated using salt spray. EIS results revealed a higher corrosion inhibitive activity of MBI compared to that of MBO. Corrosion products were examined by SEM-EDX and FTIR. The results showed modification of the corrosion products in the presence of MBI and MBO. The salt spray results revealed an improved corrosion protection of the coatings formulated with MBI and MBO. There was almost no impact of MBI and MBO on adhesion strength and glass transition temperature of the coatings, meaning that their impact on the corrosion protection performance of the formulated coating could only be attributed to their effect on the corrosion products.     

Corrosion protection mechanisms of carbon steel by an epoxy resin containing indole-3 butyric acid modified clay

This work is an extension of studies into the mechanisms of corrosion protection of mild steel by an epoxy resin containing organically modified clay (Hang et al. [1]; Truc et al. [2]). In a previous study (Truc et al. [2]), it was shown that indole-3 butyric acid (IBA)-modified clay improved the corrosion performance of epoxy. In the present study, it was shown that the IBA is an anodic inhibitor and its efficiency was about 93%. Exfoliation and dispersion of the IBA-modified clay in the epoxy coating were checked by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The improvement of the corrosion performance of the epoxy coating containing IBA-modified clay by comparison with pure epoxy coating was confirmed for a low film thickness (10 μm). Local electrochemical impedance measurements performed on scratched samples revealed the inhibitive action of IBA at the carbon steel/coating interface. It was shown that the inhibitor release from the IBA-modified clay was favoured for high pH values. Thus, in neutral media, the corrosion process which induces a local increase of pH will increase the self-healing performance.     

Improvement of corrosion protective performance of organic coating on low carbon steel by PEO pretreatment

Employing pretreatment is a pressing need for preparing anticorrosive coatings on carbon steels. However, conventional pretreatments are usually based on Cr, P and some other toxic elements, which are harmful to human body. For this reason, green and environmental techniques attract more and more attention. In this paper, plasma electrolytic oxidation (PEO) process was used as a pretreatment to fabricate an underlayer for the organic coating on low carbon steel. The anticorrosive performance of the organic coated samples with and without PEO pretreatment was studied by potentiodynamic polarization, ac/dc/ac electrochemical impedance spectroscopy, salt spray and immersion tests, respectively. Results show that the PEO process produces an oxide layer with porous and rough surface structure on the low carbon steel substrate. The porous and rough PEO layer is beneficial for enhancing the adhesion strength and thickness of the organic topcoatings. The organic coated sample with PEO pretreatment exhibits improved corrosion resistance and longer service life in corrosive environment compared to that without PEO pretreatment.     

Effective corrosion protection of 8090 alloy by cerium conversion coatings

Conversion treatments based on immersion in Cr(VI) aqueous solutions are key technologies that combine low cost, easy application and high performance. However, they are environmentally problematic due to their carcinogenity and genotoxicity. Among the potential alternatives, treatments based on rare-earth compounds have drawn attention due to the stability of their oxides and their environmental acceptability. Despite the amount of work published, there is not yet an industrially suitable alternative treatment for aircraft aluminium alloys that is able to provide the required corrosion protection. A common feature of these alloys is the high level of copper in their chemical composition. Although the presence of copper in an alloy may enhance cerium deposition, high copper content alloys (AA2024, AA7075) have proven the most difficult to protect with Ce conversion coatings.In the present work, a commercial 8090-T8 aluminium alloy containing 1.15 weight percent (wt.%) Cu was coated with a Ce conversion coating at room temperature from a Ce bath without prior pretreatment of the specimens. Polarisation curves revealed that the presence of a cerium conversion coating (CeCC) reduces by two orders of magnitude the corrosion rate of the AA8090 alloy in a sodium chloride solution. Impedance measurements exhibited capacitive behaviour for the CeCC up to 216 h, showing that the cerium layer protects the bare alloy in the aggressive solution.Electrochemical tests have therefore revealed that these conversion layers afford long-lasting protection; withstanding up to 168 h in Salt Spray test.     

Influence of the curing temperature of a cataphoretic coating on the development of filiform corrosion of aluminium

Aluminium alloys are known to be particularly sensitive to filiform corrosion. The initiation of this particular type of corrosion is related to different parameters such as the presence of defects, the permeability of the coating to water and oxygen, the adherence of the paint system and the presence of salts.

In this work, the filiform corrosion resistance of Al 6016 substrates coated with a cataphoretic paint was studied. The curing of the coating was performed at different temperatures (185, 175, 165, 155 and 135 °C) in order to modify its mechanical properties and its permeability to oxygen.

The paint properties were studied by different techniques allowing the estimation of the degradation of the metal–primer system and giving some information about intrinsic paint properties.

The corrosion protection of the coating was evaluated by a normalized filiform corrosion test and by electrochemical impedance spectroscopy on scratched samples. The glass transition value and the internal stresses of the cataphoretic coatings obtained for different curing temperatures were determined by a stressmeter equipment.

This study enabled us to underline the influence of the curing temperature on the intrinsic properties of the coatings such as the glass transition temperature, the internal stresses, the adherence, the permeability and the corrosion protection properties.     

Graphene modified phosphate-based metal/ceramic composite coating for corrosion protection in the high-temperature marine environment

Graphene-modified phosphate-based metal/ceramic composite coatings were prepared for corrosion protection in the high-temperature marine environment. The morphology and structure of the coating were observed by SEM, and the high-temperature anticorrosion performance of the coating was analyzed by electrochemical measurement and salt spray-high temperature cycle test. The results showed that the addition of 0.1 wt% graphene could bridge the aluminum particles inside the composite coating and extend the sacrificial anode protection time of the coating in the 3.5 wt% NaCl solution from less than 4 days to more than 8 days, thus avoiding the local failure of the coating and improving the anticorrosion performance. Besides, the addition of graphene nanosheets at low content also enhanced the physical barrier effect of the coating and prolonged the penetration path of the corrosive medium without destroying the structure of the composite coating.     

The effect of organosilane on corrosion resistance of epoxy coating containing cerium nitrate

Structure and corrosion resistance behavior of epoxy coating containing cerium nitrate in different amounts of γ-glycidoxypropyltrimethoxysilane (γ-GPS) were investigated. Corrosion resistance ability of coating systems was characterized by using electrochemical impedance spectroscopy and polarization techniques. Also atomic force microscopy was used to evaluate dispersion of cerium nitrate in the presence of γ-GPS. Furthermore, the effect of γ-GPS on flexibility of coatings was studied by using the cupping test. Increment of 10?wt.% of γ-GPS into the coating formulation led to the superior dispersion of cerium nitrate and also highest corrosion protection performance.     

Electrochemical deposition and characterization of ZnCo alloys and corrosion protection by electrodeposited epoxy coating on ZnCo alloy

ZnCo alloys electrochemically deposited on steel under various deposition conditions were investigated. The influence of deposition current density, temperature and composition of deposition solution on the phase structure and corrosion properties of ZnCo alloys were studied. It was found that ZnCo alloy obtained from chloride solution at 5 A dm⁻² showed the best corrosion properties, so this alloy was chosen for further examination. Epoxy coating was electrodeposited on steel and steel modified by ZnCo alloy using constant voltage method. The effect of ZnCo alloy on the corrosion behavior of the protective system based on epoxy coating is interpreted in terms of electrochemical and transport properties, as well as of thermal stability.     

镍/纳米二氧化硅纳米复合镀层耐腐蚀性能的研究

制备了纳米氧化硅镍复合镀层材料,并利用静态浸泡法对纯镍镀层和由镀液中不同微粒含量制备的复合镀层样品的耐蚀性能进行了研究,讨论镀液中纳米微粒含量对镀层抗蚀性能的影响。并用扫描电镜观察镀层的表面形貌。     

聚氨酯改性环氧富锌防腐涂料的制备

通过正交实验法,以涂膜的吸水率为依据,确定了制备聚氨酯改性环氧共聚物时,聚氨酯的最佳用量,适当的反应时间和反应温度,固化剂的最佳添加量;并通过浸泡腐蚀失重法,确定了锌粉的最佳含量。对涂膜进行了红外光谱、极化曲线和扫描电镜分析,对比检测了未改性环氧富锌防腐涂料、聚氨酯改性环氧富锌防腐涂料的各方面性能。结果表明,聚氨酯改性环氧富锌防腐涂料具有较高的机械强度、低吸水率、良好的附着力和耐化学腐蚀性能。     

EIS法研究3种配套涂层体系的腐蚀电化学行为

采用电化学阻抗谱(EIS)研究了由水性无机富锌底漆、环氧中间漆和氯化橡胶面漆3种涂料配套而成的3种不同涂层体系在3.5%NaCl溶液中的电化学腐蚀行为,考察了氯化橡胶面漆、水性无机富锌底漆／氯化橡胶面漆、水性无机富锌底漆／环氧中间漆／氯化橡胶面漆这3种涂层体系的阻抗谱在浸泡过程中的演化并据此比较了3种涂层体系的防护性能。结果表明,两涂层体系的防护性能比单涂层的还要差,三复合涂层体系的防护性能最好。根据涂层腐蚀电化学阻抗谱特征推测,中间漆在三复合涂层体系中起到了使底漆和面漆结合更加紧密的桥梁作用。     

防腐环氧树脂粘接涂层的研究进展

简要介绍了粘接涂层防腐的几种机制。从填料的发展、缓蚀剂的发展、EP(环氧树脂)基体的发展和导电EP粘接涂层的发展等方面,介绍了国内外防腐EP粘接涂层的研究进展。最后基于环保性趋势对防腐EP粘接涂层的发展方向作了展望。     

环氧有机涂层对锌铁合金镀层耐蚀性的影响

利用腐蚀浸泡实验、失重法和交流阻抗谱分析等方法研究了环氧有机涂层对Q235钢电镀锌铁合金镀层耐蚀性的影响。结果表明,Q235钢基体、Q235+Zn–Fe合金镀层试样和Q235+Zn–Fe合金镀层+环氧有机涂层试样在5%NaCl溶液中浸泡504 h后,腐蚀速率分别为0.068 0、0.040 0和0.018 0 mm/a。涂覆环氧有机涂层至少能使锌铁合金镀层的防腐性能提高2倍,从而延长基体材料的使用寿命。     

Influence of uniaxial deformation on the corrosion performance of pre-coated packaging steel

The influence of uniaxial deformation on the corrosion performance of electrolytic chromium-coated steel (ECCS) in both the presence and absence of a polymer coating was studied using scanning electron microscopy (SEM), open circuit potential (OCP), potentiodynamic polarization (PP) measurements and electrochemical impedance spectroscopy (EIS). The individual and combined contribution of chromium-chromium(III) oxide and the polymer coating was investigated. Specimens were uniaxially deformed to maximum strains of 5, 10 and 25%, respectively. After deformation Lüders bands were observed on the surface of the metal substrates. The corrosion resistance of the ECCS was shown to be better than that of the bare steel, due to the protective properties of the chromium-chromium(III) oxide layer on the surface. The corrosion resistance of the ECCS was found to decrease with strain, to be attributed to the introduction of local defects in the coating leading to increasing exposure of the more active underlying steel with deformation. The PETG (a glycol-modified amorphous PET) coating as such proves to be a very effective barrier layer in protecting the underlying substrate, however, in combination with the bare steel its protective properties decrease with time of exposure and deformation. Combining the individual contributions of the chromium-chromium(III) layer and the PETG coating it was shown that the corrosion performance of the polymer-coated ECCS is significantly better than the polymer-coated bare steel after deformation, which can be also attributed to the good corrosion resistance of the chromium-chromium(III) oxide layers and the improved adhesion of the coating.     

Effect of SO4 on the corrosion behavior of cerium-based conversion coatings on galvanized steel

The cerium-based conversion coatings on galvanized steel were investigated and the influence of SO₄²⁻ on the corrosion behavior was evaluated. The coatings were prepared by a simple immersion of galvanized steels in an aqueous solution composed of cerium nitrate and sodium sulfate. The corrosion behavior was studied by means of potentiodynamic polarization measurements and neutral salt spray tests. The addition of SO₄²⁻ to the coating solution considerably improved the corrosion resistance of the conversion coatings. Atomic force microscope observation shows that deposits prepared from the solution with SO₄²⁻ have smaller crystalline size than those prepared without SO₄²⁻. The results of X-ray photoelectron spectroscopy and titration curves demonstrate that SO₄²⁻ ions are incorporated in the coating during the conversion process. This indicates that SO₄²⁻ acts as a grain refiner and/or growth inhibitor, thus enhancing the corrosion resistance.     

高效咪唑啉污水缓蚀剂的合成及现场应用

以松香、蓖麻油与二乙烯三胺在一定条件下合成咪唑啉类MB缓蚀剂，由于松香型咪唑啉和蓖麻油型咪唑啉，化学结构和相对分子质量各异。两者相互补充，能够在金属表面形成致密的保护膜。近几年来，使用MB缓蚀剂处理胜利东辛采油厂污水，使得腐蚀速率控制在较低水平，通过室内评价与现场应用实验，证明其有高效的缓蚀作用。