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.     

Corrosion protection of AA 2024-T3 by bis-[3-(triethoxysilyl)propyl]tetrasulfide in sodium chloride solution.: Part 2: mechanism for corrosion protection

The corrosion protection of AA 2024-T3 by films of bis-[3-(triethoxysilyl)propyl]tetrasulfide (bis-sulfur silane) was studied in a neutral 0.6 M NaCl solution using potential transient, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results showed that a highly crosslinked or dense interfacial layer that developed between the silane film and the aluminum oxide is the major contribution to the corrosion protection of AA 2024-T3. The formation of this interfacial layer heavily restricts pit growth underneath via retarding the transport of corrosion products, as well as effectively blocks a number of cathodic sites available for cathodic reactions.     

The corrosion resistance of hot dip galvanised steel and AA2024-T3 pre-treated with bis-[triethoxysilylpropyl] tetrasulfide solutions doped with Ce(NO3)3

The present work aims at evaluating the anti-corrosion behaviour of a novel pre-treatment based on bis-[triethoxysilylpropyl] tetrasulfide (BTESPT) doped with cerium nitrate for application on hot dip galvanised steel and AA2024-T3 substrates. The corrosion resistance was evaluated by electrochemical impedance spectroscopy (EIS) and by the scanning vibrating electrode technique (SVET), during immersion in NaCl solutions. The electrochemical results showed that the pre-treatment provides excellent corrosion protection to the substrates. Furthermore, the results evidenced improved protection comparatively to the use of undoped BTESPT pre-treatments, both for galvanised steel and AA2024-T3. This improvement is most likely due to enhanced barrier properties of the film and additional active corrosion protection originated from the inhibiting action of the cerium-based inhibitor impregnated in the silane matrix.     

镀锌钢板表面有机硅烷钝化膜的耐蚀性研究

通过极化曲线和交流阻抗测试技术,对比研究了镀锌钢板经单-BTESPT溶液处理、经添加铈盐的BTESPT溶液处理、先经y-APS预处理再经添加铈盐的BTESPT溶液处理所得3种有机硅烷钝化膜的耐蚀性.研究发现:有机硅烷成膜过程中添加一定量的铈盐,可通过其形成的三价和四价氧化物,修复单一硅烷膜存在的缺陷,从而提高防护效果;...     

A corrosion study of hot-dip galvanized steel sheet pre-treated with γ-mercaptopropyltrimethoxysilane

In the present work an organofunctional silane, γ-mercaptopropyltrimethoxysilane (γ-MPS), has been deposited on hot-dip galvanized cold rolled steel from different silane solution concentrations. Painted and unpainted silane treated samples were corrosion tested and painted samples were adhesion tested. The surface chemistry of the unpainted silane treated samples was investigated with AES, ToF-SIMS and EDS and the surface morphology was studied with SEM.The results show that the silane film thickness is dependent on the silane concentration in the silane solution and a higher silane concentration gives a thicker film. Moreover, thicker films tend to give films with a pronounced crack pattern and even detachment of film debris. Corrosion tests of unpainted samples show that γ-MPS can not work as a passivation treatment but gives a very good adhesion to the paint.     

Effect of alternating voltage treatment on the corrosion resistance of pure magnesium

Pure magnesium was treated by alternating voltage (AV) treatment technique. The optimal AV-treatment parameters for greatly improving corrosion resistance were determined by the orthogonal experiments. Polarization curves, electrochemical impedance spectroscopy (EIS), and scanning electrochemical microscopy (SECM) were performed to understand the effect of AV-treatment on the corrosion resistance of pure magnesium. AFM, contact angle measurement and XPS were employed to further investigate the influence of AV-treatment on the properties of the surface film formed on pure magnesium after AV-treatment. The results showed that a uniform and stable film was formed and the corrosion resistance of pure magnesium was greatly improved after AV-treatment. This was caused by the noticeable change of chemical structure and semi conducting properties of surface film after AV-treatment.     

石墨烯界膜剂在汽车防腐领域的推广应用

目的选用一种新型环保的金属防腐前处理新材料来代替目前所用的磷化液、钝化液等非环保界膜剂及稳定性差、耐腐蚀性不良的硅烷膜和陶瓷膜产品。方法鉴于石墨烯界膜剂是利用环境友好型的植酸(环己六醇磷酸酯)基化合物易于在金属表面自组装成膜的特点,经改性处理后,再辅以适当的催化剂、钝化剂等助剂以及改性石墨烯纳米添加剂,开发出的新一代绿色环保、价格低廉、操作简便、性能优异的革命性材料,以重卡金属零部件为基底进行石墨烯界膜剂成膜处理,考察了膜层的形貌、硬度、厚度及耐蚀性,并与前期处理的陶瓷膜、磷化膜比对。结果该产品成膜均匀、结合力好,使外涂层在金属耐蚀性、抗老化、抗冲击性等技术指标方面均达到或优于磷化膜、硅烷膜和陶瓷膜产品,且不会形成沉淀和废渣。结论该石墨烯界膜剂性能优异并且绿色环保,值得推广应用。     

Some particularities of the corrosion behaviour of Mg-Zn-Mn-Si-Ca alloys in alkaline chloride solutions

The influence of silicon and calcium on corrosion behaviour of Mg-6Zn-Mn alloys was investigated in alkaline solutions. The corrosion behaviour of the alloys with varied silicon and calcium content mainly depends on volume fractions and morphology of the intermetallics. In Cl-ion-free solutions silicon increased the corrosion resistance of alloys causing the growth of the surface passive film mostly composed of hydroxide products. Calcium had caused trouble to the formation of the stable protective film through the formation of Ca-Mg-Si intermetallics. In Cl-ion containing solutions intermetallic Ca-Mg-Si phase was responsible for extreme initial corrosion of Mg-6Zn-Mn-Si-Ca alloys.     

Effect of the reinforced boron carbide particulate content of AA6061 alloy on formation of the passive film in seawater

The effect of boron carbide (B₄C) reinforcement on the corrosion of AA6061 alloy was studied by investigating passive films formed in seawater. The higher passive current and its potential-dependence for these composites indicated formation of porous passive film. Electrochemical impedance spectroscopy (EIS) graph suggests that the alloy surface is partly or totally active. The formed passive film is n-type semiconductor junction in nature. The difference between corrosion potential (E_corr) and potential at zero charge (PZC) suggests that the chloride ions responsible for film breakdown exist within the passive film. A suitable mechanism is proposed for the passive film breakdown.     

Analytical characterisation and corrosion behaviour of bis-aminosilane coatings modified with carbon nanotubes activated with rare-earth salts applied on AZ31 Magnesium alloy

The present work investigates the corrosion behaviour of AZ31 Magnesium alloy (Mg AZ31) substrates pre-treated with a water soluble bis-aminosilane modified with multiwall carbon nanotubes (CNTs). Prior addition to the silane solution, the CNTs were submitted to a treatment in an aqueous solution containing cerium nitrate or lanthanum nitrate. The chemical composition of the treated CNTs and of the modified silane coatings was assessed by X-ray Photoelectron spectroscopy (XPS). The thickness and the morphology of the silane coatings were investigated by scanning electron microscopy (FEG/SEM).The pre-treatment of the Mg AZ31 was performed by dipping the metallic coupons in the silane solution modified with the CNTs. The electrochemical behaviour of the silane coated coupons was studied during immersion in 0.05 M NaCl solutions, using the scanning vibrating electrode technique.The electrochemical investigation showed that the activation of the CNTs with the rare-earth salt delays the corrosion activity of the Mg AZ31 substrates. The analytical and microscopic study suggested that the CNTs are homogeneously dispersed in the silane coating and that the CNTs act as support for inhibitor storage.     

Corrosion protection of AZ31 magnesium alloy by silane film of partly hydrolysed BTESPT

Abstract

The corrosion protective behaviour of bis-[triethoxysilylpropyl]tetrasulphide (BTESPT) silane film formed by partly hydrolysed BTESPT on AZ31 Mg alloy was investigated. Fourier transform infrared spectroscopy (FTIR) was used for structural characterisation of the silane film. Scanning electron microscope (SEM) and energy dispersive X-ray (EDS) analysis were used for observation of surface morphology and elements analysis of the film. The corrosion behaviours of bare and the silane treated AZ31 Mg alloy in 3·5 wt-%NaCl solution were studied using electrochemical polarisation test, electrochemical impedance spectroscopy (EIS) and immersion test. The results demonstrate that bare AZ31 Mg alloy endures severe corrosion even in NaCl water solution at pH 12, although the corrosion is lighter than that in neutral and acidic NaCl water solution, and that the BTESPT silane film can improve the corrosion protection performances of AZ31 Mg alloy and a lower corrosion rate correlated with higher pH.     

A comparative study of molybdate/silane composite films on galvanized steel with different treatment processes

Two types of molybdate/silane composite films were obtained on the surface of hot-dip galvanized steel sheets by either directly immersing in a solution containing silane and molybdate as additive (single-step process), or firstly immersing in a molybdate solution, then in a silane solution (two-step process). The chemical compositions and microstructures of the films were examined by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and reflection absorption infrared spectroscopy (RAIR). The corrosion resistances were investigated by electrochemical measurements and neutral salt spray (NSS) test. The results showed that the molybdate/silane composite film formed in the single-step process had a similar double-layer structure as that obtained in the two-step process. The inner layer was composed mainly of the elements O, Mo, Zn, and P, similar to the single molybdate film; whereas the outer layer was composed mainly of the elements C, O and Si, similar to the single silane film. Compared with the single molybdate or silane film, the corrosion current of the composite films was reduced and the impedance of the films was increased. Accordingly, the corrosion resistance of the composite films was remarkably enhanced to a level which was comparable to or even surpassing that of the conventional chromate passivation film.     

40Cr钢表面TEOS改进硅烷膜的制备及其耐腐蚀性能研究

目的为了提高钢材表面的耐腐蚀性能。方法采用含正硅酸乙酯(TEOS)的硅烷液,在40Cr合金钢表面制备TEOS改进硅烷保护膜,并采用正交试验法优选出了最佳TEOS改进硅烷液的工艺参数。采用扫描电子显微镜(SEM)、中性盐雾实验失重法、电化学阻抗法和极化法对其成膜性能和耐腐蚀性进行测试。结果 TEOS改进硅烷膜的耐硫酸铜腐蚀时间相对于硅烷膜提高了近50%。电化学极化测试可以看到TEOS改进硅烷膜的腐蚀电位正移,腐蚀电流密度大幅度下降至1.883×10-6 A/cm2。电化学阻抗谱测试中,在阻抗-频率Bode图中低频区,杂化硅烷膜试样的阻抗值大于硅烷膜试样的阻抗值,表现出良好的抗腐蚀性能;相角-频率Bode图显示TEOS改进硅烷膜在中高频区出现一个宽大的平台区,而且在中高频区相位角度数大于硅烷膜的相位角度数,表现出良好的容抗性能,表明TEOS改进硅烷膜能大幅度提高40Cr的耐腐蚀性。结论所制备的TEOS改进硅烷保护膜具有较好的成膜性,该硅烷膜坚实致密,且所形成的膜结构具有较好的耐腐蚀性能。     

Influence of hydrolysis time on the structure and corrosion protective performance of (3-mercaptopropyl)triethoxysilane film on copper

Films of (3-mercaptopropyl)triethoxysilane with different hydrolysis time were formed on copper surface. To evaluate the influence of hydrolysis time on structures and corrosion resistance of these films, Fourier-transform infrared spectroscopy, polarization curves, cyclic voltammetry and electrochemical impedance spectroscopy tests were performed on covered and uncovered copper specimens. Results indicate that the optimum hydrolysis time is 48 h. The film obtained in this case shows the best corrosion resistance in 3.5% (w) NaCl solution.     

双一[γ一（三乙氧基硅）丙基]四硫化物处理热镀铝锌层的耐蚀性研究

采用双-[γ-(三乙氧基硅)丙基]四硫化物(BTESPT)硅烷钝化液对热镀铝锌钢板进行了钝化处理.研究了在5%NaCl溶液中未钝化、硅烷钝化及铬酸盐钝化热镀铝锌钢板的极化曲线和电化学交流阻抗谱.通过中性盐雾试验比较了硅烷钝化膜与铬酸盐钝化膜的耐蚀性能.结果表明:经硅烷钝化液钝化后的热镀铝锌钢板,其腐蚀电位和电流密度下降,极化电阻增大,硅烷钝化膜抑制了热镀铝锌钢板的腐蚀过程,使得耐蚀性能远远高于铬酸盐钝化后的热镀铝锌钢板.     

Characterization and corrosion studies of ceria thin film based on fluorinated AZ91D magnesium alloy

The CeO₂ thin film was prepared via sol-gel method on fluorinated AZ91D magnesium alloy surfaces. The surface morphology, composition and the corrosion resistance of the film were investigated in details using scanning electron microscope, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy as well as potentiodynamic polarization tests. It was found that small amount of MgO and MgF₂ were encapsulated in CeO₂ thin film. The electrochemical measurement results demonstrated that the CeO₂ thin film on fluorinated AZ91D magnesium alloy could improve the corrosion resistance approximately by two orders of magnitude compared with that of the bare substrate.     

Inhibition of brass corrosion in sodium chloride solutions by self-assembled silane films

Self-assembled monolayers (SAMs) of 3-mercaptopropyltrimethoxysilane (PropS-SH), dodecyltrimethoxysilane (DTMS), 3-aminopropyl(trimethoxy)silane (APS), and chloropropyl(trimethoxy)silane (CPTMS) were investigated to evaluate the influence of the silane molecule structure towards brass corrosion protection. The results indicated that SAMs of PropS-SH, CPTMS and DTMS inhibited the corrosion of brass in 0.2 M NaCl showing a mixed type behavior, while APS was not a good inhibitor. The inhibitive action of the PropS-SH and DTMS can be explained by chemisorption which obeys the Langmuir adsorption isotherm. The thiolate bond allows a better anchorage of the silane layer to the brass surface than the oxane bond.     

Electrochemical quartz crystal microbalance and electrochemical impedance spectroscopy study of copper corrosion inhibition by imidazoles

The aim of this work is to obtain deeper insight into the mechanism of the protective action of three imidazole-based corrosion inhibitors. Investigations were performed on copper in 3% NaCl, by electrochemical impedance spectroscopy and electrochemical quartz crystal microbalance measurements. The kinetic changes in the corrosion processes were monitored over time. In spite of similar molecular structure, differences in the inhibiting mechanism of three imidazole compounds were observed. The two inhibitors with a tolyl substituent decreased the copper corrosion rate due to the formation of a thin adsorbate layer; however, slow formation of a thick layer was observed for 4-methyl-1-phenyl imidazole. From electrochemical impedance spectroscopy studies, it was observed that all three inhibitors protected the copper efficiently, and in some cases, the degree of the protection increased with time.     

The formation of a protective layer of 3-mercapto-propyl-trimethoxy-silane on copper

The formation of a protective layer of 3-mercapto-propyl-trimethoxy-silane (PropS-SH) on copper was studied by non-electrochemical (Quartz Crystal Microbalance, FTIR and XPS spectroscopy) and electrochemical (Impedance Spectroscopy, Potentiodynamic Polarization Curve recording) techniques.By simple immersion in the silanic bath (90/6/4 v/v methyl alcohol/water/silane solution), this agent immediately physisorbed on copper, but the protective effects were poor. Thiolate and siloxane bond formation improved the performances of the silanic layer. The process of curing formed a very efficient, scarcely porous, polymolecular layer, while the aging process formed a less corrosion-resistant, practically bidimensional layer.The effects of dipping and subsequent methanol rinsing on the protective performances of PropS-SH film were also determined.     

Investigating accuracy of the Tafel extrapolation method in HCl solutions

This paper discusses the validity and accuracy of the Tafel extrapolation method for determining corrosion rates of carbon steel in 1, 2 and 3 M HCl solutions open to air. Corrosion rates obtained from polarization experiments were compared with that of weight loss method. For analysing data obtained from polarization experiments electrochemical impedance spectroscopy (EIS) measurements were performed before polarization experiments. The results showed that formation of a corrosion product film and increasing the polarization resistance (R_p) of this film with time cause the corrosion rates obtained from Tafel extrapolation tend to be higher than corrosion rates obtained from weight loss test.