Effects of Ca and Ag addition and heat treatment on the corrosion behavior of Mg-7Sn alloys in 3.5 wt.% NaCl solution

The effects of 1 wt.% Ca or 1 wt.% Ca + 1 wt.% Ag addition and heat treatment on the corrosion behavior of Mg-7Sn (wt.%) alloy in 3.5 wt.% NaCl solution were investigated by electrochemical measurements and immersion tests. The alloys were characterized by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that all alloys were corroded by pitting corrosion and grain boundary corrosion and further corroded with time going. Loose layers of compounds, including Mg (OH)₂, MgO, SnO₂, and other compounds containing Ca and Ag elements, were calibrated on the surface of corroded Mg-7Sn-1Ca-1Ag alloy. The Ca addition improved the corrosion resistance of Mg-7Sn alloy due to the formation of relatively stable compounds containing calcium element and grains refinement. Furthermore, the solid solutioned alloys obtained a superior corrosion resistance due to the dissolve of eutectic Mg₂Sn phase and homogenization treatment. However, the aging treatment is slightly detrimental to the corrosion resistance of Mg-7Sn alloys with the formation of Mg₂Sn precipitates. In conclusion, the aged Mg-7Sn-1Ca-1Ag alloy exhibited a better corrosion resistance and a noticeable micro-hardness property compared with those of as-cast Mg-7Sn alloy. And this study provides an important idea for the research on the comprehensive properties of Mg-Sn alloys.     

Designing an epoxy composite coating having dual-barrier-active self-healing anti-corrosion functions using a multi-functional GO/PDA/MO nano-hybrid

The graphene oxide, functionalized with polydopamine (PDA) bio-polymers and molybdate (MO) ions, was incorporated into the epoxy coating. The FT-IR, Raman, UV-visible, XRD, and FE-SEM/EDS analyses were utilized for the GO/PDA/MO nanoparticle characterization. The sequence of inhibitors' release from the nano-hybrid and their effect on the electrochemical behavior of the steel sample was explored by the OCP, polarization, and, EIS analyses in the aquatic saline media. EIS analyses revealed inhibition efficiency of 88% for the sample immersed in the GO/PDA/MO-contained solution after 48 h immersion. The polarization results showed a 91% corrosion mitigation index for the sample submerged in the GO/PDA/MO extract-containing solution after 48 h immersion. An increase of the scratched coating Nyquist diameter, the lower corrosion product, and coating blister formation after exposure to the salt spray chamber, as well as the lower adhesion loss in the pull-off test (26%), revealed that the epoxy coating reinforced with GO/PDA/MO nano-hybrids could mitigate the mild steel corrosion by improving the barrier performance and active corrosion protection (self-healing mechanism) behavior.     

Growth behaviour of cerium-based conversion coating on Zn-5%Al alloy

Cerium-based conversion coatings were deposited on a Zn-5%Al alloy by immersing the alloy in cerium nitrate aqueous solutions with various immersion times. The growth behaviour of the cerium-based conversion coating on the Zn-5%Al alloy was investigated by the electrochemical impedance spectroscopy (EIS), SEM, energy dispersive spectroscopy (EDS), and XPS techniques. The results reveal that the coating mainly consists of ZnO, Zn(OH)₂, Ce(OH)₄, Ce(OH)₃, CeO₂, and Ce₂O₃. The growth of the cerium-based conversion coating is accompanied by metal dissolution. The dissolution mainly occurs on the η-Zn surface of the phase boundary and continues to extend to the Zn-rich phase as the coating grows. EIS results show that with increasing immersion time, the corrosion resistance of the Ce conversion coating gradually increases in the early growth stage and then decreases when the cracks appear.     

Effect of surface treatments on the localized corrosion resistance of the AA2198-T8 aluminum lithium alloy welded by FSW process

In this work, the effect of eight types of surface treatments on the corrosion resistance of friction stir welded samples of an AA2198-T8 Al-Cu-Li alloy were tested and compared in an attempt to find suitable alternatives to toxic and carcinogenic hexavalent chromium treatments. All the samples were anodized and subjected to different post-anodizing treatments. The post-anodizing treatments were (1) hydrothermal treatment in Ce (NO₃)₃ 6H₂O solution; (2) hydrothermal treatment in Ce (NO₃)₃ 6H₂O solution with H₂O₂; (3) hydrothermal treatment in boiling water; (4) hexavalent chromium conversion coating; and (5) immersion in BTSE (bis-1,2-(triethoxysilyl) ethane. The corrosion resistance of the treated samples was evaluated by immersion tests in sodium chloride solution (0.1 mol L⁻¹ NaCl) and electrochemical impedance spectroscopy (EIS) of the friction stir weldment. The results showed that among the alternative treatments, the Ce-containing solutions presented the best corrosion resistance, especially when used without peroxide.     

Corrosion behavior of CoCrMoW cast alloy in lactic acid environment for surgical applications

The corrosion behavior of CoCrMoW alloy in lactic acid environment during 168 h of immersion at 37 °C has been studied and assessed by means of electrochemical techniques (open circuit potential (OCP), potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS)). Further, the oxide film thickness formed after immersion and the quantity of ions released have been evaluated by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical spectroscopy (ICP-OES). A good correlation between the results, related to the oxide film thickness, obtained from these experimental techniques was achieved. The research has also shown that the tendency of growing of oxide film becomes slower as the time of immersion is longer. The higher corrosion resistance of CoCrMoW alloy in lactic acid environment is due to the formation of the oxide film highly enriched in Cr(III) on the alloy surface. With a small corrosion rate, e.g. 45 nm year⁻¹, this alloy is characterized as “Perfect Stable” according to ISO 8044/2000. Overall, the present study provides additional evidences with respect to the benefic influence of tungsten on passivity, explained by a higher resistance to pitting corrosion of the CoCrMoW alloy in lactic acid with sodium chloride.     

The effect of chloride concentration and pH on pitting corrosion of AA7075 aluminum alloy coated with phenyltrimethoxysilane

The effect of chloride ion concentration and pH of solution on the corrosion behavior of aluminum alloy AA7075 coated with phenyltrimethoxysilane (PTMS) immersed in aqueous solutions of NaCl is reported. Potentiodynamic polarization, linear polarization, open circuit potential, and weight loss measurements were performed. The surface of samples was examined using SEM and optical microscopy. Elemental characterization of the coating by secondary ion mass spectrometry indicates an intermediate layer between coating and aluminum alloy surface. The corrosion behavior of the aluminum alloy AA7075 depends on chloride concentration and pH of solution. In acidic or neutral solutions, general and pitting corrosion occur simultaneously. On the contrary, exposure to alkaline solutions results in general corrosion only. Results further reveal that aluminum alloy AA7075 is susceptible to pitting corrosion in all chloride solutions with concentrations between 0.05 M and 2 M NaCl; an increase in the chloride concentration slightly shifted both the pitting and corrosion potentials to more active values. Linear polarization resistance measurements show a substantially improved corrosion resistance value in case of samples coated with PTMS as compared to uncoated samples in both neutral (pH = 7), acidic (pH = 0.85 and 3), and alkaline chloride solutions (pH = 10 and 12.85). The higher corrosion resistance of the aluminum alloy coated with PTMS can be attributed to the hydrophobic coating which acts as a barrier and prevents chloride ion penetration and subsequent reaction with the aluminum alloy.     

Corrosion protection of carbon steel using a combination of Zr conversion coating and subsequent zinc-rich silicate coating with a flake ZnAl alloy

To improve the corrosion protection properties of zinc-rich silicate coatings on steel, zirconium pretreatment loaded with (3-aminopropyl)triethoxysilane (APTES) 0.025 % (v/v) and the partial replacement of spherical zinc by flake ZnAl alloy were investigated. DC polarization and electrochemical impedance spectroscopy (EIS) show that the zirconium pre-treated layer containing APTES improves the corrosion protection of the bare steel. Zinc-rich silicate coatings containing flake ZnAl with and without pretreatment were evaluated by EIS, salt spray test and pull-off test. Pretreatment with a zirconium conversion layer reduces corrosion products and adhesion loss (from 16.53% to 12.54%) while the performance of corrosion protection significantly increased from 2003 Ω.cm² to 2640 Ω.cm² in comparison with the non-pretreated samples. The results show that flake ZnAl pigment (5 wt%) significantly improves corrosion resistance and prolongs the duration of cathodic protection of zinc-rich silicate coatings.     

An inorganic route to decorate graphene oxide with nanosilica and investigate its effect on anti‐corrosion property of waterborne epoxy

This paper reported an inorganic route that uses potassium silicate, which is one type of alkali silicate as an inorganic modifier, taking advantage of its instability and water condensation to decorate graphene oxide (GO) with nano‐SiO₂. The ingredients of prepared nanocomposites were characterized by Fourier‐transform infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectroscopy (XPS), and the thermodynamic property was tested by thermal gravimetric analysis (TGA). Scanning electron microscopy (SEM) was used to observe the morphology of SiO₂‐GO nanocomposites. All the analyses above revealed the nano‐SiO₂ (<100 nm) was deposited on the surface of GO by chemical bonds. In the meantime, the dispersion test illustrated that nano‐SiO₂ played an important role in improving the dispersity of GO. The effect of SiO₂‐GO nanocomposites on barrier and corrosion protection performance of SiO₂‐GO nanocomposites was tested by immersion experiment and electrochemical impedance spectroscopy (EIS). The results indicated that GO was helped to block the corrosion of aggressive medium; moreover, SiO₂‐GO nanocomposites had the best anticorrosion performance and the slowest rate of corrosion because of its good dispersity with waterborne epoxy coatings.     

Electrochemical corrosion behaviors and corrosion protection properties of Ni–Co alloy coating prepared on sintered NdFeB permanent magnet

In this study, a protective Ni–Co alloy coating was prepared on sintered NdFeB magnet applying electrodeposition technique. A pure nickel coating was also studied for a comparison. The microstructure, surface morphologies, and chemical composition of coatings were investigated using X-ray diffraction, scanning electron microscope, and energy dispersive spectroscopy, respectively. The corrosion protection properties of coatings for NdFeB magnet in neutral 3.5 wt.% NaCl solutions were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The microstructure and surface morphologies analysis showed that the addition of cobalt element into matrix metal Ni altered the preferential orientation of pure nickel coating from (2 0 0) crystal face for pure nickel coating to (1 1 1) crystal face for Ni–Co alloy coating, and made the surface morphologies more compact and uniform due to the grain-refining. The results of potentiodynamic polarization test showed that compared with pure nickel coating, Ni–Co alloy coating exhibited much nobler corrosion potential (E _corr) and lower corrosion current density (j _corr), indicating better anticorrosive properties. The long-term immersion test by dint of EIS indicated that the Ni–Co alloy coating still presented high impedance value of 1.9 × 10⁵ Ω cm² with the immersion time of 576 h indicating the excellent anticorrosive properties, and corrosion protection properties of nickel coating for NdFeB magnet practically disappeared with the immersion time of 144 h, which also indicated that the Ni–Co alloy coating provided better corrosion protection properties for the NdFeB magnet compared with nickel coating.     

Benzalkonium chloride/titanium dioxide as an effective corrosion inhibitor for carbon steel in a sulfuric acid solution

In this study, the corrosion performance of carbon steel samples in 0.5 M sulfuric acid by the addition of novel inhibitors, 200 ppm of (25% and 50%) titanium dioxide nanoparticles in benzalkonium chloride, was thoroughly investigated. Gravimetric measurements, cyclic and linear potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and hydrogen collection by water displacement evaluated inhibition performance. Analogously, TiO₂/ILB (50%), TiO₂/ILB (75%), and ILB inhibitors enhanced corrosion protection with over 80% inhibition efficiency in electrochemical tests. In addition, weight loss and hydrogen collection measurements reached comparable results. According to potentiodynamic polarization curves, inhibitors exhibited dual behavior, but cathodic protection was more predominant. Scanning electron microscopy (SEM) was employed to examine the surface morphology before and after immersion using corrosion tests. The correlation between electronic properties and inhibition efficiencies of tilted inhibitors was determined by simple linear regression. Electronic properties were calculated for neutral and protonated forms using a polarizable continuum model by the DFT method at the B3LYP/6-311+G (d, p) level of theory. The active adsorbed sites of HM1-HM3 on the metal surface were determined by analyzing their corresponding electrostatic surface potentials (ESP). Furthermore, molecular dynamics simulations were performed to illustrate the most conceivable adsorption configuration between the inhibitors and metal surfaces.     

Auger electron spectroscopic analysis of corrosion products formed on A3003 aluminum alloy in model fresh water with different Zn2+ concentration

The corrosion morphology and composition of corrosion products of A3003 formed in model fresh water with different Zn²⁺ concentrations were investigated by immersion tests combined with surface observations and analysis using an Auger electron spectroscope (AES). The cross-sectional AES observations showed that the thickness of the corrosion product layer formed on A3003 decreases with increases in the Zn²⁺ concentration of the model fresh water. A cross-sectional AES point analysis suggested that the corrosion products formed on the A3003 in the Zn²⁺ containing model fresh water (Zn²⁺ > 0.1 mM) have a multilayered structure and that the inner of Zn-rich layer would have high corrosion protective properties.     

Surface analysis and corrosion resistance of new nickel base thin film alloys

Electroless Zn–Ni–P thin films were deposited on low carbon steel from an alkaline non‐cyanide aqueous electrolyte. The newly developed ternary alloys structure and microstructure investigations were carried out via X‐ray diffraction and SEM. Chemical composition of the coatings was investigated via energy dispersive spectroscopy. Polarization tests were used to study the corrosion properties of the coatings in a 3.5 wt.% NaCl solution. The results confirmed the high corrosion resistance of Zn–Ni–P alloy plated steel sheet. The surface analysis of the thin film samples before and after corrosion was performed by XPS. The incorporation of Zn in Ni–P thin film is proven for all initial samples to be as a mixture of zinc and zinc oxide, while nickel exists in +2 and +3 oxidized states. A passive film of a mixture of oxide and hydroxide of zinc and nickel forms on the surface and prevents the Zn–Ni–P thin films from corrosion. Copyright © 2014 John Wiley & Sons, Ltd.     

Graphene oxide-modified polyaniline pigment for epoxy based anti-corrosion coatings

In the present work, a set of polyaniline–graphene oxide (PANI–GO) nanocomposites which exhibit superior properties in terms of shelf life, processability and conductivity due to the synergistic effect of GO and PANI, have been synthesized by varying the concentration of highly non-conducting GO with respect to aniline. The obtained materials were characterized by UV–Vis, FTIR, XRD, Raman, TGA as well as FESEM, TEM analysis. The results reveal that nanocomposites show better dispersibility, crystallinity, thermal stability, and conductivity. Further, the synthesized composites have been tested for their anti-corrosion properties. The potentiodynamic results reveal that PANI nanocomposites with 1% GO exhibited long-term anti-corrosion behavior with a corrosion rate of 6.5 × 10^?5 mm year^?1, which is much lower than its individual components and commercial-grade red oxide. Also, it possesses highest impedance modulus ~33 kΩ cm² and real impedance ~32 kΩ cm², maximum coating resistance ~14.81 × 10³ Ω cm² and minimum coating capacitance after 96 h of immersion in 3.5% mass NaCl than those exhibited by all other coated samples. Higher concentration of GO could not retard the corrosion rate confirming that hydrophilicity of GO play an important role in the redox mechanism of PANI.     

Corrosion prevention of mild steel in acidic medium by 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid: Theoretical and experimental approach

The inhibition efficiency of 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid (PTCA) against mild steel (MS) corrosion was investigated in acidic solution by using quantum chemical calculations based on Density Functional Theory (DFT) method and electrochemical measurements. The electrochemical impedance spectroscopy (EIS), potentiodynamic, potential zero charge (pzc) analysis and electrochemical noise (EN) measurements at various concentrations (from 0.1 to 10 mM) and immersion times were utilized in experimental part. The surface analysis was achieved scanning electron microscope (SEM) and contact angle measurements in the absence and presence of 10 mM PTCA. According to DFT results, PTCA exhibited 3.737 eV band gap and 8.130 Debye dipole moment which were a signal of potentially convenient corrosion inhibitor properties. PTCA has a remarkable corrosion inhibition capability to mild steel, which inhibited both anodic and cathodic corrosion rates, relying on it's physically adsorption on the metal solution interface and protection ability was increased with increasing PTCA concentration. The obtained adsorption equilibrium constant was 11.11 × 10³ M^-1 and calculated standard free energy of adsorption was ?33.03 kJ mol^?1. The determined activation energy values were 55.58 kJ mol^?1 and 96.86 kJ mol^?1 in 0.5 M HCl in the absence and presence of 10 mM PTCA, respectively. PTCA demonstrated a strong inhibition efficiency of 98.3%, after 168 h immersion, according to the EIS results. As a consequently, we recommend that PTCA is a convenient inhibitor in 0.1 M HCl for mild steel protection against corrosion.     

镁合金阳极氧化膜的结构、成分及其耐蚀性

采用电压-时间曲线、膜厚-时间曲线、X射线衍射法、扫描电镜、能量色散谱仪、X射线光电子能谱法、全浸腐蚀实验和极化曲线等方法分别研究了AZ91D铸镁合金阳极氧化成膜动力学过程、阳极氧化膜的表面形貌、结构、元素组成、元素价态以及相成分和膜层的耐蚀性.结果表明,在阳极氧化的4个阶段中,由于各个阶段所生成膜的厚度、结构和成分等均不同,因此膜的耐蚀性相差很大;镁合金阳极氧化时耐蚀性最好的膜层是在阳极氧化过程中的第阶段和第阶段的交界处所生成的膜层;镁合金阳极氧化膜中含有Mg,O,Si,B和少量的Al,Na元素,膜层主要由MgO,MgSiO₃和Mg3B2O6组成.     

Corrosion inhibition of carbon steel immersed in a 1 M HCl solution using benzothiazole derivatives

Corrosion inhibition effect of 2-mercaptobenzothiazole (MBT) and 2-aminobenzothiazole (ABT) compounds on ST-37 carbon steel in 1 M hydrochloric acid solution was investigated by electrochemical impedance spectroscopy (EIS), and it was observed that both of these compounds have corrosion inhibition effect on carbon steel. Evaluation of electrochemical behavior in test solutions showed that by increasing the immersion time from 15 to 300 min, corrosion resistance of samples is increased and at the same immersion time MBT has a better corrosion inhibition in comparison to ABT. AFM technique was performed for MBT and ABT. The results of calculations showed superior inhibition efficiency of MBT in comparison to ABT. This can cause easier protonation and consequently adsorption on the metal surface occurs.     

Facile synthesis of polyaniline/TiO2/graphene oxide composite for high performance supercapacitors

The polyaniline/TiO₂/graphene oxide (PANI/TiO₂/GO) composite, as a novel supercapacitor material, is synthesized by in situ hydrolyzation of tetrabutyl titanate and polymerization of aniline monomer in the presence of graphene oxide. The morphology, composition and structure of the composites as-obtained are characterized by SEM, TEM, XRD and TGA. The electrochemical property and impedance of the composites are studied by cyclic voltammetry and Nyquist plot, respectively. The results show that the introduction of the GO and TiO₂ enhanced the electrode conductivity and stability, and then improved the supercapacitive behavior of PANI/TiO₂/GO composite. Significantly, the electrochemical measurement results show that the PANI/TiO₂/GO composite has a high specific capacitance (1020 F g⁻¹ at 2 mV s⁻¹, 430 F g⁻¹ at 1 A g⁻¹) and long cycle life (over 1000 times).     

Strong covalent bonding modulated graphene oxide/epoxy interfacial enhancement and advanced corrosion resistance

Abstract

Chemically functionalized graphene oxide [multi-amino functionalized graphene oxide (MAGO)] was achieved by building covalent bonds between graphene oxide (GO) and a small molecule containing benzene structure and multi-amino groups. Fourier transform infrared, X-ray diffraction, X-ray photo electron spectroscopy and TEM-EDX results certified that the molecule was successfully grafted onto GO nanosheets. Subsequently, functionalized GO was incorporated into waterborne epoxy (EP) coating through ball-milling method. This molecular design can significantly improve the dispersion of MAGO in EP matrix, as well as the compatibility and interaction between MAGO and EP. Compared with GO/EP, the water absorption of MAGO/EP decreased from 4.38 to 2.59%, the adhesion strength of MAGO/EP increased from 4.72 to 6.32?MPa after immersion of 40?days in 3.5% NaCl solution. Incorporation of 1?wt% of MAGO into EP matrix prominently improved the long-term corrosion resistance. The impedance modulus of GO/EP coating decreased by four orders after 40 days immersion, while that of MAGO/EP coating only decreased by one order. The impedance modulus was still 1.47?×?10⁸ Ω cm², and two-time constant wasn’t detected for MAGO/EP coating. This research developed a novel green anticorrosion coating with enhanced durability for metal protection.     

Phosphatation of iron powder metallurgical samples for corrosion protection

Recently, powder metallurgy methods have been used widely for industrial purposes. In this work, powder-metallurgically produced samples were selected for zinc phosphate coating. Zinc phosphate coating was performed at 50 and 70 °C for 20 min in a bath containing 10 g l^?1 ZnO, 25.5 g l^?1 H₃PO₄, 5.88 g l^?1 HNO₃, and 2 g l^?1 NaNO₃. The effect of temperature on the phosphating process has been studied. The structure and corrosion resistance of coats have been investigated using scanning electron microscopy (SEM) and electrochemical methods (polarization and EIS). Results show that an increase in temperature affects the crystalline structure of the coats. The formation of the zinc phosphate coat on the powder metallurgical samples significantly decreases the corrosion rate of the samples.     

新型十二烷基三甲氧基硅烷/氧化石墨烯复合膜对430不锈钢耐蚀性能的影响

使用一步电沉积法在430不锈钢上制备出十二烷基三甲氧基硅烷(DTES)/氧化石墨烯(GO)复合膜。 拉曼光谱(Raman)与扫描电子显微镜(SEM)测试表明,氧化石墨烯均匀地混合在硅烷膜中,并用电化学交流阻抗与极化曲线方法对这种复合膜所保护的430不锈钢进行耐蚀性能测试。 结果显示,在3.5%NaCl溶液中,430不锈钢会发生腐蚀反应,而存在硅烷复合膜的430不锈钢的耐蚀性能显著地提高。 研究表明,由于氧化石墨烯出色的阻隔性能一定程度上弥补了硅烷膜的缺陷,而且延长了腐蚀介质通过硅烷基质的路径,因此复合膜有着对基底物质更强的保护性能。