The corrosion behaviour of polypyrrole coating synthesized in phenylphosphonic acid solution

Electrochemical synthesis of polypyrrole (PPy) film was achieved on mild steel (MS), in monomer containing 0.1 M phenylphosphonic acid solution. The synthesis was carried out using cyclic voltammetry technique. It was found that the electrode surface could only become completely passive, after a few successive cycles in solution of 0.1 M pyrrole + 0.1 M phenylphosphonic acid. Then, the thickness of polymer film was increased with help of successive cycles in a relatively narrower potential range. The corrosion performance of polymer coating was investigated in 3.5% NaCl solution, using electrochemical impedance spectroscopy (EIS) and anodic polarization curves. It was shown that the coating had high stability and low permeability, under such aggressive conditions. The EIS results also showed that the coating exhibited important anodic protection behaviour on mild steel. The percent protection efficiency value (E%) was found to be 98.4% and the percent total porosity value (P%) was determined to be 0.752%, after 96 h exposure time to corrosive solution.     

Study of molybdenum/lanthanum-based composite conversion coatings on AZ31 magnesium alloy

The molybdenum/lanthanum-based (Mo/La) composite conversion coating on AZ31 magnesium alloy was investigated and the corrosion resistance was evaluated as well. The morphology, composition and corrosion resistance of the coating were studied by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and potentiodynamic polarization analysis, respectively. The results revealed that the conversion coating consisted of spherical nodular particles, which was mainly composed of Mo, La, O and Mg. After conversion treatment the corrosion potential shifts about 500 mV positively, and the corrosion current density decreases two orders of magnitude. The corrosion resistance of AZ31 alloy is remarkably improved by Mo/La composite conversion coating.     

Studies on influence of zinc immersion and fluoride on nickel electroplating on magnesium alloy AZ91D

The effect of zinc immersion and the role of fluoride in nickel plating bath were mainly investigated in nickel electroplating on magnesium alloy AZ91D. The state of zinc immersion, the composition of zinc film and the role of fluoride in nickel plating bath were explored from the curves of open circuit potential (OCP) and potentiodynamic polarization, the images of scanning electron microscopy (SEM) and the patterns of energy dispersive X-ray (EDX). Results show that the optimum zinc film mixing small amount of Mg(OH)₂ and MgF₂ is obtained by zinc immersion for 30-90 s. The corrosion potential of magnesium alloy substrate attached zinc film will be increased in nickel plating bath and the quantity of MgF₂ sandwiched between magnesium alloy substrate and nickel coating will be reduced, which contributed to produce nickel coating with good performance. Fluoride in nickel plating bath serves as an activator of nickel anodic dissolution and corrosion inhibitor of magnesium alloy substrate. 1.0-1.5 mol dm⁻³ of F⁻ is the optimum concentration range for dissolving nickel anode and protecting magnesium alloy substrate from over-corrosion in nickel plating bath. The nickel coating with good adhesion and high corrosion resistance on magnesium alloy AZ91D is obtained by the developed process of nickel electroplating. This nickel layer can be used as the rendering coating for further plating on magnesium alloys.     

Effect of cerium doping on corrosion resistance of amorphous silica–titanium sol–gel coating

The aim of this study was to investigate the effects of ceria doping on corrosion resistance of amorphous silica–titania coating. The microstructural and phase properties of titania–silica and titania–silica–Ceria composite films were investigated by SEM, EDAX and XRD. Potentiodynamic polarization and EIS spectroscopy have been used to study the corrosion behavior of composite coating in 3.5% NaCl solution. Results showed that by cerium doping into silica–titania coating as an inhibitor, the corrosion resistance of the film increased. In addition this study revealed that cerium doping enhanced pitting resistance of the coating.     

Preparation of the Ni-P composite coating co-deposited by nano TiC particles and evaluation of it's corrosion property

In current research, low carbon steel plates were coated by Ni-P electroless method. The effect of adding different concentrations (ranging from 0.01 g/l to 0.5 g/l) of TiC nano-sized particles to the plating bath on deposition rate, surface morphology and corrosion behavior of Ni-P-TiC composite coatings were investigated. The surface morphology and the relevant structure were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Corrosion behavior of the coated steel was evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques. The results showed that addition of TiC nano-particles to Ni-P electroless bath not only changes the surface morphology of Ni-P coating, but also improves corrosion resistance of the steel in comparison with TiC free Ni-P electroless coating. In addition, the deposition rate of coating was also affected by incorporation of TiC particles. It was also found that improvement in corrosion resistance largely depends on the phosphorous and TiC concentrations on the coatings.     

In vitro corrosion behavior of Ti-O film deposited on fluoride-treated Mg-Zn-Y-Nd alloy

In this paper, a new composite coating was fabricated on magnesium alloy by a two-step approach, to improve the corrosion resistance and biocompatibility of Mg-Zn-Y-Nd alloy. First, fluoride conversion layer was synthesized on magnesium alloy surface by immersion treatment in hydrofluoric acid and then, Ti-O film was deposited on the preceding fluoride layer by magnetron sputtering. FE-SEM images revealed a smooth and uniform surface consisting of aggregated nano-particles with average size of 100 nm, and a total coating thickness of ∼1.5 μm, including an outer Ti-O film of ∼250 nm. The surface EDS and XRD data indicated that the composite coating was mainly composed of crystalline magnesium fluoride (MgF₂), and non-crystalline Ti-O. Potentiodynamic polarization tests revealed that the composite coated sample have a corrosion potential (E_corr) of −1.60 V and a corrosion current density (I_corr) of 0.17 μA/cm², which improved by 100 mV and reduced by two orders of magnitude, compared with the sample only coated by Ti-O. EIS results showed a polarization resistance of 3.98 kΩ cm² for the Ti-O coated sample and 0.42 kΩ cm² for the composite coated sample, giving an improvement of about 100 times. After 72 h immersion in SBF, widespread damage and deep corrosion holes were observed on the Ti-O coated sample surface, while the integrity of composite coating remained well after 7 d. In brief, the data suggested that single Ti-O film on degradable magnesium alloys was apt to become failure prematurely in corrosion environment. Ti-O film deposited on fluoride-treated magnesium alloys might potentially meet the requirements for future clinical magnesium alloy stent application.     

钽在无水乙醇中的腐蚀

采用动电位极化、循环伏安、交流阻抗和扫描电镜等技术研究了钽在四乙基氯化铵(TEA)乙醇溶液中的腐蚀行为．在循环伏安曲线的扫描初期,电极表面因存在一薄层氧化物膜而使得电流密度缓慢增 加．后来钝化膜因受到氯离子的攻击而被击穿,即点蚀．扫描电镜图很好地显示出蚀孔的生长过程．点蚀电位随着TEA浓度的增加而下降,随着水含量的增加而上升．在所研究的温度范围内,电化学反应的活化能为36 kJ/mol．所有电极电位下的交流阻抗图谱都包含两个时间常数,钝化膜电阻和电荷传递电阻均随电极电位的增加而下降．     

Synthesis and characterization of silver-polypyrrole film composite

In this work, we report the chemical polymerization of pyrrole to obtain thin film of polypyrrole (PPy) hydrochloride deposited onto the electrode of the quartz crystal microbalance (QCM). The film in the base form was exposed to a solution of AgNO₃. Electroless reduction for silver ions by the PPy film took place and silver particles were adsorbed onto the film surface. The silver particles content at the PPy films were analyzed by QCM and the results showed that the concentrations of silver uptakes increase as the original AgNO₃ solution increases. The morphology of the surface of the PPy film and the silver-PPy film composite were studied by the scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDX). They showed that the obtained silver particles have spherical, cubic and tetrahedral structures. X-ray diffraction (XRD) and Fourier transformed infra-red spectroscopy (FTIR) were used to characterize the structure of the powder composite. This work reveals the capability of PPy film coating on QCM in sensing and removing silver from several environmental samples.     

Morphological, mechanical, corrosion and hydrogen permeation characteristics of Ni-nano-TiO2 composite coating compared to Ni electrodeposited on low carbon steel

Ni and Ni-nano-TiO₂ composite coatings with various amounts of TiO₂ in electrolyte, on low carbon steel, have been prepared from Watts-bath using electrodeposition process. The morphological, mechanical, corrosion and hydrogen permeation characteristics of Ni and Ni-nano-TiO₂ coatings were studied and compared with each other. The results revealed that, existence of nano-TiO₂ particles in Ni matrix improved the microstructure as well as microhardness, whereas increasing particle incorporation from 4.33 to 7.62 vol % concluded to microhardness enhancement. The corrosion behavior of Ni and Ni-nano-TiO₂ composite coatings with various amount of particle content was studied by the anodic polarization curves in 5% H₂SO₄ solution at room temperature. It was seen Ni-nano-TiO₂ composite coatings exhibited higher corrosion resistances comparing to pure Ni coating and corrosion protection improved with increasing nano-TiO₂ in coatings. In addition to the corrosion and engineering properties, comparison of hydrogen permeation characteristics of the Ni coating was made with Ni-nano-TiO₂ composite coating through Devanthan-Stachurski hydrogen permeation test. From the resulting data analysis, Ni-nano-TiO₂ composite coating was seen not only to provide longer life under corroding media, but also reduces greatly the risk of the substrate being exposed to hydrogen permeation when compared to electrodeposited Ni coating.     

水性丙烯酸聚氨酯涂料中反应性缓蚀剂掺入及其耐蚀性能

利用磷酸和双酚A环氧树脂反应得到功能性缓蚀剂羟基环氧磷酸酯(HEP). 将其添加到水性羟基丙烯酸树脂中,再与水性异氰酸酯固化剂交联,制备了水性羟基环氧磷酸酯/丙烯酸聚氨酯复合涂层(HEP-APU). 由于磷酸酯基团可以与金属基体发生反应,在金属表面形成一层磷化膜,极大的提升了金属的抗闪蚀能力. 利用电化学阻抗谱和极化曲线研究HEP-APU复合涂层对Q235碳钢在3.5wt% NaCl溶液中耐蚀性能. 结果表明,HEP-APU涂料对Q235碳钢具有优越的钝化和耐腐性能,且当HEP在水性丙烯酸聚氨酯涂料中质量分数为0.5%时,所得到的复合涂层的防腐性能最佳.     

非晶粉/硅橡胶复合薄膜应力阻抗性能

选用硅橡胶为基材,Fe73.5Cu1Nb3Si13.5B9非晶纳米晶软磁合金粉体为磁性功能填料,采用机械共混的方法制备非晶粉/硅橡胶力敏复合材料。采用自制测试夹具测试非晶粉/硅橡胶复合材料的阻抗值,采用扫描电镜分析非晶粉颗粒形貌及其在硅橡胶基材中分散情况,在此基础上研究了复合材料界面绝缘性、单层与多层叠加复合薄膜、加入导电层及其层数对复合应力阻抗性能的影响。研究结果表明:铜箔作为界面强化导电层的加入是提高复合薄膜力敏特性的有效途径之一,设计实验中的复合薄膜/铜箔/复合薄膜结构相当于聚合物/金属/聚合物三明治多层膜结构,对敏感性具有增强效应。     

Studies on adhesion characteristics and corrosion behaviour of vinyltriethoxysilane/epoxy coating protective system on aluminium

The corrosion stability of vinyltriethoxysilane/epoxy coating protective system on aluminium is strongly related to the strength of bonds forming at the metal/organic coating interface. This article is a study of adhesion, composition, electrochemical and transport properties of epoxy coatings electrodeposited on bare aluminium and aluminium pretreated by vinyltriethoxysilane (VTES) during exposure to 3% NaCl. The VTES film was deposited on aluminium surface from 2% vinyltriethoxysilane solution during 30 s. From the values of adhesion strength (pull-off test), time dependence of pore resistance and coating capacitance of epoxy coating (impedance measurements) and diffusion coefficient of water through epoxy coating (gravimetric liquid sorption measurements), the influence of VTES sublayer on the corrosion stability of the electrodeposited epoxy coating was shown.The work discusses the role of the VTES pretreatment in the enhanced adhesion and corrosion stability of epoxy cataphoretic coating. The electrochemical results showed that the aluminium pretreatment by VTES film improved barrier properties of epoxy coating (greater pore resistance and lower coating capacitance). The lower value of diffusion coefficient of water through epoxy coating indicates the lower porosity, while the smaller adhesion reduction points to better adhesion of epoxy coating on aluminium pretreated by VTES film. The composition of the deposited coatings investigated by XPS enabled the clarification of the bonding mechanism.     

Development of electroless Ni-Zn-P/nano-TiO2 composite coatings and their properties

Ni-Zn-P-TiO₂ composite coatings were successfully obtained on low carbon steel by electroless plating technique. Deposits were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis (EDS) studies. The hardness and microstructure of as plated and heat treated Ni-Zn-P and Ni-Zn-P-TiO₂ composite coatings were analyzed. The change in microstructure and higher hardness was noticed for heat treated composite. The corrosion resistance behavior of as plated and heat treated Ni-Zn-P and Ni-Zn-P-TiO₂ coatings was investigated by anodic polarization, Tafel plots and electrochemical impedance spectroscopic (EIS) studies in 3.5 wt% NaCl solution. The composite coating exhibited enhanced corrosion resistance property over Ni-Zn-P coating.     

Electrodeposition of Al-Mn alloy on AZ31B magnesium alloy in molten salts

The Al-Mn alloy coatings were electrodeposited on AZ31B Mg alloy in AlCl₃-NaCl-KCl-MnCl₂ molten salts at 170 °C aiming to improve the corrosion resistance. However, in order to prevent AZ31B Mg alloy from corrosion during electrodeposition in molten salts and to ensure excellent adhesion of coatings to the substrate, AZ31B Mg alloy should be pre-plated with a thin zinc layer as intermediate layer. Then the microstructure, composition and phase constituents of the coatings were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD). It was indicated that, by adjusting the MnCl₂ content in the molten salts from 0.5 wt% to 2 wt%, the Mn content in the alloy coating was increased and the phase constituents were changed from f.c.c Al-Mn solid solution to amorphous phase. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization measurements in 3.5% NaCl solution. It was confirmed that the Al-Mn alloy coatings exhibited good corrosion resistance with a chear passive region and significantly reduced corrosion current density at anodic potentiodynamic polarization. The corrosion resistance of the alloy coatings was also related with the microstructure and Mn content of the coatings.     

A silane pre-treatment for improving corrosion resistance performances of emeraldine base-coated aluminium samples in neutral environment

An aluminium-magnesium alloy AA5182 substrate pre-treated with a 3-aminopropyl-triethoxysilane (APS)-based solution and coated with emeraldine base (EB) showed improved corrosion resistance to neutral salt spray test, compared to samples pre-treated with phosphoric acid-based solutions prior to the EB coating. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX) characterisations of samples pre-treated with APS showed the presence of an uneven silane coating on the aluminium surface according to the surface microstructure. The potentiodynamic study performed on the EB-coated samples showed a noticeable reduction of corrosion current of coupons pre-treated with APS, while no relevant difference in corrosion behaviour was observed between APS and phosphoric acid pre-treated samples prior to the EB coating. The coupling activity of APS between the AA5182 surface and EB coating at the most sensitive corrosion sites could be responsible of an improved adhesion of the EB coating at these points and could explain the observed improved corrosion resistance.     

Surface characteristics and electrochemical behaviour of sputter-deposited NiTi thin film

Thin nanocrystalline amorphous NiTi film was deposited on Si substrate using DC magnetron sputtering. The as-deposited NiTi thin film was crystallized by heat treatment at 500 °C for 1 h. The crystal structure, surface morphology, microstructure and surface chemistry of the deposited films were studied using X-ray diffraction, atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy (XPS), respectively. Corrosion behaviour was assessed in Ringer’s solution at 37 °C by open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy as a function of exposure time. OCP values indicate that the tendency for the formation of a spontaneous oxide film is greater for the NiTi thin films than the bulk NiTi. Long time exposure to Ringer’s solution was found to have a great effect on the corrosion behaviour of the samples. Significantly low corrosion current density was obtained for the annealed NiTi film from the potentiodynamic polarization curves indicating a typical passive behaviour, but as-deposited film and bulk NiTi alloy exhibited breakdown of passivity at potentials approximately +1.4 V (vs. SCE). XPS showed that the oxide film formed on the annealed NiTi thin film mainly composed of Ti oxides, and no evidence of Ni was found up to 8.2 nm beneath the top surface, suggesting the excellent corrosion resistance of this sample in Ringer’s solution.     

Preparation and characterization of the electrodeposited Cr-Al2O3/SiC composite coating

To increase the SiC content in Cr-based coatings, Cr-Al₂O₃/SiC composite coatings were plated in Cr(VI) baths which contained Al₂O₃-coated SiC powders. The Al₂O₃-coated SiC composite particles were synthesized by calcining the precursor prepared by heterogeneous deposition method. The transmission electron microscopy analysis of the particles showed that the nano-SiC particle was packaged by alumina. The zeta potential of the particles collected from the bath was up to +23 mV, a favorable condition for the co-deposition of the particles and chromium. Pulse current was used during the electrodeposition. Scanning Electron Microscopy (SEM) indicated that the coating was compact and combined well with the substrate. Energy dispersive X-ray analysis of Cr-Al₂O₃/SiC coatings demonstrated that the concentration of SiC in the coating reached about 2.5 wt.%. The corrosion behavior of the composite coating was studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The data obtained suggested that the Al₂O₃/SiC particles significantly enhanced the corrosion resistance of the composite coating in 0.05 M HCl solution.     

Cross-linked gelatin/nanoparticles composite coating on micro-arc oxidation film for corrosion and drug release

A composite coating which could control drug release and biocorrosion of magnesium alloy stent materials WE42 was prepared. This composite coating was fabricated on the surface of the micro-arc oxidation (MAO) film of the magnesium alloy, WE42, by mixing different degrees of cross-linked gelatin with well-dispersed poly(dl-lactide-co-glycolide) (PLGA) nanoparticles. The PLGA nanoparticles were prepared by emulsion solvent evaporation/extraction technique. Nano ZS laser diffraction particle size analyzer detected that the size of the nanoparticles to be 150-300 nm. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) was used to analyze the morphology of the nanoparticles and the composite coating. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behavior of the composite coating. Drug release was determined by ultraviolet-visible (UV-vis) spectrophotometer. The corrosion resistance of the composite coating was improved by preventing the corrosive ions from diffusing to the MAO films. The drug release rate of paclitaxel (PTX) exhibited a nearly linear sustained-release profile with no significant burst releases.     

Influence of the chemical composition of the plating solution on the ability of nickel coatings to protect Nd2Fe14B magnets against corrosion

The commercial application of rare earth magnets has been in part held back by their poor corrosion resistance. As part of efforts to overcome this problem two types of nickel coatings were electroplated on the surface of Nd₂Fe₁₄B substrates, one from an acidic plating solution and the other from an alkaline solution. The corrosion characteristics of both coatings were evaluated both by electrochemical potentiodynamic polarisation and by physical exposure to high-humidity environments. The results showed that both coatings enhanced the corrosion resistance of substrate. However, both the degree of protection afforded by the coating and the strength of its adhesion to the substrate strongly depended on the chemical composition of the original plating solution. The coating plated from the acidic solution provided a high degree of protection against both aqueous and atmospheric corrosion, whilst that plated from the alkaline solution behaved only marginally better than the bare substrate. It was postulated that the poor performance of the coatings plated from the alkaline bath could have been due to the spontaneous formation of a passive oxide film between the Nd₂Fe₁₄B substrate and the nickel coating.     

The effect of carbon nanotubes on the corrosion and tribological behavior of electroless Ni-P-CNT composite coating

In this study, Ni-P-CNT composite coating was successfully deposited on the surface of copper by electroless plating. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the coatings. The wear behavior of the coatings was investigated using a pin-on-disk test rig and subsequently friction coefficient data were reported. The corrosion behavior of the Ni-P and Ni-P-CNT coated specimen were evaluated through polarization curves and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl aqueous solution at the room temperature. The results indicated that the incorporation of carbon nanotubes (CNTs) in the coating improved both tribological behavior and corrosion resistance. These improvements have been attributed to superior mechanical properties, unique topological structure and high chemical stability of nanotubes.