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1.
Fakiha El-Taib Heakal Amany Mohammed Fekry Mohammed Ziad Fatayerji 《Journal of Applied Electrochemistry》2009,39(5):583-591
The influence of pH on the corrosion behavior of Mg-based AZ91D alloy was investigated in a constant composition phosphate
medium using various electrochemical techniques, complemented with surface analysis data. The studied solutions were 0.1 M
H3PO4, NaH2PO4, Na2HPO4 and Na3PO4 having pH values of 1.8, 4.5, 9.1 and 11.8, respectively. Spontaneous passivation was substantiated from monitoring the continuous
positive shift of the open circuit corrosion potential with both immersion time and solution pH. The impedance data indicated
more improvement in the insulating properties of the corrosion products formed on the alloy surface with increase in pH. The
electrolyte pH plays a determinant influence on surface film properties, as films formed in phosphate solutions with higher
pH values are thicker, thus affording better protection for the alloy than those formed in acidic solutions. Good agreement
was observed between the results obtained from electrochemical techniques and those from EDX and XRD examinations. The alloy
is more susceptible to corrosion in acidic phosphate solutions than in the alkaline ones. Crystalline magnesium (Mg), magnesium
hydride (MgH2) and magnesium oxide (MgO) were found to be the main constituents of the surface film after holding for 2 h in the acidic
phosphate medium. 相似文献
2.
E. Gonzalez J. Pavez I. Azocar J.H. Zagal X. Zhou F. Melo G.E. Thompson M.A. Páez 《Electrochimica acta》2011,(22):7586
A new hybrid sol–gel type film, composed of tetraethylorthosilicate (TEOS) and tetraocthylorthosilicate (TEOCS), and modified with different nanoparticle systems, has been investigated as a coating for protection of AA-2024-T3 aluminium alloy. The nanoparticle systems considered were either ZrO2 or CeO2 or their combination. The zirconia nanoparticles were prepared from a Zr (IV) propoxide sol (TPOZ), using an organic stabilizer, and the CeO2 nanoparticles were developed spontaneously after adding cerium nitrate solution to the hybrid sol. The chemical composition and the structure of the hybrid sol–gel films were examined by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion resistance of the coated AA-2024 alloy was examined by potentiodynamic polarization. The results revealed that, for short exposure times in the electrolyte, incorporation of ZrO2 or CeO2 nanoparticles in the hybrid film does not provide an increase in the corrosion resistance of the coated AA-2024 alloy. Further, the resistance was significantly reduced by increasing the nanoparticle content. Conversely, by incorporating both nanoparticles (ZrO2 and CeO2), the corrosion resistance of the resulting hybrid films increased slightly. The behavior changed significantly when the coated alloy was exposed to the electrolyte for 5 days. The corrosion resistance of the coatings, unmodified and modified with CeO2 or ZrO2 nanoparticles, decreased by two or three orders of magnitude, while the film modified with both nanoparticles (CrO2 and ZrO2) showed a relatively high corrosion resistance and responsiveness to activation processes during anodic polarization. 相似文献
3.
PEO coatings were produced on AM50 magnesium alloy by plasma electrolytic oxidation process in silicate and phosphate based electrolytes using a pulsed DC power source. The microstructure and composition of the PEO coatings were analyzed by scanning electron microscopy (SEM) and X-ray Diffraction (XRD). The corrosion resistance of the PEO coatings was evaluated using open circuit potential (OCP) measurements, potentiodynamic polarisation tests and electrochemical impedance spectroscopy (EIS) in 0.1 M NaCl solution. It was found that the electrolyte composition has a significant effect on the coating evolution and on the resulting coating characteristics, such as microstructure, composition, coating thickness, roughness and thus on the corrosion behaviour. The corrosion resistance of the PEO coating formed in silicate electrolyte was found to be superior to that formed in phosphate electrolyte in both the short-term and long-term electrochemical corrosion tests. 相似文献
4.
In this work, the corrosion behaviour of magnesium alloys ZK31, EZ33 and WE54 was studied in sodium borate buffer solution at pH 9.2.The electrochemical processes were studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The composition and morphology of the alloys and corrosion products formed were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).The experimental findings highlighted the differences in the corrosion mechanisms of the different alloys tested. The results showed that the presence of rare-earth elements (RE) only increases the corrosion resistance when present in solid solution, as is the case of the WE54 alloy. At pH 9.2, an amorphous yttrium oxide/hydroxide thick film was formed, which possesses greater stability when compared to magnesium oxide/hydroxide. The role of RE in the corrosion mechanism was discussed. 相似文献
5.
Corrosion behaviors of Zn/Al-Mn alloy composite coatings deposited on magnesium alloy AZ31B (Mg-Al-Zn) 总被引:1,自引:0,他引:1
After being pre-plated a zinc layer, an amorphous Al-Mn alloy coating was applied onto the surface of AZ31B magnesium alloy with a bath of molten salts. Then the corrosion performance of the coated magnesium alloy was examined in 3.5% NaCl solution by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that the single Zn layer was active in the test solution with a high corrosion rate while the Al-Mn alloy coating could effectively protect AZ31B magnesium alloy from corrosion in the solution. The high corrosion resistance of Al-Mn alloy coating was ascribed to an intact and stable passive film formed on the coating. The performances of the passive film on Al-Mn alloy were further investigated by Mott-Schottky curve and X-ray photoelectron spectroscopy (XPS) analysis. It was confirmed that the passive film exhibited n-type semiconducting behavior in 3.5% NaCl solution with a carrier density two orders of magnitude less than that formed on pure aluminum electrode. The XPS analysis indicated that the passive film was mainly composed of AlO(OH) after immersion for long time and the content of Mn was negligible in the outer part of the passive film. Based on the EIS measurement, electronic structure and composition analysis of the passive film, a double-layer structure, with a compact inner oxide and a porous outer layer, of the film was proposed for understanding the corrosion process of passive film, with which the experimental observations might be satisfactorily interpreted. 相似文献
6.
TiO2 or SiO2 nanoparticles dispersed in an acetone solvent containing iodine were deposited on Mg-Al-Zn alloy by electrophoretic deposition (EPD). Subsequently, the composite oxide films were formed on the substrate by anodization in KOH-Na2SiO3 aqueous solutions containing TiO2 or SiO2 nanoparticles. The films formed by EPD were improved binding with the substrate by anodization under high voltages with sparking, and then the anodic films consisted of Si-Mg or Ti-Si-Mg composite oxides. The film thicknesses of TiO2 and SiO2 on the alloy increased with anodization time. In polarization tests, the films anodized under high voltages with sparking in the alkaline solutions had high corrosion resistance. Thus, the composite oxide films formed in the present method were successful in providing corrosion resistance to Mg alloy. 相似文献
7.
Effect of electrolyte additives on performance of plasma electrolytic oxidation films formed on magnesium alloy AZ91D 总被引:2,自引:0,他引:2
Various plasma electrolytic oxidation (PEO) films were prepared on magnesium alloy AZ91D in a silicate bath with different additives such as phosphate, fluoride and borate. Effects of the additives on chemical composition and corrosion resistance of the PEO films were examined by means of scanning electron microscopy (SEM), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The results showed that the PEO films obtained in solutions with both borate and fluoride had better corrosion resistance. In order to understand the corrosion mechanism of PEO films on magnesium alloy AZ91D, electronic property of the magnesium electrode with PEO films was studied by Mott-Schottky approach in a solution containing borate and chloride. The results indicated that magnesium electrodes with and without PEO films all exhibited n-type semiconducting property. However, in comparison with the magnesium electrode treated in solutions containing phosphate or borate, the electrode treated in solutions containing both borate and fluoride (M-film) had lower donor concentration and much negative flat band potential; therefore, the M-film had lower reactivity and higher corrosion resistance. 相似文献
8.
Magnesium alloy, although valuable, is reactive and requires protection before it can be applied in many fields. In this study, a novel protective environmental-friendly gradient coating was performed on AZ91D magnesium alloy by non-chromate surface treatments, which consisted of phytic acid chemical conversion coating and the sol-gel-based CeO2 thin film. The surface morphologies, microstructure and composition of the coatings were investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. The effects of the concentration, layers, temperature of heat treatment of CeO2 sol on the anti-corrosion properties of the gradient coating for magnesium were also investigated. The results showed that the gradient coating was mainly composed of crystalline CeO2. According to the results of electrochemical tests, the corrosion resistance of AZ91D magnesium alloy was found to be greatly improved by means of this new environmental-friendly surface treatment. 相似文献
9.
Anodic coatings formed on magnesium alloys by plasma anodization process are mainly used as protective coatings against corrosion. The effects of KOH concentration, anodization time and current density on properties of anodic layers formed on AZ91D magnesium alloy were investigated to obtain coatings with improved corrosion behaviour. The coatings were characterized by scanning electron microscopy (SEM), electron dispersion X-ray spectroscopy (EDX), X-ray diffraction (XRD) and micro-Raman spectroscopy. The film is porous and cracked, mainly composed of magnesium oxide (MgO), but contains all the elements present in the electrolyte and alloy. The corrosion behaviour of anodized Mg alloy was examined by using stationary and dynamic electrochemical techniques in corrosive water. The best corrosion resistance measured by electrochemical methods is obtained in the more concentrated electrolyte 3 M KOH + 0.5 M KF + 0.25 M Na3PO4·12 H2O, with a long anodization time and a low current density. A double electrochemical effects of the anodized layer on the magnesium corrosion is observed: a large inhibition of the cathodic process and a stabilization of a large passivation plateau. 相似文献
10.
The present study evaluates the effect of magnesium as an inhibitor on the performance of discharge and hydrogen evolution of lithium anode in alkaline electrolyte with additives. The electrochemical behaviors of lithium and lithium–magnesium alloy are assessed by hydrogen evolution rate, discharge current density, anodic potential, and potentiodynamic polarization. For these conditions, the results show that addition of magnesium to lithium enhances the current efficiency. Addition of 0.07 wt% Mg to lithium has minor effect on discharge current and anodic potential of lithium anode. The chemical composition and the morphology of the anode surfaces were evaluated by X-ray diffraction and scanning electron microscopy. The results show that the slow dissolution of lithium–magnesium alloy generates the formation of LiOH, LiOH·H2O, and Mg(OH)2. After discharge in saturated alkaline electrolyte with additives, the lithium–magnesium surface is less porous than lithium surface. Hydrogen evolution decrease, prompted by adding magnesium to lithium, is related to surface integrity enhanced by Mg(OH)2. 相似文献
11.
12.
Maysam Mohammadi Ali Yazdani Mohammad E. Bahrololoom Akram Alfantazi 《Journal of Coatings Technology and Research》2013,10(2):219-229
In this article, the effects of two inorganic corrosion inhibitors, permanganate and phosphate anions, on morphology, composition, thickness, and corrosion resistance of the anodic film formed on 2024 aluminum alloy in sulfuric acid were investigated. Surface morphology of the oxide films were studied by field emission scanning electron microscopy. Electrochemical impedance spectroscopy and potentiodynamic polarization tests were conducted to assess the corrosion resistance of the coatings. These analyses showed that the presence of the mentioned inhibitors changed the coating morphology, especially in the case of phosphate ions. Corrosion results indicated that using inhibitors during the anodizing process increased the corrosion resistance of the anodized samples. The increases were approximately 81% and 97% for 0.05 M of permanganate and phosphate ions, respectively, compared with the anodized coatings in the absence of additives. An increase in the inhibitor concentration results in better corrosion resistance of the aluminum anodic layer. 相似文献
13.
14.
M. Laleh Farzad Kargar A. Sabour Rouhaghdam 《Journal of Coatings Technology and Research》2011,8(6):765-771
Magnesium and its alloys have been used in many industries, but they are reactive and require protection against aggressive
environments. In this study, a compact and relatively pore-free oxide coating was formed on AZ91D magnesium alloy to improve
its corrosion resistance by means of the microarc oxidation (MAO) process via the addition of CeCl3 as an additive into the MAO electrolyte. Morphologies and compositions of the coatings were studied with scanning electron
microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. It was found that with the addition of CeCl3 into the MAO electrolyte, the obtained coating showed more uniform morphology compared with the coating produced in the CeCl3 free electrolyte. EDS analysis confirmed the presence of cerium in the coating formed in the electrolyte with CeCl3. Polarization tests results showed that the corrosion current density of the coating formed in the CeCl3 containing electrolyte was less than that of the coating formed in the electrolyte without CeCl3. Furthermore, electrochemical impedance spectroscopy (EIS) tests indicated that the coating formed in the electrolyte with
the addition of CeCl3 improved the corrosion resistance of the substrate significantly. 相似文献
15.
Although Al-Mg-Sc alloy was widely applied to aviation aerospace field, they were vulnerable to local corrosion and wear in the process of long-term service in severe environmental conditions. In this paper, micro-arc oxidation (MAO) ceramic films on Al-Mg-Sc alloy substrate were prepared in electrolyte solutions with different Na2SiO3 concentrations, and the corrosion resistance and wear resistance of the MAO samples were studied. The experimental results of potentiodynamic polarization (PDS) and long-term immersion tests indicated that the MAO ceramic film prepared in 10 g/L Na2SiO3 electrolyte solution had the best corrosion resistance, as manifested by no obvious cracks, serious collapse and corrosion products on the sample surface and no deep cracks and corrosion paths in the cross-sectional area. The increase of Na2SiO3 concentration in electrolyte solution also improved the wear resistance of MAO ceramic film, as manifested by low wear depth (10 μm)and width (1 mm) of the MAO ceramic film prepared in 10 g/L Na2SiO3 electrolyte solution against GCr15 steel ball. Studies in mechanisms suggested that as the Na2SiO3 concentration in the electrolyte increased, the MAO ceramic film became denser, which could prevent the penetration of corrosive medium, promote the generation of the anti-wear layer with SiO2 as the main component to enhance the wear resistance. MAO ceramic film formed in Na2SiO3 electrolyte solution provided good protective performance for Al-Mg-Sc alloy in the corrosion and wear conditions, which had a broader application prospect. 相似文献
16.
采用正交实验对AZ 31镁合金在碱性电解液中进行阳极氧化的工艺参数进行优化。考察了氧化时间、电流密度、脉冲频率和占空比对阳极氧化膜性能的影响,获得最佳阳极氧化工艺参数为:氧化时间15min,电流密度1.0A/dm2,脉冲频率200Hz,占空比10%。采用X射线衍射仪(XRD)、扫描电镜(SEM)和动电位极化曲线等检测手段研究了阳极氧化膜的结构、表面形貌和耐蚀性。结果表明:经优化工艺制得的阳极氧化膜,其主要成分为MgO,Al2O3和MgAl2O4,膜层孔隙分布均匀、致密,耐蚀性大幅提高。 相似文献
17.
The electrochemical behaviour of anodic films formed on pure aluminium (99.999% and 1100) and 6061-Al alloy substrates in phosphoric acid has been investigated in an aluminium saturated phosphate solution of pH 6.23. The polarization resistance data obtained after one day immersion in the electrolyte showed a strong correlation with the pit number, assessed from an outdoor atmospheric exposure test after 4 months. The cathodic polarization measurements of anodized aluminium in the electrolyte were also carried out. Electrochemical behaviour, eg corrosion, hydrogen evolution reaction, was interpreted in terms of “active sites” within the anodic film. It is suggested that the active sites were mainly formed in the presence of impurities or alloy constituents in aluminium substrates. 相似文献
18.
The effects of pH and temperature of a stannate bath on the quality of stannate chemical conversion coatings formed on AZ91 D magnesium alloy by using the potentiostatic polarization technique at E = −1.1 V were investigated in order to improve uniformity and corrosion protection performance of the coating films. It was found that the uniformity and corrosion resistance of coating films deposited by potentiostatic polarization were closely associated with pH and temperature of the coating bath. The pH and temperature to obtain the best coating film were investigated as a function of corrosion protection performance evaluated by curves of potentiodynamic anodic polarization conducted in borate buffer solution. Scanning electron microscope observation and electrochemical corrosion tests of the stannate-coated samples confirmed significant improvement in uniformity and corrosion resistivity of coating films deposited by the potentiostatic technique by modifying the pH and temperature of the coating bath. It was also found that uniformity and corrosion resistivity of the coating films deposited by the potentiostatic technique were considerably improved compared to those of coatings deposited by the simple immersion method at the best conditions of pH and temperature of the coating bath. 相似文献
19.
20.
Surface films of TiN and TiN/Ti were deposited on Ti6Al4V alloy by arc ion plating (AIP). Open-circuit potential, potentiodynamic
polarization tests and electrochemical impedance spectroscopy (EIS) were employed to investigate the corrosion performance
of TiN and TiN/Ti films in Hank’s simulated body fluid at 37 °C and pH 7.4. Scanning electron microscopy (SEM) was used to
study the surface morphology of the corroded samples after the potentiodynamic polarization tests. The results show that the
TiN and the TiN/Ti films can provide effective protection for the Ti6Al4V substrate in Hank’s fluid, and the TiN/Ti composite
film showed a corrosion resistance superior to that of the TiN film. The outer TiN layer of the composite film mainly acted
as an efficient barrier to corrosion during short-term experiments. In contrast to the bare Ti6Al4V, no pitting was observed
on the surface of the TiN and TiN/Ti films deposited on the bare alloy after potentiodynamic polarization. 相似文献