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1.
The EIS technique was used to analyze the electrochemical reaction behavior of Alloy AZ91 in H3PO4/KOH buffered K2SO4 solution at pH 7. The corrosion resistance of Alloy AZ91 was directly related with the stability of Al2O3 · xH2O rich part of the composite oxide/hydroxide layer on the alloy surface. The break down of the oxide layer was estimated to occur mainly on the matrix solid solution phase in Alloy AZ91. The mf capacitive loop arose from the relaxation of mass transport in the solid oxide phase in the presence of Al2O3 · xH2O rich part and from Mg+ ion concentration within the broken area in the absence of Al2O3 · xH2O rich part in the composite oxide structure on the alloy surface. The lf inductive loop had tendency of disappear when the dissolution rate of the alloy decreased as a result of the formation of the protective oxide layer. 相似文献
2.
Corrosion behaviour of AZ31B magnesium alloy in different concentrations of NaCl solution saturated with CO2 was studied by electrochemical techniques, Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray. The corrosion rate increases with increasing NaCl concentration both in the presence and absence of CO2. The corrosion rate in NaCl solution saturated with CO2 is bigger than that in single NaCl solution. The inhibitive effect of CO2 is also observed with immersion time increased in NaCl solution saturated with CO2, showing that CO2 reduces the average corrosion rate due to the formation of insoluble products. 相似文献
3.
AZ91HP magnesium alloy was melted by CO2 laser. Compared with as‐received Mg alloy, the grain of the melted layer was refined significantly and the content of Al was increased. The corrosion resistance of the melted layer was improved because of the grain refinement, the redistribution of β‐Mg17Al12 and the increasing of the Al content. As compared to the non‐overlapping zone, the overlapping zone of the melted layer was liable to be corroded. 相似文献
4.
Kunitsugu Aramaki 《Corrosion Science》2010,52(4):1464-1471
An ultrathin, ordered and two-dimensional polymer coating was prepared on a passivated iron electrode by modification of 16-hydroxyhexadecanoate ion HO(CH2)15CO2− self-assembled monolayer with 1,2-bis(triethoxysilyl)ethane (C2H5O)3Si(CH2)2Si(OC2H5)3 and octadecyltriethoxysilane C18H37Si(OC2H5)3. Subsequently, the electrode was healed in 0.1 M NaNO3. Protection of passivated iron against passive film breakdown and corrosion of iron was examined by monitoring of the open-circuit potential and repeated polarization measurements of the polymer-coated and healed electrode in an aerated 0.1 M NaCl solution during immersion for many hours. Localized corrosion was markedly prevented by coverage with the polymer coating and the healing treatment in 0.1 M NaNO3. Prominent protection of iron from corrosion in 0.1 M NaCl was observed before the breakdown occurred. The electrode surface covered with the healed passive film and polymer coating was analyzed by contact angle measurement, X-ray photoelectron spectroscopy and electron-probe microanalysis. 相似文献
5.
In this work, CeO2/stannate multilayer coatings on AZ91D magnesium alloy were successfully obtained by chemical conversion and sol–gel dip coating. The stannate conversion coatings were prepared from a stannate aqueous bath containing Na2SnO3, CH3COONa, Na3PO4 and NaOH at different temperatures and immersion times. Ceria films were produced on stannate/AZ91D starting from Ce(III) nitrate solutions in H2O. In some cases, the PVA was added as chelating agent. Ceria top coatings were fired at 200 °C for 1 h. Coating microstructure was examined by FE-SEM. Finally, the corrosion resistance features of the coatings were tested by the electrochemical impedance spectroscopy (EIS) in 3 wt.% NaCl solution. The effect of PVA addition was evaluated in terms of microstructure and corrosion resistance features. CeO2/stannate multilayer films, 3 μm thick, uniform, well adherent and nearly crack free were obtained. The formation of CeO2 phase was confirmed by XRD and XPS analyses. The XPS depth profiles showed a limited diffusion of Mg towards the ceramic film. The EIS tests showed a significant improvement of corrosion resistance of the multilayer coatings (~ 16.6 kΩ after 48 h in NaCl solution) with respect to the blank alloy (~ 2.4 kΩ after 48 h in NaCl solution). 相似文献
6.
The influence of salt deposits on the atmospheric corrosion of high purity Al (99.999%) was studied in the laboratory. Four chloride and sulfate-containing salts, NaCl, Na2SO4, AlCl3 · 6H2O and MgCl2 · 6H2O were investigated. The samples were exposed to purified humid air with careful control of the relative humidity (95%), temperature (22.0 °C), and air flow. The concentration of CO2 was 350 ppm or <1 ppm and the exposure time was four weeks. Under the experimental conditions all four salts formed aqueous solutions on the metal surface. Mass gain and metal loss results are reported. The corroded surfaces were studied by ESEM, OM, AES and FEG/SEM equipped with EDX. The corrosion products were analyzed by gravimetry, IC and grazing incidence XRD. In the absence of CO2, the corrosivity of the chloride salts studied increases in the order MgCl2 · 6H2O < AlCl3 · 6H2O < NaCl. Sodium chloride is very corrosive in this environment because the sodium ion supports the development of high pH in the cathodic areas, resulting in alkaline dissolution of the alumina passive film and rapid general corrosion. The low corrosivity of MgCl2 · 6H2O is explained by the inability of Mg2+ to support high pH values in the cathodic areas. In the presence of carbon dioxide, the corrosion induced by the salts studied exhibit similar rates. Carbon dioxide strongly inhibits aluminum corrosion in the presence of AlCl3 · 6H2O and especially, NaCl, while it is slightly corrosive in the presence of MgCl2 · 6H2O. The corrosion effects of CO2 are explained in terms of its acidic properties and by the precipitation of carbonates. In the absence of CO2, Na2SO4 is less corrosive than NaCl. This is explained by the lower solubility of aluminum hydroxy sulfates in comparison to the chlorides. The average corrosion rate in the presence of CO2 is the same for both salts. The main difference is that sulfate is less efficient than chloride in causing pitting of aluminum in neutral or acidic media. 相似文献
7.
8.
Tribocorrosion of stainless steel 316L and titanium alloy TA6V4 has been conducted in a sulphuric acid solution using an apparatus designed and built for evaluating the joint action of corrosion and wear. The material electrochemical and wear behaviours have been investigated during friction tests under electrochemical potential control. The specimens have been submitted to friction against an alumina ball under cathodic, free and anodic potentials. The friction coefficient, the wear rate and the current density were measured and the obtained results were discussed in terms of passivating film stability and repassivation kinetics. 相似文献
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10.
Zhongping Yao Yongjun XuYunfu Liu Dali WangZhaohua Jiang Fuping Wang 《Journal of Alloys and Compounds》2011,509(33):8469-8474
The aim of this work is to study the structure and the corrosion resistance of the plasma electrolytic oxidation ZrO2 ceramic coatings on Mg alloys. The ceramic coatings were prepared on AZ91D Mg alloy in Na5P3O10 and K2ZrF6 solution by pulsed single-polar plasma electrolytic oxidation (PEO). The phase composition, morphology and element distribution in the coating were investigated by X-ray diffractometry, scanning electron microscopy and energy distribution spectroscopy, respectively. The results show that the coating thickness and surface roughness were increased with the increase of the reaction time. The ceramic coatings were of double-layer structure with the loose and porous outer layer and the compact inner layer. And the coating was composed of P, Zr, Mg and K, of which P and Zr were the main elements in the coating. P in the coating existed in the form of amorphous state, while Zr crystallized in the form of t-ZrO2 and a little c-ZrO2 in the coating. Electrochemical impedance spectra (EIS) and the polarizing curve tests of the coatings were measured through CHI604 electrochemical analyzer in 3.5% NaCl solution to evaluate the corrosion resistance. The polarization resistance obtained from the equivalent circuit of the EIS was consistent with the results of the polarizing curves tests. 相似文献
11.
Mg alloy, AZ91D, which has a two-phase structure, was successfully electroplated in an alkaline Cu-plating bath. The Cu-coated Mg alloy specimen was further electroplated in eco-friendly acidic Cu and then trivalent Cr baths to obtain an anti-wear and anti-corrosion Cr/Cu coating. Experimental results show that the wear and corrosion resistance of the Mg alloy specimen was considerably improved by trivalent Cr electrodeposition. The hardness of the as-plated Cr deposit was drastically increased by using reduction-flame heating for 0.5 s. The above-mentioned results were measured via bonding strength, hardness, wear and corrosion tests. A superior wear and corrosion resistance was obtained when a Cu-coated Mg alloy specimen was electroplated with a trivalent Cr deposit, followed by heating with reduction-flame heating for 0.5 s. 相似文献
12.
The corrosion process in the Cu/CuSO4 + H2SO4 system is considered as the sum of two coupled single-electron electrochemical reactions that occur simultaneously and independently on the surface of the copper electrode. Our numerical model incorporates diffusion and migration of solution species including cuprous ions, as well as the chemical equilibria for copper sulphate and sulphuric acid dissociation. Numerical simulations are compared with the trends discovered during experimental investigation of copper corrosion in similar systems. 相似文献
13.
The corrosion inhibitive efficiencies of two crown type polyethers, namely dibenzo-bis-imino crown ether (C-1) and dibenzo-diaza crown ether (C-2), which are macrocyclic Schiff base and its reduced form (macrocyclic amine), respectively, for the steel in 1 M H2SO4 have been investigated by Tafel extrapolation and linear polarization methods. Corrosion and adsorption isotherm parameters were determined from current-potential curves. The studies show that C-1 and C-2 inhibit the corrosion of the steel in H2SO4 solution. Semiempirical AM1 method was used for theoretical calculations. The obtained results of these calculations for the compounds were found to be consistent with the experimental findings. 相似文献
14.
Kunitsugu Aramaki 《Corrosion Science》2010,52(1):1-6
For preparing an ultrathin two-dimensional polymer coating adsorbed on passivated iron, a 16-hydroxyhexadecanoate ion HO(CH2)15CO2− self-assembled monolayer (SAM) was modified with 1,2-bis(triethoxysilyl)ethane (C2H5O)3Si(CH2)2Si(OC2H5)3 and octadecyltriethoxysilane C18H37Si(OC2H5)3. Protection of passivated iron against passive film breakdown and corrosion of iron was investigated by monitoring of the open-circuit potential and repeated polarization measurements in an aerated 0.1 M Na2SO4 solution during immersion for many hours. The time required for passive film breakdown of the polymer-coated electrode was markedly higher in this solution than that of the passivated one, indicating protection of the passive film from breakdown by coverage with the polymer coating. The protective efficiencies of the passive film covered with the coating were extremely high, more than 99.9% in 0.1 M Na2SO4 before the passive film was broken down, showing prominent cooperative suppression of iron corrosion in the solution by coverage with the passive film and polymer coating. The polymer-coated surface was characterized by contact angle measurement and electron-probe microanalysis (EPMA). Prevention of passive film breakdown and iron corrosion for the polymer-coated electrode healed in 0.1 M NaNO3 was also examined in 0.1 M Na2SO4. 相似文献
15.
The corrosion inhibition of commercial copper by means of isatin was studied in aerated 0.5 M H2SO4 in the temperature range 25-55 °C using weight-loss, potentiodynamic and spectrophotometric tests, and determination of double layer capacitance. Inhibition efficiencies up to 94% in the concentration range of 1×10−4-7.5×10−3 M of isatin were obtained. The corrosion rates estimated with weight-loss measurements were higher than those correspondingly determined with the potentiodynamic test, especially at higher concentrations of inhibitor. This is in accord with other researches that have pointed out the limitation of the Tafel line extrapolation method in the determination of corrosion rates. The kinetics of cuprous and cupric ion formation and UV-visible spectra support the formation hypothesis of a complex between copper and isatin. The adsorptive behaviour of isatin on copper 0.5 M H2SO4 was also investigated. 相似文献
16.
The corrosion behaviour of an HVOF Ni–5Al/WC–17Co coating on Al-7075 is investigated in 0.5 M H2SO4. In the temperature range of 25–45 °C, the coating exhibits pseudopassivity that effectively protects from localized corrosion. At 25 °C, pseudopassivity proceeds via three stages: during the first stage, oxidation of W in the binder phase occurs. The second stage is characterized by oxidation of W in both the binder and the carbide particles. The third stage is characterized by intensive hydration of WO3 and formation of Co3O4. During the second and third pseudopassive stages, the formation of a bi-layer surface film is postulated. The inner layer, consisting of anhydrous oxides, has a barrier character. The outer layer, composed of WO3 · xH2O, is unstable. In case of surface film disruption, the bond coat successfully hinders corrosion propagation into the Al-alloy. Higher electrolyte temperatures lead to faster corrosion kinetics and higher tendency for pitting. 相似文献
17.
The corrosion behavior of cold isostatically pressed (CIP) high purity alumina ceramics in aqueous HCl and H2SO4 solutions with various concentrations has been studied simultaneously at room temperature (25 °C). Corrosion tests were also performed with 0.65 mol/l HCl and 0.37 mol/l H2SO4 solutions at 40, 55 and 70 °C for 48 h. Chemical stability was monitored by determining the amount of Al3+, Mg2+, Ca2+, Na+ Si4+ and Fe3+ ions eluted in different concentrations of HCl and H2SO4 solutions by means of atomic absorption spectrometry (AAS). By increasing the concentration from 0.37 to 6.5 mol/l, it was notified that the corrosion susceptibility in HCl and H2SO4 solutions for the CIP alumina specimens at room temperature decreases. 相似文献
18.
Corrosion product formation during NaCl induced atmospheric corrosion of magnesium alloy AZ91D 总被引:2,自引:0,他引:2
Magnesium alloy AZ91D was exposed in humid air at 95% relative humidity (RH) with a deposition of 70 μg/cm−2 NaCl. The corrosion products formed and the surface electrolyte were analysed after different exposure times using ex situ and in situ FTIR spectroscopy, X-ray diffraction and Ion Chromatography. The results show that magnesium carbonates are the main solid corrosion products formed under these conditions. The corrosion products identified were the magnesium carbonates hydromagnesite (Mg5 (CO3)4 (OH)24H2O) and nesquehonite (MgCO3 3H2O). The corrosion attack starts with the formation of magnesite at locations with higher NaCl contents. At 95% RH, a sequence of reactions was observed with the initial formation of magnesite, which transformed into nesquehonite after 2-3 days. Long exposures result in the formation of pits containing brucite (Mg(OH2)) covered with hydromagnesite crusts. The hydromagnesite crusts restrict the transport of CO2 and O2 to the magnesium surface and thereby favour the formation of brucite. Analysis of the surface electrolyte showed that the NaCl applied on the surface at the beginning was essentially preserved during the initial corrosion process. Since the applied salt was not bound in sparingly soluble corrosion products a layer of NaCl electrolyte was present on the surface during the whole exposure. Thus, Na+ and Cl− ions can participate in the corrosion process during the whole time and the availability of these species will not restrict the atmospheric corrosion of AZ91D under these conditions. It is suggested that the corrosion behaviour of AZ91D is rather controlled by factors related to the microstructure of the alloy and formation of solid carbonate containing corrosion products blocking active corrosion sites on the surface. 相似文献
19.
Jolanta ?wiatowska 《Corrosion Science》2010,52(7):2372-9636
The dissolution of Mg has been investigated with atomic emission spectroelectrochemistry at open circuit and during potentiostatic control in chloride (NaCl) and sulfate (Na2SO4) electrolytes. A dissolution stoichiometry of approximately n = 2 is observed under all the conditions of these experiments with no evidence for the commonly invoked Mg+ intermediate. Nevertheless, in chloride electrolyte it is shown that anodic polarization results in a cathodic activation of the surface with increased hydrogen production during the polarization and an increased corrosion rate following the pulse. The formation of insoluble Mg oxides/hydroxides was also investigated in the sulfate electrolyte. 相似文献
20.
Fe1−xMgx alloy films (with x ? 43.4 at.% Mg) were deposited by dc magnetron sputtering onto glass slide substrates. The objective of this study was to characterise the corrosion properties of these alloys in saline solution for application as new friendly environmentally sacrificial coatings in the protection of steel structures. The morphological and structural properties of the alloys were systematically studied prior to electrochemical experiments, and then the degraded surfaces were analysed to determine the composition and nature of corrosion products. Alloys with <25 at.% Mg were single-phase body-centred cubic (bcc) with enlarged lattice parameters, whereas for magnesium contents above 25 at.%, amorphisation occurred. The reactivity of the alloys in saline solution is strongly dependent on the Mg content and the alloy structure. The incorporation of magnesium leads to an open circuit potential shift of the alloy towards more negative values, that confers an attractive interest of these alloys as sacrificial coatings. A transition in corrosion activity is observed at 25 at.% Mg from which the reactivity decreases with the magnesium content increase. The evolution of the alloy corrosion behaviour is discussed in terms of structural and corrosion products evolution versus magnesium content. 相似文献