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1.
As a first step towards studying pitting corrosion of Zn in deaerated neutral sodium nitrite solutions (pH 6.9), we have reported the results of potentiodynamic polarization and cyclic voltammetry measurements on the passivity and passivity breakdown of Zn in these solutions. Measurements were conducted under the influence of various experimental conditions, complemented by ex situ scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) examinations of the electrode surface. The voltammograms involve active/passive transition prior to the initiation of pitting corrosion as a result of breakdown of the passive film by NO2− ions. The active region displays one anodic peak due to the formation of ZnO passive film on the anode surface. SEM examinations confirmed the existence of pits on the electrode surface. The potential at which pits initiated (Epit) was determined, together with a pit transition potential (Eptp) that appeared as an abrupt current discontinuity on the reverse potential scan (hysteresis loop), and a protection potential (Eprot) that appeared at the end of the hysteresis loop. The value of Epit shifted negatively as either Cnitrite or temperature was increased, while it increased with the increase in potential scan rate. The effect of adding some environmentally acceptable inorganic inhibitors, as tungstates, molybdates and silicates (water glass), on the pitting corrosion behaviour of Zn in nitrite solutions has also been studied. The mechanism of inhibition was discussed. 相似文献
2.
Mohammed A. Amin Sayed S. Abd El Rehim S.O. Moussa Abdallah S. Ellithy 《Electrochimica acta》2008,53(18):5644-5652
The influence of various concentrations of NaClO4, as a pitting corrosion agent, on the corrosion behaviour of pure Al, and two Al–Cu alloys, namely (Al + 2.5 wt% Cu) and (Al + 7 wt% Cu) alloys in 1.0 M Na2SO4 solution was investigated by potentiodynamic polarization and potentiostatic techniques at 25 °C. Measurements were conducted under the influence of various experimental conditions, complemented by ex situ energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) examinations of the electrode surface. In free perchlorate sulphate solutions, for the three Al samples, the anodic polarization exhibits an active/passive transition. The active dissolution region involves an anodic peak (peak A) which is assigned to the formation of Al2O3 passive film on the electrode surface. The passive region extends up to 1500 mV with almost constant current density (jpass) without exhibiting a critical breakdown potential or showing any evidence of pitting attack. For the three Al samples, addition of ClO4− ions to the sulphate solution stimulates their active anodic dissolution and tends to induce pitting corrosion within the oxide passive region. Pitting corrosion was confirmed by SEM examination of the electrode surface. The pitting potential decreases with increasing ClO4− ion concentration indicating a decrease in pitting corrosion resistance. The susceptibility of the three Al samples towards pitting corrosion decreases in the order: Al > (Al + 2.5 wt% Cu) alloy > (Al + 7 wt% Cu) alloy. Potentiostatic measurements showed that the rate of pitting initiation increases with increasing ClO4− ion concentration and applied step anodic potential, while it decreases with increasing %Cu in the Al samples. The inhibitive effect of SO42− ions was also discussed. 相似文献
3.
M. Reffass 《Electrochimica acta》2007,52(27):7599-7606
Pitting corrosion of carbon steel electrodes in 0.1 mol L−1 NaHCO3 + 0.02 mol L−1 NaCl solutions was induced by anodic polarisation. The evolution of the breakdown potential Eb with NO2− concentration was investigated by linear voltammetry. Eb increased from −15 ± 5 mV/SCE for [NO2−] = 0 up to 400 ± 50 mV/SCE for [NO2−] = 0.1 mol L−1. During anodic polarisation at potentials comprised between Eb([NO2−] = 0) and Eb([NO2−] ≠ 0), the behaviour of the whole electrode surface, followed by chronoamperometry, was compared to the behaviour of one single pit, followed via scanning vibrating electrode technique (SVET). Addition of a NaNO2 solution after the beginning of the polarisation led to a rapid repassivation of pre-existing well-grown pits. In situ micro-Raman spectroscopy was then used to identify the corrosion products forming inside the pits. The first species to be detected in the presence of NO2− were mainly dissolved Fe(III) species, more likely [FeIII(H2O)6]3+ complexes. Iron(II) carbonate FeCO3, siderite, and carbonated green rust GR(CO32−) were also detected in the active pits, as in the absence of nitrite. But they were accompanied by maghemite γ-Fe2O3, a phase structurally similar to the passive film, that forms from the Fe(III) complexes. The Raman analyses then correlate with the SVET observations and confirm that the main effect of nitrite ions is to oxidize iron(II) into iron(III). The passive film would then form from the Fe(III) species still bound to the steel surface. 相似文献
4.
Pitting of Al and Al-6%Zn and Al-12%Zn alloys in KSCN solutions was studied by means of potentiodynamic anodic polarization, cyclic voltammetry, potentiostatic and impedance techniques. Measurements were conducted under different experimental conditions, complemented by ex situ scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA). The potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of thin film of Al2O3 on the anode surface (in case of Al) and the formation of ZnO on the Al2O3 matrix, in case of the two Al-Zn alloys (as evidenced from EDXA). The passive region is followed by pitting corrosion as a result of passivity breakdown by the aggressive attack of SCN− anions. SEM images confirmed the existence of pits on the electrode surface. Alloyed Zn was found to enhance pitting attack. The pitting potential (Epit) decreases with an increase in SCN− concentration and temperature, but increases with increasing potential scan rate. The current/time transients show that the incubation time for passivity breakdown decreases with increasing applied positive potential, SCN− concentration, and temperature. Impedance measurements showed that Nyquist plots are characterized by a depressed charge-transfer semicircle, the diameter of which is a function of SCN− concentration, applied potential, solution temperature and sample composition. 相似文献
5.
Jiin-Jiang Jow Huen-Hua Lai Cheng-Chin Wang Tzong-Rong Ling 《Electrochimica acta》2010,55(8):2793-655
Hydrothermal treatment (HTT) of RuO2-Ta2O5/Ti electrode, as a method for improving their performance, for use in supercapacitors was investigated.The results show that HTT significantly enhances the stability of the electrodes. The specific capacitance of electrodes, subject to HTT in the temperature range 180-250 °C remains unchanged after 1000 CV cycles between −0.2 and 1.1 V vs. SCE; without HTT a decay to 97% of the initial is observed. The results also show that HTT decreases the activity of the electrodes for O2 and H2 evolution and increases the voltage window by 56-135 mV for supercapacitors, but with a specific capacitance decrease of 7-27%. XPS analyses show the existence of more hydroxides after the HTT, which leads to a little increase in the interplanar distance as indicated in the XDR results. Contact angle measurements show the presence of a more hydrophilic surface after HTT. 相似文献
6.
S. S. Abd-El Rehim N. H. Amin L. I. Ali N. F. Mohamed 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1998,72(2):197-201
The electrochemical behaviour and corrosion of lead in various concentrations of acetic, lactic (0·01 M –1·0 M ), oxalic and tartaric (0·01 M –0·15 M ) acid solutions were studied at 25°C by a potentiodynamic method. The lead anode is readily soluble both in acetic and lactic acid solutions up to 2000 mV. In these two acid solutions, the anodic dissolution of lead increases with increases in the acid concentration and the dissolution process is under charge transfer control. Lactic acid is more corrosive than acetic acid. However, in oxalic and tartaric acid solutions, the E/i profiles depend on the acid concentration. Above a certain specific concentration, the profiles exhibit an anodic current peak associated with a dissolution of the metal and the formation of a passivating lead salt film and a cathodic peak which is related to the reduction of the film. The active dissolution of the lead increases with the acid concentration, the scan rate and stirring of the solution. The passivation of lead in these two acid solutions occurs by a dissolution–precipitation mechanism and the process is controlled by diffusion. X-ray diffraction analysis confirmed the presence of a passivating salt film (either lead oxalate or lead tartrate) on the electrode surface. © 1998 SCI 相似文献
7.
M. M. Laz R. M. Souto S. González R. C. Salvarezza A. J. Arvia 《Journal of Applied Electrochemistry》1992,22(12):1129-1134
The pitting corrosion of copper in alkaline solutions in the presence of benzotriazole (BTA) was investigated. The presence of BTA shifts the breakdown (E
b) and the repassivating (E
p) potentials positively with respect to the blanks. However, the shift ofE
p becomes smaller than that ofE
b, particularly at pH9 and 11. Pitting corrosion involves the formation of crystallographic pits. The kinetics of the process fits a nucleation and growth mechanism involving instantaneous nucleation and 3D growth under charge transfer control. The spatial distribution of pits indicates that there is no marked influence of a pit on the nucleation and growth of other pits. 相似文献
8.
Aimed at the problem of tubing corrosion in environment that containing hydrogen sulfide (H2S), carbon dioxide (CO2), and chlorides (Cl−), the corrosion behaviour of two nickel based alloys (UNS 06985 and UNS 08825) in 15 wt%NaCl solution containing H2S/CO2 in high temperature and high pressure environment was investigated. The pitting corrosion behaviour of Ni-based alloys was studied in FeCl3·6H2O solution by means of polarisation curve and immersion tests. The scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) was applied to analyse the microstructure and corrosion performance of the samples. The results showed that the pitting-resistant of nickel alloy UNS 06985 was superior to UNS 08825. With the rising of experimental temperature, the corrosion increased and some slight pitting attacks appeared on the surface of UNS 08825. The test temperature was the crucial factor that influenced not only the compactness and the growing rate of corrosion product scale, but also the corrosion rate of the alloys. Elemental sulfur is a strong oxidant, the presence of S0 leads to a serious localized corrosion. XRD showed that the corrosion films formed on nickel base alloys consisted of NiS, CrO3, and the oxides of Ni and Fe. The polarisation curves showed a different corrosion behaviour of two alloys, anodic curve of UNS 06985 has a wider passivation area, and there has higher transpassive potential. 相似文献
9.
J.E Sweitzer 《Electrochimica acta》2003,48(9):1223-1234
The role of isothermal aging on the localized corrosion behavior of Al90Fe5Gd5 and Al87Ni8.7Y4.3 alloys was characterized in 0.6 M NaCl solution. The pitting (Epit) and repassivation (Erp) potentials were both increased ∼400 mV by the presence of transition and rare earth metal additions in supersaturated solid solution and amorphous structure. A statistical distribution in Epit observed on small electrodes was due, in part, to the sensitivity of this critical potential to the presence of a population of critical surface flaws that serve as pit initiation sites. Mechanistic insight on the spacing of critical flaws was enabled by varying the tested electrode surface area. Erp was not dependent on electrode surface area due to the similarity of pit depths in all electrode sizes. The critical potentials were also characterized after heat treating the amorphous ribbons isothermally at 150 °C for 25 h and 550 °C for 1 h. The former produced Al-rich nanocrystals embedded in the remaining amorphous matrix while the latter produced a fully crystalline condition containing intermetallic phases. Notably, the improved resistance to the formation of micrometer-scale pits was not lost compared with the fully amorphous condition when small Al-rich nanocrystals were present in an amorphous matrix. However, improvement in pitting corrosion resistance was completely lost in the fully crystallized condition as indicated by values for Epit and Erp that were similar to those of high purity, polycrystalline aluminum. 相似文献
10.
The pitting corrosion of different positions (Top, Middle and Bottom) of weld nugget zone (WNZ) along thickness plate in friction stir welded 2219-O aluminum alloy in alkaline chloride solution was investigated by using open circuit potential, cyclic polarization, scanning electron microscopy and atomic force microscope. The results indicate that the material presents significant passivation, the top has highest corrosion potential, pitting potential and re-passivation potential compared with the bottom and base material. With the increase of traverse speed from 60 to 100 mm/min or rotary speed from 500 to 600 rpm, the corrosion resistance decreases. 相似文献
11.
The influence of NO2− on the corrosion of Ni in acid phosphate solutions were analysed by means of potentiodynamic scans and impedance spectroscopy under electrode rotation. The complex nitrite reduction reaction involves adsorbed intermediates which interfere with the surface process occurring during the active dissolution and passivation of Ni. Near the corrosion potential, the reduction of NO2− follows a Tafel’s behaviour independent from nitrite concentration and electrode rotation speed, denoting a surface-controlling step. Without NO2−, the adsorption of H predominates in the cathodic polarisations. The adsorption of NO2− near the corrosion potential has several consequences: (i) it brings about a lower surface coverage of NiOH decreasing the rate of Ni active dissolution and (ii) its preferential adsorption against that of passivating species, such as NiOH and Ni(OH)2, hinders the formation of the pre-passive layer at low pH-values increasing the passivation current. 相似文献
12.
Vanessa N. Santos Murilo F. Cabral Jefferson S. Ferreira Alda K.M. Holanda Sergio A.S. Machado Jackson R. Sousa Luiz G.F. Lopes Adriana N. Correia Pedro de Lima Neto 《Electrochimica acta》2011,(16):5686
The modification of a gold electrode surface by electropolymerization of trans-[Ru(NH3)4(Ist)SO4]+ to produce an electrochemical sensor for nitric oxide was investigated. The influence of dopamine, serotonin and nitrite as interferents for NO detection was also examined using square-wave voltammetry (SWV). The characterization of the modified electrode was carried out by cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM) and SERS techniques. The gold electrode was successfully modified by the trans-[Ru(NH3)4(Ist)SO4]+ complex ion using cyclic voltammetry. The experiments show that a monolayer of the film is achieved after ten voltammetric cycles, that NO in solution can coordinate to the metal present in the layer, that dopamine, serotonin and nitrite are interferents for the detection of NO, and that the response for the nitrite is much less significant than the responses for dopamine and serotonin. The proposed modified electrode has the potential to be applied as a sensor for NO. 相似文献
13.
NaBiO3 crystal of high purity has been synthesized through chemical oxidization. The morphology and thermal stability of NaBiO3 were examined with scanning electron microscope (SEM) and thermogravimetry-differential scanning calorimetry (TG-DSC). The electrochemical properties of MnO2 electrodes with and without doping NaBiO3 were studied through galvanostatic charge/discharge and cyclic voltammetry. The results indicate that the MnO2 electrode doped with NaBiO3 possesses remarkably higher discharge voltage and capacity and better reversibility than the pure MnO2 electrode and Bi2O3 doping MnO2 electrode. 相似文献
14.
Darko Grujicic 《Electrochimica acta》2004,49(26):4719-4732
Nucleation mechanisms of cobalt on a glassy carbon electrode (gce) from aqueous ammonium sulfate solutions were investigated through the electrochemical techniques of cyclic voltammetry (cv) and chronoamperometry (ca), coupled with atomic force microscopy (AFM) studies. The studied parameters were pH, cobalt concentration, temperature, scanning rate, and deposition potential. It was found that scanning in the cathodic direction produced two peaks, corresponding to cobalt and hydrogen reduction, respectively. Scanning in the anodic direction was characterized by cobalt dissolution, which was interrupted by formation of cobalt hydroxide, causing a second anodic peak. The amperometric study found progressive nucleation mechanisms, in contrast to the instantaneous nucleation mechanisms determined by the AFM study. An explanation for the contradictory nucleation mechanisms shown in the two studies is provided. 相似文献
15.
16.
Pitting corrosion of AZ91D and AJ62x magnesium alloys in alkaline chloride medium using electrochemical techniques 总被引:1,自引:0,他引:1
A.-M. Lafront 《Electrochimica acta》2005,51(3):489-501
Pitting corrosion of AZ91D-DC (die cast), AZ91D-ESTC (electromagnetically-stirred billets; thixocast), AZ91D-SFTC (billets solidified freely; thixocast) and AJ62x-DC (die cast) specimens was studied in alkaline chloride medium (0.1 M NaOH + 0.05 M NaCl + 2 ml H2O2) at 25 °C and pH 12.3. Electrochemical noise (EN) measurements have confirmed to some extent the polarization results (passive zone, pitting current and average corrosion rate). AZ91D-ESTC specimens have shown the best corrosion resistance followed by AZ91D-SFTC and AZ91D-DC. Intense corrosion rate was observed at the beginning of experiment and it decreased with immersion period. Localized corrosion with dense pitted areas was observed during a 16 h immersion period for AZ91D-SFTC and AZ91D-ESTC specimens. The best passive zone was observed for AJ62x-DC because of the corrosion products formed at the surface. After a 6 h of immersion, EN analyses in the frequency domain indicated a change in the sub-mode of pitting, becoming a classical pitting type, for AJ62x and AZ91D die cast specimens. Analysis with the scanning reference electrode technique (SRET) has showed that AJ62x specimen presented the biggest potential difference between the most active anode and the most active cathode and more numerous zones of intense localized corrosion. It was also found that the lifetime of the pit appeared after 8:20 h of immersion was longer for AJ62x and AZ91D die cast specimens being associated to a classical pitting. 相似文献
17.
Mohammed A. Amin 《Electrochimica acta》2005,50(6):1265-1274
The passivation and pitting corrosion behaviour of a zinc electrode in aerated neutral sodium nitrate solutions was investigated by cyclic voltammetry and chronopotentiometry techniques, complemented by ex situ scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) examinations of the electrode surface. Measurements were conducted under different experimental conditions. The potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of thin film of ZnO on the anode surface. The passive region is followed by pitting corrosion as a result of breakdown of the passive film. SEM images confirmed the existence of pits on the electrode surface. The breakdown potential decreases with an increase in NO3− concentration and temperature, but increases with increasing potential scan rate. Addition of SO42− ions to the nitrate solution accelerates pitting corrosion, while addition of WO42− and MoO42− ions inhibits pitting corrosion. The chronopotentiometry measurements show that the incubation time for pitting initiation decreases with increasing NO3− concentration, temperature and applied anodic current density. Addition of SO42− ions decreases the rate of passive film growth and the incubation time, while the reverse changes produced by addition of either WO42− or MoO42− ions. 相似文献
18.
The reaction of H2O2 on SIMFUEL electrodes has been studied electrochemically and under open circuit conditions in 0.1 mol l−1 NaCl (pH 9.8). The composition of the oxidized UO2 surface was determined by X-ray photoelectron spectroscopy (XPS). Peroxide reduction was found to be catalyzed by the formation of a mixed UIV/UV (UO2+x) surface layer, but to be blocked by the formation of UVI (UO22+) species on the electrode surface. The formation of this UVI layer blocks both H2O2 reduction and oxidation, thereby inhibiting the potentially rapid H2O2 decomposition process to H2O and O2. Decomposition is found to proceed at a rate controlled by desorption or reduction of the adsorbed O2 species. Reduction of O2 is coupled to the slow oxidative dissolution of UO2 and formation of a corrosion product deposit of UO3·yH2O. 相似文献
19.
Mohammed A. Amin Sayed S. Abd El Rehim Essam E.F. El Sherbini 《Electrochimica acta》2006,51(22):4754-4764
The pitting corrosion behaviour of Al in aerated neutral sodium perchlorate solutions was investigated by potentiodynamic, cyclic voltammetry, galvanostatic, potentiostatic and electrochemical impedance spectroscopy (EIS) techniques, complemented by ex situ scanning electron microscopy (SEM) examinations of the electrode surface. The potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of thin film of Al2O3 on the anode surface. The passive region is followed by pitting corrosion as a result of breakdown of the passive film by ClO4− ions. SEM images confirmed the existence of pits on the electrode surface. Cyclic voltammetry and galvanostatic measurements allow the pitting potential (Epit) and the repassivation potential (Erp) to be determined. Epit decreases with increase in ClO4− concentration, but increases with increase in potential scan rate. Potentiostatic measurements showed that the overall anodic processes can be described by three stages. The first stage corresponds to the nucleation and growth of a passive oxide layer. The second and the third stages involve pit nucleation and growth, respectively. Nucleation of pit takes place after an incubation time (ti). The rate of pit nucleation (ti−1) increases with increase in ClO4− concentration and applied step anodic potential (Es,a). EIS measurements showed that at Es,a < Epit, a charge-transfer semicircle is obtained. This semicircle is followed by a Warburg diffusion tail at Es,a > Epit. An attempt is made to compare the values of Epit and Erp obtained through different methods and to determine the factors influencing these values in each particular method. 相似文献
20.
Birame Boye Enric Brillas Beatrice Marselli Christos Comninellis Giuseppe Farnia 《Electrochimica acta》2006,51(14):2872-2880
The electrochemical degradation of saturated solutions of herbicides 4-chloro-2-methylphenoxyacetic acid, 2-(4-chlorophenoxy)-2-methylpropionic acid and 2-(4-chloro-2-methylphenoxy)propionic acid in 1 M HClO4 on a boron-doped diamond (BDD) thin film anode has been studied by chronoamperometry, cyclic voltammetry and bulk electrolysis. At low anodic potentials polymeric products are formed causing the fouling and deactivation of BDD. This is reactivated at high potentials when water decomposes producing hydroxyl radical as strong oxidant of organics. Electrolyses in a batch recirculation system at constant current density ≥8 mA cm−2 yielded overall decontamination of all saturated solution. The effect of current density and herbicide concentration on the degradation rate of each compound, the specific charge required for its total mineralization and instantaneous current efficiency have been investigated. Experimental results have been compared with those predicted by a theoretical model based on a fast anodic oxidation of initial herbicides, showing that at 30 mA cm−2 their degradation processes are completely controlled by mass transfer. Kinetic analysis of the change of herbicide concentration with time during electrolysis, determined by high-performance liquid chromatography, revealed that all compounds follow a pseudo first-order reaction. Aromatic intermediates and generated carboxylic acids have been identified using this technique and a general pathway for the electrochemical incineration of all herbicides on BDD is proposed. 相似文献