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1.
M. Bojinov 《Journal of Solid State Electrochemistry》1997,1(2):161-171
Two model approaches to the formation of passive films as adsorbed layers during the active anodic dissolution of a metal
in acid and their subsequent growth are presented. The first depicts passivation as proceeding in parallel to active dissolution.
Adsorption of water on active surface sites leads to passivation, whereas adsorption of acid leads to active dissolution of
the metal. The model is consistent with the impedance response during passivation of Fe and an Fe-20%Mo alloy in concentrated
H3PO4. The second model is an updated version of the so-called surface charge approach to the mechanism of conduction of anodic
passive films. It is based on the assumptions that oxygen vacancies are the main ionic charge carriers and the field strength
in the barrier layer is constant. A negative surface charge built up at the film/solution interface via accumulation of metal
vacancies accelerates oxygen vacancy transport, thus explaining the pseudoinductive behaviour of the metal/film/electrolyte
system under small amplitude a.c. perturbation. The model describes the growth of thin anodic films on Fe, Mo and an Fe-20%Mo
alloy in concentrated H3PO4.
Received: 24 January 1997 / Accepted: 18 April 1997 相似文献
2.
V. Riveros M. Gulppi M. Páez J. H. Zagal C. M. Rangel D. Huerta P. Skeldon G. E. Thompson 《Journal of Solid State Electrochemistry》2006,10(2):83-90
Using voltage-time responses and cyclic voltammetry, the initial stages of anodizing of Al–2.1 at.% Ag and Al–4 at.% Ag alloys
are shown to depend upon the heat treatment of the alloys and the pre-treatment of the alloy surfaces. Chemical polishing
of solution-treated alloys leads to relatively uniform anodic oxidation on a relatively smooth alloy surface, in the absence
of significant effects of coarse, silver-rich intermetallics. In contrast, losses of current to oxygen generation arise for
the roughened alloy surface from mechanical polishing. With ageing, secondary reactions at the relatively silver-rich intermetallics
are more prevalent, although the effects on the voltage-time response depend upon the balance between processes occurring
on the matrix and intermetallic regions, including film growth, oxygen generation within the anodic film, film damage due
to release of oxygen, dissolution of silver species and re-growth of damaged film. 相似文献
3.
铅及铅锑合金阳极膜中硫酸铅的氧化过程 总被引:2,自引:0,他引:2
应用电位阶跃和交流阻抗法分别研究铅和Pb-5wt% Sb合金在4.5mol·dm^-^3H~2SO~4(30℃)中于1.3V(vs. Hg/Hg~2SO~4, 下同)生长20min后的阳极膜在0.9V还原5min后再在1.4V将膜中硫酸铅氧化的过程。实验结果表明在0.9V还原二氧化铅而得到的硫酸铅能在1.4V于1min内氧化为二氧化铅。这是由于此种硫酸铅处于硫酸铅颗粒表层的缘故。至于颗粒内部由铅直接生成的硫酸铅的氧化为二氧化铅就要缓慢得多。合金中的锑能使二氧化铅晶核形成和生长速率显著降低。 相似文献
4.
Jeanette M. Torrescano-Alvarez Michele Curioni Xiaorong Zhou Peter Skeldon 《Surface and interface analysis : SIA》2019,51(12):1135-1143
The effects of applied current density, anodizing time, and electrolyte temperature on the cell and pore morphology of anodic films and the voltage-time response obtained during galvanostatic anodizing of AA2024-T3 alloy in sulphuric acid electrolytes have been studied. Scanning electron microscopy was employed to observe the film morphology. Sponge-like porous structure was promoted by anodizing at relatively low current density and high electrolyte temperature. In contrast, linear porous structure was favoured under the converse conditions. Intermediate conditions resulted in films containing either sequential layers of the 2 morphologies or a morphology incorporating features of the 2 types; such conditions were associated with anodizing voltages in the range 25 to 35 V. The reasons for the morphological differences are proposed to be due to interactions between film growth stresses and stresses arising from oxygen evolution on the development of the alumina cells. 相似文献
5.
The resistance of the anodic PbO film fonned on lead at 0.9 V (vs. Hg/Hg2SO4) in 4.5 mol/dm3 H2SO4 was measured using alternating-current impedance method. The resistance of the anodic PbO film was found to be close to that of the interstitial liquid among the PbO particles in the film, suggesting that the interstitial liquid may serve as the major passage for ion transportation during the film growth. 相似文献
6.
Growth mechanism of anodic oxide films on pure aluminium in aqueous acidic and alkaline solutions 总被引:1,自引:0,他引:1
The present work was conducted to explore the growth mechanism of anodic oxide films on pure aluminium in aqueous acidic
and alkaline solutions by using a.c. impedance spectroscopy and a beam deflection technique. From the analyses of a.c impedance
data, it was found that the reciprocal capacitance of anodic oxide film on pure aluminium increased linearly with increasing
film formation potential in both acidic and alkaline solutions, indicating a linear increase in the film thickness with film
formation potential. However, as the film formation potential increased, the resistance of anodic oxide film decreased in
acidic solution, while it increased in alkaline solution. From the measurements of the deflection, the deflection was observed
to move towards only a compressive direction with time in acidic solution, but it showed a transition in the direction of
movement from compressive to tensile in alkaline solution. Based upon the above experimental results, it is suggested that
the movement of oxygen vacancy through the oxide film contributes to the growth of anodic oxide film on pure aluminium in
acidic solution, but the movement of both aluminium vacancy and oxygen vacancy accounts for that oxide film growth in alkaline
solution.
Received: 12 August 1997 / Accepted: 9 October 1997 相似文献
7.
Irena Lj. Arsova Abdurauf R. Prusi Ljubomir D. Arsov 《Journal of Solid State Electrochemistry》2003,7(4):217-222
Anodic oxide films formed potentiostatically on niobium surfaces, from open circuit potential (OCP) to 10 V, were studied
by performing in situ and ex situ ellipsometric measurements. The kinetics of the film thickness growth in 1 M H2SO4 and complex indices of refraction of these films were determined. A strong influence of the surface preparation conditions
on the complex refractive indices of the metal substrate and anodic oxide films was shown. By steady-state measurements at
OCP, a small thickening of the natural air-formed oxide film with chemical composition Nb2O5 in 1 M H2SO4 solution was detected. With cathodic pre-treatment, only partial reduction and small thinning of the natural air-formed oxide
film was possible. The thicknesses of the natural air-formed oxide films on fine mechanically polished and electropolished
Nb surfaces were determined. The build up of the natural air-formed oxide film, at ex situ conditions, on the already formed
anodic oxide films was confirmed. It was shown that electropolishing gives more similar optical surface properties to the
bare metal than the fine mechanical polishing.
Electronic Publication 相似文献
8.
WANG Qun-Zhou LIU Gang LIU Hou-Tian ZHOU Wei-FangDepartment of Chemistry Fudan University Shanghai China 《中国化学》1996,14(3):244-251
The composition and properties of the anodic films formed on Pb and Pb-3at.%Sb alloy at -0.10 V (vs. Hg/HgO) for 2.5 h in 0.1 mol.dm-3 NaOH solution (25℃) were investigated by cyclic voltammetry, linear sweep voltammetry, open circuit decay curve, photocurrent technique, X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the anodic film formed oh Pb mainly consists of t-PbO, while that on Pb-3at.%Sb consists of o-PbO, t-PbO and a small amount of orthorhombic Sb2O3. The dominant component of the film anodically grown on Pb-3at.%Sb for less than 5 min is o-PbO, however, t-PbO is the major component of the anodic film formed for 1 h or longer. It is established that Sb suppresses the growth of t-PbO. The anodic film formed on Pb-3at.%Sb is less porous than that on Pb. The bandgap energies of t-PbO and o-PbO in the films were determined by photocurrent measurements to be 1.83-1.84 eV and 2.60 eV, respectively. 相似文献
9.
10.
11.
An electrochemical procedure of anodic deposition of cobalt oxyhydroxide film on a glassy carbon substrate in an alkaline medium (i.e. pH 11.6) is described. The electrodeposited film was obtained either by voltage cycling or by potentiostatic conditions using non-deaerated 0.1 M Na2CO3 solutions containing 40 mM tartrate ions and 4 mM CoCl2. The effects on the film formation and growth, such as tartrate–cobalt ratio, pH, applied potential, etc. were widely evaluated. The electrodeposition process, under anodic conditions and moderately alkaline solutions, most likely involves a redox transition Co(II)→Co(III)/Co(IV) with destruction of the tartrate complex and formation of insoluble oxide/hydroxide cobalt species on the glassy carbon surface. The resulting cobalt oxyhydroxide films were characterised by cyclic voltammetry (CV) in 0.1 M NaOH solutions and by scanning electron microscopy (SEM) analysis after different strategies of preparation and various electrochemical treatments. The electrochemical activity of the deposited films was checked using various organic molecules as model compounds. 相似文献
12.
利用电化学阻抗(EIS)、扫描微参比技术(SRET)、接触角、粗糙度、附着力、盐雾等测试方法,研究了铝合金阳极氧化与贻贝黏附蛋白(MAP)/CeO2/硅烷γ-APS(MCA)表面复合修饰的腐蚀防护性能以及对改性聚氨酯涂层附着力和耐蚀性的影响。结果表明,MCA复合膜可抑制铝合金的腐蚀,并具有一定的自修复功能;阳极氧化和MCA表面复合修饰可为铝合金提供有效的早期腐蚀防护作用,且能提高铝合金表面粗糙度和润湿性,显著提升改性聚氨酯涂层在铝合金表面的附着力和耐蚀性,因而结合改性聚氨酯涂层和表面复合修饰可实现对铝合金长期有效的腐蚀防护。 相似文献
13.
Electrochemistry of fluorine production 总被引:2,自引:0,他引:2
Henri Groult 《Journal of fluorine chemistry》2003,119(2):173-189
The electronic properties of carbon-fluorine films (denoted C-F) formed on carbon electrodes in KF-2HF during fluorine evolution reaction were investigated in aqueous solution containing a redox couple and in mercury. It was shown that the passivating C-F films behave as electronic conductors. STM measurements have shown composition heterogeneities at the surface of fluorinated HOPG (conducting ans insulating areas). The influence of the amount of insulating graphite fluorides on the surface of the electrodes was demonstrated. Thus, the high anodic overvoltage observed during fluorine evolution on C/C-F anodes in KF-2HF is mainly attributed to the poor wettability of the electrodes by the melt, which results in a small electroactive area. A new model was proposed for representing the electrode/electrolyte interface; it includes the presence of a “fluidized” layer between the surface C-F film and the fluorine gas film. The “fluidized” layer is composed of liquid KF-2HF melt and dissolved fluorine gas. The influence of the mass transfer phenomenon occurring in that layer was pointed out mainly by impedance measurements. Finally, the contributions of the C-F film, ηC-F, and of the “fluidized” layer, ηfluid, to the total anodic overvoltage, ηT, were studied using a numerical calculation method. Both contributions must be taken into account for a global understanding of the fluorine evolution process. 相似文献
14.
用交流阻抗、开路电位衰退及线性电位扫描等方法在0.9V(vs.Hg/Hg2SO4)和4.5mol/LH2SO4溶液中,研究了铅及Pb-Sn合金电极上所生长的阳极氧化物膜.实验结果表明,阳极膜由溶解-沉淀机理控制生长,膜中微粒间为液膜,借助液膜作为离子通道可使膜中微粒发生阳极反应,锡有利于膜中PbO微粒表层阳极氧化为PbO1+x(0相似文献
15.
《Electroanalysis》2005,17(7):549-555
Carbon film disk electrodes with Nafion coatings have been characterized by electrochemical impedance spectroscopy (EIS) with a view to a better understanding of their advantages and limitations in electroanalysis, particularly in anodic stripping voltammetry of metal ions. After initial examination by cyclic voltammetry, spectra were recorded over the full potential range in acetate buffer solution at the bare electrodes, electrodes electrochemically pretreated in acid solution, and Nafion‐coated pretreated electrodes in the presence and absence of dissolved oxygen. EIS equivalent circuit analysis clearly demonstrated the changes between these electrode assemblies. In order to simulate anodic stripping voltammetry conditions, spectra were also obtained in the presence of cadmium and lead ions in solution at Nafion‐coated electrodes, both after metal ion deposition and following re‐oxidation. Permanent changes to the structure of the Nafion film occurred, which has implications for use of these electrode assemblies in anodic stripping voltammetry at relatively high trace metal ion concentrations. 相似文献
16.
The efficiency of stearate as a corrosion inhibitor for magnesium alloy ZE41 has been studied in sodium sulfate medium, employing electrochemical techniques like potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results of polarization study imply that stearate functions as a mixed-type corrosion inhibitor with a predominant anodic control. The adsorption of stearate on alloy surface is found to obey the Langmuir adsorption isotherm. The proposed inhibition mechanism involved adsorption of stearate onto metal surface, followed by precipitation of magnesium stearate within the microdefects of Mg(OH)2 surface film which enhanced the barrier effect of an otherwise porous partially protective film. 相似文献
17.
Kuang X.-Y. Jin S.-Q. Cao Y.-H. Zhang Y.-M. Dong S.-G. Zhu L.-H. Lin L.-W. Lin C.-J. 《电化学》2021,(6):624-636
The ordinary organic coatings on aluminum alloy usually encounter a problem of low adhesion to the substrate, which results in destruction and failure of the long-term protective performance of the anticorrosion systems. The surface modification of aluminum alloy is able to enhance the adhesion of organic coating on aluminum alloys, and to improve their protective performance. In this work, a combined surface modification of anodic oxidation and mussel adhesion protein/CeO2/3-aminopropyltriethoxysilane composite film (MCA) was developed on the aluminum alloy. The adhesion of modified polyurethane coated on the treated aluminum alloy and its corrosion protective performance were evaluated comprehensively by using contact angle, adhesion strength, electrochemical impedance spectroscopy (EIS), and scanning reference electrode technique (SRET). The measurements of EIS and SRET demonstrated that the MCA composite film on anodic oxidized Al possessed self-healing function and provided effective protection against early corrosion of aluminum alloy. The pull-off test showed that both anodic oxidation treatment and MCA composite film modification were able to increase the adhesion of modified polyurethane coating on aluminum alloy, and their combined action were supposed to remarkably enhance the adhesion strength up to 17.1 MPa. The reason for the improvement of adhesion was that the anodic oxidation treatment and MCA composite film modification could improve the surface roughness of aluminum alloy, and enhance the surface wettability and surface polarity, which is beneficent to enhance the bonding of the modified polyurethane coating to aluminum alloy surface. The EIS results showed that no any corrosion occurred for the modified polyurethane coating on the treated aluminum alloy during 65 d immersion in 3.5wt.% NaCl solution. The impedance value in low frequency range of the modified polyurethane coating always maintained at a high order of magnitude on the aluminum alloy treated by anodic oxidation and MCA composite film modification, showing an excellent protective performance of the coating system. The evaluation of Neutral Salt Spray (NSS) indicated that the modified polyurethane coating on the treated aluminum alloy owned superior corrosion protection performance, and the adhesion strength remained 13.1 MPa and no any corrosion was found at the scratch locations even after 1200 h of salt spray testing. It was concluded that combination of anodic oxidation and MCA composite film were capable of significantly improving the adhesion of modified polyurethane coating on aluminum alloy and providing long-term effective corrosion protection for aluminum alloy. © 2021 Authors. All rights reserved. 相似文献
18.
19.
The anodic oxidation of tungsten has been studied in 1 M Na2SO4 solutions containing 0–0.25 M NaF. Steady-state currents measured in the passivation and passivity ranges increase significantly
with increasing fluoride concentration, indicating enhanced dissolution of the oxide film. The electrochemical impedance response
is dominated by the processes in the barrier layer and at its interface with the electrolyte. The presence of a pseudo-inductive
loop in the impedance spectra at intermediate frequencies indicates point defect interaction during film growth and dissolution
processes. A kinetic model including the recombination reaction between oppositely charged point defects at the film/solution
interface as well as a kinetic scheme for tungsten dissolution through the film mediated by cation vacancies is proposed.
It is found to reproduce satisfactorily the steady-state currents and the impedance spectra in the potential range 0.2–2 V.
Such a model for the conduction mechanism in the barrier layer is believed to be an essential part of a modelling approach
to the formation of a nanoporous overlayer on tungsten in fluoride-containing solutions. 相似文献
20.
Bogdan Tzvetkov Martin Bojinov Assen Girginov 《Journal of Solid State Electrochemistry》2009,13(8):1215-1226
The influence of hydrofluoric acid (HF) concentration and applied potential on the processes of anodic oxidation of Nb in
sulphuric acid solution was studied by chronoamperometry, electrochemical impedance spectroscopy and scanning electron microscopy.
During the first stage of the process, a compact barrier film is formed. On top of this film, a porous overlayer starts to
form, then the nanopores grow into an ordered nanostructure. Subsequently, secondary 3D flower-shaped structures begin to
form. These structures gradually spread all over the surface as an irregular multilayer film. The rates of the process of
porous overlayer formation and subsequent growth of nanopore arrays increase with applied potential as well as with the HF
concentration. The films have been characterised ex situ by electrochemical impedance spectroscopy at open circuit potential
and capacitance vs. potential measurements to follow the different stages of nanoporous film formation with electrochemical
methods. The impedance spectra and capacitance vs. potential curves have been interpreted using previously proposed models
for the amorphous semiconductor/electrolyte interface. An attempt to rationalise the mechanism of nanoporous layer growth
is presented by using the conceptual views of the mixed-conduction model and recent ideas for porous film formation on valve
metals. 相似文献