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The thermal fatigue behavior of 441 ferritic stainless steel was investigated in air and synthetic automotive exhaust gas by the cyclic tests under 100°C–800°C and 900°C conditions. After the fracture failure, the microstructure, oxide film, and precipitated phases were analyzed using optical microscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. In both atmospheres, increasing the maximum temperature from 800°C to 900°C results in lower strength and fatigue life and higher elongation and grain size. At the same maximum temperature, the thermal fatigue life of the specimen is lower in the synthetic exhaust gas than in the air. Both the higher maximum temperature and the synthetic exhaust gas facilitate fatigue failure. The failure mechanism is discussed according to the grain size, thermal stress, high-temperature oxidation rate, and the precipitation of secondary phases. Some precipitated carbides play an important role in the rapid fatigue failure of specimens in the synthetic exhaust gas.

Pitting initiation and stable propagation behaviors of 2205 duplex stainless steel were investigated in the hot concentrated seawater under vacuum pressures by potentiostatic polarization. Both applied potentials and vacuum pressures greatly influence the pitting corrosion. Higher potentials lead to much faster stable pitting initiation and growth rates in both static (101.3 kPa) and dynamic (28.4 kPa) solutions. The pressure reduction can also accelerate the pitting initiation rate. However, the boiling of solution can influence the pitting propagation mechanism. The dynamic actions of boiling bubbles are unfavorable to the pit propagation and result in the formation of relatively smooth pit bottom without secondary pits.

The corrosion behavior of enamel coating on carbon steel was investigated in the tap water at 80°C (i.e., the simulated electric hot water tank environments) by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and electrochemical measurement techniques. The through porosity of enamel coating is about 0.0076%, simply measured by in-situ electrochemical impedance spectroscopy (EIS) in the dilute sulfuric acid solution. The through defects facilitate the solution penetration in the coating and the formation of occluded corrosion cell on the steel substrate in the hot tap water. The occluded zones have low resistances to both ionic transport and active corrosion. The steady steel corrosion is controlled by the oxygen diffusion via the enamel coating defects, which is accompanied by the transport of anion ions and corrosion products.

The oxidation behaviors of type 444 ferritic stainless steel (FSS) were studied in air and synthetic exhaust gas at 1000, 1050 and 1100 oC, respectively, by means of mass gain, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The oxidation rate of 444 FSS enlarges in both environments with the increase of temperature, but is faster in synthetic exhaust gas than in air under isothermal conditions. The oxidation rate becomes very fast since the occurrence of breakaway transition. Both the higher temperature and the synthetic exhaust gas facilitate the breakaway oxidation. The breakaway oxidation results mainly from the growth of oxide nodules and the spallation of oxide scale. The synthetic exhaust gas isn’t conducive to the formation of SiO2 layer in comparison with the air. The oxidation mechanisms are discussed on the basis of the oxide scale characteristics.

The corrosion behavior of 2205 duplex stainless steel was investigated in hot concentrated seawater with different dissolved oxygen (DO) concentration by electrochemical measurement techniques and surface analysis methods. DO obviously enhances the cathodic reaction process, the formation of passive film and polarization resistance. With increasing the DO concentration from 0.34 to 3.06 mg L−1, the relative contents of Fe2O3 and Cr2O3 and the Cr-enrichment gradually enlarge in the passive film. The higher DO concentrations result in lower defect densities and thicker of space charge layers in the passive films, which may effectively inhibit the intrusion of aggressive chloride ions. The increment in DO concentration clearly increases the pitting potential, but decreases the repassivation potential. It may weaken both the occurrence and repassviation tendencies of stable pitting corrosion.

Purpose The purpose of this paper is to investigate the electrochemical corrosion behavior of type 444 stainless steel (SS) in synthetic tap water from 25°C to 80°C, i.e. the operation environment of the electric water heater. Design/methodology/approach The corrosion behavior was studied by using electrochemical measurements such as electrochemical impedance spectroscopy and polarization curve. The specimen surfaces were observed with scanning electron microscopy. The passive films were characterized with X-ray photoelectron spectroscopy. Findings In the typical tap water, 444 SS passivates spontaneously under different temperatures. The passive films formed at higher temperatures contain relatively less Cr-species and more Cl− ions, resulting in lower polarization resistances. The stable pitting corrosion takes place in the potential region of oxygen evolution as the temperature increases to about 55°C. The critical Cl− concentration of pitting corrosion reduces from about 160 mg L−1 to 60 mg L−1 with changing temperature from 25°C to 80°C. Practical implications The pitting corrosion probability was assessed through the statistical analysis of tap water quality. The results are useful for the application of 444 SS as well as the design of electric water heater. Originality/value This paper shows the variation of polarization resistance, pitting potential, passive film composition and critical pitting chloride concentration with the temperature of tap water. It is of great significance for the development and application of SS in tap water environments.

Pitting initiation and propagation at the deformation bands intersection of cold-rolled 14Cr10Mn stainless steel in acidic ferric chloride solution with a pH of 1.3 were investigated by a scanning electron microscope equipped with electron back scatter diffraction and a high-resolution transmission electron microscopy. The experimental results show that the pits with regular morphology are a sort of dislocation etch pit with strict triggering conditions. The pitting corrosion resistance of the etch pits is closely related to the orientations in the increasing order of {100}〈001〉

Pitting corrosion resistance of 2205 duplex stainless steel aged at 850 °C was investigated in the hot concentrated seawater (i.e., the simulated low-temperature multi-effect distillation environment) by optical microscopy (OM), scanning electronic microscopy (SEM), and electrochemical measurement techniques. The precipitation of the σ phase leads to sensitization in the specimens during the aging treatment. The degree of sensitization (DOS) presents a maximum value with the change of σ phase content. The pitting corrosion resistance of the specimens degrades markedly in the presence of very weak sensitization. The pitting potential decreases almost linearly with the logarithm of DOS. The pit propagation mainly takes place along the Cr-depleted region around the σ phase. The repassivation ability of the specimens changes insignificantly with the aging time.

A Cr–Mn–Ni–N series high strength metastable austenitic stainless steel (14Cr10Mn) was used to investigate the effect of cold rolling reduction on mechanical properties at various low testing temperatures. Microstructures of tested samples were observed by transmission electron microscope (TEM) and electron back scatter diffraction (EBSD) at the gauge section. The experimental results show that the size of the rib-like α′- martensite formed during tensile testing is sensitive to temperature but insensitive to cold rolling reduction. The results also show that tensile strength is more sensitive to temperature than yield strength, while the effect of cold rolling is completely opposite. The cold rolling inhibits the martensite transformation kinetics of the tensile process after promoting it at a certain temperature condition, and the promotion effect reaches a maximum value approximately 4% when the cold rolling reduction is 10%. However, it also suppresses the α′- martensite content finally formed during tensile testing due to the high stress-strain state when the cold rolling reduction exceeds 10%, while a larger cold reduction promotes the production of α′- martensite. In addition, lowering temperature can effectively promote the formation of e-martensite at the end of the Stage I of work hardening, and becomes a transitional phase of subsequent transformation to α′- martensite, which directly leads to the enhancement of strength in the stage II of work hardening.

In order to understand the mechanism of substitution for nickel with manganese in metastable austenitic stainless steels 14Cr10Mn and 16Cr6Mn, the transformation behavior of e- and α′- martensite and the corresponding mechanical properties were investigated in this study. The microstructures and tensile and hardness properties of the cold-rolled steels under different rolling reductions at ambient temperature were measured using X-ray diffraction (XRD), scanning electron microscope (SEM) together with an electron back scatter diffraction (EBSD) and transmission electron microscope (TEM). The results show that α′- martensite is not easy to be transformed from austenite, and the martensite transformation γ → e → α′ in 14Cr10Mn and 16Cr6Mn metastable stainless steels is found during cold rolling. The results also reveal that e- martensite acts as an hardness reinforcing phase, and high total martensite volume fraction and ratio of e- and α′- martensite content are helpful to achieve higher tensile strength with sigmoidal shape stress-strain curves. In addition, a model considering cold rolling reduction was developed to predict the contents of e- and α′- martensite in the steels.

Long-term corrosion behavior of 2205 duplex stainless steel was investigated in the hot concentrated artificial seawater under intermittent vacuum boiling and atmosphere conditions during the immersion of more than one year by using electrochemical impedance spectroscopy (EIS). Compared to the atmosphere state, the passive film formed on specimen surface is thinner and the induction time for pitting corrosion decreases notably under intermittent vacuum boiling condition. However, the pit propagation is retarded by the lower dissolved oxygen content and violent boiling of solution. The vacuum boiling of solution has opposite effect on the initiation and stable growth processes of pitting corrosion.

The corrosion behaviour of hot-dip Al–Zn–Si and Al–Zn–Si–3Mg coatings on steel sheets in NaCl solution were investigated by microstructural characterization, weight loss tests, and electrochemical methods Localized corrosion of the Al-rich phase in the Al–Zn–Si coating was observed. The exposure of the intermetallic layer was supposed to present galvanic corrosion and remarkably accelerate the consumption of remnant Al-rich phase. The MgZn2 phase was detected in the interdendritic Zn-rich region of the Al–Zn–Si–3Mg coating. The presence of the MgZn2 and Mg2Si phases contributed to delaying the occurrence of localized corrosion.

Self-assembled monolayers (SAMs) of 3-mercaptopropyltrimethoxysilane (PropS-SH) modified with La 2 O 3 nanoparticles were investigated to evaluate the doping effect of La 2 O 3 nanoparticles on PropS-SH silane film towards brass corrosion protection in NaCl solution. The results indicated that SAMs of PropS-SH modified with La 2 O 3 nanoparticles presented improved barrier properties because La 2 O 3 nanoparticles filled the holes of silane film, which in turn improved the density of silane film, thus enhanced the barrier properties of silane-metal interface. Further, part of La 2 O 3 nanoparticles was transformed to lanthanum oxide hydroxide (LaOOH) by hydrolysis reaction, and the formed La compounds covered the cathode sites, giving rise to a blocking effect.

The corrosion behavior of Zircaloy-4 (Zry-4) at 360 °C 0.01 M LiOH aqueous solution was in-situ monitored by electrochemical impedance spectroscopy (EIS). The EIS spectra of the as-received Zry-4 (Zry-4A) shows two-time constants feature during corrosion. The oxide layer impedance and capacitive show cyclic behavior while those of β-quenched Zry-4 sample (Zry-4Q) increased with exposure time increases. It may relate to the evolution of the defects and dielectric property of the oxide film and relaxation which evolves after the stress relief. The effect of heat treatment on the corrosion mechanism of the Zircaloy-4 was discussed.

The effects of alloyed magnesium on the corrosion behavior of hot-dip Al–Zn–Si– x Mg ( x = 0, 1.25, 3 and 4 wt.%) coatings were investigated by analysis of the phase composition, long-term immersion test and electrochemical measurements. Mg 2 Si phase appeared in the Al–Zn–Si–1.25Mg and Al–Zn–Si–3Mg coatings but only MgZn 2 phase existed on the surface of Al–Zn–Si–4Mg coating. The alloyed magnesium improves the corrosion resistance of the Mg-containing coatings and the Al–Zn–Si–3Mg coating shows the highest protective properties in the investigation.

The corrosion behavior of 2205 duplex stainless steel (DSS) was investigated in the hot concentrated seawater under vacuum pressures by using electrochemical measurement techniques. The vacuum pressure results in the decrease of dissolved oxygen concentration and even boiling of solution. 2205 DSS passivates spontaneously under various vacuum pressures. The vacuum pressures (no lower than 28.4 kPa) greatly influence the polarization resistance, passive film composition and oxygen reduction reaction. The pressure reduction and the violent boiling of solution distinctly decrease the pitting potential, but increase the repassivation potential. They may enhance both the occurrence and repassivation tendencies of stable pitting corrosion.

Preparation of 3-mercaptopropyl)trimethoxylsilane (PropS-SH) film on brass surface and its corrosion resistance performance were investigated by surface energy analysis, Fourier transform infrared reflection (FT-IR) spectroscopy and electrochemical measurements. The results indicated that the generation of PropS-SH sialne film on brass was based on spontaneous reactions to produce Cu-S, Zn-S bond and Si-O-Si bonds. When the brass substrate was covered with the prepared PropS-SH silane film, the dezincification coefficient of brass decreased from 4.45 to 0.47. The PropS-SH silane film was able to minimize the dissolution of both Cu and Zn, improving the corrosion resistance of brass in natural seawater.

The corrosion behaviour of 316L stainless steel was studied in the concentrated artificial seawater at 72 °C, i.e., the simulated low temperature-multi effect distillation environments, by using electrochemical measurement techniques. The corrosion state changes from spontaneous passivation to pitting after about 1150 h of immersion. Pitting corrosion is under mixed control of charge transfer and diffusion processes in the long-term immersion. The salt deposits retard the diffusion of oxygen to the metal surface. The pit depth only reaches about 38 μm after one year of immersion due to the alloying effect of Mo, low dissolved oxygen levels and weak occlusion states.

The influence of trace SO 2 in simulated automotive exhaust gases at 400 °C on the oxidation and subsequent condensate corrosion of 409 stainless steel was investigated by means of mass gain, SEM, Raman spectroscopy, GDOES, Mott–Schottky and polarisation curves. SO 2 suppresses the growth of oxide films, especially nodular oxides rich in magnetite and maghemite, due to forming sulphates on the oxide surfaces. The oxidised specimens show passive corrosion in simulated condensate solutions. The passive current density decreases noticeably with adding SO 2 into the oxidation environments, indicating that SO 2 may inhibit the condensate corrosion of mufflers through the thermal oxidation process.

Effect of Mg41Sm5 second-phase on corrosion of as-cast and extruded Mg-Sm-Zn-Zr alloys in NaCl solution was investigated. The net-like Mg41Sm5 phase played a cathodic role in the as-cast alloy and induced obvious localized corrosion of adjacent anodic α-Mg grains. However, hot-extrusion deformed the relatively large net-like Mg41Sm5 phase into uniformly dispersed finer particles, which effectively mitigated localized corrosion and formed uniform protective film on the whole alloy surface. It enhanced the corrosion resistance of the extruded alloy for three times compared with the as-cast counterpart and outperformed that of benchmark Mg alloy AZ91.

The pitting resistance of anodic passive films formed on 316L stainless steel was studied in the concentrated artificial seawater with the concentration ratio (cR) ranged from 1.5 to 3 times under typical operation temperature condition of multi effect distillation (MED) by using the polarization curve and Mott-Schottky analysis. The pitting potential decreases linearly with the logarithm of cR. The anodic passive films are characterized by both n- and p-type semiconductive behavior, i.e., a bilayer microstructure. The density values of defects (i.e. ND and NA) are in the range of 1020 to 1021 cm−3, and increase with cR linearly. According to the point defect model (PDM), the increase of both Cl− concentration and defect density ND can facilitate the absorption of Cl− ions in the passive films, which is mainly responsible for the deterioration of pitting resistance in the concentrated artificial seawater.

In order to replace the hazardous chromate-based surface treatment, a new cerium chemical conversion coating was developed on 316L stainless steel through a mixed solution of hydrated cerium nitrate, citric acid, and hydrogen peroxide. The chemical composition was characterized by energy-dispersive spectroscopy, X-ray photoelectron spectroscopy and atomic force microscope. The dense conversion coating is composed of CeO2 with a small amount of Ce2O3 and has small grain size lower than 50 nm. Its thickness is about 47.4 nm as determined by spectroscopic ellipsometry analysis. Potentiodynamic polarization was used to study the corrosion behavior of the coatings in the concentrated artificial seawater at 72 °C. In comparison with the conventional nitric acid-chromate passivated specimens, the cerium conversion coatings show much higher pitting potentials. It is suggested that the cerium conversion treatment is more effective than the nitric acid-chromate passivation to improve the pitting resistance of 316L stainless steel used in the hot seawater environments.

The electrochemical corrosion behavior of 409 stainless steel after cyclic oxidation below 400 °C was investigated in the simulated muffler condensates by using surface analysis and electrochemical measurement techniques. In the cyclic processes of condensate-dipping and oxidation, specimens may form defective oxide films and weak Cr depletion underlying the oxide films. Sulfate from the condensate-dipping will give rise to sulfidation during the cyclic oxidation, being detrimental to both the oxidation and corrosion properties of stainless steel. The oxidation above 300 °C deteriorates the corrosion resistance, even leading to active corrosion in the acidic condensate solutions. Comparatively, specimens oxidized cyclically without condensate-dipping show much higher condensate corrosion resistance. It is suggested that the acidic condensate corrosion is accelerated by the synergetic effect of oxidation and condensation in the mufflers, and then may result in perforation through the defects such as cracks and nodules in oxide films on the stainless steel surface.

The influence of passivation on pitting corrosion of 316L stainless steel in concentrated seawater was investigated by using cyclic anodic polarization and critical pitting temperature. The results indicated that the pitting potential of passivated specimen was higher than that of matrix specimen in concentrated seawater at 25°C and 85°C. Critical pitting temperature value of passivated specimen was 56°C, which was much higher than 11°C for matrix specimen. Pitting corrosion occurred in the formed pit of passivated specimen, and metastable pit, lacy cover and new pit were observed in pit morphology.

The corrosion behavior of 316L stainless steel was investigated in seawater at different temperature by using cyclic anodic polarization. The results indicated that two 316L specimens with different grain size showed similar pitting potential at 25°C. The increase of seawater temperature led to the linear decrease of pitting potential and repassivation potential. Because the pitting resistance of fine grain steel reduced larger than that of coarse grain steel with increasing temperature, the latter had a higher pitting potential about 60 mV at 85°C. Compared with the coarse grain steel, the fine grain steel showed a longer induction time for pitting at 65°C.

The relationship between the morphology and protective action of hot-dip aluminizing coatings on Q235 steel have been investigated by SEM, EDS and EIS in 3.5 wt% NaCl aqueous solution. The results indicated that the anti-corrosion performance of the hot-dip aluminizing coatings using steel substrate rinsed by the distilled water at 25 oC was higher than that at 80 oC. The evolution of localized corrosion from pitting to exfoliation corrosion has been found on the aluminum coating surface during immersion, and corresponding equivalent circuit models were proposed to fit the EIS data in the initiation and propagation stages of corrosion process.

Electrodeposition of Mg with Zn in acidic sulfate solutions with polyethylene glycol and octadecyl dimethyl benzyl ammonium chloride as additives was investigated by scanning electron microscopy, X-ray diffraction, and potentiodynamic polarization techniques. The results show that these two compounds act in a synergetic way to suppress Zn deposition markedly and facilitate Mg reduction. Zn–0.46%Mg coatings are produced under high cathodic current densities, which have lower corrosion potentials than Zn coatings and hydrogen evolution in neutral chloride solutions. Magnesium hydroxide may cause current oscillations at high cathodic polarizations in plating solutions without zinc salts due to its formation and peel-off. An “induced co-deposition” mechanism is proposed for Zn–Mg alloy electrodeposition.

The influence of pulse electrodeposition parameters (i.e., current-on time, current-off time and peak current density) on the grain size and orientation of zinc deposits was investigated in acidic sulfate electrolyte. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses indicate that the pulse parameters play an important role in the grain refinement of nanocrystalline zinc coatings. As varying peak current density (1–2 A/cm2), current-on time (1–6 ms) and current-off time (4–18 ms), nanocrystalline zinc coatings are produced in the grain range 60 to 35 nm. The pulse parameters have a slight influence on the orientation of nanocrystalline zinc coatings.

Corrosion of X-70 pipe steel as a function of stress distribution was investigated by scanning localized electrochemical impedance spectroscopy (LEIS) technique. The deformation-induced stress, if not sufficiently high, has an inhibitive effect on corrosion reaction, pitting occurrence and crack initiation in pipe steel under high-pH condition. Such an inhibitive effect is due to the enhanced generation of carbonate product and the resultant surface block effect at the stressed zones. The tensile and compressive stresses have identical effect on inhibition of dissolution and pitting of the steel. However, tensile stress enhances the steel dissolution more significantly than compressive stress, and thus, generates more carbonate product, resulting in higher localized impedance. Pits are easy to occur around the neutral axis of the U-bend specimen, where the steel deformation and the resultant stress are ignorable. For pipelines encountering non-uniform stress distribution, the role of stress in crack initiation is critically different. Scanning LEIS technique provides a promising method to map and characterize corrosion of the steel as a function of the stress distribution.

The effects of hydrogen-charging on anodic dissolution of pipe steel under near-neutral pH condition were studied by electrochemical techniques. Hydrogen-charging enhances the anodic dissolution rate of the steel. The hydrogen-enhanced dissolution increases with increasing charging current density. The hydrogen effect is attributed to the alteration of chemical potential and exchange current density of steel. Hydrogen-charging affects the corrosion process of the steel. In particular, at a high charging current density, a layer of corrosion product forms on the electrode surface to change corrosion potential and interfacial double-charge layer capacitance as well as charge-transfer resistance. The hydrogen effect factor for enhanced anodic dissolution of steel at an anodic potential of −0.4 V (SCE) is 1.53 only. Hydrogen-enhanced anodic dissolution of steel by itself may not be the major factor contributing to the high rate of crack growth in pipe steel in near-neutral pH electrolyte. A further investigation of the synergistic effect of hydrogen and stress on dissolution at the crack-tip is essential to determine the mechanism of near-neutral pH stress corrosion cracking of pipelines.

The corrosion behavior of electrodeposited nanocrystalline (NC) zinc coatings with an average grain size of 43 nm was investigated in 3.5% NaCl solutions in comparison with conventional polycrystalline (PC) zinc coatings by using electrochemical measurement and surface analysis techniques. Both polarization curve and electrochemical impedance spectroscopy (EIS) results indicate that NC and PC coatings are in active state at the corrosion potentials, and NC coatings have much higher corrosion resistance than PC ones. The corrosion products on both coating surfaces are mainly composed of ZnO and Zn5(OH)8Cl2·H2O, but the corrosion products can form a relatively more protective layer on NC coating surfaces than on PC coatings. The EIS characteristics and corrosion processes of PC and NC zinc coatings during 330 h of immersion were discussed in detail.

The photocatalytic degradation of organics in aqueous solution is an active research field. Currently, the relatively low degradation efficiency is the key problem to be solved that caused by the simple recombination of the photo-generated electrons and holes. The electrode was prepared by anodic oxidation on titanium thin plate and produced multiporous nano-crystalline titanium dioxide film with anatase structure on titanium substrate. In order to inhibit the simple recombination of the electrons and holes, the electric potential bias was applied to the electrode to drive away the chargers. The change of the photocurrent and the discolouration of the dye solution containing either methylene blue or acid red G with different magnitude of the applied bias were measured. It shows that the photocurrent increased by three orders of magnitude from μA to mA level by the applied bias. Correspondingly, the discolouration rate of the methylene blue in dye solution was increased greatly with the increasing applied bias up to 3.5V. The different kinds of transitional metal ions dopants of Mn2+, Cr3+, Fe3+, and Ni2+ to the electrodes was done by anodic oxidation method. The effects of different types of dopants on the photocatalytic activity were revealed by measuring the degradation of an organics aqueous solution containing a dye using a combination of ultraviolet light energy in the presence of these electrodes. The photocatalytic efficiency, which was remarkably enhanced by the incorporation of Mn2+、 Cr3+.、 Mn2+, showed the largest enhancement. However, Fe3+ changed only slightly, and Ni2+ showed no enhancement. These effects were related to the difference of these transitional metal dopants electron work function values and also to the difference of their ionic radii in respect to that of Ti4+. The configuration of the reactor for water treatment with the rotating electrode and 365nm wavelength UV radiation was described.

Nanocrystalline zinc coatings were produced by pulse electrodeposition in acid sulfate bath containing thiourea and benzalacetone additives and characterized by X-ray diffraction and scanning electron microscopy techniques. The influence of benzalacetone concentration and pulse peak current density on the grain size and crystallographic orientation of zinc deposits was investigated. Zinc electrodeposited from additive-free solutions or with one of the two additives is not composed of nanosized crystals. The mixture additives of thiourea and benzalacetone give rise to the formation of particle-like nanocrystalline zinc with a (10ī1) random orientation. A change in peak current density from 2 to 1 A/cm2 only increases the grain size from 60 to 62 nm.

The photoelectrocatalytic oxidation characteristics of salicylic acid, formic acid and methanol on anodized nanoporous titanium dioxide (TiO2) thin-films were investigated by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. From dark to ultraviolet illumination, the open circuit potential (OCP) and film resistance of TiO2 films decreased markedly. A general equivalent circuit model was proposed for the photoelectrochemical system anodic TiO2 thin-film electrode/test solution. The photoelectrochemical oxidation process of the organic compounds showed similar impedance features at OCP and was controlled by the charge transfer step. According to the polarization curves of the base solution and organic solutions, the kinetic rate curves for the photoelectrocatalytic oxidation of pure organic species were obtained as a function of the potential bias. One photooxidation peak was first observed at a bias potential of ca. 0.26 V for these species with low concentrations.

Titanium dioxide (TiO2) films were prepared by anodization of titanium foils at different voltages in dilute NaOH solutions and characterized by XRD and scanning electron microscopy (SEM) techniques. The thin TiO2 films are mainly composed of anatase phase in the form of nano-crystallites. The photoelectrochemical behavior and photocathodic protection effect, for these films were also investigated in 3% NaCl solutions by using electrochemical measurement techniques and coupling test. The tremendous decrease of film resistance and open circuit potential of each TiO2 film takes place under ultraviolet (UV) illumination. TiO2 film formed at 120 V can serve as photoanode and supply a protective photocurrent about 8 8 m A/cm(2) to carbon steel, when it is connected to carbon steel in test solution with an area ratio of 2:1. But TiO2 films can accelerate the corrosion of carbon steel in the dark. In addition, electrochemical impedance spectroscopy (EIS) characteristics and coupling behaviors for TiO2 films were discussed in detail. C 2005 Elsevier Ltd. All rights reserved.