纳米CdTe/TiO2复合材料对304不锈钢的光生阴极保护行为

目的研究纳米CdTe/TiO_2复合材料对304不锈钢的光生阴极保护行为。方法采用阳极氧化法制备二氧化钛纳米管,通过循环伏安沉积法在纳米管上进行CdTe修饰。应用扫描电镜(SEM)、X射线衍射(XRD)等测试方法对比纯TiO_2与CdTe/TiO_2的表面形貌与晶相特征。结合开路电位(OCP)、光电流密度-时间曲线(J-t)、Tafel极化曲线等电化学方法,研究复合材料的光电转化性能及其对304不锈钢的阴极保护行为。结果在光照条件下,耦连CdTe/TiO_2复合材料的304不锈钢的开路电位从初始的-190mV负移至-730mV,光电流密度可达0.15mA/cm~2,闭光后,开路电位上升至-350mV,仍然具有保护作用,说明制备的纳米CdTe/TiO_2复合材料具有储存电子的能力。结论在可见光照射下,与纯二氧化钛相比,制备的CdTe/TiO_2复合材料对304不锈钢的阴极保护性能显著提高,且在闭光状态下仍能维持对不锈钢的保护,对不锈钢起到一定的延时保护效果。     

Erosion-corrosion of stainless steel under impingement by a fluid jet

The localised corrosion of 304L stainless steel is described by electrochemical measurements made under impact of a fluid jet of sodium chloride solution, in the absence of the entrained solid particles. Impingement by the fluid jet causes the open-circuit potential of 304L stainless steel in 0.6 M NaCl solution to increase with time until it attains the pitting potential. This is due primarily to acceleration of the cathodic reaction because the mass transfer rate of oxygen is increased under impingement by the fluid jet. Once the pitting potential has been achieved, the open-circuit potential decreases because of growth of stable pits. Fluid flow can itself thereby initiate stable pitting corrosion in open circuit.     

Photogenerated cathodic protection of stainless steel by liquid-phase-deposited sodium polyacrylate/TiO2 hybrid films

Sodium polyacrylate/TiO₂ hybrid films that served as photoanodes for cathodic protection application were prepared by liquid phase deposition. Under white-light illumination, the open-circuit potential of the hybrid films coupled with SUS304 stainless steel could shift to a more negative value and offer an effective photogenerated cathodic protection for stainless steel. Moreover, the hybrid films also exhibited stronger photocurrents in both the ultraviolet-light and visible-light regions compared to that of control TiO₂ films. In summary, the addition of sodium polyacrylate could greatly improve the photogenerated cathodic protection properties of the liquid-phase-deposited TiO₂ films.     

Photogenerated cathodic protection of flower-like, nanostructured, N-doped TiO2 film on stainless steel

Flower-like, nanostructured, N-doped TiO₂ (N-TiO₂) films were fabricated using a low-temperature hydrothermal method. The morphology, crystalline phase, and composition of these flower-like nanostructured films were characterized systematically by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-vis spectroscopy. The photoelectrochemical properties of N-TiO₂ films in 0.5 M NaCl solution were evaluated under illumination and in the dark through electrochemical measurements. Flower-like nanostructured TiO₂ films exhibited a drastically enhanced photocurrent in the UV light region and a notable absorption in the visible light region (600-700 nm). The negative shifts of the electrode potentials of 316L stainless steel coupled with N-doped TiO₂ photoanodes are 470 and 180 mV under UV and visible light irradiation, respectively. The flower-like, nanostructured, N-doped TiO₂ films were able to function effectively as photogenerated cathodic protection for metals under UV and visible light illumination. Such photogenerated cathodic protection could last a period of 5.5 h even in darkness.     

Photogenerated cathode protection properties of nano-sized TiO2/WO3 coating

Nano-sized TiO₂/WO₃ bilayer coatings were prepared on type 304 stainless steel substrate by sol-gel method. The performance of photo-electrochemical and photogenerated cathode protection of the coating was investigated by the electrochemical method. The results show that the bilayer coating with four TiO₂ layers and three WO₃ layers exhibits the highest photo-electrochemical efficiency and the best corrosion resistance property. Type 304 stainless steel with the coating can maintain cathode protection for 6 h in the dark after irradiation by UV illumination for 1 h. In addition, the mechanism of the photogenerated cathode protection for the bilayer coating was also explored.     

Poly(ortho-ethoxyaniline) in corrosion protection of stainless steel

Corrosion protection of stainless steel (13% Cr) coated with poly(ortho-ethoxyaniline) (POEA) has been investigated. The layers of POEA were synthesised from sulphuric and phosphoric acid solutions by means of cyclic voltammetry. The protecting properties of the layers in supporting electrolytes were investigated by monitoring the open circuit potential (E_oc) vs. time, and by electrochemical impedance spectroscopy (EIS). It was found that polymer layers provide corrosion protection, i.e. they help to stabilise the potential of the metal in the passive potential region. The protective properties of POEA layers have shown to be superior to polyaniline (PANI) layers, which is explained by a denser morphology of POEA. The behaviour of POEA obtained on stainless steel, examined by EIS, is different from the one obtained for POEA on Pt electrode. The registered resistance in the case of POEA on stainless steel represents the charge transfer resistance at polymer/solution interface, i.e. the polymer resistance. These measurements show that a part of the layer is reduced, i.e. that there is an interaction between polymer layer and stainless steel. EIS measurements prove the influence of monomer on stainless steel oxide formation and suggest that polymer is partly incorporated into the oxide film.     

Study of localized corrosion of 304 stainless steel under chloride solution droplets using the wire beam electrode

Localized corrosion of 304 stainless steel under droplets of 1 M sodium chloride solution was investigated by the wire beam electrode (WBE) method. It was found that the current distributions were heterogeneous with isolated anodic current peaks mostly located near the edge of the droplet. During the corrosion process, the stainless steel WBE exhibited the stochastic characteristics with the disappearance of some anodic sites. In addition, stainless steel suffered more serious localized corrosion with the increase of the droplet size. The increase of the cathodic area and the three-phase boundary (TPB) length was believed to be the reason.     

Use of inkjet printing to deposit magnesium chloride salt patterns for investigation of atmospheric corrosion of 304 stainless steel

Inkjet printing was used to deposit MgCl₂ salt patterns on 304 stainless steel foils to investigate atmospheric corrosion. Results were found to be more consistent if initial hydration (1 h at ∼90% RH) of the printed salt pattern was carried out. The pit diameter following exposure at 45% RH and 300 K for 24 h was found to increase with the diameter of the original salt deposit, which is consistent with the idea of cathodic limitation of the pit current. For a constant deposition area, the pit diameter increases with increased salt deposition density, which may be associated with a lower ohmic drop resulting from a higher droplet, or could be influenced by enhanced corrosion during the initial hydration stage.     

Electrolytic pickling of the oxide layer on hot-rolled 304 stainless steel in sodium sulphate

Electrolytic pickling of hot-rolled 304 stainless steel in Na₂SO₄ electrolyte was investigated with electrochemical, weight loss and SEM-EDX measurements. Pickling took place upon both active and transpassive polarisations. Mechanism and kinetics of pickling during active and transpassive polarisations were unravelled. Metallic phase in oxide layer was dissolved during active polarisation while the oxide layer was significantly undercut. Chromium oxide in the oxide layer was oxidised to soluble anions during transpassive polarisation, while iron oxide and metallic phase could either be remained or removed. Pickling due to undercutting with active polarisation was highly pronounced.     

Corrosion behaviour in alkaline medium of zinc phosphate coated steel obtained by cathodic electrochemical treatment

The present work evaluated the ability of zinc phosphate coating, obtained by cathodic electrochemical treatment, to protect mild steel rebar against the localized attack generated by chloride ions in alkaline medium. The corrosion behaviour of coated steel was assessed by open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy. The chemical composition and the morphology of the coated surfaces were evaluated by X-ray diffraction and scanning electron microscopy. Cathodically phosphated mild steel rebar have been studied in alkaline solution with and without chloride simulating the concrete pore solution. For these conditions, the results showed that the slow dissolution of the coating generates the formation of calcium hydroxyzincate (Ca(Zn(OH)₃)₂·2H₂O). After a long immersion time in alkaline solution with and without Cl⁻, the coating is dense and provides an effective corrosion resistance compared to mild steel rebar.     

Environmental factors affecting pitting corrosion of type 304 stainless steel investigated by electrochemical noise measurements under potentiostatic control

Electrochemical noise measurements on anodically polarised type 304 stainless steel surfaces in contact with buffer solutions of neutral pH were performed to study the effect of chloride ions in the nucleation of pitting corrosion. Passive layer stability and susceptibility to pitting corrosion after pickling and passivation at different environmental conditions were also investigated by means of electrochemical current noise measurements under cathodic and anodic polarisation. According to the obtained experimental results pits nucleate independently on the presence of chloride ions. It has been also shown that protectiveness of stainless steel surfaces after pickling strongly depends on the relative humidity of the environment in which the surface is subsequently passivated.     

Effect of hydrochloric acid on pickling of hot-rolled 304 stainless steel in iron chloride-based electrolytes

Weight loss, corrosion potential and EIS measurements were performed to understand the role of HCl in the pickling of oxidised 304 stainless steel in iron chloride-based electrolytes. The surface finish was analysed with SEM-EDX. The oxidised 304 stainless steel is active on immersion, resulting in a low corrosion potential and a high weight loss. After certain duration the stainless steel either remains active or becomes passive depending on HCl content. At low HCl contents, an ongoing active-to-passive transition results in localised corrosion at pits, grain boundaries and honeycombed recesses. The corrosion potential becomes high and the weight loss is suppressed. The weight loss decreases in the initial stage and rises on extended pickling with adding HCl. Because of anodic brightening, the 304 stainless steel is always active as HCl is concentrated. In contrast with the material that is passivated, the charge transfer resistance is considerably low and the double layer capacitance is large during that brightening.     

Cathodic protection of steel in concrete using magnesium alloy anode

Corrosion of steel embedded in concrete structures and bridges is prevented using cathodic protection. Majority of the structures protected employ impressed current system. Use of sacrificial system for the protection of steel in concrete is not as widely employed. The use of magnesium anodes for the above purpose is very limited. This study has been carried out with a view to analyse the use of magnesium alloy anode for the cathodic protection of steel embedded in concrete.Magnesium alloy anode, designed for three years life, was installed at the center of reinforced concrete slab, containing 3.5% sodium chloride with respect to weight of cement, for cathodic protection. Potential of the embedded steel and the current flowing between the anode and the steel were monitored, plotted and analyzed. Chloride concentration of concrete at different locations, for different timings, were also determined and analyzed.The magnesium anode was found to shift the potential of the steel to more negative potentials initially, at all distances and later towards less negative potentials. The chloride concentration was found to decrease at all the locations with increase in time. The mechanism of cathodic protection with the sacrificial anode could be correlated to the removal of corrosive ions such as chloride from the vicinity of steel.     

Effect of Geobacter sulfurreducens on the microbial corrosion of mild steel, ferritic and austenitic stainless steels

The influence of Geobacter sulfurreducens was tested on the anaerobic corrosion of four different steels: mild steel 1145, ferritic steel 403 and austenitic steels 304L and 316L. Within a few hours, the presence of cells induced a free potential (E_oc) ennoblement around +0.3 V on 1145 mild steel, 403 ferritic steel and 304L austenitic steels and slightly less on 316L. The kinetics of E_oc ennoblement depended on the amount of bacteria in the inoculum, but the final potential value depended essentially on the nature of the material. This effect was due to the capacity of G. sulfurreducens to create a direct cathodic reaction on steel surfaces, extracting the electrons directly from material. The presence of bacterial cells modified the corrosion features of mild steel and ferritic steel, so that corrosion attacks were gathered in determined zones of the surface. Local corrosion was significantly enhanced on ferritic steel. Potential ennoblement was not sufficient to induce corrosion on austenitic steels. In contrast G. sulfurreducens delayed the occurrence of pitting on 304L steel because of its capability to oxidize acetate at high potential values. The electrochemical behaviour of 304L steel was not affected by the concentration of soluble electron donor (acetate, 1–10 mM) or the amount of planktonic cells; it was directly linked to the biofilm coverage. After polarization pitting curves had been recorded, microscopic observations showed that pits propagated only in the surface zones where cell settlement was the densest. The study evidenced that Geobacter sulfurreducens can control the electrochemical behaviour of steels in complex ways that can lead to severe corrosion. As Geobacteraceae are ubiquitous species in sediments and soils they should now be considered as possible crucial actors in the microbial corrosion of buried equipment.     

Assessing the tribocorrosion performance of Ti–6Al–4V, 316 stainless steel and Monel K500 alloys in artificial seawater

The electrochemical and tribocorrosion behaviors of Ti–6Al–4V, 316 stainless steel and Monel K500 alloys sliding against Al₂O₃ in artificial seawater are investigated in this paper. It can be observed that the open circuit potential drops down to more negative values due to the removal of passive film. And a rapid dissolution occurs in the wear track compared with the unworn area. The wear loss polarized in cathodic potential is lower than that in anodic potential and open circuit potential conditions, because the material deterioration is enhanced by corrosive attack. The wear volumes of 316 stainless steel are much higher than the ones measured for Ti–6Al–4V and Monel K500 alloys. Friction coefficients are significant large in cathodic polarization compared with anodic polarization for all alloys. Moreover, the 316 stainless steel exhibits large friction coefficients compared with Ti–6Al–4V and Monel K500 alloys.     

金属光电化学阴极保护材料及其防腐功能化实现研究进展

与传统的腐蚀保护方法相比,光电化学阴极保护是一种节能、环保、经济的腐蚀防护技术.该技术的关键特征是,利用光电化学阴极保护材料在光照条件下产生光生电子,而光生电子以电势差作为驱动力转移到金属上,并富集在金属表面,导致金属的电位负移,从而实现对金属的强制保护.总结了近年来国内外光电化学阴极保护材料的制备方法与性能特点,针对目前TiO2薄膜材料存在的问题,阐述了通过形貌调控、元素掺杂、半导体复合、异质结构成、材料耦合等方式,提升光电化学阴极保护性能的策略和技术.概括了非TiO2类光电化学阴极保护纳米材料的性能及应用,主要有ZnO、SrTiO3、In2O3、g-C3N4、铋基金属氧化物等半导体材料.明确了近年来光电化学阴极保护材料防腐功能化实现的途径和方法,包括光阳极法和直接涂敷法,并比较了二者之间的优缺点.最后,提出了金属光电化学阴极保护材料及防腐功能化研究的发展趋势及存在的问题.     

Protective properties of hexacyanoferrate containing polypyrrole films on stainless steel

The protective properties of polypyrrole coatings containing hexacyanoferrate anions are presented. The composite coatings were electrodeposited galvanostatically on stainless steel from the aqueous solutions containing pyrrole monomer and potassium hexacyanoferrate(II) together with traces (10 μmol dm⁻³) of free CN⁻ ions. The protective properties of the resulting coatings were investigated in the highly aggressive medium of 0.1 mol dm⁻³ HCl and 0.4 mol dm⁻³ NaCl. Diagnostic experiments included measurements of open circuit potential with time of exposure, chronoamperometric (current-time) examination of the steel samples at a selected constant potential of 0.5 V and potentiodynamic measurements. To get insight into the dynamics of the steel dissolution at open circuit potential and at the selected anodic potential, changes of concentrations of iron and chromium in the test solution as a function of exposure time were determined using atomic absorption spectrometry. Morphology of the composite film was examined using scanning electron microscopy.     

Electrodissolution of 304 stainless steel in neutral electrolytes for surface decontamination applications

Brightening of 304 stainless steel in concentrated electrolytes of Na₂SO₄, Li₂SO₄, NaNO₃, LiNO₃, NH₄NO₃, and Ca(NO₃)₂ was studied. It is observed that the current efficiency and quality of the surface depend on the electrolyte concentration, ions present in the electrolyte and the operating current density. While sulfate electrolytes etch the electrodes, oxidizing electrolytes generally yield brightened surfaces. Surface brightening is achieved at the lowest current density in LiNO₃/Na₂Cr₂O₇ composite electrolyte at a pH of 5.2. The results are explained on the basis of salt film formation near the specimen surface.     

Critical pitting temperature for Type 254 SMO stainless steel in chloride solutions

The variation with time of the open circuit potential of high molybdenum containing stainless steel (Type 254 SMO) was measured in 4% sodium chloride solution in the temperatures range 30-100 °C. The plot of steady state potentials as function of temperature showed an inflection at 50 °C, attributed to the decrease of oxygen solubility in test solution above 50 °C. Potentiodynamic cycling anodic polarization technique was used to determine the critical pitting potential (E_pit) and the critical protection potential (E_prot) of the steel in 4-30% NaCl solutions at temperatures between 30 and 100 °C. By plotting the two values versus solution temperature, the corresponding critical pitting (CPT) and the critical protection (CPrT) temperatures were determined. Both parameters decreased with increasing chloride content. Above the CPT, E_pit and E_prot decreased linearly with log[Cl⁻]. The addition of bromide ions to the solution shifted both E_pit and E_prot towards positive values. In 4% NaCl, E_pit increased linearly with pH in the range 1-10. The combined effect of chloride ion concentration and pH on the morphology of the pits was examined by scanning electron microscopy (SEM) following potentiodynamic cycling anodic polarization.     

Acoustic emission during pitting corrosion of 304 stainless steel

Acoustic emission (AE) during pitting corrosion of 304 stainless steel (304 SS) in H₂SO₄ solutions with different pH values and Cl⁻ concentrations was studied. Two types of AE signals are detected in all solutions. Each type of signals is characterized by AE parameters (rise time, counts number, duration and amplitude) and waveform carefully. It is believed that the hydrogen bubbles evolution inside the pits is the AE source.