Electrochemical behaviour of high nitrogen bearing stainless steel in acidic chloride solution: Effects of oxygen, acid concentration and surface roughness

The effects of oxygen, H₂SO₄ concentration and surface roughness on the electrochemical behaviour of high nitrogen bearing stainless steel (HNS) in acidified 0.5 M NaCl solution were investigated using potentiodynamic polarization method. The results revealed three corrosion potentials indicating an unstable system. The number of the potentials was influenced by H₂SO₄ concentration. Three potentials existed above 0.011 M H₂SO₄, two between 0.011 and 0.0065 M H₂SO₄ and one below 0.0065 M H₂SO₄. Oxygen increased the number of corrosion potential at 0.005 M H₂SO₄ + 0.5 M NaCl solution while surface roughness had no noticeable influence on the number of potentials but increased the values of the corrosion potentials and passivation current densities with increase in the surface roughness. The corrosion mechanism has been discussed using the ideal polarization curve models.     

Electrochemical behaviour of an AISI 304L stainless steel implanted with nitrogen

In this paper the electrochemical behaviour of AISI 304L stainless steel implanted with nitrogen is studied in alkaline media and chloride-containing media, and it is compared with the behaviour of the unimplanted material. Implantation was done at a saturation dose (4 × 10¹⁷ ions cm⁻²) at an acceleration voltage of 150 keV. The results show a clear improvement of the corrosion resistance for the implanted specimens. No pitting potential is observed in the alkaline media or in the neutral media containing high chloride concentration. The improved corrosion resistance is presumed to be due to the modifications that N⁺ implantation induces in the passive layer that is naturally formed on the alloy. XPS analysis reveals Ni⁰ and Cr³⁺ enrichment in this passive layer. Moreover, a carbon-rich layer is found at the outermost part of the passive layer. The presence of this outermost layer is verified with electrochemical impedance measurements and SEM observations.     

Electrochemical pitting behaviour of type 321 stainless steel in sulfide-containing chloride solutions

The pitting behaviour of type 321 stainless steel in sulfide-containing chloride aqueous environments was studied using cyclic potentiodynamic polarization. A well-established correlation between H₂S and Na₂S₂O₃ in the study of corrosion was applied, that is, H₂S was simulated by Na₂S₂O₃. The major factors affecting the pitting corrosion of type 321 stainless steel are the Cl^- concentration, solution pH and temperature. The results clearly indicate that both E_pit and E _pp decrease with increasing Cl^- concentration and temperature, while I _pass is more sensitive to temperature variation. E _pit decreased with decreasing pH in the range 2 < pH < 7.5. The surface morphology and chemistry of the corroded type 321 stainless steel resulting from anodic polarization in 0.01 M S₂O ₃ ^2- -containing Cl^- solution were analysed by XRD, SEM and EPMA. A higher concentration of sulfur was found in the pits, and the dark surface film was mainly composed of FeS and -Fe₂O₃. The results describe the pitting behaviour of type 321 stainless steel in sulfide-containing Cl^- aqueous environments.     

Electrochemical behaviour of silica basic hybrid coatings deposited on stainless steel by dipping and EPD

The aim of this work is the characterisation of the corrosion behaviour of stainless steel (AISI 304) substrates coated by dipping and electrophoretic deposition (EPD) from a sol-gel basic sol. Particulate silica sols (labelled NaSi) were prepared by basic catalysis from ethyltriethoxysilane (TEOS), methyltriethoxysilane (MTES) and sodium hydroxide. Coatings between 2 and 10 μm were prepared by using concentrated and diluted sols by dipping and EPD process and the corrosion behaviour of the coated substrates were studied through potentiodynamic and impedance spectroscopy measurements (EIS). Potentiodynamic studies of coatings produced by dipping reveal a strong dependence of the protective properties with the concentration of the sol. This behaviour was confirmed by EIS showing that only the coatings obtained from concentrated sol present enough protective properties. On the contrary, EPD coatings prepared from diluted NaSi sol showed an excellent corrosion resistance, maintaining a pure capacitive behaviour for long periods of immersion. EPD deposition is thus proposed as a good alternative method for obtaining thicker and denser coatings with good protective properties from dilute and stable sols.     

Electrochemical investigations of pitting corrosion behaviour of type UNS S31603 stainless steel in thiosulfate-chloride environment

The pitting corrosion behaviour of type UNS S31603 stainless steel (316L SS) in 0.01, 0.05 and 0.1 M thiosulfate ion (S₂O₃ ^2–) in the absence and presence of various concentrations of chloride ion (Cl^–) was studied using the cyclic potentiodynamic polarization method. The influence of major factors which affect pitting corrosion such as pH and temperature, were also investigated. It was found that both the pitting potential (E _pit) and the repassivation potential (E _rp) decreased with increase in Cl^– concentration and solution temperature and a more pronounced difference in E _pit values for various concentrations of S₂O₃ ^2– in 1.0 M Cl^– was obtained at lower temperatures. The effect of pH on E _pit, E _corr and E _rp values for different concentrations of S₂O₃ ^2– in the presence of 1.0 M Cl^– was also determined.     

Electrochemical potential noise of 321 stainless steel stressed under constant strain rate testing conditions

An investigation was carried out on the features of potential electrochemical potential noise of stressed AISI321 stainless steel in solution 0.5 mol/L Na₂SO₄ + 5 × 10⁻³ mol/L H₂SO₄ under constant-strain-rate-testing (CSRT) conditions. The results showed that the strained steel exhibited a white noise feature at low frequencies and the amplitude of potential fluctuation depended on elongation of the steel. Power spectral density (PSD) of the noise increased with increasing strain level. The noise level in the elastic region of the steel was relatively low, which increased with elongation. After the steel yielded, the electrochemical noise level became higher but it increased less significantly with increasing strain. In the fracture region, the potential noise reached the maximum level. In addition to the dependence of electrochemical noise on strain level, it was also found that the electrochemical noise level increased with increasing strain rate. To interpret the generation mechanism of electrochemical noise, a simple model was proposed based on an assumption that strain results in breakdown and repairing of the passive film on the steel. With this model, the dependence of electrochemical potential noise and its power spectral density on strain level and strain rate can be successfully explained.     

不锈钢表面电化学磷化及膜层性能

采用由4.0 g/L ZnO、4 g/L CaCl₂、5%(体积分数)H₃PO₃、4 g/L酒石酸和3 g/L氯酸钠组成的锌钙系磷化液,在温度为70°C和电流密度为4 mA/cm²的条件下对1Cr₁₈Ni₉Ti不锈钢表面进行电化学磷化20 min。对比了所得磷化膜与采用相同磷化液化学磷化2 h所得膜层的表面形貌、相结构和耐蚀性。结果表明,与化学磷化相比,电化学磷化所需时间较短,所得膜层的结晶大小和分布均匀,耐腐蚀性更好。     

Electrochemical properties and corrosion protection of stainless steel for hot water tank

The state in which a stainless steel (STS) exhibits a very low corrosion rate is known as passivity, which is self-healing in a wide variety of environments. However, for those STS the corrosion includes pitting, crevice corrosion, galvanic corrosion, hydrogen embrittlement and stress corrosion cracking etc. And the corrosion resistance of STS is affected by area ratio, solution temperature and solution condition etc. Corrosion characteristics of STS 304, welding parts STS 316, STS 329 and STS 444 were investigated with parameters such as corrosion potential, galvanic current measurements, cathodic and anodic polarization behaviors as a function of area ratio and solution temperature in solution for hot water tank. It was found that galvanic current is affected by the area ratio, temperature and a kind of STS for hot water tank. Corrosion potential of welding part STS 316 was lower than that of STS 304, STS 329, STS 444 in solution for #1, #2 hot water tank. Therefore, it is suggested that the welding part STS 316 acts as anode for the other STSs. The amplitude of galvanic current between welding parts STS 316 and STS 304, STS 329, STS 444 in #1 solution is smaller than that in #2 solution. This is the reason that chloride ion quantity in #2 solution is more than that for #1 solution. And then welding part STS 316 corrodes easily by acting as anode compared to the other STS.     

MIC of stainless steel in freshwater and the cathodic behaviour of biomineralized Mn-oxides

Microbially influenced corrosion by manganese oxidizing microorganisms (MIC by MOMOs) is a corrosion phenomenon occurring in freshwater systems affecting stainless steels. Typically, chloride induced corrosion is observed at chloride concentrations normally not considered as critical. The initiation of corrosion is attributed to an anodic shift of the open circuit potential of the passive stainless steel caused by manganese dioxide biomineralized by the specific organisms. However, not only the potential of the passive steel seems of interest. For the stabilization of localized corrosion, the ability of the cathodic reaction to drive enough current for promoting the switch from metastable pitting to stable pit growth is considered important. Consequently, experiments have been carried out in order to compare the dynamic cathodic properties of the usual oxygen reduction reaction with that of biofilm incorporating biomineralized MnO₂. The results indicate a significantly better cathodic performance of such biofilm which might explain the fast and extensive damages observed in certain cases of MIC by MOMOs.     

Electrochemical synthesis and anticorrosive properties of Nafion-poly(aniline-co-o-aminophenol) coatings on stainless steel

The objective of this work was to compare the electrochemical behavior and possible anticorrosive properties of composite with Nafion^®, poly(aniline-co-o-aminophenol) (P(An-co-OAP)) and polyaniline (PAn) films with those of corresponding simple films. The electrochemical synthesis of polymer films was carried out on stainless steel AISI 304 (SS) surfaces by using the cyclic potential sweep (CPS) deposition. Scanning electron microscopy (SEM) was used for the characterization of the structure and morphology of deposited films. Evaluation of anticorrosive properties of films in 0.5 M H₂SO₄ without and with chlorides was achieved by monitoring the open circuit potential (E_OC) of coated SS electrodes as well as by tracing the anodic current-potential polarization curves. These studies have shown that the SS remains in its passive state in the presence of polymer coatings. Composite with Nafion^®, P(An-co-OAP) and PAn films, keep their redox activity in chloride-containing acid solutions providing almost a complete protection of the SS substrate against pitting corrosion. These films prevent chloride exchange with solution because of the cation permselectivity of the Nafion^® membrane. The charge compensation during redox reactions occurs mainly by protons since sulfonate groups of Nafion^® act as dopants in composite films. The redox behavior of the Nafion^®-P(An-co-OAP) film is improved as compared with that of the Nafion^®-PAn film in both Cl⁻-free and Cl⁻-containing solutions. This behavior may be ascribed to the functional group -OH that facilitates charge compensation through proton during redox reactions.     

Electrochemical polymerization of phenol on 304 stainless steel anodes and subsequent coating structure analysis

Anodic oxidation was carried out using 304 stainless steel anodes in neutral 0.1 mol/L phenol solution with an electrolyte composed of 0.1 mol/L sodium sulfate. This oxidation generated a yellow brown polyphenol coating on the steel anode surface. The reaction conditions discussed in this report relate to the methods of linear scanning, cyclic voltammetry and constant current oxidation. The proper anodic electrode potential for polyphenol deposition was observed to be 1.45 V, with a bath voltage of 2.5 V. The chemical structure of the polyphenol coating was analyzed by infrared spectroscopy and the molecular weight of the soluble part of the coating was detected by gel permeation chromatography. A scanning electron microscope was used to analyze the microstructure of the polyphenol coating, taking advantage of the partial solubility of the polyphenol in tetrahydrofuran. The observed linear and flake-layer modes of the polyphenol coating growth are summarized herein.     

基于碳酸氢钠溶液的304与316L不锈钢电化学试验研究

采用电化学噪声、动电位极化和电容测量方法研究了304、316L不锈钢在不同NaHCO3溶液中的电化学行为及生成钝化膜的半导体性质。在NaHCO3溶液中,304、316L不锈钢存在明显相近的钝化区间;点蚀电位、零电流电位随着NaHCO3浓度的增大而减小。在0.5V电位形成钝化膜的Mott-Schottky曲线表明,304、316L不锈钢在NaHCO3溶液中生成的钝化膜为双层结构,具有相近的成膜特性。但随着NaHCO3溶液浓度变化所生成钝化膜的性质也不同,304不锈钢形成的表面膜稳定性稍好于316L。     

Electrochemical and gas evolution characteristics of direct methanol fuel cells with stainless steel mesh flow beds

Carbon dioxide gas management and bipolar plate/(flow bed) design are important to the development of direct methanol fuel cell (DMFC) systems. If the gas produced at the anode is not removed rapidly and efficiently a gradual deterioration in electrical performance can occur. This paper examines the feasibility of using stainless steel mesh materials as flow beds for the DMFC. A flow visualization study, using a high-speed video camera and appropriate computer software, of the anode side, carbon dioxide gas evolution and flow behaviour with flow beds based on stainless steel mesh is reported. The electrochemical behaviour of the direct methanol fuel cell with stainless steel flow beds is also reported. A number of the flow bed designs, based on stainless steel mesh, showed promising behaviour in terms of gas removal characteristics and electrical performance.     

Anodic decomposition of citric acid on gold and stainless steel electrodes: An in situ-FTIR-spectroscopic investigation

The electrochemical decomposition of citric acid on gold and stainless steel AISI 304 (18% Cr, 10% Ni) electrodes was investigated using the technique of in situ InfraRed Reflection Absorption FTIR Spectroscopy (IRRAS) in combination with cyclic voltammetric measurements. The applied potential sweep starts from −0.265 up to +2.5 V on gold and from +0.4 up to +2.4 V on steel electrodes. The initial potentials of the anodic decomposition of citric acid could be observed on both electrode materials. Carbon dioxide was detected as decomposition product. Using stainless steel electrodes, the decarboxylation of citric acid and the forming of citrate complexes were observed. The consumption of citric acid is both due to its anodic decomposition and the generation of soluble citrate complexes of iron, nickel and chromium, resulting from the transpassive dissolution of the electrode material. At potentials more positive than +500 mV both processes are occurring simultaneously.     

Surface and electrochemical characterization of pitting corrosion behaviour of 304 stainless steel in ground water media

The effectiveness of aminotrimethylidene phosphonic acid (ATMP) as a corrosion inhibitor in association with a bivalent cation like Zn²⁺ and non-ionic surfactant like polyoxyethylene sorbitan monooleate (Tween 80) were investigated by measuring corrosion losses using electrochemical techniques. The corrosion of 304 stainless steel in the ground water medium was inhibited by complexation of the inhibitor. A combined inhibition effect was achieved by adding both ATMP and Zn²⁺ along with Tween 80. The formulation functioned as a mixed type inhibitor. The synergistic effect of the inhibitor compound is calculated. Luminescence spectra, FTIR spectra, XRD, XPS and scanning electron microscopic studies were carried out to understand the mode of corrosion inhibition and also the morphological changes on the metal surface.     

Electrochemical behaviour of benzylamine, 2-phenylethylamine and 4-hydroxyphenylethylamine at gold. A comparative study

The electrooxidation of benzylamine, 2-phenylethylamine and 4-hydroxyphenylethylamine (tyramine) at a gold electrode in contact with an alkaline electrolyte solution was studied. The effect of amine concentration, electrolyte pH and potential scan rate on the electrooxidation was analysed. The adsorption of amines on the gold-solution interface was found to play a significant role in the oxidation mechanism. The rate determining step was the heterogeneous dehydrogenation of the amine molecule, involving electron transfer to the gold electrode and the formation of a water molecule. The catalytic effect of the gold electrode on both benzylamine and 2-phenylethylamine oxidation is higher than that for tyramine.     

CD-4MCu双相不锈钢在稀硫酸介质中的腐蚀磨损行为

用失重法测定了固溶处理态和固溶+时效处理态CD-4MCu双相不锈钢在稀硫酸介质中的腐蚀磨损速率。结果表明,CD-4MCu在固溶态时硬度低,耐腐蚀磨损性能差;在固溶+时效处理态时硬度高,耐腐蚀磨损性能好。介质温度和浓度升高,CD-4MCu双相不锈钢腐蚀及磨蚀增加,腐蚀磨损交互作用增大。     

Modifications in the structural,morphological, optical properties of Ag45Se40Te15 thin films by proton ion irradiation for optoelectronics and nonlinear applications

This current work reports the 30 keV proton ion irradiation induced structural, morphological, and optical properties change in Ag₄₅Se₄₀Te₁₅ films at different fluences. The thin films were irradiated with different ion fluences, such as 5 × 10¹⁵ ions/cm²,1 × 10¹⁶ ions/cm² and 5 × 10¹⁶ ions/cm². The electronic loss (S_e) dominates over the nuclear loss (S_n) in proton irradiation. The X-ray diffraction study shows the phase transformation from amorphous to crystalline upon ion irradiation. The Raman analysis confirms the change in chemical and vibrational bonds due to structural alterations in the films. The surface morphology has been studied by field emission scanning electron microscopy and the composition of the films has been checked by the energy dispersive X-ray analysis. The particle size increased upon the increase in ion irradiation fluence. The surface roughness of the films has been studied by atomic force microscopy. The transmission data is used to calculate the linear optical parameters. The absorption edge shifts towards the high wavelength region inferring the reduction in the optical bandgap. The linear refractive index of the films increased with ion fluence. The optical density increased at the high wavelength region while the skin depth decreased with fluence. The carrier concentration per effective mass decreased while the plasma frequency increased with proton irradiation. The nonlinearity (χ ⁽³⁾ and n₂) values increased significantly with the increase in fluences. Such kind of materials with optimization in their optical parameters are primarily essential for cutting-edge photonic, optoelectronic, and nonlinear optical applications.     

Numerical modelling of the electrochemical behaviour of 316L stainless steel based upon static and dynamic experimental microcapillary-based techniques

Microcapillary-based techniques allow the selection and interrogation of single metallurgical sites and are therefore becoming increasingly popular to investigate the electrochemical behaviour of metallic phases and non-metallic heterogeneities in alloys. This study has been carried out to assess the differences between current measurements made using a ‘closed’ microcapillary system (the electrochemical microcell technique) with current measurements derived from a flowing ‘open’ microcapillary droplet cell (the scanning droplet cell). The experimental results were compared with calculations derived from a model system adopting a finite element approach. The corrosion system consists of four parallel electrochemical reactions: three cathodic reactions (the oxygen reduction reaction, the hydrogen evolution reaction and water dissociation) and one anodic reaction (metal dissolution reaction). Comparative experimental results have shown there is a large discrepancy between the magnitudes of the cathodic current obtained by the two techniques. The results of this study allow an assessment of the parameters responsible for the mass transport and distribution of species in the closed and open systems. Critical parameters (for example, microcell crevice geometry, specimen surface-capillary gap distance, etc.) which lead to significant modifications of the curves were then identified using the numerical simulation.     

Effect of PgTPhPBr on the electrochemical and corrosion behaviour of 304 stainless steel in H2SO4 solution

Weight-loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements were used to study the inhibition of 304 stainless steel corrosion in 1 M H₂SO₄ at 50 °C by propargyltriphenylphosphonium bromide (PgTPhPBr). The inhibiting effects of propyltriphenylphosphonium bromide (PrTPhPBr) and propargyl alcohol (PA) were also studied for the sake of comparison. For the investigated compounds, Tafel extrapolation in the cathodic region gave a corrosion inhibition efficiency of 98% at 1 × 10^–3 M. Adsorption of both PgTPhPBr and PA was found to follow Frumkin's isotherm while adsorption of PrTPhPBr obeys that of Temkin. In the anodic domain, PgTPhPBr acted as a good passivator. The impedance spectra recorded at the corrosion potential (E _cor) revealed that the charge transfer process in the inhibited and uninhibited states controls corrosion of 304 stainless steel.