Microbially influenced corrosion of 303 stainless steel by marine bacterium Vibrio natriegens: (II) Corrosion mechanism

Electrochemical techniques (electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves) and surface analysis (scanning electron microscopy (SEM)) were carried out to determine the possible mechanism of the microbially influenced corrosion of 303 stainless steel (303 SS) by marine bacterium Vibrio natriegens (V. natriegens). In order to clarify the mechanism, 303 SS coupons were immersed in four different mediums. EIS results were interpreted with different equivalent circuits to model the physicoelectric characteristics of the electrode/biofilm/solution interface. The results showed that N₂-fixation actually promoted the corrosion of 303 SS; however, the influence of the produced NH₃ was negligible. It can be speculated that the electron transfer and/or the nitrogenase catalyzing the process may influence the corrosion.     

Effect of bias voltage on the electrochemical properties of TiN coating for polymer electrolyte membrane fuel cell

The electrochemical properties of TiN film coated on AISI 316 stainless steel (SS) by the magnetron sputtering physical vapor deposition (PVD) were studied for application as a bipolar plate. The crystal structure and surface morphology of the coatings were examined by x-ray diffractometry (XRD) and atomic force microscopy (AFM), respectively. The corrosion behaviors of the TiN films were investigated by electrochemical methods, including potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) under + 600 mV_SCE application. The electrochemical behavior of the TiN coatings was enhanced with increasing bias voltage due to lower corrosion current density and higher R_ct values during an immersion time of 168 h. This result was attributed to the formation of crystalline-refined TiN(200) at high bias voltage, which increased the coating compactness and the protective efficiency, and decreased passive current density.     

Corrosion behaviour of CrN/Cr multilayers on stainless steel deposited by unbalanced magnetron sputtering

This paper reports the results of the influence of bilayer period (Λ) and total thickness (f) on the corrosion resistance of magnetron-sputtered CrN/Cr multilayers. Corrosion tests were carried out by potentiodynamic polarization with 0.5 M H₂SO₄ + 0.05 M KSCN solution and electrochemical impedance spectroscopy (EIS) with 3% NaCl solution. Measurements were also taken on the uncoated substrate and hard chromium coatings for comparison. Multilayer microstructure and morphology were studied by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) and chemical composition was studied by energy dispersive X-ray analysis (EDX).The experiments showed that CrN/Cr coatings having lower bilayer period and lower thickness increased their efficiency as a barrier and improved the corrosion resistance of all coatings evaluated.     

铁氧化菌作用下316L不锈钢点蚀电化学特性的研究

采用电化学测量、交流阻抗技术、扫描电镜观察和能谱分析等实验方法,研究了316L不锈钢在铁氧化菌(IOB)溶液中的腐蚀电化学行为,分析了炼油厂冷却水系统微生物腐蚀的特征及机制,结果表明,在含有IOB溶液中的自腐蚀电位(Ecorr)、点蚀电位(Epit)和极化电阻(Rp)均随浸泡时间的增加呈现出降-升-降的变化趋势;在含有IOB溶液中的腐蚀速率均大于在无菌溶液中;IOB的生长代谢活动及其生物膜的完整性和致密性影响了316L不锈钢表面的腐蚀过程,使不锈钢表面的钝化膜层腐蚀破坏程度增加,加速了316L不锈钢的点蚀.     

Pitting corrosion protection of low nickel stainless steel by electropolymerized conducting polymer coating in 0·5?M NaCl solution

Conducting polymers of polyaniline (PANi) and poly(o-phenylenediamine) (PoPD) were electropolymerized by cyclic voltammetric technique on low nickel stainless steel (LN SS) in H₂SO₄solution containing aniline and o-phenylenediamine monomers. The coatings were characterized by Fourier transform infrared spectroscopy, UV-visible and scanning electron microscopic techniques and the results are discussed. The corrosion protective properties of PANi and PoPD coatings on LN SS in 0·5 M NaCl were evaluated using potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) techniques. The potentiodynamic polarization and electrochemical impedance spectroscopic results indicate that the PoPD coating inhibits the corrosion of LN SS in 0·5 M NaCl solution more effectively than PANi.     

Microbiologically influenced corrosion of titanium caused by aerobic marine bacterium Pseudomonas aeruginosa

Microbiologically influenced corrosion (MIC) is a big threat to the strength and safety of many metallic materials used in different environments throughout the world. The metabolites and bioactivity of the microorganisms cause severe deterioration on the metals. In this study, MIC of pure titanium (Ti) was studied in the presence of a highly corrosive aerobic marine bacterium Pseudomonas aeruginosa. The results obtained from electrochemical test showed that Ti was corrosion resistant in the abiotic culture medium after 14 d, while the increased corrosion current density (i_corr) obtained from polarization curves and the decreased charge transfer resistance (R_ct) from electrochemical impedance spectroscopy (EIS) indicated the accelerated corrosion of Ti caused by P. aeruginosa biofilm. For further confirmation of the above results, the surface of Ti was investigated using scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and X-ray photoelectron spectroscopy (XPS). According to the XPS results, TiO₂ was formed in both abiotic and biotic conditions, while unstable oxide Ti₂O₃ was detected in the presence of P. aeruginosa, leading to the defects in the passive film and localized corrosion. Pitting corrosion was investigated with the help of CLSM, and the largest pit depth found on Ti surface immersed in P. aeruginosa was 1.2 μm. Ti was not immune to MIC caused by P. aeruginosa.     

Corrosion behavior of pure titanium in the presence of Actinomyces naeslundii

It is well known that some microorganisms affect the corrosion of dental metal. Oral bacteria such as Actinomyces naeslundii may alter the corrosion behavior and stability of titanium. In this study, the corrosion behavior of titanium was studied in a nutrient-rich medium both in the presence and the absence of A. naeslundii using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). A. naeslundii was able to colonize the surface of titanium and then form a dense biofilm. The SEM images revealed the occurrence of micropitting corrosion on the metal surface after removal of the biofilm. The electrochemical corrosion results from EIS showed a significant decrease in the corrosion resistant (R_p) value after immersing the metal in A. naeslundii culture for 3 days. Correspondingly, XPS revealed a reduction in the relative levels of titanium and oxygen and an obvious reduction of dominant titanium dioxide (TiO₂) in the surface oxides after immersion of the metal in A. naeslundii culture. These results suggest that the metabolites produced by A. naeslundii can weaken the integrity and stability of the protective TiO₂ in the surface oxides, which in turn decreases the corrosion resistance of titanium, resulting in increased corrosion of titanium immersed in A. naeslundii solution as a function of time.     

Corrosion behaviour of β-Ti20Mo alloy in artificial saliva

To evaluate the potential of β-Ti20Mo alloy as a dental material, we tested its corrosion behaviour in artificial saliva in comparison to that of cp-Ti. Open-circuit potential (E_OC), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used as electrochemical methods to characterize the corrosion behaviour of Ti20Mo alloy and cp-Ti, respectively. Corrosion current and passive current densities obtained from the polarization curves showed low values indicating a typical passive behaviour for Ti20Mo alloy. The EIS technique enabled us to study the nature of the passive film formed on the binary Ti20Mo alloy at various imposed potentials. The Bode phase spectra obtained for Ti20Mo alloy in artificial saliva exhibited two-time constants at higher potential (0.5 V, 1.0 V), indicating a two-layer structure. According to our experimental measurements, Ti20Mo alloy appears to possess superior corrosion resistance to that of cp-Ti in artificial saliva.     

Effect of temperature on corrosion behavior of alloy 690 in high temperature hydrogenated water

The influence of temperature on the corrosion behavior of Alloy 690 is evaluated using potentiodynamic polarization curves,electrochemical impedance spectra(EIS),scanning electron microscopy(SEM),Xray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM).The corrosion rate of Alloy 690 reaches a local maximum at 250?C.The kinetic control step of the growth of oxide film changes from the diffusion process of aqueous-phase ions to the growth of Cr-rich barrier layer in the temperature range of 200–300?C.A modified double-layer model is proposed to describe the effect of temperature on the structure and composition of the oxide film.     

Investigation of inhibition effect of rhodanine-N-acetic acid on mild steel corrosion in HCl solution

Corrosion inhibition effect of rhodanine-N-acetic acid (R-NA) on mild steel (MS) corrosion in 0.1 M HCl solution was investigated. For this purpose, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) as well as hydrogen gas evolution (VH₂−t) and the change of open circuit potential as a function of immersion time (E_ocp − t) were used. The MS surfaces exposed to 0.1 M HCl solution in the absence and presence of inhibitor were examined by scanning electron microscopy (SEM). The thermodynamic parameters of adsorption were calculated and discussed. In order to gain more information about the adsorption mechanism, the EIS technique was used to evaluate the potential of zero charge (PZC) and a mechanism of adsorption process was proposed. It was found that, R-NA is a good corrosion inhibitor for the MS corrosion in 0.1 M HCl solution. The inhibition efficiency increased with increasing inhibitor concentration and reached 98% at 1.0 × 10⁻² M R-NA. The high inhibition efficiency was related to adsorption of R-NA on steel surface. Surface SEM images showed a good surface coverage of inhibitor on the metal surface.     

Green approach to corrosion inhibition of mild steel in two acidic solutions by the extract of Punica granatum peel and main constituents

The effect of the extract of Punica granatum (PG) and their main constituents involve ellagic acid (EA) and tannic acid (TA), as mild steel corrosion inhibitor in 2 M HCl and 1 M H₂SO₄ solutions was investigated by weight loss measurements. The results obtained from the weight loss measurements show that the inhibition efficiency of TA even in high concentration is very low. Thus, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) investigations were used for different concentrations of PG and EA and best concentration of TA. Potentiodynamic polarization curves indicated that PG and EA behave as mixed-type inhibitors. EIS measurements show an increase of the transfer resistance with increasing inhibitor concentration. The temperature effect on the corrosion behavior of steel without and with the PG extract was studied. The inhibition action of the extract was discussed in view of Langmuir adsorption isotherm.     

The inhibition of mild steel corrosion in 1 M hydrochloric acid solutions by triazole derivative

The title compound 1-(4,5-dihydro-3-phenylpyridine-1-yl)-2-(1H-1,2,4-triazole-1-yl)ethyl ketone (DTE) was synthesized and its inhibiting action on the corrosion of mild steel in 1 M hydrochloric acid solutions was investigated by means of weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electronic microscope (SEM). Results obtained revealed that DTE performed excellently as a corrosion inhibitor for mild steel in 1 M hydrochloric acid media and its efficiency attains more than 90.9% at 1.0 × 10^− 3 M at 298 K. Polarization curves indicated that the inhibitor behave mainly as mixed-type inhibitor. EIS showed that the charge transfer controls the corrosion process in the uninhibited and inhibited solutions. Adsorption of the inhibitor on the mild steel surface followed Langmuir adsorption isotherm. And the values of the free energy of adsorption ΔG_ads indicated that the adsorption of DTE molecule was a spontaneous process and was typical of chemisorption.     

Chrome-free neodymium-based protective coatings for magnesium alloys

The microstructure of chrome-free neodymium-based conversion coating on magnesium alloy was investigated and the corrosion resistance was evaluated as well. The micro-morphology, transverse section, crystal structure and composition of the coating were observed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS), respectively. The corrosion resistance was evaluated by potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS).The results revealed that the morphology of neodymium conversion coating is of crack-mud structure. Tiny cracks distribute in the compact coating deposited by neodymium oxides. EDS results characterize that the coating is made of neodymium oxides. The potentiodynamic polarization curve, EIS and OCP indicate that the neodymium conversion coating can improve the corrosion resistance of magnesium alloys.     

An investigation on effects of heat treatment on corrosion properties of Ni–P electroless nano-coatings

Electroless Ni–P coatings are recognized for their excellent properties. In the present investigation electroless Ni–P nano-crystalline coatings were prepared. X-ray diffraction technique (XRD), scanning electron microscopy (SEM), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were utilized to study prior and post-deposition vacuum heat treatment effects on corrosion resistance together with the physical properties of the applied coatings.     

Electrochemical characterization of the corrosion of a Mg-Li Alloy

The corrosion characteristic of a novel Mg-Li alloy with RE in alkaline NaCl solution was investigated by electrochemical means, such as open circuit potential vs time curves, potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS). The result showed that Cl⁻ concentration and pH value affected the corrosion of Mg-Li alloy, and in high Cl⁻ concentration solution Cl⁻ concentration was the major factor. Corrosion of the alloy was slighter in the stronger alkaline solution, because corrosion current(I_corr) reduced, corrosion potential (E_corr) turned to positive direction and the capacitive loops enlarged. When Cl⁻ increased, I_corr increased and capacitive loops shrinked, this means that corrosion of the alloy was more serious with the increase in Cl⁻ concentration.     

The effect of Pseudoxanthomonas sp. as manganese oxidizing bacterium on the corrosion behavior of carbon steel

The present study investigated the role of manganese oxidizing bacterium (MOB), namely Pseudoxanthomonas sp. on the corrosion behavior of carbon steel. This bacterium was isolated from sewage treatment plants and identified by biochemical and molecular methods. The electrochemical techniques such as open circuit potentiometry, electrochemical impedance spectroscopy, potentiodynamic and cyclic polarization were used to measure the corrosion rate and observe the corrosion mechanism. Also, scanning electron microscopy and X-ray diffraction studies were applied to surface analysis. This study revealed the strong adhesion of the biofilm on the metal surface in the presence of Pseudoxanthomonas sp. that enhanced the corrosion of carbon steel. X-ray diffraction patterns identified a high content of MnO₂ deposition within these biofilms. This is the first report that discloses the involvement of Pseudoxanthomonas sp. as manganese oxidizing bacteria on the corrosion of carbon steel.     

New material for orthopedic implants: Electrochemical study of nickel free P558 stainless steel in minimum essential medium

Nickel, a component of stainless steels (SS) applied in orthopedic implants may cause allergic processes in human tissues. P558 nickel free SS was studied to verify its viability as a substitute for stainless steel containing nickel. Its performance is compared to ISO 5832-9 and F138 most used nowadays grades in implants fabrications, in minimum essential medium, MEM, at 37 °C. Potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and “in vitro” cytotoxicity were used as techniques. From the electrochemical point of view P558 SS is comparable to ISO 5832-9 SS in MEM. It remains passivated until the transpassivation potential, above which generalized corrosion occurs. F138 presents pitting corrosion at 370 mV/SCE. The cytotoxicity results showed that P558, ISO 5832-9 and F138 do not present cytotoxic character. Therefore, these results suggest that P558 SS can be applied in orthopedic implants.     

Surface Protection and Morphological Study of Copper by Green Corrosion Inhibitor: 8QSC in HNO<Subscript>3</Subscript> Medium

The inhibition performance and surface protection of green corrosion inhibitor 8-quinoline sulphonyl chloride (8QSC) on copper (Cu) was evaluated by chemical (weight loss) method in 0.5, 1.0 and 2.0 M HNO₃ solutions and by electrochemical methods such as potentiodynamic polarization (PDP), AC-impedance spectroscopy (AC-IS) and linear polarization resistance in 1.0 M HNO₃ solution at room temperature. Both chemical and electrochemical techniques showed that 8QSC is an efficient green corrosion inhibitor for copper and the efficiency reached 90.4% by weight loss method and 88.4% by AC-IS method at optimum concentration of (300 ppm) 8QSC. The adsorption behavior of 8QSC on copper metal in acid medium obeyed the Langmuir isotherm. The thermodynamic parameters of the adsorption processes were calculated and discussed. AC-IS technique exhibits one capacitive loop, indicating that the corrosion reaction was controlled by charge transfer process. The PDP curves revealed that 8QSC acts as a mixed-type inhibitor. Protective layer of 8QSC on copper surface was examined by SEM, AFM and FT-IR techniques. The experimental results corroborated with results obtained from theoretical DFT studies.     

Corrosion resistant Zn-Co alloy coatings deposited using saw-tooth current pulse

Micro/nanostructured multilayer coatings of Zn-Co alloy were developed periodically on mild steel from acid chloride bath. Composition modulated multilayer alloy (CMMA) coatings, having gradual change in composition (in each layer) were developed galvanostatically using saw-tooth pulses through single bath technique (SBT). CMMA coatings were developed under different conditions of cyclic cathode current densities (CCCDs) and number of layers, and their corrosion resistances were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) method. Optimal configuration, represented as (Zn-Co)_2·0/4.0/300 was found to exhibit ～ 89 times better corrosion resistance compared to monolithic (Zn-Co)_3·0 alloy deposited for same time, from same bath. The better corrosion resistance of CMMA coatings was attributed to changed interfacial dielectric properties, evidenced by dielectric spectroscopy. Improved corrosion resistance was attributed to formation of n-type semiconductor film at the interface, supported by the Mott-Schottky plot. Further, the formation of multilayer and corrosion mechanism was analysed using scanning electron microscopy (SEM).     

Cu(II), Co(II) and Ni(II) complexes of –Br and –OCH<Subscript>2</Subscript>CH<Subscript>3</Subscript> substituted Schiff bases as corrosion inhibitors for aluminium in acidic media

A group of Cu(II), Ni(II) and Co(II) complexes of –Br and –OCH₂CH₃ substituted Schiff bases as a new class of corrosion inhibitors for aluminium has been studied in 0.1 M HCl by the addition of 10 ppm compound using potentiodynamic polarization, electrochemical impedance spectroscopy, linear polarization methods and gas evolution tests at 25 °C. The inhibition efficiencies obtained from all methods employed are in good agreement. Results show Ni(II) complex of –OCH₂CH₃ substituted Schiff bases was the best inhibitor with a mean efficiency of 69% at 10 ppm additive concentration. The potentiodynamic polarization curves showed both the cathodic and the anodic processes of aluminium corrosion were suppressed, and the Nyquist plots of impedance gave mainly a capacitive loop. Scanning electron microscopy (SEM) was done from the surface of the exposed sample indicating uniform film on the surface.