The paper introduces briefly the ecological and physiological characteristics of SRB and the reliability of cathodic polarization (CP) on metallic material in environment containing SRB with emphasis on the influence of CP on microbiological influenced corrosion, including the impact of CP on susceptibility to hydrogen embrittlement and mechanical properties of metallic material, the ambient environment around metallic structures and the activity of metabolic products of the microorganism. Meanwhile the interaction between SRB and CP was elaborated in details. Finally, the future trend of researches on microbiological influenced corrosion is also given.
Microbial corrosion induced by sulphate-reducing bacteria (SRB) for carbon steel Q235 beneath coating defects was studied by means of electrochemical impedance spectroscopy (EIS), polarization measurement and microscopic surface observation. Results showed that, in acid red soil environment, SRB have no significant effect on the electrochemical process during the initial environmental adaptation period. Then in the next period, the respiratory metabolic activities of the growing SRB lead to decrease of the free corrosion potential of Q235 steel and accelerate corrosion process of the carbon steel. Bacteria can react with iron oxides in the red soil, causing microbial dissimilatory reduction of iron oxides, which promotes electrochemical corrosion process of the carbon steel.
It is known that calcareous deposit formed on the surface of metallic material may have effect on the adhesion of marine micro-organism to and the corrosion behavior of the substrate material. Meanwhile, micro-organisms may in turn affect the formation process of calcareous layer. To clearly understand the above mentioned phenomena, the electrochemical behavior of the Q235 carbon steel without and with a pre-deposited calcareous layer in the f/2 culture media with the absence and presence of chlorella vulgaris respectively, as well as, the adhesion behavior of chlorella vulgaris on the substrate were investigated by using fluorescence microscopy, surface analysis techniques and electrochemical measure method. Results show that the adhesion process of chlorella vulgaris reached the equilibrium phase of adsorption-desorption after immersion of the steel in the medium for 48 h. Absorption is the decisive step in the initial attachment stage of chlorella vulgaris on the steel with calcareous deposit, and then the adherent microalgae began to proliferate. The calcareous deposit could promote the adhesion of microalgae, however, the calcareous deposit was apt to spall off in the f/2 culture medium without chlorella vulgaris. During the immersion process, composite films of calcareous deposit and microalgae may formed on the steel surface, which was compact with good adhesion to the substrate and presented blockage effect to the charge transfer and inward diffusion of oxygen, thereby can effectively inhibit the corrosion of the steel.
The pitting corrosion behavior of high nitrogen stainless steel (HNSS) and 316L stainless steel (316L SS) in 6%(mass fraction) FeCl3 solution was compared by time domain, frequency domain spectrum and Weibull distribution analysis of electrochemical noise (EN) data. The time domain analysis results show that after immersion in the solution of 6%FeCl3 for 5 h, the noise transient peaks appear on the measured potential noise and current noise of 316L SS, implying the occurrence of metastable pitting, however, at the same time, the noise transient peak does not appear on the EN plot of HNSS, while the potential noise and current noise only presented a slight high-frequency fluctuations, indicating the surface passivation film suffered from slightly attack, while presented ability of repassivation to certain extent. Moreover, the noise resistance fluctuation amplitude of 316L SS is larger than that of HNSS, which suggesting the ability in self-passivation and re-healing of the passivation film of HNSS is better than that of 316L SS. Plots of power spectral density show that the values of slope of high frequency and plateau intensity of white noise of 316L SS are larger than those of HNSS, and the relevant Weibull distribution analysis reveals that the rate of pitting inoculation for 316L SS is twice of that for HNSS, which predicating that the 316L SS is much prone to pitting than HNSS.
The influence of the pH value, impact velocity and impact angle of the corrosive medium (HCl droplet) on the dew point corrosion behavior of 10# carbon steel in a simulated HCl-H2O dew point corrosion environment of the atmospheric tower system was investigated by means of mass change measurement, scanning electron microscopy (SEM), X-ray diffraction (XRD). Results indicate that: the dew point corrosion rate of 10# carbon steel increases with the impact velocity, and decreases with the increasing pH value and impact angle of HCl droplet, while a turning point of the dew point corrosion rate exists at the impact angle of 45°. The corrosion mode of 10# carbon steel in the HCl-H2O environment is pitting corrosion, and there are many pits with different sizes and shapes on its surface, and Cl- in the solution will deepen the pits. The main composition of corrosion product on 10# carbon steel is α-FeOOH and Fe2O3.
The microstructure and corrosion resistance of hot rolled Cr/Ni micro-alloyed high strength weathering steels Q500H and Q700H were studied by means of electrochemical test, immersion test, SEM, EDS and XRD. Results showed that the two hot rolled high strength weathering steels present the same microstructure composed of pearlite and ferrite, while Cr was distributed evenly in the above mentioned two phases, and Ni was more rich in ferrite phase. The Q700H weathering steel with higher Cr- and Ni-content showed lower annual corrosion rate. After immersion in 3.5%(mass fraction) NaCl solution for 60 d, the corrosion current density of the two steels increased, but Q700H weathering steel has higher charge transfer resistance and smaller corrosion current density. The corrosion pits on the surface of Q700H steel was smaller after 150 d immersion. The increase of Cr- and Ni-content promoted the for mation of α-FeOOH, which was dense and stable. Cr was concentrated in the inner rust layer, Ni was enriched at the interface between the substrate and the rust layer, the higher the content of Cr and Ni was, the much obvious enrichment they had.
A high-nitrogen containing face-centered-cubic phase (γΝ) formed on AISI 304L austenitic stainless steel surface via plasma source nitriding. The chemical composition of the passive film on the γΝ-phase was characterized by means of AES and XPS, which formed in a borax buffer solution with pH value of 8.4. The semi-conductive characteristic of the passive film on the γΝ-phase was investigated by Mott-Schottky analysis. The results showed that the passive film on the γΝ-phase was of a two-layered structure: of which the outer portion composed of iron hydroxide/oxides and chromium hydroxide/oxides exhibiting n-type semi-conductive and inner portion composed of mainly chromium oxides with a little chr-omium- and iron-nitrides exhibiting p-type semi-conductive. In comparison with the passive film on the plain stainless steel, the passive film on the γΝ-phase is much densified with lower donor- and acceptor-density and more negative of the flat band potential, thus leading to the lowering corrosion rate.
The stress corrosion crack propagation behavior of the elbow pipe of nuclear grade 316LN stainless steel (SS) in high temperature high pressure water was studied by means of direct current potential drop (DCPD) method coupled with in-situ measuring the crack length of the compact tension (CT) specimen, as well as scanning electron microscope (SEM) and electron back scattering diffraction (EBSD) technique. Results indicated that the crack growth rate monotonically increased with the increase of temperature ranging from 270 ℃ to 330 ℃, and the crack growth rate at 330 ℃ was 1.7 fold of that at 270 ℃. The apparent activation energy (Eaae) for stress corrosion crack propagation of 316LN SS was 52 kJ/mol. The crack growth rate of 316LN SS was affected by the solution with dissolved 1500 mg/L B+2.3 mg/L Li in high temperature high pressure water and the influence extent depended on the pH of the solution. The results of the crack growth rates could provide data support for the plant safety evaluation and remnant life prediction. Intergranular stress corrosion cracking was observed for the fractured surface of 316LN stainless steel tested in pressurized high temperature water. The crack propagated along with the large angle grain boundaries instead of the coincidence site lattice (CSL) boundaries and lots of secondary cracks were observed. Moreover, the residual strain at the grain boundary was larger than that of the interior of grains.
The corrosion inhibition and adsorption behavior of sodium diethyldithiocarbamate (SDDTC) on AZ31B Mg-alloy in 3.5% (mass fraction) NaCl solution were investigated by means of potentiodynamic polarization measurement, electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Results showed that SDDTC could inhibit effectively the corrosion for AZ31B Mg-alloy in NaCl solution, and acted as a mixed-type inhibitor with predominant control of the cathodic reaction. When the concentration of SDDTC was 5 mmolL-1, the inhibition efficiency was the best. The physical adsorption of SDDTC on the AZ31B Mg-alloy surface obeyed the Langmuir adsorption isotherm. While SDDTC adsorbed on the surface of Mg-alloy forms a much compact protective film, effectively inhibiting the corrosion of AZ31B Mg-alloy.
Cellular automata method was adopted to simulate the corrosion damage behavior of steel. According to the results of experimental study on steel in corrosive environments and the principle of cellular automata method, a local evolution rule of cellular automata was defined, and then the evolution process of corrosion morphology for a pit were simulated. By comparing the simulation results for different initial concentrations c and dissolution probability p, the real simulation condition for the corrosion pit was determined. At the same time, the influence of different initial solution concentration c and dissolution probability p on the morphology was discussed. It was shown that with the increasing initial concentration c and dissolution probability p, the equivalent radius or depth of corrosion pit presents an approximate power function of etching time t. Meanwhile, the simulation results of pit depth were compared with the theoretical prediction proposed by Komp, which showed that both results are agreeable and the proposed CA model is feasible and efficient.
A model of equivalent conversion coefficient for UV radiation was firstly proposed, and which then was coupled with the existed acceleration corrosion testing method to establish a test spectrum for the assessment of aging performance of polyurethane coating on 7B04 Al-alloy plate. The aging behavior of polyurethane coating were characterized by means of macroscopic- and microscopic-observation, gloss loss-, color change- and adhesion strength-measurement, and electrochemical impedance spectroscopy (EIS) etc. Results show that the gloss loss and color change are not the suitable index for representing coating degradation degree, but the adhesive force and EIS are the appropriate ones to characterize the aging behavior of coating. The aging process of coating can be broadly divided into three stages: in the initial stage, the coating was intact with impedance above 1010 Ωcm2; in the middle stage, the anticorrosion performance of the coating was impaired to a certain extent with impedance within a range of 107~109 Ωcm2, while pores increase in the coating; and in the late stage, coating was failed with blisters on its surface, while, of which the impedance lowered to 106 Ωcm2 and the adhesive was reduced to 35% of the original value. It was found that the coating service life was ca 8 a, which is in line with the behavior conditions of the coating at the local airport. On this account, the rationality and feasibility coating accelerated aging test spectrum were verified.
High surface-active ammonium perfluorooctanoic acid (PFOA) was selected as a surface treatment agent, and the influence of the concentration of PFOA on the rust removal effect for the rust scale and the corrosion behavior of the cleaned Q235 steel was investigated. The rust Q235 steel samples were derust in solutions with 1, 10, 100, 150 and 200 g/L PFOA respectively, and which then were characterized by means of contact angle measurement, electrochemical polarization curve measurement, and electrochemical impedance spectroscopy and SEM with EDS . Results show that PFOA solution has great speadability and wettability for the surface of rust steel and can penetrate the porous rust scale to the substrate surface to form adsorption film, which can weaken and even destroy the bonding between the rust and the substrate, thereby the rust can easy spall off. Among others the solution with 150 g/L PFOA presented the best derusting efficiency, i.e. the rust scale was completely removed, correspondingly the contact angle, the time of corrosion occurrence by copper sulfate drop test and electrochemical impedance all increased by 111.9%, 70% and 193% respectively, while the corrosion current decreased by 53.3% for the derust steel in comparison with the reference one.
