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Zinc ion is a common heavy metal in marine pollution, but its impact on corrosion of steels without passive films in natural seawater is far from being investigated. In this study, the impact of zinc ion addition (1.5 and 15 mmol/L) on corrosion of EH40 steel commonly utilized for building ships and offshore platforms was studied by numerous methods and technologies. It was found that EH40 steel corrosion was inhibited with the addition of zinc ion, and corrosion inhibition efficiency increased with the concentration added. The deposited ZnO and Zn(OH)2 on the steel surface was believed to hamper electron transfer, thus inhibiting corrosion. Meanwhile, the bactericidal zinc ion and ZnO mitigated the activity of microorganisms in biofilms to reduce the damage caused by microbiologically influenced corrosion. But pitting corrosion was enhanced with a high concentration of zinc ion added due to the inhomogeneity of ZnO layers. [ABSTRACT FROM AUTHOR]

To investigate the corrosion behavior of WC–Co composite coating, plasma transferred arc (PTA) welding was applied to prepare WC–Co coating on hull steel EH40 for achieving good metallurgical bonding. The phases of coatings were mainly composed of WC particles, solid solution γ-Co, Fe3Ni2, SiO2 and Mo2C. After electrochemical test, it can be concluded that Co-based coating with 45% WC content has better corrosion resistance in low temperature marine environment for obtaining denser oxide film. Through X-ray photo electron spectroscopy (XPS) analysis, the main corrosion products of immersion were Co(OH)2 and Co3O4. These corrosion products aggregate to form a stable corrosion product film, which plays some protective role for the coating. Hard particle WC is also partially oxidized to WO3. The pitting hole of 60% WC is the most serious. Pitting corrosion is easy to occur at the interface defects.

• The dynamic WLC of EH40 steel in sterile and biotic media is investigated. • Areas of low water-line in the sterile medium are cathodic but anodic with bacteria. • The metabolism of H. titanicae reduces the oxygen in the area of low water-line. The fluctuating water-line corrosion of EH40 steel in sterile and biotic media was investigated with a wire beam electrode. When the coupons were partially immersed in the sterile medium, the position of the low water-line acted as the cathodic zone and the area below the low water-line constantly served as the main anodic zone. The thin electrolyte layers with uneven thickness promoted the galvanic current of the region below the low water-line. Different from the sterile environment, the metabolism of Halomonas titanica with oxygen as the final electron acceptor reduced the dissolved oxygen concentration, which resulted in the position of the low water-line acting as the anodic zone. [ABSTRACT FROM AUTHOR]

The corrosion behavior of three types of EPS of Pseudomonas aeruginosa , i.e., soluble, loosely bound, and tightly bound EPS (S-EPS, LB-EPS, and TB-EPS) on the surface of EH40 steel were studied. Results indicated that three EPS have distinct adhesion mechanisms and corrosion influence on EH40 steel. S-EPS with an inhibitory effect on corrosion interact with EH40 steel through electrostatic force, whereas LB-EPS and TB-EPS can promote corrosion due to their stronger adhesion forces provided by hydrogen and coordination bonds. • Interaction between three EPS from P. aeruginosa and EH40 steel was elucidated. • S-EPS adhere to EH40 steel surface by electrostatic force to inhibit corrosion. • Corrosion of EH40 steel was accelerated by B-EPS due to chemical coordination. • Adhesion forces between three EPS and EH40 steel is S-EPS＜LB-EPS＜TB-EPS. [ABSTRACT FROM AUTHOR]

The effects of coating defect, cathodic protection (CP), and sulphate-reducing bacteria (SRB) on EH40 steel corrosion were investigated in seawater. Results showed that the presence of − 0.85 V CSE and SRB result in the current density fluctuate around 0 μA·cm−2 for EH40 steel with different coating defects. EH40 steel corrosion with coating defect of 0.2 mm is inhibited, but promoted with 1.0 mm and 2.0 mm under effects of − 0.95 V CSE and SRB. The CP of − 0.95 V CSE and current density of − 0.6 μA·cm−2 inhibit adhesion of SRB on EH40 steel with coating defect of 0.2 mm. • Adhesion of SRB and coating defect size influence CP efficiency on EH40 steel. • CP of − 0.85 V CSE promotes EH40 steel corrosion with different coat defect sizes in SRB medium. • CP of − 0.95 V CSE can protect EH40 steel with coating defect of 0.2 mm in SRB medium. • CP of –0.95 V CSE and current density of –0.6 μA·cm−2 inhibit SRB's adhesion on EH40 steel. [ABSTRACT FROM AUTHOR]

A nanostructured Fe 2 O 3 /CdZnS/ZnS composite film was constructed on EH40 steel using anodization, hydrothermal, and successive ionic layer absorption and reaction method. The film can inhibit the diffusion of dissolved oxygen to the substrate steel in aerobic seawater, and anodic dissolution of the substrate steel in D. vulgaris containing anaerobic seawater, respectively. The film can inactivate bacteria by producing active chlorine under light, which improves its anti-adhesion efficiency. The film prepared by 50 times of ZnS deposition reaches the highest anti-adhesion efficiency of 71.0 % and 63.3 % toward P. aeruginosa and D. vulgaris under dark, and 98.5 % and 96.0 % under light, respectively. [Display omitted] • A multilayered Fe 2 O 3 /CdZnS/ZnS composite film was constructed on EH40 steel surface. • Film keep integrity in seawater and P. aeruginosa or D. vulgaris containing seawater. • Film inhibit P. aeruginosa or D. vulgaris adhesion under dark and light irradiation. • Film generates active chlorine under light to inactivate bacteria on its surface. [ABSTRACT FROM AUTHOR]

The effects of exogenous electron intermediaries, i.e., 9，10-anthraquinone-2-carboxylic acid (AQC), neutral red and thionine, on EH40 steel corrosion were investigated in seawater with Methanococcus maripaludis. Results showed that M. maripaludis can acquire electrons from EH40 steel through indirect electron transfer facilitated by these three exogenous electron intermediaries, thereby enhancing the charge transfer during corrosion process. This promotion effect on EH40 steel corrosion follows an order: AQC > neutral red > thionine, which correlates with their respective charge transfer capacities. The introduction of exogenous electron intermediaries enhances pitting corrosion of EH40 steel induced by M. maripaludis. • The corrosive capacity of M. maripaludis is enhanced due to exogenous electron intermediaries. • Corrosion promoting effects are AQC > neutral red > thionine in M. maripaludis medium. • A wide variety of electronic intermediaries can be utilized by M. maripaludis. • Charge transfer capacity of intermediaries determines corrosive capacity of M. maripaludis. [ABSTRACT FROM AUTHOR]

The riboflavin-mediated indirect electron transfer process during EH40 steel corrosion was investigated in Methanococcus maripaludis medium. The results showed that exogenous riboflavin participates in the process of EH40 steel corrosion induced by M. maripaludis. The presence of riboflavin promotes pitting corrosion of EH40 steel in M. maripaludis medium, but this trend is mitigated by increasing concentrations of riboflavin. Both anodic and cathodic processes of EH40 steel corrosion are enhanced in M. maripaludis media with riboflavin. The speed of transportation of electron on EH40 steel surface through riboflavin reduction is faster than proton reduction. • The exogenous riboflavin participates in EH40 steel corrosion induced by M. maripaludis. • The presence of riboflavin promotes pitting corrosion of EH40 steel in M. maripaludis medium. • Enhancement effect of riboflavin on EH40 steel corrosion is mitigated with concentrations. • The electron transportation speed is faster through riboflavin than proton reductions. [ABSTRACT FROM AUTHOR]

Soluble, loosely bound and tightly bound extracellular polymeric substances (S-EPS, LB-EPS, TB-EPS) of Desulfovibrio vulgaris were extracted to investigate their effects on EH40 steel corrosion in 3.5 wt% NaCl solution. Results showed that three types of EPS with different components have opposite effects on corrosion. S-EPS mainly composed of humic acids adhere to EH40 steel surface to form a passive film and inhibit corrosion. However, proteins are the main components in LB-EPS and TB-EPS, the presence of which accelerates corrosion. Especially for TB-EPS, the anodic and cathodic reactions are both promoted due to binding and catalyzing ability of active protein. • S-EPS, LB-EPS, TB-EPS of Desulfovibrio vulgaris were extracted successfully. • S-EPS mainly composed of humic acids can form a passive film to inhibit corrosion. • LB-EPS and TB-EPS mainly composed of proteins show corrosion acceleration effects. • Localized corrosion in MIC may be related to influences of different EPS types. [ABSTRACT FROM AUTHOR]

Biofilm formation is an important cause of microbiologically influenced corrosion (MIC), and inhibition of microbial adhesion is one of the most effective ways to control biofilm formation. In this work, nanostructured functional film of EH40 steel is prepared by one-step anodization in NaOH solution to inhibit adhesion of Pseudomonas aeruginosa (P. aeruginosa) without and with light. Results show that the functional films fabricated on EH40 steel surface in a series of NaOH solutions inhibit the adhesion of P. aeruginosa , and its anti-adhesion performance first increases and then decreases with varying concentrations of NaOH solution. The optimal anti-adhesion performance under dark condition, i.e., anti-adhesion rate of 92.7% compared with bare steel, is obtained for the nanostructured oxide film fabricated in 12 M NaOH solution under anodization potential of 1.0 V for 2 h. Under visible light irradiation, the best anti-adhesion rate increases to 99.9% due to hydroxyl radicals (OH) produced by the nanostructured oxide film with photocatalytic activity. • The nanostructured film with optimal bacterial anti-adhesion performance was obtained in 12 M NaOH under 1.0 V for 2 h. • The highest bacterial anti-adhesion rate of nanostructured functional film is 92.7 % without illumination. • Under illumination, the bacterial anti-adhesion rate of nanostructured functional film increases to 99.9 %. • The bacterial anti-adhesion performance of anodized steel is further enhanced due to generation of •OH under illumination. [ABSTRACT FROM AUTHOR]