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Riboflavin, a soluble redox mediator for electron transfer, is involved in various redox processes in biogeochemical systems. This work gives some insights into the MIC mechanism of pure nickel (Ni) caused by Desulfovibrio vulgaris. Compared with pure copper (Cu) metabolite (M)-MIC, Ni MIC by D. vulgaris exhibits distinctly different corrosion behavior. 20 ppm (w/w) riboflavin dramatically enhances the corrosion rate of Ni (59% increase in weight loss), while it has no impact on Cu MIC. Furthermore, headspace H2 detection reveals that neither proton nor H2S corrosion occurs in Ni MIC (Cu MIC caused by biogenic H2S produces large amounts of H2, whereas Ni MIC does not). The thermodynamic analysis and experimental results indicate that Ni D. vulgaris MIC is caused by trapping extracellular electrons from Ni oxidation for energy, which belongs to extracellular electron transfer (EET)-MIC. [ABSTRACT FROM AUTHOR]

The microbiologically influenced corrosion (MIC) behavior of the copper-nickel (Cu-Ni) alloy welded joint induced by Desulfovibrio vulgaris was investigated. Distinct gradient changes in MIC behavior were observed in different regions, with the heat-affected zone (HAZ) consistently exhibiting higher localized corrosion sensitivity. Specifically, the asymmetric corrosion of HAZ was attributed to the galvanic effect between HAZ and welding zone (WZ). On a submicroscopic scale, the WZ acted as a cathode, mitigating corrosion in the later stages of Desulfovibrio vulgaris incubation. Additionally, the deep corrosion propagation at the HAZ/WZ interface was caused by the combined action of galvanic effect and Desulfovibrio vulgaris. [Display omitted] • The MIC behavior in different regions of Cu-Ni alloy welded joint is investigated. • The microstructure evolution and its correlation with microhardness is analyzed. • The corrosion behavior in HAZ is quite different from those of in BM and WZ. • The HAZ is an active region that can be preferentially and more quickly corroded. • D. vulgaris intensifies the galvanic and asymmetric corrosion in the welded joint. [ABSTRACT FROM AUTHOR]

The proposed study aimed to examine the impact of stress on the microbiologically influenced corrosion (MIC) behavior of a 90/10 copper-nickel (Cu-Ni) alloy using a self-made three-point bending device in the Desulfovibrio vulgaris inoculation system. The corrosion rate of alloy under plastic deformation was higher compared to elastic deformation, leading to the initiation of more severe cracks as well as the emergence of numerous secondary cracks at the bottom of the primary cracks. The stress played a vital role in strengthening the alloy's MIC process. A comprehensive mechanism for stress-assisted 90/10 Cu-Ni alloy MIC by D. vulgaris was proposed. [Display omitted] • The stress-assisted MIC behavior of 90/10 Cu-Ni alloy by D. vulgaris is investigated. • Elastic stress is not significant in promoting the 90/10 Cu-Ni alloy MIC. • Plastic deformation causes more severe intergranular corrosion than elastic deformation. • Interaction between tensile stress and D. vulgaris leads to the formation of microcracks. • A comprehensive mechanism for stress-assisted 90/10 Cu-Ni alloy MIC by D. vulgaris is proposed. [ABSTRACT FROM AUTHOR]

• Nitrate reduction coupled with Ni oxidation is thermodynamically favorable. • Ni corrosion is more severe in carbon starvation than the full-strength medium. • Riboflavin enhances the biocatalytic activity of P. aeruginosa biofilm. • EET is responsible for the accelerated corrosion of Ni by P. aeruginosa. • Data provide support for Ni EET-MIC with electron uptake by Ni oxidation. The primary objective of this study is to elucidate the synergistic effect of an exogenous redox mediator and carbon starvation on the microbiologically influenced corrosion (MIC) of metal nickel (Ni) by nitrate reducing Pseudomonas aeruginosa. Carbon source (CS) starvation markedly accelerates Ni MIC by P. aeruginosa. Moreover, the addition of exogenous riboflavin significantly decreases the corrosion resistance of Ni. The MIC rate of Ni (based on corrosion loss volume) is ranked as: 10 % CS level + riboflavin > 100 % CS level + riboflavin > 10 % CS level > 100 % CS level. Notably, starved P. aeruginosa biofilm demonstrates greater aggressiveness in contributing to the initiation of surface pitting on Ni. Under CS deficiency (10 % CS level) in the presence of riboflavin, the deepest Ni pits reach a maximum depth of 11.2 μm, and the corrosion current density (i corr) peak at approximately 1.35 × 10−5 A·cm−2, representing a 2.6-fold increase compared to the full-strength media (5.25 × 10−6 A·cm−2). For the 10 % CS and 100 % CS media, the addition of exogenous riboflavin increases the Ni MIC rate by 3.5-fold and 2.9-fold, respectively. Riboflavin has been found to significantly accelerate corrosion, with its augmentation effect on Ni MIC increasing as the CS level decreases. Overall, riboflavin promotes electron transfer from Ni to P. aeruginosa , thus accelerating Ni MIC. [ABSTRACT FROM AUTHOR]

Currently, the microbiologically influenced corrosion (MIC) of 90/10 copper-nickel (Cu–Ni) has garnered increased attention. Pseudomonas aeruginosa , a prevalent nitrate-reducing bacteria in seawater, is a notable participant in the process of marine nitrogen cycle. This study seeks to investigate the impact of NH 4 + on the corrosion process of 90/10 Cu–Ni alloy in the P. aeruginosa media. The results revealed that the average pit depth of the alloy coupons was 4.4 ± 0.2μm in the P. aeruginosa media, whereas the average pit depth reduced to 2.8 ± 0.1 μm in the P. aeruginosa + NH 4 + media. In the P. aeruginosa media, the corrosion current density (i corr) was 4.96 × 10−7 A cm−2, while in the P. aeruginosa + NH 4 + media, the i corr decreased to 2.45 × 10−7 A cm−2. The excess NH 4 + led to a reduction in the P. aeruginosa biofilm thickness (23.4 μm vs. 35.6 μm), facilitated the underlying P. aeruginosa sessile cells to obtain energy from free organic carbon more easily. Additionally, the interaction of Cu with NH 3 led to the formation of the unstable complex Cu(NH 3) 2 +, ultimately resulting in the formation of a protective Cu 2 O layer on the alloy surface, thus mitigating the 90/10 Cu–Ni alloy MIC. [Display omitted] • Excess NH 4 + reduces the biofilm thickness of P. aeruginosa , thus affecting the alloy MIC. • Excess NH 4 + can alleviate the alloy MIC caused by P. aeruginosa. • The unstable complex Cu(NH 3) 2 + as an intermediate leads to the further formation of Cu 2 O. • The effect of NH 4 + and P. aeruginosa on the corrosion behavior of 90/10 Cu–Ni alloy is studied. [ABSTRACT FROM AUTHOR]

• N and P in nutrients influence SRB growth and biogenic H 2 S production significantly. • More nutritious media led to more biogenic H 2 S and more severe Cu corrosion. • A protective film against uniform corrosion was formed in all nutritional conditions. The eutrophication of seawater is not only harmful to the environment, but also influence microbes' proliferation and then influence biocorrosion of marine engineering materials to a great extent. This study investigated the microbiologically influenced corrosion (MIC) of Cu immersed in the Desulfovibrio vulgaris (a sulfate reducing bacterium) medium with four defined nutritional degrees: total nutrition, P lacking, N lacking, and P&N lacking. When D. vulgaris was cultured in more nutritional medium, more H 2 S was generated and more serious corrosion of Cu occurred. The concentration of H 2 S corresponding to the medium with total nutrition was as high as 4.9 × 104(±913.0) ppm. The weight loss of Cu in medium with total nutrition increased by at least 50% compared with other nutritional conditions. The depth of pitting pits on Cu increased obviously with more abundant nutrient elements N and P. The electrochemical tests supported the weight loss and also showed that an obvious passivation zone was formed on the anodic polarization curve. This indicated that a protective film was formed on the surface of Cu against uniform corrosion. The analyses of thermodynamics and experiment data indicated that metabolite MIC (M-MIC) account for the Cu corrosion by D. vulgaris. [ABSTRACT FROM AUTHOR]

Abstract: The microbially influenced corrosion of stainless steel (SS) by marine bacterium Vibrio natriegens (V. natriegens) was investigated using surface analysis (atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDXA)) and electrochemical techniques (the open circuit potential, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization curves ). AFM images corroborated the results from the EIS models which show biofilm attachment and subsequent detachment over time. The SEM images revealed the occurrence of micro-pitting corrosion underneath the biofilms on the metal surface after the biofilm removal. The presence of carbon, oxygen, phosphor and sulfur obtained from EDXA proved the formation of biofilm. The electrochemical results showed that the corrosion of SS was accelerated in the presence of V. natriegens based on the decrease in the resistance of the charge transfer resistance (R ct) obtained from EIS and the increase in corrosion current densities obtained from potentiodynamic polarization curves. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Corrosion induced by microorganisms and seawater can accelerate the failure of metals. To inhibit the corrosion process, in this work, an aluminum oxide coating with tubes-pyramids structure and SLIPS (AO-TP-SLIPS) is fabricated by employing a three-step method, which includes anodizing of Al, fluorination modification and lubricant infusion. To this end, the AO-TP-SLIPS coating affords stable mechanical properties and high corrosion-resistance against microorganisms and seawater. The pyramids structure of the AO-TP-SLIPS surface forms a barrier and slows down the consumption of the lubricant in the tubes, which is one of the key reasons for the improved corrosion resistance. The electrochemical measurements show that the AO-TP-SLIPS coating attains a corrosion current density of 3.39 × 10−12 A cm−2 in Pseudomonas aeruginosa broth and 3.17 × 10−13 A cm−2 in seawater. A high corrosion resistance of the AO-TP-SLIPS specimen retains for 36 days in seawater. This work demonstrates that a composite structure with tubes and pyramids can prolong the service life of coatings in an efficient way, which offers a theory basis for applications of SLIPS in marine environment. • A stable slippery coating with structure of tubes and pyramids was fabricated. • The pyramids structure slows down the consumption of lubricant in the tubes. • The coating showed stable, high and long-term corrosion resistance. [ABSTRACT FROM AUTHOR]

• Sulfate reduction coupled with Ni oxidation is thermodynamically favorable. • Carbon starvation significantly accelerates Ni MIC by D. vulgaris. • The pit depth of Ni MIC up to 18.8 µm is observed after 7-d incubation in D. vulgaris media. • H 2 detection support that neither proton nor H 2 S corrosion occurs in Ni MIC by D. vulgaris. • The mechanism for Ni D. vulgaris MIC is extracellular electron transfer-MIC (EET-MIC). Carbon starvation can affect the activity of microbes, thereby affecting the metabolism and the extracellular electron transfer (EET) process of biofilm. In the present work, the microbiologically influenced corrosion (MIC) behavior of nickel (Ni) was investigated under organic carbon starvation by Desulfovibrio vulgaris. Starved D. vulgaris biofilm was more aggressive. Extreme carbon starvation (0% CS level) reduced weight loss due to the severe weakening of biofilm. The corrosion rate of Ni (based on weight loss) was sequenced as 10% CS level > 50% CS level > 100 CS level > 0% CS level. Moderate carbon starvation (10% CS level) caused the deepest pit of Ni in all the carbon starvation treatments, with a maximal pit depth of 18.8 μm and a weight loss of 2.8 mg·cm−2 (0.164 mm·y−1). The corrosion current density (i corr) of Ni for the 10% CS level was as high as 1.62 × 10−5 A·cm−2, which was approximately 2.9-fold greater than the full-strength medium (5.45 × 10−6 A·cm−2). The electrochemical data corresponded to the corrosion trend revealed by weight loss. The various experimental data rather convincingly pointed to the Ni MIC of D. vulgaris following the EET-MIC mechanism despite a theoretically low E cell value (+33 mV). [ABSTRACT FROM AUTHOR]

The present work investigated the microbial-induced pitting behavior of the 70/30 copper-nickel (Cu-Ni) alloy. Unlike the MIC of Cu by Desulfovibrio vulgaris , the alloy exhibited considerable pitting sensitivity and pit nucleation frequency under the 10%, 50%, and 100% carbon source (CS) levels. The metastable pit was more likely to evolve into stable growth in the full-strength medium. Meanwhile, a model was established to explain the alloy pitting mechanism induced by D. vulgaris. New evidence further verified that Cu-Ni alloy MIC was not only ascribed to the biogenic H 2 S but the electroactive D. vulgaris biofilms via extracellular electron transfer (EET) for energy harvest. ● The pitting corrosion of 70/30 Cu-Ni alloy by D. vulgaris is studied using Hilbert spectroscopy analysis. ● The alloy exhibits high pitting sensitivity for the 10%, 50%, and 100% CS levels. ● A model is established to explain the pitting mechanism induced by D. vulgaris. ● Metastable pitting is more likely to transform into stable in the full-strength medium. ● New evidence further proves that two types of MIC mechanisms coexist in the Cu-Ni alloys MIC. [ABSTRACT FROM AUTHOR]

The microbiologically influenced corrosion (MIC) of 90/10 copper-nickel (Cu-Ni) alloy in the presence of anaerobic Desulfovibrio vulgaris was investigated in this work. The corrosion rate of the alloy varied remarkably with different energy starvation levels, which was attributed to various biogenic H 2 S concentrations and extracellular electron transfer (EET) by D. vulgaris. The biogenic H 2 S caused the degradation of passive films generated on the alloy. 20 ppm (w/w) riboflavin accelerated the weight loss of alloy by 52%. The EET routes resulted in localized corrosion of Ni contained in the alloy. Two types of MIC mechanisms coexisted in the 90/10 Cu-Ni alloy MIC by D. vulgaris. • Biogenic H 2 S facilitates the degradation of passive films formed on 90/10 Cu-Ni alloy. • The corrosion product is layered and the highest enrichment of Ni is in the inner layer. • Intergranular corrosion and localized Ni preferential corrosion occur on the alloy surface. • Cu M-MIC and Ni EET-MIC coexist in 90/10 Cu-Ni alloy MIC caused by D. vulgaris. [ABSTRACT FROM AUTHOR]

Headspace to liquid volumetric ratio can impact bacterial activity, which affects the metabolic process and extracellular electron transportation (EET) of microbial biofilms. In this work, the ratio of headspace volume to culture medium volume was varied to investigate the behavior of Cu microbiologically influenced corrosion (MIC) by P. aeruginosa as a nitrate reducing bacterium (NRB). This NRB produced ammonia as a toxic metabolite that inhibited its growth in anaerobic bottles. The results showed that a larger headspace volume led to lower ammonium concentration in the liquid phase (due to escape of ammonia to the headspace), higher planktonic and sessile cell counts, deeper pits and higher uniform corrosion rate. With a fixed culture medium volume of 200 mL, the weight loss of Cu coupons corresponding to 500 mL and 200 mL headspace volumes were approximately 1.9-fold and 1.5-fold larger than that for 50 mL headspace volume, respectively, with corresponding pit depth increased by 2.6 times and 1.7 times, respectively. Ammonia acted as a complexing agent, not an oxidant (electron acceptor) in the system. The terminal electron acceptor was nitrate. The reduction of nitrate in the cytoplasm of P. aeruginosa using extracellular electrons released by Cu oxidation is thermodynamically favorable. Thus, Cu corrosion by the nitrate reducing P. aeruginosa biofilm belongs to EET-MIC. • Nitrate reduction coupled with Cu oxidation is thermodynamically favorable. • NH 4 + in P. aeruginosa broth inhibits sessile cell growth and thus impacts MIC. • Increased headspace leads to higher sessile cell count and more severe Cu MIC. • Localized corrosion and general corrosion are observed in 14-day tests. • Data support the mechanism for Cu MIC with electron uptake by the nitrate reducer. [ABSTRACT FROM AUTHOR]

• Cu MIC by sulfate reducing bacteria (SRB) is proven to be metabolite-MIC (M-MIC). • A smaller headspace leads to a higher dissolved [H 2 S] and lower sessile cell count. • This higher [H 2 S] with fewer sessile cells leads to more severe Cu weight loss. • High [H 2 S] causes severe uniform corrosion accompanied by pitting corrosion of Cu. • Low [H 2 S] causes uniform corrosion accompanied by intergranular corrosion of Cu. Microbiologically influenced corrosion (MIC) of copper by Desulfovibrio vulgaris , a sulfate reducing bacterium (SRB), was investigated in anaerobic vials with a fixed broth volume of 40 mL but varied headspace volumes (10 mL, 85 mL 160 mL). It was found that the headspace volume variation had a very large effect on the dissolved [H 2 S] in the broth and the cell counts of planktonic and sessile cells, as well as Cu corrosion severity. A 16× smaller headspace led to a 1.6-fold increase in the dissolved [H 2 S], a 13-fold decrease in sessile SRB cell count, a 32-fold decrease in planktonic cell count and a 3.7-fold increase of Cu weight loss. SEM images revealed that different headspace volumes caused different corrosion patterns on the immersed coupons. With a lower headspace volume, pitting corrosion was observed, while with a higher headspace volume, intergranular corrosion was seen. The results confirmed that SRB MIC of Cu belongs to metabolite-MIC (M-MIC) by H 2 S, unlike SRB MIC of carbon steel that belongs to extracellular electron transfer-MIC (EET-MIC) that is directly correlated with sessile cell counts rather than dissolved [H 2 S].. [ABSTRACT FROM AUTHOR]