Jizhou Duan

Electron transfer process from marine biofilms to graphite electrodes in seawater.

It is known that electron transfer processes exist between microorganisms and electrodes. Many anaerobic bacteria, which can transfer electrons to solid electrodes, had been identified. However, little attention has been paid to the interactions between aerobic biofilms and electrodes. In this study, marine biofilms formation on graphite electrodes was characterized by open circuit potential and field emission scanning electron microscopy. Electron transfer between marine aerobic biofilms and graphite electrodes was investigated primarily by cyclic voltammograms and electrochemical impedance spectroscopy techniques. Herein, we suggest that marine biofilms are a kind of conductive biofilms that can transfer electrons to graphite electrodes under anaerobic and aerobic conditions. Some cytochrome species in bacterial biofilms may play a key role in the electron transfer process.

Electrochemical study on 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one-added zinc coating in phosphate buffer saline medium with Escherichia coli

Zinc coating with 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) was found to supply better antifouling properties by decreasing the attached bacterial concentration (especially living ones) in an Escherichia coli-suspended buffer aqueous medium through fluorescence microscopy. Using electrochemical methods, the DCOIT-added zinc coating exhibited more stable electrochemical performance than the pure zinc coating because of the inhibition on the oxygen diffusion process and the biofilm formation, which were also confirmed by the scanning electron microscopy observation.

Influence of Sulfate-Reducing Bacteria on the Corrosion Behavior of High Strength Steel EQ70 under Cathodic Polarization.

Certain species of sulfate-reducing bacteria (SRB) use cathodes as electron donors for metabolism, and this electron transfer process may influence the proper protection potential choice for structures. The interaction between SRB and polarized electrodes had been the focus of numerous investigations. In this paper, the impact of cathodic protection (CP) on Desulfovibrio caledoniens metabolic activity and its influence on highs trength steel EQ70 were studied by bacterial analyses and electrochemical measurements. The results showed that EQ70 under -0.85 VSCE CP had a higher corrosion rate than that without CP, while EQ70 with -1.05 VSCE had a lower corrosion rate. The enhanced SRB metabolic activity at -0.85 VSCE was most probably caused by the direct electron transfer from the electrode polarized at -0.85 VSCE. This direct electron transfer pathway was unavailable in -1.05 VSCE. In addition, the application of cathodic protection led to the transformation of sulfide rusts into carbonates rusts. These observations have been employed to provide updated recommendations for the optimum CP potential for steel structures in the presence of SRB.

Synthesis and characterization of chitosan–zinc composite electrodeposits with enhanced antibacterial properties

Zinc electrodeposits are one of the most popular safeguard procedures for steel constructions. However, in natural aquatic environments, especially marine environments, zinc electrodeposits suffer significantly from microbial induced corrosion and biofouling which lead to metal failure. To better confront the microbial induced problems, a biocide-zinc electrodeposit was synthesized based on chelating action. In this paper, nontoxic and biocidal natural polysaccharide, chitosan, was successfully incorporated into the zinc electrodeposit matrix, synthesizing a kind of chitosan–zinc composite electrodeposit. The addition of chitosan in the electrolyte influenced the surface morphology and crystalline structure of the resultant electrodeposits significantly, while a chitosan–zinc chelation complex was also found in the electrodeposits. A synthesis model was proposed in which a chitosan molecule could chelate zinc ions in the electrolyte by means of its N atoms in amino groups and O atoms in hydroxide radicals, which promoted the codeposition of zinc and chitosan during synthesis. Furthermore, remarkably enhanced broad-spectrum bactericidal properties of the chitosan–zinc electrodeposits were revealed through Escherichia coli, Pseudomonas aeruginosa and Shewanella oneidensis exposure. The best antibacterial properties of the resultant electrodeposits were obtained when the chitosan concentration was 0.6 g L−1 in the electrolyte.

Corrosion of mild steel in sea mud containing sulphate reducing bacteria

Abstract In this work, the corrosion behaviour of a mild steel was studied in a sea mud extracted solution in the absence and presence of sulphate reducing bacteria (SRB) by electrochemical impedance spectroscope measurements and scanning electron microscope characterisation. The presence of SRB in the sea mud extracted solution affects corrosion of steel remarkably. In the absence of SRB, the steel corrosion is somewhat inhibited by the formed corrosion product layer. However, the addition of SRB enhances corrosion of the steel due to its metabolism activity. It is speculated that the formed sulphide product may experience transformation decreasing the protectiveness of the product layer. Dans ce travail, on a étudié le comportement à la corrosion d’un acier doux dans une solution extraite de la boue marine, avec ou sans la présence de bactéries sulfatoréductrices (SRB), au moyen de mesures au spectroscope de l’impédance électrochimique et de la caractérisation au microscope électronique à balayage. La présence de SRB dans la solution extraite de la boue marine affecte la corrosion de l’acier de façon remarquable. En absence de SRB, la corrosion de l’acier est quelque peu inhibée par la couche formée par le produit de la corrosion. Cependant, l’addition de SRB augmente la corrosion de l’acier à cause de l’activité de son métabolisme. L’hypothèse est que le produit sulfuré formé peut se transformer, diminuant ainsi l’effet protecteur de la couche produite.

Influence of Calcareous Deposit on Corrosion behavior of Q235 Carbon Steel in f/2 Culture Medium with Amphora

Calcareous deposit was formed on Q235 carbon steel surface in nature seawater by ap- plying cathodic protection, afterwards, the corrosion test of the steel covered with and without cal- careous deposit was carried out in f/2 culture medium containing Amphora. Then the morphology and chemical composition of corrosion products were characterized by means of XRD, SEM, FTIR and EIS. The result revealed that the calcareous deposit prepared by a current density of -30 µA/cm 2

Influence of calcareous deposit on corrosion behavior of Q235 carbon steel with sulfate-reducing bacteria

Cathodic protection is a very effective method to protect metals, which can form calcareous deposits on metal surface. Research on the interrelationship between fouling organism and calcareous deposits is very important but very limited, especially sulfate-reducing bacteria (SRB). SRB is a kind of very important fouling organism that causes microbial corrosion of metals. A study of the influence of calcareous deposit on corrosion behavior of Q235 carbon steel in SRB-containing culture medium was carried out using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and surface spectroscopy (EDS). The calcareous deposit was formed with good crystallinity and smooth surface under the gradient current density of −30 μA cm−2 in natural seawater for 72 h. Our results can help elucidate the formation of calcareous deposits and reveal the interrelationship between SRB and calcareous deposits under cathodic protection. The results indicate that the corrosion tendency of carbon steel was obviously affected by Sulfate-reducing Bacteria (SRB) metabolic activity and the calcareous deposit formed on the surface of carbon steel under cathodic protection was favourable to reduce the corrosion rate. Calcareous deposits can promote bacterial adhesion before biofilm formation. The results revealed the interaction between biofouling and calcareous deposits, and the anti-corrosion ability was enhanced by a kind of inorganic and organic composite membranes formed by biofilm and calcareous deposits.

Analysis of Bacterial Community Composition of Corroded Steel Immersed in Sanya and Xiamen Seawaters in China via Method of Illumina MiSeq Sequencing

Metal corrosion is of worldwide concern because it is the cause of major economic losses, and because it creates significant safety issues. The mechanism of the corrosion process, as influenced by bacteria, has been studied extensively. However, the bacterial communities that create the biofilms that form on metals are complicated, and have not been well studied. This is why we sought to analyze the composition of bacterial communities living on steel structures, together with the influence of ecological factors on these communities. The corrosion samples were collected from rust layers on steel plates that were immersed in seawater for two different periods at Sanya and Xiamen, China. We analyzed the bacterial communities on the samples by targeted 16S rRNA gene (V3–V4 region) sequencing using the Illumina MiSeq. Phylogenetic analysis revealed that the bacteria fell into 13 phylotypes (similarity level = 97%). Proteobacteria, Firmicutes and Bacteroidetes were the dominant phyla, accounting for 88.84% of the total. Deltaproteobacteria, Clostridia and Gammaproteobacteria were the dominant classes, and accounted for 70.90% of the total. Desulfovibrio spp., Desulfobacter spp. and Desulfotomaculum spp. were the dominant genera and accounted for 45.87% of the total. These genera are sulfate-reducing bacteria that are known to corrode steel. Bacterial diversity on the 6 months immersion samples was much higher than that of the samples that had been immersed for 8 years (P < 0.001, Student’s t-test). The average complexity of the biofilms from the 8-years immersion samples from Sanya was greater than those from Xiamen, but not significantly so (P > 0.05, Student’s t-test). Overall, the data showed that the rust layers on the steel plates carried many bacterial species. The bacterial community composition was influenced by the immersion time. The results of our study will be of benefit to the further studies of bacterial corrosion mechanisms and corrosion resistance.

Inhibition of Zinc Corrosion by Fucoidan in Natural Sea water

Research on corrosion behaviour of zinc in natural sea water without and with fucoidan was carried out by potentiodynamic polarisation test and electrochemical impedance spectroscopy (EIS). The results revealed that fucoidan serves as a good inhibitor for zinc in sea water. Polarisation curves suggested that corrosion potential values shifted to the positive ones after adding inhibitor and fucoidan retards anodic reaction more. Thus, fucoidan can be acted as anodic inhibitor. EIS results showed two phenomena including a charge transfer and an adsorption film. The corrosion inhibition of fucoidan was further confirmed by the scanning electron microscope (SEM) and atomic force microscope (AFM) analysis. Langmuir’s adsorption isotherm was found the appropriate adsorption model.