Xiaofan Zhai

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.

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.