| In the tropic marine environment,the microorganisms exist on the metal surface will transform the total corrosion into local corrosion,increasing the uncontrollability of material corrosion and making corrosion more serious than in the sterile environments.A lot of research about the effect of bacteria on the electrochemical corrosion of carbon steel in tropical marine have been done in the preliminary study of the laboratory work,and providing a lot of experimental data for the application of 45 steel in tropical marine environment.However,the effect of fungi on corrosion of carbon steel is rarely study.Due to the wide distribution of Rhodotorula mucilagino in the marine environment,it is important to study the effect of Rhodotorula mucilagino on the corrosion behavior of 45 steel.In this study,a single strain was isolated from the corrosion products of 45 steel after immersed in natural seawater for 30 days and was named X731.By identifying and aligning,the X731 was identified as Rhodotorula mucilagino.The microbial diversity of the corrosion products obtained from 45 steel was analyzed by high-throughput sequencing(HTS),it was shown that the relative content of Rhodoiorula mucilaginos can reach 92%,which is the dominant specie when 45 steel is immersed in seawater for 30 days.Further research about the growth characteristics of was Rhodotorula mucilaginos studied.The XPS technology was used for analysis.It was found that the relative content of S6-increased by 10.6%in the presence of Rhodotorula mucilaginos,which proved that Rhodotorula mucilaginos has an oxidation effect on sodium thiosulfate.To study the electrochemical corrosion behavior of the 45 steel immersed in the synergistic condition of Rhodotorula mucilaginos and sulfate-reducing bacteria,the electrochemical effect of single Rhodotorula mucilaginos and sodium thiosulfate on 45 carbon steel were studied respectively.Meanwhile,the coefficient of Rhodotorula mucilaginos and sodium thiosulfate was also researched in this study.It was found that the maximum capacitive semicircles could reach 4200 ?.cm2 of 45 steel immersed in the Rhodotorula mucilaginos containing natural seawater,which was significantly higher than that in the sterilized seawater system after immersion for 30 days.In the system containing sodium thiosulfate,the diameter was at a minimum when the content of sodium thiosulfate was 0.5 g,and then increased.It demonstrated that the corrosion of 45 steel was inhibited when the content of sodium thiosulfate reached 0.7 g.In the system containing Rhodotorula mucilaginos,the maximum diameter of the capacitive semicircles gradually decreases with the increase of sodium thiosulfate,and then there was no increment.It is indicated that sodium thiosulfate was metabolized by Rhodotonla mucilaginos.laybe resulting in the decrease of sodium thiosulfate compared to the sterile condition.Meanwhile,it was clear that the sodium thiosulfate accelerated the corrosion of 45 steel compared to the natural seawater.The surface analysis of 45 steel after the removal of the corrosion product showed that the pitting in natural seawater was significantly smaller than that in the sodium thiosulfate containing seawater,indicating the corrosion of 45 steel was promoted by sodium thiosulfate.The pitting depth was analyzed and was found that the average pitting depth of 45 steel immersed in natural seawater immersion system for 30 days was 10.769 ?m and 6.958 ?m for the sterile and Rhodotorula mucilaginos containing system,respectively.When the 45 steel immersed in sodium thiosulfate containing seawater,the average pitting depth both increased in the sodium thiosulfate and Rhodotorzla mucilaginos containing system.By analysing the results of XRD and XPS spectra,the corrosion products consist of Fe2O3,FesO4 and FeOOH were all in the sterilized seawater and sodium thiosulfate containing seawater,which demonstrated that neither sodium thiosulfate nor Rhodotorula can change the components of corrosion products of 45 steel. |
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