The Effects Of Microorganismson Biodegradation And The Corrosion Process Of Aluminum-rich Epoxy Coatings In Marine Environment

With the increasing demands for energy resources and the deepening on marine resources development operation around the world,ships and marine facilities protection measures appear increasingly important.Coating polymer materials have become indispensable substances with its superior performance in people's daily life and anti-corrosive coatings have become the most effective methods the world recognized to prevent marine facilities from biological fouling.The anti-corrosive coating can greatly cut off the contact of various marine microbes with ships and marine facilities and reduce the problem of marine facilities equipment corrosion,slow speed,increased fuel consumption and great economic losses due to the marine microorganisms.So the corrosion process decomposition mechanism of the surface coating determines the service life of anti-corrosion coating,ultimately affecting the corrosion degree and service life of metal matrix components.Biological decomposition has become one of the key issues for limiting the further development and application of polymer coating material.However,the corrosion process and decomposition mechanism of bacteria on the epoxy coatings is unknown and not reported elsewhere.In this research,aluminum-rich epoxy coatings that provided by Institute of Metal Research were used as base material and were immersed in bacteria sea solution and compared to the corresponding coating immersed in sterile sea solution using electrochemical impedance spectroscopy(EIS)technique,scanning electron microscopy(SEM),energy spectrum(EDS),infrared spectroscopy(FTIR)and contact angle measurement techniques respectively to detect corrosion process and assess the most suitable biodegradation mechanism for aluminum-rich epoxy coatings.The EIS results revealed that the pseudomonas,vibrio and flavobacterium all had a effect on the coating impedance which resulted in the reduction of Protective performance and service life.Among them,the effect of pseudomonas was remarkable and vibrio was more gently but flavobacterium had no obvious effect.The corrosion resistance decreased about three orders of magnitude after immersion in pseudomonas immersion system for 48 hours and permeable failure phenomenon occurred 45 days,100 days earlier than that in sterile sea solution.For comparison,the impedance of coated steel exposed to vibrio and flavobacterium immersion system respectively decreased two and only one orders of magnitude after immersion for 48 hours and permeable failure phenomenon occurred until 80d and 140 days immersion.The SEM observation revealed that coatings in bacteria sea solution showed lot of bioslimefilm attached to their surface and obvious corrosion and degradation phenomenon contrast to coatings immersed in sterile sea solution.The EDS element surface scan results also revealed element content changes of coatings.Compared to the coating in the sterile water system,pseudomonas made dramatic increase oxygen content in coating,oxygen element content of coating under the action of vibrio rise slightly,while oxygen element content of coating in flavobacterium did not change obviously.FTIR results revealed that the coating functional and structural changes under the action of microorganisms.Compared with the coating in sterile sea water,-OH absorption strength of coatings in pseudomonas showed a sharp increase,that in vibrio increases slightly,while that in flavobacterium showed no obvious changes.Combined with the feature of infrared spectra of other functional groups,we can infer that-OH absorption relative strength reflected the changes of hydroxyl and carboxyl for epoxy coating structures.Coating in pseudomonas showed dramatic increase in hydroxyl and carboxyl,vibrio showed a slight increase,while that in flavobacterium did not change obviously.Contact angle reflects the hydrophilic or hydrophobic of coatings and the results of contact angle showed good consistence with the FTIR analysis.Therefore pseudomonas and vibrio had decomposition effect on epoxy coatings and the effect of pseudomonas was more apparent while flavobacterium had no effect.The functional group changes in FTIR revealed the biodegradation mechanism of pseudomonas and vibrio was that the epoxy coatings were oxidized forming hydroxyl and carboxyl group leading to the hydrophilic enhancement and the reduction of protective performance and the service life.