A Comparsion Of Analytical Techniques On Lead Corrosion By Fungi

Lead(Pb)materials were widely applied due to its specific physical and chemical properties,such as low melting point,excellent ductility and radiation resistance.Microorganisms are inevitable in the environment,in which Pb and Pb alloys are utilized.They(bacteria and fungi)are able to accelerate the corrosion of lead materials via secretion(organic acids or other metabolites).It was reported that the corrosion caused by microorganisms accounts for about 20%of metal corrosion.At present,most studies were focused on the corrosion of metal materials by bacteria,but there are limited studies on the corrosion of lead metal by fungi.Fungi(or mold),the common microorganisms in nature,are widely distributed in various environments.Moreover,the biomass and secretion of fungi are often larger than that of bacteria,and their activity can significantly affect the corrosion process of metal materials.In this experiment,A.niger were selected as representative fungi to study the corrosion of lead materials,and lead foil was selected as the material(because it has a flat surface to facilitate the cultivation of fungi on the surface of metal materials)Three techniques were used to investigate the influence of A.niger on lead foil corrosion.Scanning electron microscopy(SEM)surface analysis technique was used to characterize the morphology of A.niger and corrosion products on the surface of lead foil,and the elemental composition of the corrosion products was identified by EDS.In addition,the diffuse reflection infrared Fourier transform(DRIFT)was applied.We tracked the changes of chemical characteristics on the surface of corroded lead foil every day,and representative functional groups and specific molecular structures were identified by DRIFT.Finally,component analysis and corrosion product identification were performed using Raman imaging and scanning electron microscopy(RISE).The specific research results were as follows:1.SEM confirmed that A.niger can grow normally on the surface of the lead foil both above and below the surface of the solid medium.There were numerous mycelium branches and a large number of spore clusters gathered on the surface of the lead foil.We also observed that the corrosion products formed with two different morphologies,and EDS showed that the corrosion products contained carbon,oxygen and lead,which were confirmed to be lead-containing minerals.2.The results of DRIFT showed that intensity of the representative peaks(676,836 and 1050 cm-1)of organic matter increased continuously,indicating that the mycelium covered more and more on the lead foil.However,DRIFT cannot accurately identify mineral phases.3.This study firstly applied RISE technology to study microbial corrosion of metallic materials.RISE technology provided the morphological and spectral information of the formed corrosion products.The spectrum contained three major Raman characteristic peaks of lead oxalate:?1440,?1480 and?1590 cm-1.In addition,the imaging module in RISE technology can also show the distribution of lead oxalate on the surface of lead foil.4.The main metabolite of A.niger was identified as oxalic acid,a relatively highly corrosive organic acid,which was the primary cause of the corrosion on lead foil.When the lead metal was corroded,it reacted with the released lead ions to form lead oxalate.