Scholarship & Research
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Item Biofouling and corrosion of stainless steels in natural waters(2002) Lewandowski, Zbigniew; Avci, Recep; Geiser, Michael Joseph; Braughton, K. R.; Yurt, NurdanThe noble shift in corrosion potential to values between +300 and +400 mVSCE and the accompanying increase in cathodic current density and polarization slope at mild cathodic potentials that develop during microbial colonization of passive metals, are collectively known as ennoblement. This phenomenon is of concern as the noble shift in the corrosion potential may lead to pitting corrosion. We have demonstrated, by growing pure cultures of manganese oxidizing bacteria (MOB) Leptothrix discophora SP-6 under well defined conditions, that microbial deposition of manganese oxides causes ennoblement of 316L stainless steel (SS). Exposing 316L corrosion coupons in lakes and streams supported this conclusion; the rate and extent of ennoblement were positively correlated with the rates of deposition and the amounts of biomineralized manganese oxides deposited on the surfaces of the SS corrosion coupons. X-ray photoelectron spectroscopy (XPS) analyses of the deposits from the ennobled coupons revealed a mixture of manganese oxides, as expected. Many natural waters can support growth of MOB. When manganese-oxidizing biofilms accumulate on surfaces of passive metals there is a potential for manganese redox cycling on the metal surface. This process is initiated by depositing minute amounts of manganese oxides on the metal surface. These microbially deposited manganese oxides are then reduced by the electrons derived from anodic dissolution of the metal; the metal is corroding and the manganese oxides are reduced to divalent manganese ions. However, since the manganese ions are liberated within the manganese-oxidizing biofilm, the manganese ions are immediately reoxidized, and the cycle continues.Item Manganese dioxide as a potential cathodic reactant in corrosion of stainless steels(2000) Olesen, Bo H.; Avci, Recep; Lewandowski, ZbigniewBiofilms of leptothrix discophora SP-6, grown on 316L stainless steel (SS), ennobled the open circuit potential to 410 mVSCE. X-ray Photoelectron Spectroscopy (XPS) identified MnO2 was studied using electroplated SS. Plated MnO2 was reduced amperometrically. The process was interrupted at different reduction stages. XPS analysis of remaining oxides showed that MnO2 was reduced through MnOOH to Mn2+. We conclude that biomineralized MnO2 may increase corrosion rates by serving as a cathodic reactant.Item A practical method for determining pit depths using X-ray attenuation in EDX spectra(2015-04) Avci, Recep; Davis, Bret H.; Wolfenden, Mark L.; Kellerman, Laura R.; Lucas, Kilean; Martin, Joshua; Deliorman, MuhammedinA practical method has been developed for rapidly determining the depth of a corrosion micro-pit from the path lengths of X rays passing through the walls of the pit on their way to an X-ray detector. The method takes advantage of the attenuation of the Bremsstrahlung and characteristic X-ray radiation accompanying each X-ray spectrum, and the results are verified independently using AFM and the special pit geometry surrounding MnS inclusions in 1018 carbon steel. The method has general validity and is especially valuable in those cases where the pit depth-to-width ratio is too steep to measure using the conventional methods.