Browsing by Author "Geiser, Michael Joseph"

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Biofouling and corrosion of stainless steels in natural waters
(2002) Lewandowski, Zbigniew; Avci, Recep; Geiser, Michael Joseph; Braughton, K. R.; Yurt, Nurdan
The 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.
Comparative study in chemistry of microbially and electrochemically induced pitting of 316l stainless steel
(2003-11) Shi, X.; Avci, Recep; Geiser, Michael Joseph; Lewandowski, Zbigniew
Ennoblement of stainless steel (SS) by microbially deposited manganese oxides can lead to pitting corrosion at low chloride concentrations, causing unexpected material failures. We exposed 316L SS to manganese oxidizing bacteria Leptothrix discophoraunder well-defined laboratory conditions, and then placed the ennobled coupons in a 0.5 M sodium chloride solution until pitting developed. Using time-of-flight secondary ion mass spectroscopy we demonstrated that the pits and their immediate vicinity associated with microbial influenced corrosion had different chemical signatures than those associated with electrochemically induced pitting, suggesting a possibility that the microorganisms were directly involved in pit initiation. Based on the differences in the chemical signatures we were able to distinguish the microbially induced pits from those induced by anodic polarization.
Corrosion of 316L stainless steel influenced by manganese oxidizing bacteria
(Montana State University - Bozeman, College of Engineering, 2001) Geiser, Michael Joseph
Microbially initiated pitting on 316l stainless steel
(2002-06) Geiser, Michael Joseph; Avci, Recep; Lewandowski, Zbigniew
Pitting corrosion of 316L stainless steel ennobled in the presence of manganese-oxidizing bacteria, Leptothrix discophora, was studied in a low-concentration sodium chloride solution. Corrosion coupons were first exposed to the microorganisms in a batch reactor until ennoblement occurred, then sodium chloride was added, which initiated pitting. The pits had aspect rations (length divided by width) and shapes closely resembling the aspect ration and the shape of the bacteria, which suggested that the microorganisms were involved in pit initiation.
Pit initiation on 316l stainless steel in the presence of bacteria leptothrix discophora
(2001-01) Geiser, Michael Joseph; Avci, Recep; Lewandowski, Zbigniew
Ennoblement of stainless steel by microbially deposited manganese oxides can cause pitting corrosion of the SS in natural waters at low chloride concentrations, leading to unexpected material failures. To study the effects of microbially deposited manganese oxides on pit initiation, we exposed 316L stainless steel to manganese oxidizing bacteria Leptothrix descophora under well-defined laboratory conditions. We then placed the ennobled coupons in a solution of low concentration sodium chloride until pitting initiated. The pits had different morphologies that those initiated by electrochemical polarization, hypothetically indicating a direct involvement of the bacteria in pit initiation.