Browsing by Author "Olesen, Bo H."

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Effect of biomineralized manganese on pitting corrosion of type 304l stainless steel
(2001-11) Olesen, Bo H.; Yurt, Nurdan; Lewandowski, Zbigniew
During the past few years, biomineralized manganese has been shown to cause ennoblement of various stainless steels to open circuit potentials of 3 mV/SCE. We have demonstrated that ennoblement, caused by biologically deposited manganese minerals, along with a relatively low stainless steel pitting potential, caused by the presence of chloride, is sufficient to initiate and drive active pitting corrosion. Stainless steel samples (type 304L), chemically or microbiologically ennobled with manganese dioxide, were exposed to a 0.35% w/v NaCl solution; an environment otherwise not corrosive against the 304L stainless steel. In the first case, steel samples were ennobled by electroplating the sample with a thin film of manganese dioxide, except for a small anodic area. In the latter case, the manganese dioxide was deposited on the steel within biofilms of the manganese oxidizing bacterium Leptothrix discophora SP-6. After 24 h exposure to the chloride solution the samples were investigated by atomic force microscopy (AFM). Both types of ennobled samples were found severely pitted, whereas reference samples (w/o manganese minerals) had remained intact.
Effect of biomineralized manganese on the corrosion behavior of c1008 mild steel
(2000-01) Olesen, Bo H.; Nielsen, P. H.; Lewandowski, Zbigniew
The possibility that biomineralized manganese dioxide (MnO2) might serve as an efficient cathodic reactant in mild steel corrosion was studied using stainless steel (SS) covered with microbially or electrochemically deposited MnO2 and galvanically coupled to mild steel and mild steel covered with microbially deposited MnO2. Biofilms of the manganese-oxidizing bacteria, Leptothrix discophora SP-6, were used to deposit biomineralized MnO2. When MnO2 was biologically deposited on the SS, the corrosion rate of the galvanically coupled mild steel was initially about eight times higher than that in a control experiment without depositing manganese. After a few minutes, the MnO2 discharged and the corrosion rate of the mild steel decreased to values comparable with biofouled cathodes without manganese. When MnO2 was electroplated on SS, a linear relation between the amount of MnO2 and the duration of the elevated corrosion rate of mild steel was observed. However, when MnO2 was biologically deposited directly onto the mild steel, the corrosion rate did not increase, possible because the corrosion product buildup on the mild steel surface prevented electrical contact between the manganese oxide and the underlying metal.
Ennoblement of stainless steel by the manganese-depositing bacterium leptothrix discophora
(1997-07) Dickenson, William H.; Caccavo, Frank; Olesen, Bo H.; Lewandowski, Zbigniew
The noble shift in open-circuit potential exhibited by microbially colonized stainless steel (ennoblement) was investigated by examining the relationship among surface colonization, manganese deposition, and open-circuit potential for stainless steel coupons exposed to batch cultures of the manganese-depositing bacterium Leptothrix discophora. Open-circuit potential shifted from -100 to +330 mV(infSCE) as a biofilm containing 75 nmol of MnO(infx) cm(sup-2) formed on the coupon surface but changed little further with continued MnO(infx) deposition up to 270 nmol cm(sup-2). Increased open-circuit potential corresponded to decreasing Mn(II) concentration in solution and to increased MnO(infx) accumulation and attached cell density on the coupon surfaces. MnO(infx) deposition was attributable to biological activity, and Mn(II) was observed to enhance cell attachment. The experimental results support a mechanism of ennoblement in which open-circuit potential is fixed near +350 mV(infSCE) by the cathodic activity of biomineralized MnO(infx).
Ennoblement of stainless steel studied by x-ray photoelectron spectroscopy
(1998) Olesen, Bo H.; Avci, Recep; Lewandowski, Zbigniew
Manganese dioxide as a potential cathodic reactant in corrosion of stainless steels
(2000) Olesen, Bo H.; Avci, Recep; Lewandowski, Zbigniew
Biofilms 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.