Browsing by Author "Little, Brenda J."

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Biofilm and Their Effects on Local Chemistry
(1988-10) Characklis, William G.; Little, Brenda J.; McCaughey, M. S.
Dissolved oxygen and pH microelectrode measurements at water-immersed metal surfaces
(1989-02) Lewandowski, Zbigniew; Lee, Whonchee; Characklis, William G.; Little, Brenda J.
Dissolved oxygen (DO) and pH were measured at metal/artificial seawater interfaces using microelectrodes in biotic and abiotic systems. Measurements in a closed system proved that presence of electrochemical and/or biological reaction products substantially influence the conditions at the metal surface. For long-term studies, only open (e.g., continuous flow) reactors should be used. An open channel flow reactor suitable both for microbiological and electrochemical measurements has been constructed and successfully tested.
Impact of biofouling on the electrochemical behavior of 304 stainless steel in natural seawater
(1991-02) Little, Brenda J.; Ray, Richard; Wagner, Patricia A.; Lewandowski, Zbigniew; Lee, Whonchee; Characklis, William G.; Mansfeld, Florian
Biofilm formation on 304 stainless steel (S30400) does not necessarily result in an ennoblement of the corrosion potential. Instead, biofilms composed of aerobic and anaerobic bacteria from Gulf of Mexico water formed an anaerobic biofilm/metal interface and caused the corrosion potential to move in the negative direction. Biofilms from the same source containing photosynthetic diatoms in the presence of light produced aerobic biofilm/metal interfaces and a positive shift (ennoblement of the corrosion potential). Corrosion potentials of stainless steels exposed in natural seawater cannot be predicted without an understanding of the composition of the biofilm and its impact on interfacial chemistry. In this paper, measurements of corrosion potential, interfacial pH and dissolved oxygen have been correlated with SEM/EDAX surface analyses to evaluate the electrochemical behaviour of stainless steels exposed to Gulf of Mexico water. The interfacial chemistries that influence the corrosion potential are also discussed.
Iridium oxide ph microelectrode
(1992-08) VanHoudt, P.; Lewandowski, Zbigniew; Little, Brenda J.
The manufacture, calibration, and signal conditioning during construction of an iridium/iridium oxide pH microsensor is described. The microsensor was designed to be used extracellularly, primarily in biofilm research. The sensing tip diameters were typically in the range of 3–15 μm. The iridium oxide was formed by potential cycling in dilute sulfuric acid. A pH profule across a denitrifying biofilm was measured as an example of an application. The higher Nernstian slope (70–80 mV/pH for fresh electrodes), increased rigidity, and restriction of the sensing tip to the outermost end of the electrode are features which make the iridium/iridium oxide pH microelectrode superior to a glass microelectrode.
Mic issues: commentary from the corrosion 2002 mic panel discussion
(2002) Lewandowski, Zbigniew; Cloete, Thomas E.; Dexter, Stephen C.; Dickinson, Wayne H.; Kikuchi, Yasushi; Little, Brenda J.; Rossmoore, Harold; Sand, Wolfgang; Videla, Hector A.
Invited panelists, prominent Microbiologically Influenced Corrosion (MIC) researchers from universities, government agencies, and industrial companies, were asked to select and to present issues they felt were vital to understanding MIC. The discussion took place during the MIC symposium at the NACE 2002 Conference in Denver. The notes presented in this paper are commentary from this discussion.
pH at polarized metal surfaces: theory, measurement and implications for mic
(1990) Lewandowski, Zbigniew; Lee, Whonchee; Characklis, William G.; Little, Brenda J.
The role of biomineralization in microbiologically influenced corrosion
(1998) Little, Brenda J.; Wagner, Patricia A.; Lewandowski, Zbigniew
Spatial distribution of ph at mild steel surfaces using an iridium oxide microelectrode
(1994) Lewandowski, Zbigniew; Funk, T.; Roe, Frank L.; Little, Brenda J.
The distribution of pH near a metal surface indicates the positions of anodic (low pH) and cathodic sites (high pH). A microsensor, small enough that the pH sensing tip is confined to the diffusion layer, can be used to monitor pH near metal surfaces. This paper describes the mapping of pH near water-immersed mild steel surfaces using miniaturized iridium/iridium oxide pH microelectrodes in conjunction with a computer controlled micropositioner and data acquisition system. Two systems were analyzed: (1) a bare mild steel coupon exposed to artificial sea water, and (2) a mild steel coupon, first partially covered with the biopolymer, calcium alginate, and then exposed to artificial seawater. After 8 h exposure to seawater both coupons exhibited localized corrosion. On the coupon partially covered with calcium alginate gel, corrosion was limited to the area covered by biopolymer. On the bare coupon, corrosion was widespread. pH mapping of the coupons showed that low pH regions were identified with the corroded areas, and high pH regions with the uncorroded areas. These observations demonstrate that, in the abiotic environment, anodic sites on a mild steel surface can be fixed by partially covering the metal with biopolymer.
Spatial relations between bacteria and metal surfaces
(1997) Little, Brenda J.; Wagner, Patricia A.; Lewandowski, Zbigniew
Surface structure effects on direct reduction of iron oxides by shewanella oneidensis
(2003-12) Neal, Andrew L.; Rosso, Kevin M.; Geesey, Gill G.; Little, Brenda J.
The atomic and electronic structure of mineral surfaces affects many environmentally important processes such as adsorption phenomena. They are however rarely considered relevant to dissimilatory bacterial reduction of iron and manganese minerals. In this regard, surface area and thermodynamics are more commonly considered. Here we take a first step towards understanding the nature of the influence of mineral surface structure upon the rate of electron transfer from Shewanella oneidensis strain MR-1 outer membrane proteins to the mineral surface and the subsequent effect upon cell “activity.” Cell accumulation has been used as a proxy for cell activity at three iron oxide single crystal faces; hematite (001), magnetite (111) and magnetite (100). Clear differences in cell accumulation at, and release from the surfaces are observed, with significantly more cells accumulating at hematite (001) compared to either magnetite face whilst relatively more cells are released into the overlying aqueous phase from the two magnetite faces than hematite. Modeling of the electron transfer process to the different mineral surfaces from a decaheme (protoporphyrin rings containing a central hexacoordinate iron atom), outer membrane-bound cytochrome of S. oneidensis has been accomplished by employing both Marcus and ab initio density functional theories. The resultant model of electron transfer to the three oxide faces predicts that over the entire range of expected electron transfer distances the highest electron transfer rates occur at the hematite (001) surface, mirroring the observed cell accumulation data. Electron transfer rates to either of the two magnetite surfaces are slower, with magnetite (111) slower than hematite (001) by approximately two orders of magnitude. A lack of knowledge regarding the structural details of the heme-mineral interface, especially in regards to atomic distances and relative orientations of hemes and surface iron atoms and the conformation of the protein envelope, precludes a more thorough analysis. However, the results of the modeling concur with the empirical observation that mineral surface structure has a clear influence on mineral surface-associated cell activity. Thus surface structure effects must be accounted for in future studies of cell-mineral interactions.