Patricia Wagner

BIOFILMS - AN ESEM EVALUATION OF ARTIFACTS INTRODUCED DURING SEM PREPARATION

SummaryDescriptions of biofilms and their elemental compositions based on scanning electron micrographs and energy dispersive x-ray analysis cannot be related to the original condition of the biofilm on the surface. Solvent replacement of water removes extracellular polymeric material and reduces the concentration of elements bound within the biofilm. In the wet state, bacteria and microalgae are enmeshed in a gelatinous film that is either removed or dried to a thin inconspicuous residue during sample preparation for scanning electron microscopy. The environmental scanning electron microscope provides a fast, accurate image of biofilms, their spatial relationship to the substratum and elemental composition.

An overview of microbiologically influenced corrosion

Abstract Biofilms on metal surfaces produce an environment at the biofilm/metal interface that is radically different from that of the bulk medium in terms of pH, dissolved oxygen, organic and inorganic species. The term microbiologically influenced corrosion (MIC) is used to designate corrosion due to the presence and activities of microorganisms within biofilms. In this review we have correlated electrochemical reactions to the activities of microorganisms to show that microorganisms can accelerate rates of partial reactions in corrosion processes or alter the corrosion mechanism.

Factors Influencing the Adhesion of Microorganisms to Surfaces

Abstract Starvation, growth phase, and carbon source influenced bacterial cell surface hydrophobicity. Both the number and kind of microorganisms that colonized metal surfaces depended on the type of metal and the presence of an imposed electrical potential. No significant differences in attachment and growth of a pure culture were observed when metal surfaces were dipped in an exogenous energy source. The chemical composition of naturally occurring adsorbed organic films on metal surfaces was shown to be independent of surface composition and polarization.

The Involvement of a Thermophilic Bacterium in Corrosion Processes

Abstract A rapidly proliferating obligate thermophilic bacterium with an optimum temperature range of 60 to 70 C was isolated from a failed nickel 201 brazed joint. Corrosion experiments have demonstrated that the isolate is responsible for the (1) in situ production of acidic metabolites and (2) creation of differential aeration cells, resulting in a significant corrosion current.

Impact of biofouling on the electrochemical behaviour of 304 stainless steel in natural seawater

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 d...

An electrochemical and surface analytical study of stainless steels and titanium exposed to natural seawater

Abstract Samples of three stainless steels and titanium grade 2 were exposed to flowing seawater at Port Hueneme, California under natural and reduced light environments. A total of four sets of samples were exposed for times up to 120 days. Open-circuit potential ( E corr ) and electrochemical impedance data as a function of exposure time were used to monitor the electrochemical behavior of the four materials. Surface examination showed a gradual increase in coverage by the biofilm as a function of exposure time. A small increase of E corr was observed, independent of exposure conditions and similar in magnitude to that observed in an abiotic, synthetic salt solution. Impedance data remained capacitive over the entire test period. Capacitance values were similar in natural and synthetic seawater. Localized corrosion was not observed for any sample. Pitting scans in 3.5% NaCl, performed as a function of pH, showed that the pitting potential of 304 stainless steel (SS) reached a value of about 0 mV at pH = 2.

Microbiologically influenced degradation of fiber-reinforced polymeric composites

Abstract General weight loss corrosion measurements have been conducted on a variety of metals and their alloys that have been used, or have potential use, in liquid ammonia including carbon and lo...

An Investigation of Microbiologically Mediated Corrosion of Copper-Nickel Piping Systems Selectively Treated with Ferrous Sulfate

Microbiologically induced corrosion in 90/10 Cu-Ni pipes was evaluated using estuarine water from the Gulf of Mexico at the mouth of the Pascagoula River, maintained at a flow rate of 3-6 ft/sec over an 8-month period. The impact of surface preparation, batch FeSO4(50 ppb Fe2+for 48 hours) pretreatment and intermittent treatment was evaluated. Surface deposits were characterized by scanning electron microscopy and energy-dispersive x-ray fluorescence spectrometry. Water analyses included pH, dissolved oxygen, dissolved sulfide and sulfate, total organic carbon, total suspended solids and dissolved heavy metal analyses, as well as quantification of bacteriological components. Batch FeSO4treatment did not result in a persistent increase in surface-bound iron or decreased localized corrosion. Surface pitting appeared to be associated with accumulations of chlorine, sulfur, and microbiological colonization.

Application of Electrochemical Techniques to the Study of Microbiologically Influenced Corrosion

As indicated by the data presented in this chapter, modem electrochemical techniques are useful for MIC investigations. However, the nature of MIC makes it extremely difficult to use electrochemical techniques for detection, quantification, mechanistic studies, or monitoring. MIC is often the result of viable microorganisms within a viscoelastic, nonconducting biofilm. Techniques that do not require application of an external signal (E corr, dual-cell measurements, and ENA) permit electrochemical measurements without disruption of the causative processes. Most corrosion reactions in MIC are of a very localized nature. This makes use of electrochemical techniques, which in general produce an average signal over the entire surface, difficult. As with all studies of localized corrosion phenomena, more detailed and reliable information can be obtained when a number of different electrochemical techniques are combined. MIC does not produce a unique form of corrosion, so any analytical technique must be accompanied by differentiation between biological and abiological processes. Resolution requires the use of microbiological, surface analytical, and surface imaging techniques.