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Metal reducing bacteria (MRB) are capable of utilizing different metals, such as iron, chromium, manganese or uranium as well as many organic compounds, as electron acceptors for their metabolism. Via direct and indirect electron transfer processes MRB are able to convert insoluble passive film species like Fe(III)-oxides to soluble Fe(II)-oxides and hydroxides. This weakening of the passive film not only leads to an acceleration of the general corrosion processes, but also increases the susceptibility of stainless steels to pitting corrosion. Electron transfer mechanisms are not yet fully understood and the role of bacteria in corrosion processes is controversially discussed in the literature. Moreover, recent research indicates that the secretion of electron shuttles like riboflavins by MRB also contributes to the extracellular electron transfer.
This project aims at clarifying the chemical and electrochemical interaction mechanisms of MRB with stainless steel surfaces. To investigate the changes in the oxide chemistry on the stainless steel surface in the presence of biomolecules and MRB a new flow cell has been designed and constructed which enables the collection of XANES (X-ray Absorption Near Edge Structure) spectra in fluorescence mode at the Fe K-edge and electrochemical analysis. Availability of oxygen and the pre-exposure of the MRB to Fe(III) during cultivation have been investigated as parameters with significant effect on the corrosion rates. XANES analysis is supplemented by ex-situ X-Ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) to complete the surface characterisation in terms of the oxide chemistry and the composition of organic residues. Complementary electrochemical quartz crystal microbalance (e-QCM) measurements have been performed to quantify the kinetics of bacterial attachment and biofilm formation. Together with the frequency shift, the evolution of the dissipation signal has been analyzed to investigate the changes in viscosity and structure of the biofilm from initial stages up to maturation. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) has been used to study the structure and viscoelastic properties of the biofilms after e-QCM experiments.
The presentation will summarize our results on the effects of individual surface and environment related parameters on the chemical/electrochemical interaction mechanisms of MRB leading to passive film degradation on stainless steel surfaces and provide useful insights from a fundamental aspect for the development of novel mitigation strategies for microbiologically influenced corrosion.
Microbiologically influenced corrosion (MIC) on steel occurs where the presence and activity of microbes change the localized conditions on the surface of a metal substrate. For instance, metal reducing bacteria (MRB) are capable of utilizing metal compounds in the passive layer on stainless steel as electron acceptors during their metabolism. This weakening of the passive film not only leads to an acceleration of the general corrosion processes, but also increases the susceptibility of stainless steels to pitting corrosion. Even though the electron transfer mechanisms are not yet fully understood, recent research shows that the secretion of electron shuttles like flavins contribute significantly to the extracellular electron transfer (EET). Electron shuttle molecules like riboflavin (RB) or flavin mononucleotide (FMN) are secreted by MRB after the transition from planktonic to sessile mode and exist in the biofilm at low concentrations. Therefore, they are precise early phase indicators of bacterial settlement.
This project aims at clarifying the electrochemical interaction mechanisms of MRB with stainless steel surfaces, with a special focus on the role of the extracellular redox molecules. The analysis of corrosion processes as a function of chloride and flavin concentration have been performed by means of electrochemical methods. Due to the differences in their chemical structure, FMN and RB have shown significant differences in terms of their adsorption behavior and the stability of the formed films, which directly influences the electron transfer processes. Therefore, Electrochemical Quartz Crystal Microbalance (eQCM) studies have been performed on sputtered FeCr electrodes to investigate the adsorption/desorption kinetics of flavins.
The results of electrochemical studies are complemented by the analysis of the changes in the passive film chemistry and the chemical composition of the adsorbed films by means of Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) and X-ray photoelectron spectroscopy (XPS). Changes in surface morphology have been investigated by means of Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).The presentation will summarize our results on the degradation mechanisms of passive films on stainless steel surfaces in the presence of flavins and provide useful insights from a fundamental aspect for the understanding of the initial stages of microbiologically influenced corrosion.
The interface of a metal substrate and a biofilm can differ significantly from the surrounding environment. Metal reducing bacteria (MRB), for instance, are capable of utilizing various metallic compounds as electron acceptors. Besides chromium, uranium and manganese as well as many organic compounds, Fe(III) is converted to the soluble form Fe(II) during the bacterial metabolism. This could lead to a weakening of the protective passivation layer on stainless steel and thereby facilitate microbiologically influenced corrosion (MIC). Even tough the processes of electron transfer are not yet entirely explained, the contribution of flavins and other humic substances as electron shuttles is widely discussed in the literature. Moreover, the adsorption of organic thin films on steel surfaces can lead to surface preconditioning and thus to changes in adhesion behavior of bacteria.
The aim of this work is to understand the chemical and electrochemical interaction mechanisms of MRB with steel surfaces by combining electrochemistry and surface-analytical techniques. The investigations primarily focus on the effect of pre-adsorbed thin organic films and self-assembled monolayers (SAMs) on the electron transfer processes between bacteria and steel surfaces. Electrochemical Quartz Crystal Microbalance (eQCM) studies have been performed to investigate the adsorption/desorption kinetics of organic films as well as the formation of biofilms on FeCr electrodes. Furthermore, the evolution of the biofilms on steel surfaces has been analyzed by means of electrochemical impedance spectroscopy (EIS) to support the QCM studies with information on structural changes during different stages of biofilm growth. Electron transfer and corrosion processes have been analyzed by means of square wave voltammetry (SWV) and linear sweep voltammetry (LSV), respectively. The results of electrochemical studies are complemented with microscopic and spectroscopic characterisation of organic adsorbates and analysis of changes in the passive film chemistry and surface morphology.
This presentation will summarize our results on the chemical and electrochemical interaction mechanisms of MRB on steel surfaces leading to passive film degradation. The role of flavins in accelerating corrosion processes will be elucidated in detail to provide useful insights from a fundamental aspect for the understanding of the initial stages of microbiologically influenced corrosion in the presence of MRB.
The role of metal reducing bacteria (MRB) in corrosion is being controversially discussed in the literature. They can utilize metals including iron, uranium and manganese as well as many organic compounds as electron acceptors. The reduction of Fe(III) compounds to soluble Fe(II) species leads to the destruction of passive films on steel, resulting in acceleration of general and local corrosion processes. Recent research shows that the secretion of electron shuttles like riboflavins also contribute to the extracellular electron transfer (EET).
The aim of this project is to understand the chemical and electrochemical interaction mechanisms of MRB with steel surfaces by means of combined in situ techniques. An electrochemical XANES (x-ray absorption near edge spectroscopy) cell has been designed to study the changes of passive film chemistry in the presence of biomolecules and MRB. Electrochemical quartz crystal microbalance (eQCM) is used for studying the kinetics of bacterial cell attachment and diffusion of biomolecules in model biofilms. In situ investigations are complemented by ex situ spectroscopic and microscopic analysis to investigate the biofilm structure, composition and cell viability.
Via the combination of electrochemical methods with spectroscopic techniques and QCM we are able to follow biological processes and resulting degradation of steel surfaces in a non-destructive manner. The selection of model systems and a defined biological medium allows the identification of the effects of individual surface and environmental parameters. The fundamental understanding of bacterial attachment mechanisms and initial steps of biofilm formation will contribute to the development of new antifouling strategies.
Metal reducing bacteria (MRB) are able to utilize various materials such as iron, uranium and manganese as well as many organic compounds as electron acceptors. This process leads to the conversion of Fe(III) containing passive film species to soluble Fe(II) oxides and hydroxides. The reduction process triggers the acceleration of general and local corrosion processes. Electron transfer mechanisms are not yet fully understood. In literature it has been controversially discussed to which extend secreted electron shuttles contribute to the extracellular electron transfer (EET).
To understand the chemical and electrochemical interaction mechanisms of MRB with steel surfaces this project combines a variety of in-situ techniques. The changes in oxide chemistry on Fe/steel surfaces in the presence of biomolecules and MRB are under investigation using a newly designed electrochemical cell for in situ XANES (x-ray absorption near edge structure) spectroscopy. Electrochemical quartz crystal microbalance (eQCM) studies support the spectroscopic investigations to gain information about the kinetics of attachment processes and changes in biofilm viscosity. The biofilm structure and composition as well as cell viability are investigated by complementary ex situ spectroscopic and microscopic analysis.
Combining spectroscopic techniques and eQCM data with electrochemical measurements, biological processes and the resulting degradation of steel surfaces can be observed in a non-destructive manner. Selecting model systems and a defined biological medium allows the determination of individual effects of diverse surface and environmental parameters. The fundamental understanding of bacterial attachment mechanisms and initial steps of biofilm formation will contribute to the development of new antifouling strategies.
Biofouling constitutes a major challenge in the application of biosensors and biomedical implants, as well as for (food) packaging and marine equipment. In this work, an antifouling surface coating based on the combination of mussel-inspired dendritic polyglycerol (MI-dPG) and an amine-functionalized block copolymer of linear polyglycerol (lPG−b−OA11, OA = oligo-amine) was developed. The coating was compared to a MI-dPG surface which was postfunctionalized with commercially available amine-terminated Polyethylene glycol (HO−PEG−NH2) of similar molecular weight. In the current work, These coatings were compared in their chemical stability, protein fouling characteristics, and cell fouling characteristics. The lPG−b−OA11-functionalized coating showed high chemical stability in both phosphate buffered saline (PBS) and sodium dodecyl sulfate (SDS) solutions and reduced the adhesion of fibrinogen from human plasma with 99% and the adhesion of human serum albumin with 96%, in comparison to the bare titanium dioxide substrate. Furthermore, the Proliferation of human umbilical vein endothelial cells (HUVECs) was reduced with 85% when the lPG−b−OA11 system was compared to bare titanium dioxide. Additionally, a reduction of 94% was observed when the lPG−b−OA11 system was compared to tissue culture polystyrene.
The effect of the presence of Fe(III) during the cultivation on the electrochemical activity and corrosion behaviour of dissimilatory iron reducing bacteria Shewanella putrefaciens was studied by means of ex situ and in situ X-ray absorption near-edge spectroscopy (XANES). Stainless steel AISI 304 and thin iron films were studied as substrates. XANES analysis indicated an accelerated iron dissolution and growth of an oxide/hydroxide film for the culture grown with Fe(III) in comparison to the culture grown in absence of Fe(III). Electrochemical Analysis indicated that the biofilm resulted in acceleration of the general corrosion but provides protection against local corrosion.
This paper reports results from in situ electrochemical X-ray absorption near-edge spectroscopy (XANES) studies of the corrosion processes on model thin iron films in the presence of iron reducing bacteria Shewanella putrefaciens. Here we investigate the electrochemical activity of two cultures grown in the presence and absence of Fe(III) citrate in the culture medium. The XANES spectra and the OCP data of the Fe sample incubated with the culture grown in absence of Fe(III) did not show any significant changes during twenty hours of monitoring. In the case of the culture grown in Fe(III) containing medium, an accelerated dissolution of the iron film was observed together with the formation of a mixed Fe(II)-Fe(III) hydroxide surface layer. The open circuit potential (OCP) steadily approached the free corrosion potential of iron in neutral chloride containing electrolytes, indicating a continuous dissolution process without passivation.
Stainless steel AISI 304 surfaces were studied after a mild anodic polarization for oxide growth in the presence and absence of two derivatives of vitamin B2 (riboflavin and flavin mononucleotide) that can be secreted by metal‐reducing bacteria and act as a chelating agent for iron species. The alterations in oxide chemistry were studied by means of surface‐sensitive techniques such as X‐ray photoelectron spectroscopy and time‐of‐flight secondary ion mass spectrometry analysis. The complementary electrochemical characterization revealed a preferential growth of an oxide/hydroxide iron‐rich film that is responsible for an altered pit initiation and nucleation behavior. These findings suggest that as the corrosion behavior is determined by the interplay of the chemical and electronic properties, only a mild anodic polarization in the presence of redox‐active molecules is able to alter the chemical and electronic structure of the passive film formed on stainless steel AISI 304. This helps to achieve a profound understanding of the mechanisms of microbially influenced corrosion (MIC) and especially the possible effects of the redox‐active biomolecules, as they may play an important role in the corrosion susceptibility of stainless steel surfaces.
Biofilm formation and microbially influenced corrosion of the iron-reducing microorganism Shewanella putrefaciens were investigated on stainless steel surfaces preconditioned in the absence and presence of flavin molecules by means of XANES (X-ray absorption near-edge structure) analysis and electrochemical methods. The results indicate that biofilm formation was promoted on samples preconditioned in electrolytes containing minute amounts of flavins. On the basis of the XANES results, the corrosion processes are controlled by the iron-rich outer layer of the passive film. Biofilm formation resulted in a cathodic shift of the open circuit potential and a protective effect in terms of pitting corrosion. The samples preconditioned in the absence of flavins have shown delayed pitting and the samples preconditioned in the presence of flavins did not show any pitting in a window of −0.3- to +0.0-V overpotential in the bacterial medium. The results indicate that changes in the passive film chemistry induced by the presence of minute amounts of flavins during a mild anodic polarization can change the susceptibility of stainless steel surfaces to microbially influenced corrosion.