Browsing by Author "Mansfeld, Florian"

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Evaluation of coating degradation with electrochemical impedance spectroscopy and electrochemical noise analysis
(1994) Xiao, H.; Mansfeld, Florian
The performance of two coating systems on cold‐rolled steel has been evaluated with electrochemical impedance spectroscopy and electrochemical noise analysis during exposure to 0.5N Formula for five months. The decrease of the pore resistance Formula and the polarization resistance Formula and the increase of the double layer capacitance Formula show qualitatively that the disbonded area Formula increased with time for the alkyd system (CR‐2). No deviation from capacitive behavior was observed for the epoxy polyamide coating (CR‐9) which showed excellent performance. Potential and current noise data have been collected simultaneously. This approach allows evaluation of the frequency dependence of the spectral noise response and determination of the spectral noise resistance Formula . From the statistical analysis of the noise data the noise resistance Formula has been obtained. Good agreement between these two parameters has been observed. Formula and Formula show the same time dependence as Formula and Formula . However, their numerical values are much lower. For CR‐2 a parallel shift of the potential power spectral density (PSD) curves to lower values and of the current PSD curves to higher values with a constant slope of −20 dB has been observed for CR‐2. No obvious time dependence was indicated for CR‐9.
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.