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To investigate early stage corrosion processes of stainless steel 1.4301 taking place during the biofilm formation of the organism Shewanella putrefaciens electrochemical impedance spectroscopy (EIS) in a multielectrode approach has been used. The multielectrode array consisted of up to 25 electrically isolated electrodes made of stainless steel wires of diameters ranging from 100 µm to 500 µm. They were connected to a multichannel microelectrode analyzer (MMA) electrically coupled through zero resistance ammeters. Current flow between electrodes in the array as well as changes in impedance of individual electrodes over time were recorded and analyzed with respect to the onset of localized corrosion and biofilm formation. The results were complemented by optical microscopy, SEM and AFM images which were taken immediately after the respective experiment. To verify that the multielectrode arrays correctly indicated the initial stages of the corrosion process and of biofilm formation they were introduced in a flow cell reaction vessel containing test specimens made from stainless steel 1.4301, which were checked regularly for signs of localized corrosion and biofilms. Preceding results with the multielectrode array in solutions containing high amounts of chloride ions and hydrogen peroxide at low pH also showed that it is possible with the MMA to monitor individual electrodes becoming local anodes as local corrosion set in, while the remaining electrodes predominantly acted as cathodes.
Verteilte faseroptische Sensorik eignet sich sehr gut für eine Zustands- und Gefährdungsüberwachung von ausgedehnten Hochspannungskabelinstallationen. Basierend auf der Messung von verschiedenen faseroptischen Rückstreueffekten in der Sensorfaser lassen sich ortsaufgelöste Profile von Messgrößen wie Temperatur, Dehnung oder Vibrationen erzielen.
Hier demonstrieren wir die Leistungsfähigkeit verschiedener faseroptischer Sensorikansätze bezüglich dieser Größen anhand von Experimenten u.a. an einem Mittelspannungskabel. Des Weiteren zeigen wir, wie die Verwendung von verschiedenen Sensorkabeltypen mit unterschiedlicher Applikation auf der Kabeloberfläche die Messergebnisse bei einem Biegeversuch beeinflussen und schlussfolgern damit auf die für die Einbettung in Kabeln geeigneten Sensoren.
In the development of certified reference materials (CRM), it is necessary to examine appropriate materials in advance for homogeneity and stability to meet the criteria of a CRM.
In this case, the materials properties are characterized at the actual time without being possible to give a prognosis for suitability in the following years.
It is, therefore, necessary to follow the certified material parameters via a monitoring system over the years on sale.
For the current development of CRMs, the gained experience from long-term stability studies about the first generation of porous CRMs is significant. This experience is useful to better assess the suitability of candidate materials and thus develop higher quality CRMs in the future.
A comparison between the gas sorption CRM materials silica, activated carbons, alpha alumina and anatase titanium oxides will illustrate the importance of long-term stability studies on porous CRMs.
Previous work has shown that ultrasonic monitoring using externally applied or embedded transducers and imaging methods based on coda wave interferometry are able to detect subtle changes in concrete elements. In this study, a limited number of embedded transducers has been used to monitor changes in several 12 m long two-span concrete beams subjected to point or linear loads until failure.
The ultrasonic results showed the high sensitivity to stress changes and the nonlinear character of the associated effects. However, the ultrasonic features showed a very good correlation to several conventional monitoring parameters. For higher loads (significant amount of cracking), the technique had to be modified to cope with large wave velocity variations and high decorrelation compared to the reference signal.
Using a very simple imaging procedure, the 2D stress field inside the beam has been visualized including inhomogeneities and artifact at places where cracking occurred at higher loads. The technique has the potential to be included in real time monitoring systems.