Rafael Leiva-García

Study of Passive Films Formed on AISI 316L Stainless Steel in Non-Polluted and Underwater-Volcano-Polluted Seawater

This work studies the semiconducting behavior of passive films formed on AISI 316L (UNS S31603) in two different sea-water solutions, non-polluted and polluted, collected from the volcano of El Hierro Island. Polarization measurements, potentiostatic passivation tests, electrochemical impedance spectroscopy, and capacitance measurements were performed. Results show that the polluted seawater worsens passivation kinetics. Additionally, passive films formed on AISI 316L stainless steel in polluted seawater have been found to be less protective than those formed in non-polluted seawater, showing a more defective structure, owing to the acidity of the polluted medium.

Application of Confocal Laser Scanning Microscopy to the In-situ and Ex-situ Study of Corrosion Processes

1.1 Background of confocal microscopy In 1955 Marvin Minsky developed the basic concept of confocal microscope when he was a Junior Fellow at Harvard University (Minsky, 1957). The principle of confocal microscopy is based on the rejection of the light from the planes out of focus. Minsky’s design performs a point-by-point image construction by focusing a point of light sequentially across a specimen and then collecting some of the returning rays. In this way, Minsky avoided most of the undesirable scattered light that obscures an image if the entire specimen is illuminated at the same time. In addition, the light that the specimen returns passes through a second pinhole aperture that rejects rays that are out of the focal point. The remaining selected light rays are then collected by a photomultiplier and the image is gradually reconstructed using a long-persistence screen. A real image was not formed in Minsky’s original microscope; the output from the photodetector was translated into an image of the region of interest. In Minsky’s original design the image was built up on the screen of a military surplus long persistence oscilloscope with no facility for hard copy. Minsky said later that the image quality in his microscope was not very impressive due to the quality of the oscilloscope display and not due to lack of resolution achieved with the microscope itself (Minsky, 1988). To obtain the image, Minsky scanned the specimen by moving the stage rather than the light rays. Using a 60 Hz solenoid to move the platform vertically and a lower-frequency solenoid to move it horizontally, Minsky obtained a frame rate around one image every 10 sec. Fig. 1 shows a scheme of Minsky’s invention. Although Minsky built his microscope with two objective lenses he realized that the system could work using a single objective lens operated in a reflected light mode. This mode is, in fact, how all current commercial confocal laser scanning microscopes (CLSM) systems work. Minsky’s invention remained largelly unnoticed, due most probably to the lack of intense light sources necessary for imaging and the computer horsepower required to handle large amounts of data. The great advances in computer, laser technology, and digital images acquisition have permitted to discover the application of the confocal microscope in a widely number of fields such as biology, geology or materials research. Laser light offers

Effect of Volcano-Polluted Seawater on the Corrosion Behaviour of Different Alloys

During a subsea volcano eruption, gases and thermal water emissions are released. This might change the behaviour of the materials that are in contact with the seawater caused by the decrease of the pH value. For this reason, the materials for marine applications are selected to maintain the integrity of the structure and to be corrosion resistant. In spite of this, corrosion can cause great damage to marine steel infrastructures such as bridges, wharfs, platforms and pipeline systems. These corrosion problems could be aggravated if the medium is altered, due to volcano emissions, since the resistance of the surface film is influenced by the environmental conditions. Electrochemical techniques are useful to evaluate the corrosion behaviour of different metals and alloys. However, literature regarding the influence of underwater-volcanopolluted seawater on the passivation/corrosion behaviour of stainless steels is scarce. According to this, the objective of the chapter is the evaluation of the influence of an underwater volcano eruption on the corrosion behaviour of different materials that might be used in seawater environments. Electrochemical techniques are applied to evaluate the performance of the different materials when they are immersed in polluted volcano seawater. The results are relevant in the evaluation of natural hazard risk assessments involving critical infrastructures.