Drawn steel surface analysis in contact with saline solution by electrochemical atomic force microscopy (EC-AFM)

Abstract

Trabajo presentado en el European Congress and Exibithion on Advanced Materials and Processes EUROMAT 2013, celebrado en Sevilla (España), del 8 al 12 de septiembre de 2013High strength steels in concrete structures used as reinforcement have high durability. The corrosion resistance is due to the physical barrier that concrete provides, and by a protective passive film developed on the surface by the high alkaline media. In presence of chloride ions, they can break the passive film. These ions can be found into the mixing water or in the structures near marine environment. The current work studies corrosion phenomena of drawn wire steels with eutectoid composition containing a pearlitic microstructure, which is composed by a ferritic matrix with cementite layers observed by Atomic Force Microscopy. Continuous sweeps in contact mode are performed in areas of 5 x 5 microns, obtaining topographic images. An electrochemical cell is developed in order to assemble it into Atomic force Microscopy. The cell set up is composed with three electrodes: a reference micro-electrode of Ag/AgCl, a drawn wire steel like working electrode, and a slim wire made of Pt/Ir like a counter electrode in a cell of 400 µL. The cell was subjected to different solution media, both neutral and alkaline in presence of chloride ions. Electrochemical conditions were changed by the application of different potentials. The experimental results give images of topography ¿in situ¿. They are extracted directly from the steel surface. The main advantage of this technique is the observation of preferential attack of the ferrite, with the cementite as cathode