Protective effect of the corrosion products layers of atmospheric exposure [Efecto protector de las capas de productos de corrosión de exposición atmosférica]
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abstract
The electrochemical techniques of evolution of the corrosion potential (Ecorr), polarisation resistance (Rp) and potentiodynamic polarisation, were used to evaluate the protectiveness of the corrosion products layers developed on commercial grade low carbon steel, zinc (galvanised steel), copper and aluminium, after an outdoor exposure of 1, 2 and 5 year in an urban atmosphere. Results obtained using a 0.1 M Na2SO4 solution revealed a greater anticorrosive protection of the four metallic materials as a result of the corrosion products formation. In addition, it was observed that when the outdoor exposure time increased the Ecorr values were more noble, those of Rp increased and the potentiodynamic anodic polarisation curves showed a greater slope of the inner regions and a shifting to the area of smaller current density in the E vs. log i diagrams. These results were not in a total agreement with those obtained by weight loss.
