Electrochemical Impedance Response of Zn Under Anodic Polarization in Simulated Concrete Solution

An understanding of the corrosion behaviour of the zinc alloy coating when placed in concrete and the characteristics of the corrosion products so formed is fundamental to a full appreciation of the corrosion protection afforded by the galvanizing of reinforcement. Pure Zn was chosen because it simulates well the behaviour of galvanized steel, yielding more reproducible results. The aim of this study was to analyze the electrochemical behaviour of pure Zn in Ca(OH)2 saturated solution (simulating the pore solution of concrete) by means of electrochemical impedance spectroscopy measurements under potentiodynamic anodic polarization tests and scanning electron microscopy. Samples used in this work were zinc (99%) alloy, high-grade reagents and distilled water were used to make the solution of saturated Ca(OH)2, anodic polarization and impedance experiments were carried out on a Biologic SP-300 potentiostat. Before the electrochemical tests the specimens are subjected to an exposure of 1 hour in the test solution, the anodic potential scan (0.1 mV s-1) was performed without stirring the solution, starting from the rest potential (E_corr) and scanning in the anodic direction to 800 mV and 60 mV, during the scanning of anodic polarization from rest potential to 60 mV under a polarization of 10, 20, 30, 40, 50 and 60 mV, the impedance was measured with a sinus amplitude of 10 mV in a frequency range from 200 kHz  to 100 mHz. The impedance spectrum shows changes both shape and magnitude indicating more than one process to take place on the surface of zinc, duo to the gradual formation of two semicircles with the increment of potential. (fig.1) These studies are expected to provide technique for development of a protective passive layer on galvanized coatings prior to their embedding in concrete.