EIS characterisation of the layer of corrosion products on various substrates in differing atmospheric environments

The layer of corrosion products forming on zinc in atmospheric environments of varying aggressivity have been characterised and compared with previous results obtained for carbon steel. The characteristics of said layers have been linked to the nature of the products found. Likewise, we have found that EIS is a useful tool towards characterising the layers of corrosion products of carbon steel and zinc. The equivalent circuit which gives the best fit of impedance data for both metals is type R(C(R(C(R(CR))))), where the Nyquist diagrams are composed of two time constants. It is observed that the value of the capacitance of the corrosion product layer (Cpc) diminishes as the time of exposure increases, which is directly related with an increase in the thickness of the corrosion product layer. Also, it is observed that when the nature of the corrosion products doesn't vary with the time of exposure, the decrease of the charge transfer resistance is related with the increase in the thickness of the corrosion product layer.