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EIS characterization of the evolution of calcium carbonate scale in circulating cooling water systems in presence of inhibitors
Abstract
Electrochemical impedance spectroscopy (EIS) was used to assess the relative effects of scale and corrosion for steel electrodes in cooling water media and to obtain information on corrosion inhibition and scale inhibition properties of 1-hydroxyethylidene-1,1-diphos- phonic acid (HEDP) and hydroxyphosphonoacetic acid (HPAA). Steel electrodes were preliminary scaled with CaCO3 in simulated cooling water and then immersed in the characterization solution. Analysis of the impedance spectra with a simple model allowed following of the time evolution of physical parameters corresponding to the calcium carbonate islands and to the corrosion productsaccumulated in areas not covered by the scale. In uninhibited solutions, the main effect was the progressive deposit of corrosion products with no additional scale and little restructuring of the initial carbonate islands. When the solution contained HEDP alone, part of the initial scale was detached from the surface, but the presence of HPAA or the mixture HPAA+HEDP only induced structural modifications of the initial scale. Moreover, the impedance analysis also showed that HPAA exhibited better corrosion inhibition properties than HEDP.
Kwywords: Electrochemical impedance spectroscopy . Scale . Corrosion . carbon steel . Cooling waters . HEDP . HPAA
EIS characterization of the evolution of calcium carbonate scale in circulating cooling water systems in presence of inhibitors