The Behavior of Carbon Steel in Artificial Cooling Water in Presence of Hydroxyphosphonoacetic Acid and Different Oxygen Content Using Electrochemical Impedance Spectroscopy

Abstract

This paper presents the results of the interfacial evolution of 1018 steel exposed to artificial cooling water in presence of two different environments: the oxygen content and the 1,2-hydroxyphosphonoacetic acid (HPA). The aerated solution in presence of HPA supported two processes; the first was the sequestration of calcium ions with the subsequent complexation of the calcium carbonate (CaCO 3); the second was the precipitation of a layer formed mainly by hematite (Fe 2 O 3) mixed with CaCO 3 and phosphorous-based compounds. Conversely, de-aerated conditions in the absence of HPA lead to the formation of a combination of iron oxides (Fe 3 O 4 + Fe 2 O 3) at the surface of the steel. The HPA addition in deaerated solution produced the formation of plate shape phosphorous-based layer with a mixture of iron oxides (Fe 3 O 4 + Fe 2 O 3). In this work, we could characterize the evolution of the corrosion products layers by Electrochemical Impedance Spectroscopy (EIS) measurements and electrical passive circuits. The continuous EIS results helped to establish interfacial mechanisms of the HPA used as inhibitor and de-aerated (oxygen low content) conditions simulating the presence of oxygen scavengers.