Electrochemical Evaluation of the Protective Properties of Steel Corrosion Products Formed in Ibero-American Tropical Atmospheres

Abstract

The purpose of the MICAT project (Ibero-American Map of Atmospheric Corrosiveness) was to foster collaborative ventures between groups conducting research on atmospheric corrosion. Overall 14 Ibero-American countries, including Spain and Portugal were involved with a network of 75 test stations distributed throughout the region and on 3 continents, and many of them were set within tropical regions representing a broad spectrum of climatological and atmospheric pollution conditions. The general objective of the MICAT electrochemical studies was to characterize the electrochemical and protective properties of the corrosion products formed during different periods of atmospheric exposure (1 to 4 years). The particular objective of the present work is to present electrochemical results associated to the protective properties of steel corrosion products formed in test sites with tropical atmospheres. After atmospheric exposure, pre-rusted mild steel specimens were immersed in a sodium sulfate solution and electrochemically evaluated. Linear polarization resistance (LPR) and electrochemical potential noise (EPN) measurements were performed after one hour of immersion. Electrochemical measurements were related to the presence of the atmospheric oxides formed and associated to climatological and atmospheric pollution data; its protective properties reflected in the weight loss data obtained during exposure. For specimens rusted in marine atmospheres, the presence of chlorides promotes localized corrosion. The electrochemical measurements were able to characterize and evaluate the protective properties of oxides according to the nature and environmental conditions to which specimens were exposed.