This article presents the results obtained at 16 tropical test sites participating in the “Ibero-American Map of Atmospheric Corrosiveness” (MICAT), a project on atmospheric corrosion carried out during the period 1988–1994 at some 70 test sites distributed across 12 countries of the Latin-American region, Spain and Portugal. The tropical climate and its different climatic variants are characterized by high average air temperatures, with considerable daily thermal fluctuations, high average relative humidity, and generally high precipitation volumes. The work is structured in three main blocks: apparently unpolluted atmospheres (i), and marine atmospheres, differentiating between pure marine atmospheres (ii) and those in which both chloride (Cl-) and sulfur dioxide (SO2) pollutants coexist (iii). In each block an attempt was made to determine the role of the tropical climate in the magnitude of corrosion attack shown by four typical reference metals (mild steel, zinc, copper and aluminum) exposed for one-year periods in tropical atmospheric exposure conditions.

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.