Môssbauer spectroscopy and X-ray powder diffraction (in selected samples) have been used to characterize corrosion products on carbon steels after atmospheric exposure to the tropical Panamanian locations of Panama and Colon, classified according to ISO 9223 as C3 and C5, respectively. Goethite (a-FeOOH) of intermediate particle size (20-100 nm), lepidocrocite (y-FeOOH), a spinel phase consisting of non-stoichiometric magnetite (Fe3,x04) and/or maghemite (y'Fe203) and nano-sized particles were identified in the corrosion products. The spinel phase is related to short term atmospheric exposure transforms in time to other corrosion products. The corrosion resistance increased with fraction of goethite following a saturation-type behavior.

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.

No abstract