Study of the corrosion products formed on carbon steels in the tropical atmosphere of Panama

Mössbauer 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 (α-FeOOH) of intermediate particle size (20-100 nm), lepidocrocite (γ-FeOOH), a spinel phase consisting of non-stoichiometric magnetite (Fe3-xO4) and/or maghemite (γ-Fe2O3) 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.