Mössbauer studies of corrosion products developed in Prohesion test over galvanized steel sheets

M. ZAPPONI; T. PÉREZ; C. P. RAMOS; C. SARAGOVI

Panamá

Conferencia; Eighth Latin American Conference on Applications of the Mössbauer Effect (LACAME 2002); 2002

The use of precoated galvanized steel in the building sector is continuously increasing. Customers require extended warranties in terms of corrosion. Different tests are used to evaluate the corrosion protection properties of coating materials to meet customer specification and for development purposes. Outdoor exposure test is the most suitable method for evaluating the corrosion resistance of painted coated sheets, but it takes a long time to have results. Accelerated tests do not necessarily correlate with outdoor exposure results. In recent years, claims of improved correlations with outdoor results have been reported based on the use of cyclic wet/dry corrosion chambers, for example Prohesion test (ASTM G-85). With the aim of contributing to the understanding of the corrosion mechanism in Prohesion test and its relationship with the mechanism in outdoor corrosion, corrosion products of 1000 hours Prohesion test and one year exposure at marine atmosphere were analyzed by Mössbauer Spectroscopy complemented by X-ray diffraction. Mössbauer measurements were performed at RT and at 15 K in both samples. The corrosion products were different in both samples: surprisingly greigite was detected in samples of Prohesion test and its formation in these samples is under study. Magnetite, goethite, lepidocrocite, akaganite and sulfates were also found in Prohesion and in outdoor samples.