Four metallic materials of economic significance were exposed to an urban atmosphere up to five years. These materials were low carbon steel, zinc (as galvanized steel), copper and aluminum all of commercial quality. The corrosion rate was measured after 1, 2, 3 and 5 years using a weight loss method. Sulfur dioxide deposition rate and climatological parameters were determined monthly. At the same time, different techniques were used to characterize the corrosion products developed on the above materials. Results obtained by polarization resistance technique (Rp) in a 0.1 M Na2S04 solution revealed that, the longer the exposure time, the greater the corrosion products protection, as result of broadening and compactness of such products, this was verified by scanning electron microscopy (SEM). Through x-rays diffraction (XRD), the expected crystalline compounds on steel and copper were identified and also, the transformation of middling protective initial products into other more protective was followed. For aluminum and zinc it was not possible to identify the crystalline compounds perhaps due to the very thin corrosion products layers. So, these materials were analyzed by means of Raman spectroscopy. a-Al2O3, was identified on an aluminum sample whereas on zinc any corrosion product could not be identified due to excessive fluorescence.
Structures and materials are exposed to the atmosphere more than to any other environment. Therefore it is of paramount importance to assess its aggressiveness. Studies on atmospheric corrosion are made in order to get information about the atmospheric corrosivity, fix criteria to appraise the behavior of the more used metallic materials when they are barely exposed to weathering, and attempt to establish the polluted substances effect over the metallic corrosion. The prediction of corrosion or atmospheric aggressiveness may serve as an indicator for protective measures to be taken in the conservation of metallic structures, and may be used at the design stage of a project in order to specify the most appropriate metal or alloy to be used, the type of protective coating and the frequency of maintenance ?.
Kinetic parameters, like corrosion rate measured by weight loss, are usually determined and very often it has been intended to correlate them with the atmospheric pollutant level, mainly sulfur dioxide and chlorides, and with meteorological data (temperature, relative humidity (RI-I), time of wetness, etc). Weight loss measurements are obtained after one or more years of outdoor exposure. Only in a small fraction of all weight loss determinations it has been gone beyond the plain gravimetric method. For a deeper understanding of atmospheric corrosion phenomena it is evidently insufficient to rely solely on weight loss data and over the years it has become obvious that a detailed characterization of corrosion products not only may improve the basic knowledge of atmospheric corrosion phenomena but also may aid in interpreting weight loss data Born field exposure programs ?.
The aim of this work is to attempt to develop a relationship between the identification and properties of the chemical compounds present in the corrosion products layer and its protective ability,
