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artículo con referato
"Corrosion Layers of Low-Alloy Carbon Steels in CO2(g)-Saturated Solutions by Mössbauer Spectroscopy"
I. Raspini, E. Chung and C. Saragovi
Corrosion NACE 56(8) (2000) 832-838
Transmission Mössbauer spectroscopy (TMS), which is a powerful tool for atmospheric and marine corrosion studies, was presented as a tool for characterizing corrosion products formed in aqueous carbon dioxide (CO2[g])-saturated brines. An electrochemical process was applied to simulate a corrosion process at the bottom of an oil well (turbulence and aggressive environment) to obtain corrosion products. Their formation depends on the composition of steels and environmental conditions. The characterization through TMS of corrosion films formed on two low-alloy C steels, one without Cr and another with 1% Cr, exposed to CO2(g)-flushed solutions has shown morphological and qualitative differences between corrosion films. Ferrous carbonate (FeCO3, siderite), a faulted cementite (Fe3C*), and a particular carbide (Fe-C*), both of the latter not reported before, were found in the corrosion products. The so-called Fe3C* is a cementite with two forms: an alloyed cementite as (Fe,M)3C (M = Mn,Cr) and.or as Fe3-xC1+x, a cementite with more C atoms than interstitials. The Fe-C* carbide is possibly a small particle Fe-C phase also with two possible forms. Fe3C* and a little Fe-C* carbides were identified on the probes without Cr. FeCO3 and Fe-C carbide were identified on the probes with 1% Cr, FeCO3 being the more adhesive constituent firmly linked to the base metal. It was suggested that the alloying elements in the steel (Cr in this case), other than Fe2+ ion concentration and neutralizing agents in the solution, are responsible for the formation of FeCO3. The better performance of the 1% Crcontaining steel can be attributed to the presence of a protective film formed by a mixture of Fe-C* carbide and FeCO3.
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