Corrosion is a major obstacle to a safe implementation of geotechnical applications. Using a novel approach that includes vertical scanning interferometry (VSI) and electrochemical impedance spectroscopy (EIS) we discuss timedependent carbon steel corrosion and film formation at geothermally relevant temperatures (80-160°C) in CO2saturated mildly acidic Na-Cl brine. Iron dissolution kinetics follows a logarithmic rate at 80 and 160°C and a linear rate at 120°C. At 80°C, high initial corrosion rates (first 24 hours) generate H2 at a minimum rate of 12 µmol h-1 cm-2 and lead to the formation of a continuous ~100 µm thick porous corrosion film. It exhibits a duplex structure with a crystalline outer FeCO3 layer and an inner layer composed of a skeletal network of Fe3C impregnated with FeCO3. Being an electrical conductor we hypothesize the Fe3C to strongly enhance corrosion rates by providing additional cathodic sites. Pseudo-passivity due to an anodic film-forming reaction (presumably Fe-oxide) was observed at 120 and 160°C, soon followed by the initiation of pitting at 120°C. Steady-state corrosion rates at 160°C are at least one order of magnitude lower than for 120°C. Our experimental approach demonstrated potential for general applicability in studying corrosion-related phenomena.
We discuss kinetic and thermodynamic aspects of carbon steel corrosion in CO 2 -containing NaCl fluids up to 240°C. Crystalline nm-thick Fe-oxide films only form at 160°C and 240°C providing instantaneous and moderate corrosion protection. The absence of Fe-oxide at 80°C results in high initial corrosion rates until a moderately protective, but thick and porous, FeCO 3 film forms. From the metal/film interface it grows inwards by replacing ferrite with FeCO 3 . TEM reveals a precursory, likely hydrated and chloride-containing, phase that predates FeCO 3 formation. Thermodynamic predictions agree well with experimental results in that Fe-oxide formation is favored over FeCO 3 towards higher temperatures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.