RESUMEN
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 time-dependent carbon steel corrosion and film formation at geothermally relevant temperatures (80-160⯰C) in CO2-saturated mildly acidic NaCl 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 24â¯h) generate H2 at a minimum rate of 12⯵molâ¯h-1â¯cm-2 and lead to the formation of a continuous ~100⯵m 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.