The Pourbaix diagrams for an Fe-CO2-H2O system at elevated temperatures were constructed using thermodynamic theory and data and then correlated with observed CO2 corrosion phenomena of mild steel up to 250°C. In the range 80-150°C corrosion product layer formed and the surface analysis showed a mixture of crystal morphologies on the steel surfaces, for experiments lasting 4 days. Kinetic studies conducted at 120°C show full transformation from plate-like to oblong prismatic crystals over 30 days. No obvious crystal morphology was identified on the surfaces of samples studied at 200°C and 250°C. XRD analysis indicates that FeCO3 and Fe2(OH)2CO3 formed on the steel surface at 80-150°C. At 200-250°C, the corrosion product was exclusively Fe3O4. With surface pH consideration, the generated Pourbaix diagrams were validated by the experimental results. Maximum weight loss corrosion rates were observed at 120°C.

Subject
Scanning electron microscopy, X-ray diffraction, Steel surfaces, Thermodynamics, Corrosion rate, Electrochemical reactions, Iron, Pourbaix diagrams, Acidity, Corrosion products, Constants, Steel, Chemical reactions
Keywords:
Pourbaix diagram, CO2 corrosion, elevated temperature, mild steel
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2012
Association for Materials Protection and Performance (AMPP)
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