FeCO3 layer evolution for API 5L X52 steel in carbon dioxide-saturated NaCl brine in the presence of 1-decyl-3-methylimidazolium chloride

• Interfacial evolution for steel/CO2-brine with imidazolium ionic liquid was studied.
• Impedance spectrum was used to characterize FeCO3 layering process.
• Imidazolium ionic liquid slowed down the formation of FeCO3 layer.
• Two models based on impedance data accounted for the experimental findings.

The FeCO3 layer evolution process for API 5L X52 carbon steel in CO2-saturated NaCl brine in the presence of 1-decyl-3-methylimidazolium chloride ionic liquid was characterized using electrochemical techniques. Four layer-formation stages were described: active-adsorption, porous layer, compact layer-formation, and the compact layer state. The ionic liquid slowed the layering process by influencing both crystal precipitation and structural changes. Two models were developed to account for the interfacial evolution: the first model considered the balance of positive and negative charges at the interface of the metal and electrolyte in blank solution, while the second one considered the layer coverage and evolution with the imidazolium compound.