In situ synchrotron X-ray diffraction study of scale formation during CO2 corrosion of carbon steel in sodium and magnesium chloride solutions

In situ synchrotron X-ray diffraction was used to follow the formation of corrosion products on carbon steel in CO2 saturated NaCl solution and mixed NaCl/magnesium chloride (MgCl2) at 80 degrees C. Siderite (FeCO3) was the only phase formed in NaCl solution, while Fe(OH)(2)CO3 was also detected when MgCl2 was present. The proposed model is that siderite precipitation, occurring once the critical supersaturation was exceeded within a defined boundary layer, caused local acidification which accelerated the anodic dissolution of iron. The current fell once a complete surface scale was formed. It is suggested that MgCl2 addition decreased the required critical supersaturation for precipitation. (C) 2011 Elsevier Ltd. All rights reserved.