XPS analysis of CO2 corrosion product scales on P110 steel

In order to confirm the composition of CO_2 corrosion product scale and the difference of both component and the content(between) various layers of the scale,autoclave was employed to prepare the scales on P110 steel exposed to carbon dioxide corrosion.The surface and cross-section morphology were observed with scanning electron microscope(SEM),and the difference between surface and inner in chemical composition was analyzed with X-ray photoelectron spectroscopy(XPS) and X-ray diffraction(XRD) used adjectively.The results show that the cross-section of the corrosion product scales of P110 steel is with double-layer structure,and there are mainly FeCO_3 and a little of CaCO_3 with ferreous oxides in two layers structure of the scale.The amount of CaCO_3 in surface layer is less than one in inner layer,but the oxides are slight more than that in inner layer including a little intermixtures of Fe and Fe_3C.It is concluded from the difference of Ca~(2+) ion between the surface and the inner that the inner corrosion scale produces first on P110 steel in corrosion process.