PROPERTIES OF SURFACE FILM FORMED ON X70 PIPELINE STEEL IN HCO3^-/CO3^2- ENVIRONMENT
X70管线钢在HCO-3/CO2-3体系中表面膜性能研究

The electrochemical behavior of X70 pipeline steel in 0.5 mol/LNa_2CO_3+1 mol/LNaHCO_3 solution has been studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods.X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to examine the composition and morphologies of the surface film.The results showed that there were two anodic peaks appeared at -600 mV and -350 mV respectively in the process of anodic polarization.For the surface film formed at -600 mV,the reaction resistance of electrode surface was small,it was mainly consisted of FeCO_3?Fe_2(OH)_2CO_3 and FeOOH.There were many hollows and microcracks existed in the film.The film was metastable and poorly protective.For the film formed at -350 mV,the reaction resistance of electrode surface was big,it was mainly consisted of Fe_2O_3 and Fe_3O_4 and it has good protectiveness.