Abstract: The passive behavior and electrochemical characterization of the passive films formed on X80 and X70 pipeline steels in 0.5 mol/L NaHCO₃ solution were discussed by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and capacitance measurements. It is show that X80 and X70 pipeline steels present a wide passive anodic region (-0.16~0.90 V), the passive current density (ip) of X80 and X70 steels are 6.76 μA/cm² and 18.38 μA/cm², respectively. EIS results indicate that the surface of the passive film formed on X80 steel is much denser and uniformer than that of X70, and the result is also show by AFM. Mott-Schottky analyses displayed that the passive films on X80 and X70 pipeline steels in 0.5 mol/L NaHCO₃ exhibit n-type semiconductive characters in the potential region of -0.20 V to 0.80 V. Compared with the passive film of X70 steel, the donor density is much lower and the width of space charge layer is thicker for the passive film of X80 steel, so the corrosion resistance of the latter is better.

Key words: X80 pipeline steel   ,   , Passive films  ,   ,  Mott-Schottky plots  ,  ,  Corrosion resistance

摘要： 采用动电位极化、交流阻抗和电容测量等方法研究了X80和X70管线钢在0.5mol/LNaHCO3 溶液
中的活化-钝化行为及生成的钝化膜的电化学性能。极化曲线表明,X80和X70钢在-0.16 ~ 0.90V 发生了钝
化,X70钢的维钝电流密度(ip)约为18.38μA/cm²,而X80钢的维钝电流密度约为6.76μA/cm ²。交流阻抗表明,
X80钢表面生成的钝化膜比X70钢的更加致密,均匀性更好,与原子力显微镜(AFM)的观察结果相吻合。电容测量
表明,X80和X70钢在该溶液中表面生成的钝化膜在-0.20~0.80V为n型半导体,且X80钢比X70钢表面钝化膜
的施主密度更低,空间电荷层更厚,耐蚀性更好。

关键词: X80管线钢   , 钝化膜  ,  Mott-Schottky曲线  ,   , 耐蚀性