不锈钢钝化膜形成和破坏过程的原位ECSTM研究

IN SITU ECSTM INVESTIGATION ON FORMATION AND BREAKDOWN OF PASSIVE FILM FOR POLYCRYSTALLINE STAINLESS STEEL

利用电化学扫描隧道显微镜（ＥＣＳＴＭ），原位研究不同电位下不锈钢在 ０．５Ｍ Ｈ２ＳＯ４十 ０．０２Ｍ ＮａＣｌ溶液中表面形貌的动态行为，并讨论电位对不锈钢电化学阻抗谱（ＥＩＳ）的影响 结果表明：不锈钢在活化－钝化过渡区电位表面粗糙度最大；进入钝化区后，在钝化膜完整处，电位越高，表面粗糙度越小，钝化膜呈有序生长， 在钝化膜薄弱处．电位控制在０．２Ｖ时，钝化膜最为完整 在０．５Ｖ时，表面微点蚀坑开始萌生，电位为０．８Ｖ时，已有的微点蚀坑有所生长，不锈钢表面ＥＣＳＴＭ形貌与电化学阻抗谱测量呈对应关系：电位为 ０．２Ｖ时，表面钝化膜最为完整，阻抗最大；电位为 ０．５Ｖ时，在钝化膜薄弱处萌生点蚀坑，钝化膜阻抗有所下降；电位为０．８Ｖ时，钝化膜完整处得到明显的整平，阻抗相比０．５Ｖ时明显提高，但由于已萌生的微点蚀坑开始生长，阻抗相比 ０．２ Ｖ时仍有所降低。

The dynamic behavior of surface topography for the stainless steel in 0.5M H2SO4+ 0.02M NaCl was traced in situ by electrochemical scanning tunneling microscope (ECSTM). The results showed a different response for the integrated passivated domain and pit-prone location on the surface when a given potentials was applied to the sample. The roughness parameter Sa for both domains appeared a maximum when controlled potential in the transition passivation region. In the potential region of passivation, passivated grains began to grow orderly on the integrated domain, and Sa decreased with increasing potential. While on the pit-prone domain, metastable micro-pits were observed when a passive potential was controlled at 0.5 V and 0.8 V. The impedance behaviors for steel sample in the different potential regions of passivation were examined by electrochemical impedance spectroscopy (EIS) and discussed based on the ECSTM results. At 0.2 V potential, the flawless surface showed the greatest impedance, and at 0.5 V, the impedance droped due to the initiation of metastable micro-pit. When controlled potential at 0.8 V, the surface roughness decreased considerably on the integrated domain, but the total impedance showed smaller resulted from the development of micro-pit in the preference location.