Studying the fine microstructure of the passive film on nanocrystalline 304 stainless steel by EIS,

• 作 者: Z.J.Zbeng Y.Gao Y.Gui M.Zhu
• 机 构: School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641
• 出 处: 2014腐蚀电化学与测试方法专业委员会学术交流会
• 发表日期: 2014年3期

The fine microstrueture of the passive films on nanocrystalline (NC) and coarse crystalline (CC) 304 stainless steels (SSs) in 0.5 M H2SO4 were investigated by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM).The results indicate that the passive film on both CC and NC SSs exhibits a two-layer microstructure consisting of a compact inner layer and a porous outer layer as shown in Fig.1.Some hydrated compounds (HC) were present in the porous outer layer ofNC SS but not CC SS in 0.5 M H2SO4 solution.The pores in the outer layer of the NC SS were observed to be in the nanoscale by AFM as shown in Fig.2.HC filling of the pores in the passive film on NC SS may occur due to capillary forces endowed by the nanosize pores.XPS analysis of the passive films on both CC and NC SSs,however, doesnt show such a composition difference which is attributed to dehydration occurring in the XPS vacuum chamber.Both the inner and outer layers of the NC SS were determined by EIS analysis to be more compact and protective than the corresponding films on CC SS as evidenced by the lower Q value, higher n and much higher R value in the corresponding layer.