Acta Phys. -Chim. Sin. ›› 2014, Vol. 30 ›› Issue (8): 1465-1473.doi: 10.3866/PKU.WHXB201405211

• ELECTROCHEMISTRY AND NEW ENERGY • Previous Articles     Next Articles

AMechanistic Study on Semiconductivity Conversion of Passive Films under Varying Sulfate to Chloride Concentration Ratios

XIA Da-Hai1,2,3, YANG Li-Xia3,4   

  1. 1. School of Materials Science and Engineering, Tianjin University, Tianjin 300072, P. R. China;
    2. Tianjin Key Laboratory of Composite and Functional Materials, Tianjin University, Tianjin 300072, P. R. China;
    3. Department of Chemical and Materials Engineering, University of Alberta, Edmonton T6G 2V4, Alberta, Canada;
    4. Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074, P. R. China
  • Received:2014-04-16 Revised:2014-05-20 Published:2014-07-18
  • Contact: XIA Da-Hai, YANG Li-Xia E-mail:dahaixia@yeah.net;yanglx2000@gmail.com
  • Supported by:

    The project was supported by the Foundation of the China Scholarship Council.

Abstract:

Alloy 800 is an important steamgenerator material used in nuclear power plants, and so there is significant interest in the properties of passive films of this alloy under service conditions. In this work, the semiconductivity of Alloy 800 in sulfate and chloride solutions was investigated using Mott-Schottky analysis, electrochemistry impedance spectroscopy (EIS), scanning electron microscopy (SEM), and scanning electrochemical microscopy (SECM). The Mott-Schottky results show that the semiconductivity is affected by the sulfate to chloride concentration ratio; p-type semiconductivity is exhibited at high concentration ratios but transitions to n-type when the concentration ratio is low. EIS, SEM, and SECM results indicate that the degradation formof the passive filmchanges fromtranspassive dissolution to pitting as the concentration ratio decreases while the film's surface reactivity increases, an effect that is related to the semiconductivity conversion. The observed variation in semiconductivity results fromthe competitive adsorption of sulfate and chloride, a process that modifies the potential drop at the film/solution interface, changes the vacancy types and ultimately determines the semiconductivity.

Key words: Passive film, Alloy 800, Semiconductivity, Sulfate ion, Chloride ion

MSC2000: 

  • O646