Influence Of Zn²⁺ On Semi-conductivity Of Passive Films Of Stainless Steel

Stainless steel is one of the main construction materials of the nuclear reactor. The Zn2+ injection technique is used to inject Zn2+ into the first loop of the reactors in many countries to prevent the corrosion of metal materials. This article aims to study the influence of Zn2+ on the semi-conductor properties of passive films of the stainless steel and tries to explain why it reduces the corrosion. The Mott-Schottky curve and electrochemical impedance of 304 stainless steel are measured after immersed in the Na2SO4 and ZnSO4 solutions under the temperature of 50℃,99℃and 280℃.The semi-conductivity of passive films of 304 stainless steel formed in a series concentration of ZnSO4 solutions under a series temperature is studied through the electrochemical measurement. At the same time, the factors that affect the semi-conductivity of the passive films are discussed. It is indicated that within the experimental range, the passive films show semiconductor property. The impurity concentration of 280℃is the lowest and declines along with the concentration of Zn2+. Compared to the flat electric potential under lower temperature, it moves to the lower value under the higher temperature and moves with the increase of the concentration of Zn2+. The equivalent circuit R(Q(R(QR)))is adopted under 50℃and 99℃, while R(C(R(QR)))is adopted under 280℃.