不锈钢点腐蚀发生的早期过程 Ⅰ. 扫描微参比电极法研究

本文应用扫描微参比电极联机测量系统对18-8型不锈钢在含Cl~-介质中点腐蚀发生的早期过程进行研究。结果表明, 在点腐蚀发生的早期阶段, 可用特征电位E_r表征表面钝化膜的局部破坏和微点腐蚀的发生, E_r电位与传统的E_P电位不同, E_r电位通常比E_p, 电位更负100—400 mV, E_r电位值与钝化膜的表面状态直接有关, 且随介质Cl~-浓度的增加和pH的降低而负移。在E_r电位附近, 微点腐蚀开始发生, 但一般不能稳定发展, 电位越接近于E_p, 则已发生的微点腐蚀越容易扩展为宏观点腐蚀, 由此, 作者提出“不稳定微点腐蚀”的新概念, 并对不锈钢点腐蚀发生的早期过程机理加以讨论。

INVESTIGATION OF THE PITTING CORROSION OF 18-8 STAINLESS STEEL IN EARLY STAGE I. BY USING THE SMRE TECHNIQUE

An improved scanning micro reference electrode (SMRE) technique controlled by micro-computer was used to study the pitting initiation in early stage of 18/8 stainless steel in chloride containning solution. It is shown that there exsists a critical potential E_r which characterizes the breakdown of passive film and initia- tion of the micropit corrosion in an early stage of pitting corrosion. The potential value of E_r is usually 100—400 mV less than the pitting potential E_p which corre- sponds to rapid increase of anodiccurrent in the polarization curve. The value of E_r is related closely to the surface states of specimens. On increasing the content of Cl~- and H~+ ions in solution, E_r will become more negative. when the potential is controlled in the vicinity of E_r, the micropit cannot grow to a macropit corrosion generally.The new concept of “unstable micropitting” was suggested and the physical significance of the characteristic potential of E_r and E_p was expounded according to the experimental facts. Furthermore, the mechanism of local breakdown of passive film and pitting initiation of 18/8 stainless steel in chloride containing solution was also discussed in this paper.