孔蚀过程中电流噪声特征研究

A STUDY ON THE FEATURES OF CURRENT NOISES DURING PITTING CORROSION

研究了钝化的纯铁在含 Cl^-的中性溶液中及304和321不锈钢在含 Cl^-的硫酸溶液中在低于孔蚀电位的恒电位条件下电流噪声的特征。结果表明,噪声电流峰具有线性上升而后按指数规律衰减的特征。在一定条件下噪声电流上升到最大值所需时间ιc 大致恒定,但ιc 随电位的升高而增大。功率密度谱(SPD)曲线的截止频率都低于20Hz,表明孔核的发生、成长与再钝化过程是相当缓慢的过程。所有 SPD 曲线在极低频率下具有白噪声的特征,即功率密度的水平不随频率改变。随着频率的升高,SPD 曲线显示噪声转变为1/f^n 噪声。视腐蚀体系和控制的电位之不同,测得的表观 n 值在2～4之间。实验结果征实了前一篇文章中导出的 SPD 方程式[1]是适用的。讨论了表砚 n 值落在2～4之间的原因。

Investigations on the features of electrochemical noises during pitting corrosion of iron and two sorts of stainless steels were carried out under potentiostatic conditions.The results show that the fea- tures of the electrochemical noises from the fluctuation of current are common to all the systems studied,namely,the fluctuation spikes rise linearly and decay exponentially.Curves of spectral power density (SPD)for all the systems studied show that the electrochemical noises are low frequency 1/f^n noise and turn to“whitenoise”at very low frequencies.The estimated values of n lie between 2 and 4 depen- ding upon the nature of metals and the applied potential.The equation of SPD proposed in a previous paper is confirmed by the data in this work and the variation of the value of n is discussed based on this equation.