304不锈钢点蚀的电化学噪声特征

使用电化学噪声技术,通过长期连续实时监测,对304不锈钢在0.5 mol/L FeCl3溶液中发生局部腐蚀的点蚀发展过程和腐蚀机理进行研究。综合谱图分析、时域统计分析,小波分析等诸多方法进行分析和论证。结果表明:电化学噪声的谱图可以明显地分为4个阶段,分别对应于点蚀发展过程中的钝态期、亚稳态点蚀期、稳态点蚀期及稳态点蚀后期。在时域分析时,先用3阶多项式拟合移除漂移,电流噪声标准偏差Si在亚稳蚀和稳态点蚀阶段发生明显的升高,噪声电阻(R_n)、点蚀指标(PI)在对应时间点表现出相应的降低或升高。小波分析表明,随着反应的进行,能量积累开始逐步增大;亚稳态点蚀期能量开始向d4～d6处累积,当进一步发展为稳态点蚀时d5～d8出现极大值。

ELECTROCHEMICAL NOISE ANALYSIS OF 304 STAINLESS STEEL PITTING CORROSION IN FERRIC CHLORIDE SOLUTION

The localized corrosion behavior of 304 stainless steel immersed in 0.5 mol/L FeCl₃ solution was investigated for a long-term monitoring as long as 350 h by electrochemical noise（EN） technique.The EN data was analyzed mainly by spectrum analysis,time-domain statistical analysis and wavelet transform.The whole process can be divided into four parts,which can be differentiated clearly according to the characteristic EN transient peaks.The variations of current standard deviation,R_n and PI during the whole monitoring period all give the coincident result.The 3D energy distribution plots（EDP） give the energy contribution of each detail crystals during the whole monitoring time.The figure which only concerns contribution of detail crystals shows that,the energy accumulation in band d4～d6 increases with the metastable pits occurrence.And as this process stepped into stable pitting stage,a max of the energy contribution occurs during the band d5～d8.