碳钢在NaCl薄液膜下的电化学腐蚀行为

Electrochemical Corrosion Behavior of Carbon Steel under Thin Electrolyte Layer Containing NaCl

在自建大气腐蚀薄液膜电化学测试装置上,采用极化曲线及电化学阻抗谱研究了碳钢在NaCl薄液膜下的腐蚀电化学特征。结果表明,液膜厚度较大时,氧扩散困难,腐蚀速率较慢;随着液膜厚度的减小,氧和腐蚀产物的扩散都相对容易,腐蚀速率增加。液膜厚度为350μm时,腐蚀电流密度和极限扩散电流密度最大,腐蚀速率最大。液膜厚度继续减薄,阳极过程受到抑制,腐蚀速率减小。碳钢在350μm NaCl薄液膜下腐蚀初期阻抗谱由一个高频容抗弧和一个低频扩散阻抗组成,继续腐蚀阻抗谱由一个高频容抗弧和一个低频容抗弧组成,均表现为两个时间常数。由于Cl-的强侵蚀性破坏和疏松多孔的腐蚀产物的生成,Rct不断减小,腐蚀速率增加。

The self-built electrochemical measurement system of thin electrolyte layer was utilized to investigate the electrochemical characteristics of carbon steel corrosion under thin electrolyte layer containing Cl-by means of polarization curves and electrochemical impedance spectroscopy.In the case of a thicker electrolyte layer,a slower corrosion rate can be observed due to the difficult oxygen diffusion.With the thinning of electrolyte layer,the diffusion of oxygen and corrosion products becomes relatively easy,which promotes the corrosion process.The corrosion current density and limiting diffusion current density reach the maximum value at 350μm in layer thickness, which reveals the easiest corrosion tendency and the biggest corrosion rate.As the thickness of the electrolyte layer is reduced,the anodic process is inhibited and the corrosion rate slows down.The Nyquist curves for initial corrosion process consists of capacity reactance arc at high frequency and diffusion impedance at low frequency.As corrosion continues,the Nyquist curve comprises capacity reactance arc at high frequency and capacity reactance arc at low frequency,and all show two time constants.Electron transfer resistance decreases,suggesting the increase of corrosion rate with corrosion time,which results from the strong attack of chloride ion and the formation of loose and porous corrosion products.