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在实验室模拟含SO_2体积分数分别为0.4×10~(-6)和1×10~(-6)的污染大气环境,研究20~#碳钢的腐蚀规律.借助金相显微镜(OM)、扫描电镜(SEM)观察表面腐蚀形貌,X射线衍射仪(XRD)分析腐蚀产物成分.结果表明,随SO_2含量增加,碳钢腐蚀加快.在两种大气环境中碳钢腐蚀432 h,前者分为2个阶段,均符合指数增长规律;后者分为3个阶段,分别符合指数增加、线性增加和指数衰减规律.在SO_2含量少的大气环境中,锈层较薄,在SO_2含量多的大气环境中,腐蚀产物层向外生长速度相对较慢,锈层较厚.具有丝状腐蚀特征,丝状腐蚀物在晶界和表面活性点上开始生长,然后沿着晶界和铁索体向内延伸,同时在丝状物上有胞状锈的生成.S主要集中在胞状物上,SO_2含量增加,胞状锈的生长速度加快.

Corrosion behavior of mild steel was studied in atmosphere containing 0.4×10~(-6) and 1×10~(-6) volunle fraction of SO_2 with indoor simulated test.Corrosion morphologies were investigated by means of optical microscope(OM)and scanning electron microscopy(SEM),meanwhile corrosion products were analyzed by X-ray diffraction(XRD).The results showed that the corrosion rate of mild steel increased with increasing SO_2 concentration.The atmospheric corrosion process of mild steel was divided into two stages in atmosphere containing 0.4×10~(-6) volume fraction of SO_2 which both agreed with exponential growth law.while in atmosphere containing 1×10~(-6) volume fraction of SO_2,it was divided into three stages which respectively followed exponential growth,linear growth and exponential decay law.It can be indicated from the observation of macroscopic surface that the growth rate of corrosion products was relatively quicker and the rust layer was thin in the condition of 0.4×10~(-6) volume fraction SO_2,while in atmosphere containing 1×10~(-6) volume fraction of SO_2,the rust layer grew outward slowly and the layer was thick.Atmospheric corrosion of mild steel had filiform corrosion characteristics in atmosphere containing SO_2,filiform corrosion products which initiated from grain boundaries and surface active area spread along the grain boundaries and ferrite.At the same time,cellular products grew on the filiform corrosion products.Sulfur mainly concentrated in the cellular products.Cellular products grew faster with the increasing content of SO_2.