锈层对海水淡化一级反渗透产水中碳钢腐蚀行为的影响

采用扫描电镜(SEM)、红外光谱(IR)、X射线衍射(XRD)及电化学方法研究了碳钢在海水及海水淡化一级反渗透(RO)产水中锈层形态及其电化学特性.结果表明,碳钢在两种水体中形成的锈层在结构、成分及功能上具有显著差异,导致其腐蚀情况截然不同.海水淡化一级RO产水中,腐蚀产物γ-FeOOH的还原电位高于碳钢自腐蚀电位,易被还原成Fe3O4,使锈层形成Fe3O4内层及γ-FeOOH外层的双层结构.外锈层很薄,无阻碍氧扩散作用,且因γ-FeOOH的还原加快了腐蚀反应.Fe3O4内层具有良好导电性及Fe2+传递性,使氧还原反应从金属表面转移至内锈层表面进行;同时因其大阴极作用,显著促进了氧还原过程.由于锈层的上述作用,碳钢在一级RO产水中的腐蚀得到了极大加速,其腐蚀速率最终由溶液至内锈层之间的氧极限扩散电流密度决定.防腐方法应能抑制腐蚀产物γ-FeOOH的还原.

Effect of Rust Layer on the Corrosion Behavior of Carbon Steel in Reverse Osmosis Product Water

The morphologies and electrochemical characteristics of rust layers generated in seawater and reverse osmosis(RO)product water were investigated by scanning electron microscopy(SEM),infrared spectroscopy(IR),X-ray diffraction(XRD)and electrochemical tests.Experimental results revealed obvious differences in the components,structures and functions of rust layers in two types of solutions,so that the corrosion rates of carbon steel were markedly different.The reduction potential of γ-FeOOH is higher than the corrosion potential of carbon steel in RO product water,such thatγ-FeOOH is easily reduced to Fe 3 O 4 and two layers emerge in the rust structures.The outer layer(γ-FeOOH layer)is too thin to inhibit oxygen diffusion,and tends to accelerate the cathodic process via reduction ofγ-FeOOH.Because Fe 2+ and electrons can pass through the Fe 3 O 4 layer,oxygen can be directly reduced on the surface of the inner layer(Fe 3 O 4 layer).Therefore,the inner rust layer(Fe 3 O 4 layer)can provide a large cathode area on which to promote oxygen reduction.As a result,the corrosion process of carbon steel in RO product water can be accelerated greatly.The corrosion rate of carbon steel is determined by the limiting diffusion rate of oxygen from solution to the inner rust layer.Anti-corrosion measures should inhibit the reduction reaction ofγ-FeOOH.