磷钼酸在酯化反应体系中对316不锈钢的腐蚀抑制机理

Mechanism of corrosion inhibition of 316 stainless steel in esterification reaction by molybdophosphoric acid

采用扫描电子显微镜(SEM)和X射线光电子能谱(XPS)研究了模拟醋酸丁酯反应(CH3COOH、H2SO4、H3PMo12O40,105℃)条件下316不锈钢(316SS)的表面形貌和元素组成。结果表明,磷钼酸经物理吸附在不锈钢表面形成保护层,并发生氧化还原反应,生成的水合物、氧化物、难溶盐类沉积在不锈钢表面,形成致密的钝化膜,从而抑制316SS的局部腐蚀,阻止点蚀的扩散和蔓延,PMo12O430-、MoO42-和CrO42-使钝化膜表层具有阳离子选择性,能阻挡SO24-通过该膜到达金属表面,膜内层结晶态氧化物具有阴离子选择性,阻止基体金属离子穿过钝化膜而溶解,从而抑制局部腐蚀的进一步扩展。

The surface morphology and elemental composition of 316 stainless steel （316 SS） exposed in the solution consisting of acetic acid （HAc）,sulfuric acid,butyl acetate,and water with or without molybdophosphoric acid （HPMo） at 105℃ were investigated by using scanning electron microscopy （SEM） and X-ray photoelectron spectroscopy （XPS）.The nature of passive film forming and mechanism of corrosion inhibiting were discussed.The results showed that HPMo by means of physical absorption formed a protective layer on the surface of 316 SS,where redox reaction took place.The reaction products of hydrates,oxides,and insoluble salts deposited on the surface of 316 SS and constituted a compact protective passive film,which covered the surface active sites and retarded expanding of local corrosion and pitting.According to the bipolar model,a bipolar film consisted of a cation selective outer layer containing PMo12O3-40,MoO2-4,and CrO2-4 and an anion selectivity inner layer containing oxides.Aggressive anion SO2-4 from the solution was difficult to diffuse into the passive film,and cation from base metal was prevented from migrating into the solution.Therefore,the local corrosion was further inhibited.