MoO_4^(2-)抑制AISI304不锈钢局部腐蚀的机理

MECHANISM OF MoO_4~2- RETARDING THEDEVELOPMENT OF THE LOCAL CORROSION IN304 STAINLESS STEEL/Cl^- SOLUTION

采用X射线光电子能谱（XPS）研究了AISI304不锈钢在含（MoO42-+Cl-）的模拟闭塞电池中形成钝化膜的组成与结构及MoO42-抑制局部腐蚀的机理.结果表明:在闭塞区内AISI304不锈钢表面钝化膜的外层主要有MoO42-、CrO3、CrCl3、CrOOH、Fe2O3、γ-FeOOH、Fe（OH）3、CrO42-、Cr（OH）3、NiCl2、FeCl2和FeCl3、溅射5min时膜内层主要有 MOCl3、CrO2、FeCl2、FeCl3以及少量的FeO.MoO42-对钝化膜的影响在于:MoO42-迁入闭塞区后吸附在金属表面上,可取代或部分取代吸附在钢表面的Cl-,并与Fe2+在蚀孔内反应生成不容性的FeMoO4而沉积到蚀孔壁上,有助于蚀孔的再钝化,从而抑制腐蚀的进一步扩展;MoO42-的吸附能使水合氧化亚铁沉淀膜由阴离子选择性变为阳离子选择性,使H+可以从膜下扩散出去,而Cl-难以扩散到膜下富集,从而使MoO42-具有缓蚀作用。

XPS analysis was used to study the composition and structure of passive film of 304 stainless steel in Simulated Occluded Corrosion Cell (SOCC) containing MoO42- + Cl- and the retarding function and inhibiting effect of MoO42- to local corrosion. The effect of MoO42- to passive film is, that MoO42- was absorbed in the surface of metal when it migrated into Occluded Corrosion Cell (OCC) to replace or partly replace Cl- absorbing in the surface of steel, and to react with Fe2+ producing dissolved FeMoO4 depositing in corrosive hole, contributing to repassive of corrosive hole, and retarding propagation of corrosion; The absorption of MoO42- resulted in transform of the hydrate ferrous oxide deposition film from anions selection to cation selection and diffusion of H+ out from film, and it is difficult to diffuse for Cl- into film to rich, so MoO42- had inhibiting function.