金属表面多孔膜的保护作用与介质组分的关系

CORRELATION OF CORROSION PROTECTION OF POROUS MEMBRANE ON METAL SURFACE WITH ELECTROLYTES IN SOLUTION

研究了铝阳极氧化多孔膜层界面电性能与溶液介质组分的关系。多孔膜在介质中存在一等电点pHIEP,当溶液pH <pHIEP时 ,膜荷正电具有阴离子选择性 ;pH >pHIEP时 ,膜荷负电具有阳离子选择性。介质中的一些组分可通过与膜孔表面的相互作用改变膜的pHIEP,从而改变膜的荷电性能和离子选择性 ,但对膜内离子的迁移无明显影响。若由介质进入多孔膜的物质在膜内生成难溶盐或沉积物而堵塞膜孔 ,离子在膜内的迁移阻力将增大 ,多孔膜因其离子导电率减小而提高对基底金属的保护能力。

The relationship between the electrolytic composition and the interfacial electric characteristics of the porous membrane of anodized aluminum was investigated.The pH_IEP at isoelectric point of the porous membrane was equal to 9.20 in 1.0×10-2mol/L KCl solution.Pretreatment of the porous membranewas equal to 9.20 in 1.0×10-2mol/L KCl solution. Pretreatment of the porous membrane with F-,PO_43-,SiO_32-,S_2O_32-and tannic acid shifted the pH_IEP to 3.40,3.30,4.30,4.50 and 3.90, respectively. The change state and ionic selectivity of the membrane could be characterized by the place of its pH_IEP relative to pH_sol in solution.The membrane was positively changed and selectively permeable to anions when pH_sol<pH_IEP, and vice versa. The pH_IEP, thus the membrane charge state and ion selectivity, could be changed by the interaction between the electrolytic component and the surface of the membrane pores. However, no obvious effect on ion transportation in the membrane was detected. If the particles from the electrolyte could form insoluble salts or precipitate in the membrane, the pores would be sealed and the ion transport resistance of the membrane would be increased. Such a porous membrane could provide effective protection to the substrate metal.