Studies On Formation Mechanism Of Porous Anodic Alumina Membrane

Two forms of anodic aluminum oxide (AAO) film exist by anodization ofaluminum, barrier anodic alumina membrane (BAAM) and porous anodic aluminamembrane (PAAM). The formation mechanism of PAAM has been studied extensivelyover the last five decades. Traditional theory claims that the main reason for theformation of pores and development of channels is acidic electricfield-assisteddissolution, but it can not give a reasonable explanation for the structure of hexagonalprisms and hemispherical bottom of the pores in PAAM. Generally speaking, BAAMforms in neutral electrolyte. According to the traditional theory, PAAM forms in acidicelectrolyte and its growth mechanism is independent of that of BAAM. There are twointerfaces in aluminum anodization system, i.e. electrolyte/oxide (E/Oxide) interfaceand oxide/Al interface. Traditional theory presumes that BAAM grows simultaneouslyat the two interfaces, while PAAM forms only at oxide/Al interface and its pore growsthrough acidic electricfield-assisted dissolution existing at E/Oxide interface.Here we present a systematic study about growth mechanism of AAO, consideringthat the formation of PAAM inevitably has relationship with BAAM and they cantransform with each other under certain condition. First we study the BAAM andPAAM formation in typical BAAM and PAAM type electrolytes respectively. Then weconclude the differences and relations between them. Finally, we mixed the twoelectrolytes theoretically. From anodization in this mixed electrolyte, we find porechannels similar to PAAM in BAAM. Also we can get whole BAAM in typical PAAMtype electrolyte. Thus, we find the inherent relations between BAAM and PAAMthrough experimental proofs. Based on this result, we present new growth model andformation mechanism of PAAM and put forward that oxygen bubble mould effect(OBME) results in the regular channels of PAAM. We revise traditional theory aboutthe formation of pores by acidic electricfield-assisted dissolution. We also give a newexplanation for the V-t curve of anodization; reasonably prove the structure ofhexagonal prisms cell and hemispherical bottom of channels which can not explainedby traditional theory and gain relevant experimental proofs in PAAM; investigate thenature of self-organization of PAAM which is a popular subject in the world wide fieldfor recent years. Finally, in order to demonstrating the OBME, we do a series ofexperiments in various pressures. We can prove that OBME reduces through adding suitable deoxidizer to absorb oxygen.OBME referred in this article must have profound effect on the study of mechanismsof the other porous anodic oxide such as SiO₂, TiO₂, Ta₂O₅ and SnO₂. In PAAM, wefind sectional channels which have latent applied value. This can also provide academicbasic for the research of new PAA nanotemplate and nanofunctional materials.