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Study on the mechanism of nucleation and development of porous nanostructure of anodic alumina films

G.Patermarakis

The growth of porous anodic alumina films in a single step anodising ofAl in sulphuric and oxalic acid electrolyteswas studied by chronopotentiometry and the surface of films and the imprint of films onAlmetal surface in steady state were examined by SEM. It was shown that at the initiation of steady state the outer thin surface layer consists of nanocrystallites. On prolonged anodising due to chemical dissolution of a thin surface layer they disappear and enlarged pore mouths and a relatively compact interpore material are exhibited while the porous layer with the characteristic columnar cellular hexagonal structure constantly develops in the metal|oxide interface region. These predict that the actual reason for the nucleation of pores in the flat barrier layer and their development to pockets and then to channel-like pores in the preceding transient stages is related with a nanocrystalline recrystallization / transformation and densification of oxide towards the surface of rare oxide formed in themetal|oxide interface and the base surface of developed pockets or pores.