Author(s)

M.C. Sainte Catherine & N. Celati

Abstract

The transmission electron microscopy study of alumina films formed by anodization of aluminium in chromic bath is reported. The amorphous alumina coating has a duplex microstructure (thick irregular branching porous layer and thin barrier layer). The porous layer morphology depends on the substrate structure (tubular for commercially pure aluminium, irregular branching for aluminium alloys). During the sealing process, the hydration of alumina produces a thickness increase of the pore walls. Then, the wall irregularites induce the formation of bumps leading to a cellular structure of the hydration product which plugs the pores. 1 Introduction Porous anodic films obtained on a

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