Structural study of anodic films formed on aluminum in nitric acid electrolyte

The paper presents the results of investigations of porous Al anodic films formed in HNO3 electrolytes carried out by means of electrochemical techniques and X-ray diffraction as well as scanning electron microscopy (SEM). It was assumed that both electrochemical formation of a porous oxide and anodic dissolution of metal take place at Al/oxide interface at the same time. The analysis of short-range order (SRO) parameters for relatively high current density, 1 X 10(3) A/m(2), and anodizing time, 10 min, leads to the conclusion that films mainly consist of amorphous alumina with gamma'-Al2O3-like SRO and a small amount ( similar to 10%) of amorphous aluminum oxyhydroxide. SEM investigation of the films revealed strong dependence of the surface relief on different applied forming conditions. This marked change in the surface relief is discussed taking into account the relatively complex behavior of Al during anodization in HNO3 electrolytes, that involves both electrochemical growth and dissolution processes of anodic film associated with an electrochemical dissolution of aluminum substrate. (C) 2002 Elsevier Science B.V. All lights reserved.