Abstract
The growth of barrier-type anodic films on aluminium and its alloys is reviewed, with particular consideration of ionic transport processes in the growing anodic films. The films formed are generally amorphous, and grow both at the film/electrolyte interface by outwards migration of cations and at the metal/film interface by inwards migration of ani-ons. Various types of foreign species are incorporated into the anodic films from electrolytes or alloy substrates. The in-corporated species are mobile inwards, or outwards or immobile under the high electric field of 106-107 V cm-2. This provides us with some important information on the complex ionic transport processes in amorphous anodic films. The anodic films formed on uniform Al-valve metal alloys are generally of two layers, due to the different migration rates of A13+ ions and valve metal ions. The properties and growth behavior of the films vary almost linearly with film composi-tion.
