Kinetics of Anodic Oxidation of Aluminum and Titanium: Formation of Porous Alumina and Titanium Oxide Nanotube Layers

Abstract

Nanoporous oxide layers are produced by anodic oxidation of reactive metals in solutions where dissolution and oxidation occur concurrently. Significant research attention has focused on functional nanomaterials obtained from porous alumina and titanium oxide nanotube layers, which are produced by anodizing of aluminum and titanium, respectively. Despite the activity in this area, mechanistic understanding of self-organized porous oxide growth is not fully developed. The phenomenology and current understanding of both porous alumina and TiO2 nanotube layers are reviewed, to help elucidate whether the same conceptual framework might encompass both types of material. The following topics are included: experimental conditions necessary for porous layer formation, factors governing the porous layer geometry, porous alumina and TiO2 nanotube layer morphology evolution during anodizing, and mechanical aspects of anodizing, including contributions of elastic and plastic deformation. Finally, the present state of mechanistic understanding of porous alumina and TiO2 nanotube formation is described.