Growth Mechanism of Porous Anodic Films on Aluminium

Abstract

Fundamental research on the growth of porous anodic alumina (PAA) films has been undertaken for many years because of the complexity of the processes involved and the wide range of commercial applications. In this study, a tungsten tracer approach has been used to determine the influences of current density and electrolyte temperature on the incorporation of the tracer and its distribution and consequently, the growth mechanisms of PAA films.The efficiencies of growth of PAA films, formed during anodizing at 5 mA cm-2 in the three major forming acids at 25 °C, are ~60%, due to loss of outwardly migrating Al3+ ions at the film/electrolyte interface. Thus, only the inwardly migrating O2- ions contribute to formation of the anodic oxide at the film/metal interface. The pores are developed due to flow of alumina from beneath the pore base regions toward the cell walls, which is indicated by distortion of the incorporated Al-W alloy layers and retention of the tungsten species within the anodic films.PAA films formed at a low range of current densities (

Date of Award	1 Aug 2011
Original language	English
Awarding Institution	The University of Manchester
Supervisor	George Thompson (Supervisor)