Anodization of Aluminum in Highly Viscous Phosphoric Acid. PART 2: Investigation of Anodic Oxide Formation and Dissolution Rates

摘要

A novel self-sticking adhesive tape for the local anodization of aluminum that can be removed withoutresidue after anodization was developed. The extremely high viscosity of the electrolyte used in theanodization tape is the main difference to conventional bath anodization in aqueous phosphoric acid.Through the application of a step-like voltage program with abrupt changes in the anodization voltage,sublayers within the porous part of the anodic oxide were formed and then examined usingtransmission electron microscopy (TEM). The sublayers enable an estimation of the oxide formationand dissolution rates of bath and tape anodization. Both rates depend on the anodization voltage. At thebeginning of the anodization process, the oxide formation rates for bath anodization and tapeanodization were very similar. At a voltage of 25 V, a formation rate of 0.9 nm s-1 was obtained forbath anodization, compared to 0.8 nm s-1 for tape anodization. However, the formation rate for theanodization tape slows down considerably in the later stages of anodization. This effect, which was notfound for bath anodization, can be attributed to a local aging of the highly viscous electrolyte used forthe anodization tape. Another special feature of the anodization tape is a very low rate of chemicaloxide dissolution (≤ 0.04 nm s-1). In contrast, dissolution rates in the range of 0.1 to ≥ 0.2 nm s-1 werefound for bath anodization, which are typical for strongly dissolving electrolytes such as phosphoricacid.