Porous anodic aluminum oxide: anodization and templated synthesis of functional nanostructures.

The formation kinetics and electric properties of anodic barrier oxides on Al, Hf, Nb, Ta, Ti, and Zr depend on the migration of ions, controlled by an electric field strength of up to 107 V cm−1. The high field model, based on ideas of Guntherschulze, Betz, Verwey, Mott, and Cabrera, explains only parts of the experiments. Contradictory models and investigations of the last 60 years are compared with new results, which enable a more detailed understanding of many aspects of the high field model, e.g. the shape of experimental transients, the time and field dependent concentration of mobile ions, the nature of the mobile species and the interaction of anion and cation transport, and the location of the rate determining step.

Thin anodic oxide layers on aluminium and other valve metals: high field regime

Digital video imaging of the plasma electrolytic oxidation (PEO) of aluminium has been performed, which allowed evaluation of both dimensional characteristics of individual microdischarges appearing at the oxide–electrolyte interface and their collective behaviour throughout the oxidation process. It has been shown that the microdischarge cross-sectional dimensions vary within the range 0.01–1.35 mm2. In the course of PEO processing, small localized events (<0.03 mm3) always dominate in the microdischarge spatial distribution and the relative proportion of medium-sized to very large microdischarges is gradually redistributed in favour of the latter. Temporal dependences have been found for the fraction of surface area instantaneously experiencing the discharge, as well as for the spatial and current densities of the microdischarge. Discharge mechanisms occurring during PEO are discussed and a model of microdischarge formation is suggested, assuming the possibility of free-electron generation and glow discharge ignition in the gaseous media developed at the oxide–electrolyte interface. First approximation evaluations of thermal processes in the oxide layer under the discharge conditions have been considered. The estimated ranges of the microdischarge current density (50–18 kA m−2) and duration (0.25–3.5 ms) sufficient for initiating phase transitions (e.g. γ–α transformation and melting) in the surface oxide layer are shown to be in good agreement with experimental data.

https://iopscience.iop.org/article/10.1088/0022-3727/36/17/314/pdf

Discharge characterization in plasma electrolytic oxidation of aluminium

The review describes recent progress on understanding and quantification of the various phenomena that take place during plasma electrolytic oxidation, which is in increasing industrial use for pro...

https://www.tandfonline.com/doi/pdf/10.1080/09506608.2018.1466492

M. Machkova

Papers

Electrical breaking down of barrier anodic films during their formation

Post-breakdown anodization of aluminium

Pore filling and attendant breakdown of thick anodic films on aluminium

Breakdown phenomena during the pore filling of anodic oxide films on aluminium

Galvanoluminescence during the pore-filling of anodic films on aluminum formed in sulphuric acid