On the Prediction of Well-Ordered Porous Anodic Alumina Films
2020
Heinschke, Silvio | Schneider, Jörg J.
Porous hexagonal ordered anodic alumina (PAOX) is a long-known porous oxide material. Despite its straightforward experimental approach, a precise understanding of the microscopic processes that lead to the formation of the material and the hexagonal arrangement is only possible with the help of various theoretical models. To the best of our knowledge, there is no model that establishes a theoretical connection between the long-range order of the PAOX system and its physicochemical properties. Therefore, we present in this paper the derivation of a known key figure (“porosity number”), which makes a statement about the pore arrangement with the highest symmetry. By combining this key figure with the abstract concept of entropy production, we enable the microscopic approach to be combined with macroscopic bulk parameters. The theory is based on the most realistic assumption, that the pore habitus can be described based on the inner and outer pore volume of the PAOX cells. Herein, the former is characterized by an ion flow toward the anode and the latter by a flow toward the electrolyte bulk. In addition, the parameters required to describe PAOX growth are reduced to a minimum by showing that within our theoretical model, the growth is only controlled by migration-dependent parameters and that convection and diffusion terms are negligible.
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