A Comprehensive Study of Aluminum Anodization in Transition Modes.

Anodization is a method to fabricate a tunable nanoporosity and thickness of alumina coating. This research is devoted to large-area hard anodization (HA), ultrahard anodization (UHA), and transitional modes. The phenomenon and challenges of UHA and the transition from HA are studied on large-area samples using linear-sweep voltammetry. The findings indicate that a uniform large-area thick coating can be achieved by utilizing pre-UHA modes. The study's results indicate that UHA leads only to coatings with non-uniform thickness in large-area anodization. The peculiarities of pre-UHA are studied using different temperatures (0, 5, 10, and 15 °C) and processing times (1, 2, 4, 6, and 12 h) in a 0.3 M oxalic acid electrolyte. The current study shows the possibility for the fast growth of thick nanoporous alumina up to 235 ± 4 µm for only 12 h.