Mechanism of aluminum hydroxide layer formation by surface modification of aluminum

In this study, a new, relatively simple and rapid fabrication method for forming an Al(OH)3 film on Al substrates was demonstrated. This method, i.e., alkali surface modification, is simply comprised of dipping the substrate in a 5 × 10−3 M NaOH solution at 80 °C for 1 min and then immersing it in boiling water for 30 min. After alkali surface modification, an Al(OH)3 film was formed on Al substrate, and its chemical state and crystal structure were confirmed by XPS and TEM. The Al(OH)3 layer was composed of three regions: an amorphous-rich region, a region of mixed amorphous and crystal domains, and a crystalline-rich region near the Al(OH)3 layer surface.