Effects of the hydrogen content on the development of anodic aluminum oxide film on pure aluminum

In this study, high purity aluminum (Al) samples containing different levels of hydrogen were used as a base metal for anodization. To ensure constant current densities during the experiments, the voltage-time (V-t) curves were recorded. The differential ΔV/Δt curves were plotted and the energy consumed during different steps of anodization was calculated. Experimental observations show that differences in the hydrogen content affected the amount of energy consumed. The process was divided into three steps. When the voltage response at the end of step 2 exceeded 25 V, the energy consumed in steps 2 + 3 reached or exceeded 7.4 J/cm², and the pore channels branched or merged, creating a spike in the ΔV/Δt curves in step 3. A combination of the effects of the high voltage response at the end of step 2 and the high hydrogen content in the Al samples led to the formation of an anodic aluminum oxide (AAO) film in the sulfuric acid solution, which produced crystallized boehmite. This study proposes a unique tool for understanding certain special anodic behaviors of pure Al, wherein the branching or merging of pore channels and the partial crystallization of the AAO film can be ascertained by looking at the irregularities in the ΔV/Δt curves obtained in step 3.