Factors affecting pore length during anodizing of aluminum in phosphoric acid electrolytes

This paper focuses on the factors influencing the growth of the main pore of porous anodic aluminum (PAA) and verifies whether the field-assisted dissolution rate is equal to the oxide growth rate. Constant-current anodization and constant-voltage anodization of aluminum were carried out in three different electrolytes (with different concentrations of polyethylene glycol). The lengths of the main pores of PAA in the three electrolytes were compared. It was found that the growth rate of the PAA main pore (∼93 nm/min) was much larger than the chemical dissolution rate of the electrolyte (less than ∼15.6 nm/min), which first proved that the length of the PAA main pore was independent of the field-assisted dissolution. Meanwhile, it was found that the PAA main pore was almost linearly correlated with the magnitude of the anodizing current and electric charge. Finally, the three stages of the current-time curves were clarified in the light of the theories of the electronic current, the oxygen bubble mold and viscous flow model. • Influencing factor of main channels in porous anodic alumina (PAA) were investigated. • Channel depth of PAA is determined by the current rather than the dissolution rate. • Growth rate of main channels depends on the current density of anodizing. • The chemical dissolution or field-assisted dissolution on the channel growth is weak. • The applied voltage determines the critical electric field and anodizing current.