Effect of Etch Conditions on Expanding Surface Corrosion of Anodic Foil for Aluminum Electrolytic Capacitors

Porous aluminum with high surface area for aluminum electrolytic capacitors was obtained by etching aluminum foils in hot hydrochloric acid solution under direct current (DC). Careful etching procedure produced parallel tunnels, in which numerous (100) faces was dissolved to form [001] etch tunnels. The porosity (rho), average diameter (Phi) and average length (L) as well as the capacitance (C-p) of the etching tunnels were investigated in different etch conditions such as solution concentration, temperature and current density. Based on systematic study of the etching process, experimental parameters were optimized in obtaining porous aluminum with high specific capacitance. Growth mechanism of the porous aluminum was proposed based on the anodic polarization curves.