Etching Behavior and Dielectric Film Formation on Aluminum Foil Stocks for Electrolytic Capacitors: A Review

This review delineates the mechanisms of pit nucleation and growth, establishes the foundational principles of etching technology, and presents the findings from investigations on the behavior of anodic dissolution and anodic film formation on high-purity aluminum foils for electrolytic capacitors based on electrochemical analyses and surface electron microscopic observations of etched surfaces. To elucidate pit nucleation and growth mechanisms, the effects of crystalline oxide and small amounts of lead on etching behavior were investigated. Pits initiate at cracks surrounding MgAl2O4 spinel or γ-Al2O3, resulting from the crystallization of the oxide film at metal ridges on the aluminum substrate. Using ultra-high-resolution field-emission scanning electron microscope (FE-SEM) , high-angle backscattered electron (BSE) images revealed the presence of lead as the bright nanoparticles, approximately 10nm in size, at the surface oxidation layer along rolling lines attributable to pick-up inclusions during hot rolling.