Effect of mechanical attrition on anodizing of DC-etched aluminum foil for electrolytic capacitor

On tunnel-etched aluminum foil for electrolytic capacitor, the barrier dielectric film, γ-Al2O3, was formed by a mechanical attrition enhanced anodizing process. The anodizing was conducted in a traditional boric acid solution and the mechanical attrition (MA) action was applied by impact of nano-sized α-Al2O3 particles on the sample surface with a special vibrating frequency. The surface morphology of anodized foil was observed with SEM. The morphology and microstructure of the anodized oxide were examined by SEM, TEM and XRD. The capacitance and withstanding voltage of the oxide film were also determined with LCR meter and small-current charging. The results show that MA has significant effects on the microstructure and performance of Al anodic film. The MA-assisted barrier film becomes thinner, more crystallized but with less structure defects than the traditional one without MA, leading to increase in the film capacitance and withstanding voltage.