電解コンデンサ用高純度アルミニウム箔の鉛の表面偏析

抄録

The capacitance of aluminum foil used in electrolytic capacitors is determined by their surface area after etching. Many studies have assessed pit growth using high-purity aluminum foil during DC etching in hot hydrochloric acid solutions with respect to impurity effects. High-purity aluminum foil used for electrolytic capacitors containing small amounts of lead is known to exhibit severe rolling line effects after electrochemical etching. Apparently, the lead atoms distributed on the aluminum foil surface after annealing provide nucleation sites of pitting attacks during DC etching. For this study, lead segregation on aluminum foil surfaces containing 0.6 ppm, 5 ppm and 8.2 ppm Pb annealed at 813 K for 5 h was investigated using ultra-high resolution field emission scanning electron microscopy（FE-SEM）with selective detection of high-angle backscattered electrons （BSE） and transmission electron microscopy （TEM）. High-angle BSE images revealed the presence of Pb as brighter nanoparticles with size on the order of 10 nm at the surface oxidation layer along the rolling lines caused by pick up inclusion during hot rolling. The approximately 0.5-μm-thick surface oxidation layer microstructure resembled that of grain refined surface layer （GRSL） of alloy 8006 characterized by ultra-fine grains of nano-level size. Pitting attacks first occur at the oxidation layer because of the less noble potential for tunnel dissolution during initial DC etching.