The behavior of copper and lead during heat-treatment and surface treatment of aluminium capacitor

The influences of heat-treatment. electropolishing, etching, and anodizing treatments, applied individually or in combination. on the distributions of copper and lead in aluminum capacitor foils have been investigated for foi ls of 100 mu m thickness, containing up to 100 ppm copper and 1.5 ppm lead. The selected heat-treatment re-suits in major redistribution of lead in th e bulk foils, with a comparatively small effect upon the distribution of co pper Importantly, the lead segregates to a metal layer, probably of about 1 -2 nm thickness, located immediately beneath the thermally formed oxide fil m. The enrichments of lead developed by the heat-treatment am largely retai ned in the metal surface region during etching and subsequent anodizing tre atments. In contrast. electropolishing results in extensive loss of the seg regated lead from the foil surfaces to the electropolishing electrolyte, wh ich is attributed to transient localized corrosion of the metal in the elec tropolishing bath. Enrichments of copper am developed during electropolishi ng, etching, and anodizing treatments, with the possibility of incorporatio n of copper species into the associated oxide films. (C) 1999 The Electroch emical Society. S0013-4651(98)07-065-7. All rights reserved.