The Behavior of Copper and Lead during Heat‐Treatment and Surface Treatment of Aluminium Capacitor Foils

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 foils of 100 μm thickness, containing up to 100 ppm copper and 1.5 ppm lead. The selected heat‐treatment results in major redistribution of lead in the bulk foils, with a comparatively small effect upon the distribution of copper. Importantly, the lead segregates to a metal layer, probably of about 1–2 nm thickness, located immediately beneath the thermally formed oxide film. The enrichments of lead developed by the heat‐treatment are largely retained in the metal surface region during etching and subsequent anodizing treatments. In contrast, electropolishing results in extensive loss of the segregated lead from the foil surfaces to the electropolishing electrolyte, which is attributed to transient localized corrosion of the metal in the electropolishing bath. Enrichments of copper are developed during electropolishing, etching, and anodizing treatments, with the possibility of incorporation of copper species into the associated oxide films. © 1999 The Electrochemical Society. All rights reserved.