Roughening of surface of aluminium@ foil - in which etching tunnels are formed

摘要

Thermally treated aluminium foil is electrolytically and/or chemically roughened using an etching bath containing chloride ions and passivating components. During the process, etching tunnels are formed, and, after an intermediate rinse, these tunnels are widened by electrolytic and/or chemical etching in a further bath. The etching bath contains one or more passivating components of concentration greater than 0-5N. The components are chosen from sulphuric, oxalic, tartaric or phosphoric acids, pref. 2-10N sulphuric acid. Prior to this treatment the foil is treated in an aqueous, halide-free bath as the anode, followed by treatment in a chloride ion-contg. bath which does not contain passivating components. USE/ADVANTAGE - Treating aluminium foil to be used in high voltage, electrolytic capacitors. During the etching process the tunnel formation arises from nuclei in the oxide layer. The oxide layer free from nuclei remains in place, and acts as a protective layer for the aluminium.