Formation of PEO coating on Al microelectrode under elementary anodic/cathodic pulses

Abstract

Cathodic sweep and pulse polarization of bare and anodized Al microelectrodes were carried out in alkaline silicate solution. The sweep polarization causes a severe damage to as-polished Al, but reduced and localized damages to the anodized Al. The anodic film resists both cathodic sweep and pulse breakdown. Cathodic pulse polarization can cause capacitive charging and mechanical damage to the oxide film and the substrate depending on the degree of polarization. High cathodic pulse polarization causes sparking and subsequent modification of discharge channels formed by the prior anodic breakdown. The enhancement of plasma formation and sparking during cathodic pulse breakdown is associated with cathodic corrosion of Al, excessive H 2 gas formation and local high electric field. Although sparking cathodic breakdown explodes the discharge channels and causes the loss of coating materials, it does not alter its beneficial role to randomize the sites breakdown by succeeding anodic pulse. The sequential pulses form dense coating materials. • Elementary role of sparking cathodic breakdown on PEO coating growth • Sparking cathodic breakdown causes loss of coating materials. • Sparking during cathodic breakdown does not alter its novel role to randomize anodic breakdown sites.