Korean Institute of Surface Engineering

pISSN : 1225-8024 | eISSN : 3399-8403

공학

한국표면공학회지 (32권3호 341-343)

ELECTRICAL BREAKDOWN INITIATION OF ANODIC FILMS DURING ANODIZING IN MOLTEN BISULPHATE MELT


Han, S.H.;Thompson, G.E.;


Cleaner Production Centre, Korea Institute of Industrial Technology;Corrosion and Protection Centre, University of Manchester Institute of Science and Technology;

Abstract

The morphology and composition of anodic films, formed on aluminium at various current densities, in the range $1-100{;}Am^{-2}$, in the molten bisulphate melt at different temperatures (418-498K), have been studied using transmission electron microscopy of ultramicrotomed film sections, and ion beam thinned films. The first sign of incipient breakdown revealed by transmission electron microscopy of stripped films, is always the appearance of dark regions about 1,000 nm in diameter, representing local overgrowth of the film. The breakdown mechanism is closely related to thermal effects, because temperature rises at regions representing local overgrowth in the stripped films were observed at voltages close to the breakdown voltage, likely arising through impact ionization.

Keywords

Anodizing;Breakdown initiation;Molten salt;Electrical breakdown;Aluminum;