The Influence of Anions on the Structure of Porous Anodic Al[sub 2]O[sub 3] Films Grown in Alkaline Electrolytes

Abstract

Porous, anodic Al2O3 films were grown in a variety of alk. electrolytes. At elevated temps. film growth beyond the normal barrier thickness and the development of a well-defined pore structure is not uncommon, but only borate solns. were found to support the growth of films of a thickness comparable to com. acid anodizing processes. A transition from porous film growth to electropolishing was obsd. in the case of citrate solns. The significance of the results is discussed in relation to present theories of acid anodizing.