The Morphology of Sealed Anodic Films Formed on Aluminium in Phosphoric Acid

Abstract
The long term sealing of porous anodic films, formed on aluminium in phosphoric acid, has been studied by electron microscopical examination of replicas taken from fracture sections of the film. Sealing for 72 h results in major morphological changes, particularly in the outer 2–3 μm thickness. The outer surface becomes covered by crystalline oxide which obliterates the pores; in section the pores are completely filled even in the depths of the film and there is an intermediate layer present between the outer surface crystals and the blocked pores.