Effect of ageing in the electrolyte and water on porous anodic films on zirconium

Highlights: → Porous anodic films are formed on zirconium consisting of nanotubes embedded in a fluoride-rich matrix. →Ageing in the formation electrolyte transforms the films from porous to nanotubular. → Ageing causes losses of zirconium and fluorine, due to dissolution of the matrix. → Ageing in water has negligible influence on the film composition and the film morphology. - Abstract: The present study demonstrates the significant influence of ageing in the formation electrolyte on the morphology and composition of anodic films grown on zirconium in 0.35 M ammonium fluoride in glycerol. Ageing after anodizing, by immersion in the electrolyte for 1 h, is shown to promote a transition from a porous to a nanotubular morphology, due to the dissolution of the fluoride-rich intratubular material in which the nanotubes are embedded. The morphological change is accompanied by a significant loss of zirconium and fluorine from the film. In contrast, ageing in deionized water has little influence on the films.