Anodic zirconia nanotubes: composition and growth mechanism

The compositions of porous anodic films formed on zirconium in glycerol/fluoride electrolytes are examined prior to and following ageing in the electrolyte. The initial films are shown to contain significant amounts of fluorine, with an F:O atomic ratio between 1.0 and 2.5, dependent on the water content of the electrolyte. A three-layered film morphology is indicated, which is related to the migration rates of film species, incorporating a fluoride-rich layer at cell boundaries and bases, and outer layers compositionally differentiated by the presence of carbon species. Preferential loss of fluorine during ageing suggests degradation of the fluoride-rich material.