Atomic force microscopy of anodized zirconium substrates

Abstract

Atomic force microscopy (AFM) has been employed to probe the detailed surface morphology of chemically polished and electropolished zirconium substrates. Whilst the results are qualitatively similar to those from transmission electron microscopy of carbon replicas of the treated surfaces, AFM allows ready quantification of the surface morphology in three dimensions. Furthermore changes in surface morphology, associated with growth of relatively thin anodic oxide films on the respective surfaces, have been revealed by AFM. The development of a subtle roughness was displayed after anodizing chemically polished zirconium, whilst anodizing an originally electropolished surface revealed no changes in surface morphology. Such behaviour is related to the film growth mechanism on the respective substrates. Non-uniform film growth on the chemically polished zirconium arises through the presence of preferred paths for ionic conduction within the fluoride-contaminated, amorphous, anodic film developed initially on the chemically polished substrate and leads to an amorphous to crystalline transition. For the electropolished surface, crystalline anodic zirconia develops from the commencement of anodization of the highly flat substrate.