Porous hierarchical TiO2 nanostructures: Processing and microstructure relationships

G. A. Crawford, Nikhilesh Chawla

Research output: Contribution to journalArticlepeer-review

61 Scopus citations


A dual porous hierarchical coating of TiO2 nanotubes (∼50 nm diameter) on the nanoscale and large (∼1 to 20 μm) pores on the micro-scale can be fabricated on the surface of Ti by anodic oxidation. This unique coating may have potential applications as bioactive coatings for Ti bone implants. This paper details several important aspects of the coating microstructure. TiO2 coatings were fabricated by anodic oxidation in 1 M H2SO4 + 0.1 M NaF solution. Microstructure characterization was carried out using scanning electron microscopy. We also report on the observation of precipitates which form as both a continuous surface layer and of a conical geometry. The mechanism for nanotube formation, precipitate layer formation, and microscopic pitting was discussed. The effect of processing variables (i.e. time, temperature, pH) on the TiO2 microstructure was studied. Anodization time was found to affect nanotube length and also pit size and density. Lowering the electrolyte pH decreased the nanotube length and microscopic pit density. Increasing electrolyte temperature decreased nanotube length and increased pit/pore and precipitate density. Microscopic pitting, in the nanotube coating was found to occur above grain boundaries in the Ti substrate and above Ti grains with (0 0 0 1) orientation.

Original languageEnglish (US)
Pages (from-to)854-867
Number of pages14
JournalActa Materialia
Issue number3
StatePublished - Feb 2009


  • Anodic oxidation
  • Nanotubes
  • Scanning electron microscopy
  • TiO

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys


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