Porous hierarchical TiO2 nanostructures: Processing and microstructure relationships

Abstract 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.

[1]  Craig A. Grimes,et al.  Synthesis and application of highly ordered arrays of TiO2 nanotubes , 2007 .

[2]  Krishnan S. Raja,et al.  Electrodeposition of hydroxyapatite onto nanotubular TiO2 for implant applications , 2006 .

[3]  Ralph E. White,et al.  Comprehensive Treatise of Electrochemistry , 1981 .

[4]  Craig A. Grimes,et al.  Titanium oxide nanotube arrays prepared by anodic oxidation , 2001 .

[5]  T. Beck.  Pitting of Titanium I . Titanium‐Foil Experiments , 1973 .

[6]  S. Virtanen,et al.  Metastable and Stable Pitting Corrosion of Titanium in Halide Solutions , 2004 .

[7]  Krishnan S. Raja,et al.  Deposition of calcium phosphate coating on nanotubular anodized titanium , 2005 .

[8]  Craig A. Grimes,et al.  Highly-ordered TiO2 nanotube arrays up to 220 µm in length: use in water photoelectrolysis and dye-sensitized solar cells , 2007 .

[9]  W. Smyrl,et al.  Determination of Precursor Sites for Pitting Corrosion of Polycrystalline Titanium by Using Different Techniques , 1998 .

[10]  U. König,et al.  Microstructure of polycrystalline Ti and its microelectrochemical properties by means of electron-backscattering diffraction (EBSD) , 2001 .

[11]  Shinji Fujimoto,et al.  On wafer TiO2 nanotube-layer formation by anodization of Ti-films on Si , 2006 .

[12]  Desheng Kong.  The influence of fluoride on the physicochemical properties of anodic oxide films formed on titanium surfaces. , 2008, Langmuir : the ACS journal of surfaces and colloids.

[13]  J. Schultze,et al.  Electron-transfer reactions on pure and modified oxide films , 1986 .

[14]  V. K. Mahajan,et al.  Design of a Highly Efficient Photoelectrolytic Cell for Hydrogen Generation by Water Splitting: Application of TiO2-xCx Nanotubes as a Photoanode and Pt/TiO2 Nanotubes as a Cathode , 2007 .

[15]  Craig A. Grimes,et al.  Unprecedented ultra-high hydrogen gas sensitivity in undoped titania nanotubes , 2006 .

[16]  H. White,et al.  Pitting Corrosion of Titanium The Relationship Between Pitting Potential and Competitive Anion Adsorption at the Oxide Film/Electrolyte Interface , 2000 .

[17]  J. Macák,et al.  Nanotube oxide coating on Ti–29Nb–13Ta–4.6Zr alloy prepared by self-organizing anodization , 2006 .

[18]  J. Macák,et al.  Enhancement and limits of the photoelectrochemical response from anodic TiO2 nanotubes , 2005 .

[19]  T. Beck.  Pitting of Titanium II . One‐Dimensional Pit Experiments , 1973 .

[20]  J. Delplancke,et al.  Galvanostatic anodization of titanium—II. Reactions efficiencies and electrochemical behaviour model , 1988 .

[21]  Xiaofeng Yu,et al.  Formation of nanoporous titanium oxide films on silicon substrates using an anodization process , 2006 .

[22]  W. Smyrl,et al.  Pitting Corrosion of Titanium , 1994 .

[23]  G. Frankel.  Pitting Corrosion of Metals A Review of the Critical Factors , 1998 .

[24]  Patrik Schmuki,et al.  High-aspect-ratio TiO2 nanotubes by anodization of titanium. , 2005, Angewandte Chemie.

[25]  J. Delplancke,et al.  Galvanostatic anodization of titanium—I. Structures and compositions of the anodic films , 1988 .

[26]  P. Marcus,et al.  Corrosion Mechanisms in Theory and Practice , 1995 .

[27]  Krishnan S. Raja,et al.  Formation of self-ordered nano-tubular structure of anodic oxide layer on titanium , 2005 .

[28]  Sungho Jin,et al.  Growth of nano-scale hydroxyapatite using chemically treated titanium oxide nanotubes. , 2005, Biomaterials.

[29]  Pierre Villars,et al.  Pearson's handbook of crystallographic data for intermetallic phases , 1985 .

[30]  Craig A. Grimes,et al.  The effect of electrolyte composition on the fabrication of self-organized titanium oxide nanotube arrays by anodic oxidation , 2005 .