Synthesis of One Dimensional Nanostructures of TiO2 by Thermal Oxidation

Abstract

One dimensional (1-D) nanostructures of TiO2 are particularly suitable for various engineering applications due to their superior physical, chemical and electronic properties. Single phase and nanocomposite TiO2 are being used as functional materials in many applications such as gas sensors, capacitors, photo-catalysts, solar cells, anti-reflection coatings, optical coatings and lithium ion batteries. Complex and expensive processing routes such as hydrothermal, electrospinning, anodization, UV lithography, atomic layer depositions have been adopted for the production of 1-D nanostructures of TiO2. Recently, a very simple, inexpensive and highly scalable processing route named thermal oxidation have been employed for synthesizing 1-D nanostructures on pure Ti and Ti alloy substrates such as Ti-6Al-4V, 5Al-5V-5Mo-3.5Cr-0.5Fe and Ti-6.85Al-1.6V. This process requires heating the substrate at 700–850°C in an environment containing very low concentration of oxygen or oxygen containing species such as water (H2O), acetone (CH3COCH3), ethanol (CH3CH2OH), acetaldehyde (CH3CHO), and dibutyltin dilaurate (C32H64O4Sn) in an inert atmosphere, e.g., Ar. In this article, the thermal oxidation process for the production of 1-D nanostructures on Ti and its alloy substrates is discussed in detail. The effects of the processing parameters such as alloying elements, microstructure of the substrates, oxidation environment, temperatures, oxidation time and residual stress are summarized. During oxidation, oxide scale form on the substrates and 1-D nanostructures grow on the top surface of the oxide scale. 1-D nanostructure with different morphologies such as single TiO2, core-shell TiO2-Al2O3 and core-shell TiO2-C evolve under different experimental conditions. A mechanism for the growth of 1-D nanostructure on Ti and its alloy substrates during thermal oxidation is presented.