Phase transformation kinetics of anodic titania nanotube arrays in oxygen-rich atmosphere

Abstract

Titania substrate and ambient atmosphere are pivotal in influencing the thermal stability of anodic TiO2 nanotube arrays (TNTs) due to anatase-to-rutile phase transition (ATRPT). This paper aimed to investigate detailed relationships between morphology and the crystallite structure and phase kinetics of O2-annealed TNTs with tube length > 10 μm and the inner diameter 60–80 nm. The study shows that below 700 °C, ARPT was very slow, but accelerated above 700 °C as nanotube structures showed signs of dramatic collapse, indicating that the thermal stability became poor. The resulting phase transformation kinetics of the O2-annealed TNTs are described by the general equation Ea= -∂ln(xr)·R/∂(1/T)·1000 , yielding approximate activation energy values of E1 = 150.71 ± 14.67 kJ/mol and E2 = 31.17 ± 1.53 kJ/mol for ARPT at temperatures below and above 600 °C, respectively. The transformation kinetics were found to be dominated by a “feeding effect” and a “size effect”, respectively. These findings serve to provide a useful method for preparing anodic TNTs with anticipant phase composition and thermal stability.