The Formation Mechanism And The Structural Adjustment Of TiO₂ Nanotube Arrays By Anodic Oxidation

TiO₂ nanotube arrays, due to the excellent photoelectric properties, are widely applied in the field of energy storage, photocatalysis, photovoltaics, and sensing. Therefore, it is significant to investigate the effect of anodization parameters on the formation process and the structure of nanotube arrays.TA1 was anodized in 0.1wt%～1.0wt% HF solution and Pt was used as cathode in this work. Anodization process was carried out under different voltages from 0.4V to 20V and different solution temperatures from 5℃to 40℃. The linear sweep anodic polarization curve and current density-time(I-t)curves were gained by means of electrochemical workstation. The morphology of TiO₂ nanotube arrays was observed with the aid of field emission scanning electron microscope(FE-SEM). The effects of anodizing voltage, time, solution temperature, pH value, including organic solvent and ultrasonic-assisted on the structure of TiO₂ arrays were studied respectively. Moreover, the microstructure transformation of Ti substrate were approached by heat-treatment or high-energy shot peening technique, and the effects of grain size and martensitic transformation on the morphology of TiO₂ nanotube arrays were analyzed. Additionally, the relationship between the formation process of TiO₂ nanotube arrays and the I-t curves had been established. Furthermore, the formation mechanism of the TiO₂ nanotube arrays was discussed. Based on these researches, the structural control of TiO₂ nanotube arrays could be effectively achieved.It was demonstrated that the growth rate, nano-pore diameter and length of TiO₂ nanotube were obviously affected by anodic oxidation condition. The time to reach the stable structure could be mensurated by I-t curve test. It was found that lower voltage, higher solution temperature or higher HF concentration were beneficial to improve the growth rate, shorten the time to equilibrium and reduce the steady nanotube length at equilibrium stage. The results also indicated that oxidation time was the dominating factor to form the different TiO₂ film structures in the initial period. Pore diameter was significantly affected by the voltage. The nanotube length increased with the lower HF concentration, lower solution temperature or higher pH value. The order degree of nanotube arrays could be increased by the addition of glycerol solvent or ultrasonic-assisted. But the order degree and smoothness were mainly determined by the microstructure of the Ti substrate.