Growth and Crystallization of Titanium Oxide Films at Different Anodization Modes

Abstract

The growth process and crystallizing mechanisms of anodic oxide films on highly pure titanium plates are studied in 0.1 M H 2 SO 4 solution at potentiostatic, potential-sweep and combined anodization modes with the same final voltage of 30 V. The influences of anodization mode on the crystalline behavior, surface morphology, chemical composition and electrochemical properties of titanium anodized films are studied. The results show that the potentiostatically grown film is thicker, rougher and more crystalline than the film formed at potential-sweep and combined modes. The titanium oxide film contains an outer porous layer and an inner barrier layer, and the barrier layer of the slow-grown film is much thicker than that of the fast-grown film. For titanium oxide film formed in the potentiostatic mode, "flower-like" crystalline grains are developed due to very high local current density at the local defect sites of titanium surface. In the case of potential-sweep and combined anodization modes, the crystallization of titanium oxide film is homogeneous, which is mainly caused by the internal compressive stresses.

Formation and Crystallization of Anodic Oxide Films on Sputter-Deposited Titanium in Potentiostatic and Potential-Sweep Modes

“…The capacitance (C) and thickness of the porous layer and barrier layer of the formed anodic titanium oxide films can be calculated by using the methods presented in previous works, 8,45 and the results are shown in Table V. It is found that the porous layer capacitance (C pr ) is lower for the anodic film formed by potentiostatic mode.…”

“…The current evolution of films growth on sputter-deposited samples is similar to that of high purity titanium anodization. 8 Under potentiostatic condition, the current density is very large at the very beginning stage of anodizing process. As a result, a layer of titanium oxide quickly forms in milliseconds, and meanwhile TiO 2 nanocrystals with various sizes randomly emerge.…”

“…8 Therefore, a comparison of the structure, morphology and composition of the formed anodic films is made between the two different titanium substrates.…”

“…More detailed information about the characterization methods of anodic oxide films on titanium could be seen from our previous works. 8,10 Results Surface topography.- Fig. 1 presents the AFM images of the sputter-deposited titanium substrate and the anodic titanium oxide films obtained in potentiostatic and potential-sweep anodization modes.…”

“…Besides, as compared to the slow-grown anodic titanium oxide films (in potential-sweep mode or galvanostatic mode), the fast-grown films (in potentiostatic mode) are much thicker and more crystalline. 8,[21][22][23] The preparation and surface pretreatment of titanium substrates can also influence the formation and crystallizing process of anodic titanium oxide films. Generally speaking, commercial pure titanium sheets or highly pure titanium plates are the most common specimens used for titanium anodization, and the samples are usually pretreated by mechanical polishing and (or) chemical polishing before electrochemical treatments.…”