Easy conversion process of titanium surface covered with passive film into functional surface

Abstract

Surface functionalization of titanium metal is of great interest, especially as the conversion of the surface passive film into objective functional film can be widely used in bio‐ and environmental applications. However, since the surface passive film is very stable, the functionalization (such as conversion into photocatalytic anatase‐TiO2) has been performed using relatively complicated processes, for example, hydrothermal reaction and anodic oxidation. This is because direct oxidation of titanium metal only leads to thermodynamic formation of octahedral‐rutile‐TiO2 in the entire temperature region, while chemical synthesis using precursors can easily produce tetrahedral‐anatase‐TiO2 at 600°C or less. Here, we report a simple process for the direct formation of photocatalytic anatase‐TiO2 on titanium by simple oxidation. In the first step in our process, titanium is treated with a reducing agent to create a surface titaniumhydride layer. After that, the treated titanium covered with titaniumhydride is immerged in aqueous silica; subsequent calcination at 900°C (specific temperature) in air effectively generates the surface anatase‐TiO2 layer. This is because the covered tetrahedral‐silica stabilizes the anatase structure that is formed. The covered silica is easily removed by quenching in water to reveal the photocatalytic surface layer composed of anatase‐TiO2.

Hydrophilic property of titanium oxide aiming for bio‐applications

“…This is because direct oxidation of titanium metal leads only to thermodynamic formation of octahedral-rutile-TiO 2 in the entire temperature region. 13 The oxide layer on the titanium metal propagated as the heating temperature was increased from 400°C to 1000°C, which resulted in weight gain (~0.1 wt%). The increase in the thickness of the oxide layer was accompanied by a change in the color of the oxidized titanium metal, as shown in Figure 2.…”

“…The raw materials used in this stud from Zouza member in far north terials were all recognized as ri In accordance with our previous process, 13 the surface of titanium metal was treated as follows. After immersion in oxalic acid (0.1 M) for 24 h at room temperature, the pretreated titanium metal was rinsed using distilled water and immersed in a water glass solution (1.8-M aqueous solution of sodium silicate).…”

“…The first treatment method is direct oxidation of the titanium metal in air up to 1000°C. The second treatment is the previous process 13 we developed, in which titanium metal was immersed in oxalic acid (0.1 M) for 24 h at room temperature to reduce the surface passive film. After that, the treated titanium metal was rinsed using distilled water and immediately immersed in a water glass solution (1.8-M aqueous solution).…”

“…Previously, we developed a simple process for creating tetrahedral-anatase-TiO 2 on the surface of titanium by performing a simple oxidation in air. 13 Our simple process is based on the high-temperature stability of the SiO 2 /anatase-TiO 2 coexisting system that we proposed previously. 16 Here, we describe the changes in the surface characteristics of titanium metal after direct heat treatment in air and the abovementioned simple method for creating anatase-TiO 2 on the surface of titanium metal.…”

“…[8][9][10][11][12] This is because titanium metal forms only thermodynamically stable rutile-TiO 2 on the titanium surface by a simple oxidation in air according to the changes in Gibb's free energy of oxidation in the entire temperature region. 13 On the other hand, the importance of the crystalline structure, composition, and hydrophilic property of the titanium surface for improving osteoblast behavior has been reported. 14,15 In these cases, to improve osteoblast behavior, a chemical treatment using a very strong alkaline solution and subsequent heat treatment at high temperatures is widely employed.…”