The formation of a porous TiO 2 layer by immersing Ti in 5 M NaOH at 303 K was investigated using electrochemical measurements, a scanning electron microscope, and grazing incident X-ray diffraction. The porous layer was readily obtained in the case of the presence of titanium hydride (TiH 2 ) on the surface before immersion. The crystalline structure of the porous layer is composed of a mixture of the rutile and anatase type TiO 2 . The porous layer is hard to produce without the presence of TiH 2 . The TiH 2 is directly changed to TiO 2 by a dissolution reaction in alkaline solution. The presence of TiH 2 on the surface is an important factor for the preparation of the porous TiO 2 layer.

The influence of hydrogen on the formation of porous TiO2 in alkaline solution was investigated using an electrochemical measurement, a scanning electron microscope, and a grazing incident X-ray diffraction technique. The porous TiO2 was not obtained on the surface of titanium in 5 M NaOH solution at 303 K for 3 h. When the titanium was charged with hydrogen in 1 M H2SO4 at 303 K for 1 h before immersion, the porous TiO2 was readily produced on the surface under the same experimental conditions. The anodic polarization measurement indicated that the hydrogen-charged titanium was more readily dissolved in alkaline solution than the titanium. The cathodic reaction was the hydrogen evolution reaction on both the titanium and the hydrogen-charged titanium. For titanium, although the hydrogen penetrated into the inside of the material due to the side reaction of hydrogen evolution, the hydrogen content in the inside was so small that porous TiO2 was not produced under this condition. © 2002 The Electrochemical Society. All rights reserved.

The catalytic activity for the hydrogen evolution reaction was investigated in 1 M NaOH at 303 K. The hydrogen overpotentials of Raney-Ni electrodes obtained from NiAl 3 and Ni 2 Al 3 were lower than those from nickel rich alloys (NiAl and Ni 3 Al). Especially, NiAl 3 yielded the most active Raney-Ni cathode. This is because the fast aluminum leaching from NiAl 3 phase gives large surface area of the electrode, the formation of small micropores, and the appearance of the Ni phase.

Microporous layers on titanium (Ti) are formed by chemical treatment in highly concentrated alkaline media, and their properties and growth mechanism are examined using electrochemical techniques, in situ resistometry, scanning electron microscopy (SEM), grazing-incident X-ray diffraction (GIXRD), and glow discharge optical emission spectroscopy (GD-OES). Chemical treatment in a 5 M aqueous KOH solution yields results superior to those from the same treatment in a 5 M aqueous NaOH solution, while a 3 M aqueous LiOH solution does not produce porous layers. The cation constituting the solution plays a vital role in the process. An SEM analysis reveals that the KOH solution is the most effective in forming microporosity and that the longer the treatment time, the more porous the near-surface layer. The results of GIXRD analysis show the presence of Na(2)Ti(5)O(11) and K(2)Ti(6)O(13) in the layers formed in the NaOH and KOH solutions, respectively; in the case of the LiOH solution, TiO(2) is formed. Chemical treatment in the NaOH and KOH solutions resembles a general corrosion process with the existence of local cathodic and anodic sites. The reduction reaction produces H(2), some of which becomes absorbed in the near-surface region of Ti, while the oxidation reaction produces the above-mentioned compounds and/or an oxide layer. The presence of hydrogen (H) within the solid is detected using GD-OES. The H-containing near-surface layer partially dissolves, yielding a microporous structure. The development and dissolution of the H-containing near-surface layer of Ti upon chemical treatment in the NaOH and KOH solutions are confirmed by resistometry measurements. They point to the formation of a compact passive layer on Ti upon exposure to the LiOH solution.