According to inventors Keisuke Nakayama, Takaya Kubo, Yoshinori Nishikitani and Hideki Masuda, nanotube-shaped titania having an aspect ratio of 6 or greater can be produced by anodizing a titanium metal or an alloy containing mainly titanium in an electrolyte solution containing a halogen atom-containing ion, such as a perchloric acid aqueous solution.
The nanotube-shaped titania with an aspect ratio of 6 or greater can be produced by anodizing a titanium metal or an alloy containing mainly titanium in the following manner.
Anodization carried is a technique wherein a voltage is applied to an anode made of titanium or an alloy thereof and a cathode made of any electrically conductive material in an electrolyte so as to form an oxide of titanium on the anode. During the anodization, titanium or an alloy only needs to be the anode at least once. The anodization includes a case wherein titanium or an alloy can be the anode and the cathode alternately.
Titanium and an alloy used in manufacturing the titania nanotubes may be any commercially pure titanium the quality of which is modified with oxygen, iron, nitrogen, or hydrogen, or any low-alloy titanium with a certain degree of press-moldability. Examples of such titanium and alloys include various commercially pure titanium of JIS classes 1 to 4, titanium alloys with anticorrosion properties improved by adding nickel, ruthenium, tantalum, palladium, or the like, and titanium alloys containing aluminum, vanadium, molybdenum, tin, iron, chromium, niobium, or the like. The titanium alloy used herein denotes an alloy containing 50 percent or more of titanium.