Anodic Oxidation of Titanium by Using Choppings Method

Abstract

The anodic oxidation of titanium was carried out by the repetition of a method so-called choppings, in which the applied voltage was linearly raised from 0 to a maximum voltage (V_p) and then was gone down to 0 at the same speed. Electrolytic baths used in this experiment were : single baths of phosphoric acid, sulfuric acid and sodium hydroxide ; a mixed bath of phosphoric acid and sulfuric acid ; and a bath added hydrogen peroxide to the mixed bath.
As a result, when V_p was below the voltage which can ignite a spark discharge, the color of the film changed during the repetition (n) of the choppings. The films, except for the one formed in the single bath of sodium hydroxide, were colored an interference color when n<5 and gray color when n>10. The thickness of this gray-colored film was about 1.5 to 3.0 μm. However, in the single bath of sulfuric acid, the mixed bath and the hydrogen peroxide added bath, when the Vp was 150 V in the choppings, the gray-colored film was obtained at only n=1, and the color of the film changed little by increasing of n. It was implied that this reason was due to the spark discharge occurred in these baths before reaching Vp. SEM observation showed that the blister and the crack were increased with increasing n. Even after the choppings with n=20 in the single bath of sodium hydroxide, the interference-colored film, with a thickness of below 1.0 μm, was yet obtained.