THE STATES OF BROMIDE ON TITANIUM SURFACE PRIOR TO PIT INITIATION

The pit initiation process of commercially pure titanium in bromide solutions was investigated by means of surface analysis. Prior to the pit initiation. Br̄ ions were absorbed and accumulated on localized spots of the TiO2 film forming bromide nuclei containing mostly TiBr. The bromide nuclei grew up into "critical nuclei" when the specimen was polarized just below the pitting potential. The depth of the critical nuclei was less than 3 nm. It might be the requisite condition for pit initiation that concentration of Br in bromide nuclei reached the critical concentration. In the system of titanium/bromide solution, the critical concentration of Br (not measured in situ) was 25-35 wt% and was almost independent of the temperature and concentration of solution. © 1990.