A.c. Impedance Measurement of CP-Ti in 0.1 M NaOH Solution

Abstract

A.c. impedances of mechanically polished CP-Ti specimens were measured at open-circuit potential (OCP) with immersion time and under applied anodic potentials between −0.2 and 1 VAg/AgCl in 0.1 M NaOH solution. Capacitances of native oxide films (Cox,na) grown naturally and capacitances of anodic oxide films (Cox,an) formed under applied anodic potentials were obtained to examine the growth of native and anodic oxide films in 0.1 M NaOH solution and how to use Cox,na for the surface area measurement of Ti specimen. 1/Cox,na and 1/Cox,an appeared to be linearly proportional to OCP and applied potential (Eapp), with proportional constants of 0.086 and 0.051 uF �1 V �1 , respectively. The Cox,na also appeared to be linearly proportional to geometric surface area of the mechanically polished CP-Ti fixture specimen, with proportional constants of 11.3 and 8.5 µF cm �2 at −0.45 VAg/AgCl and −0.25 VAg/AgCl of OCPs, respectively, in 0.1 M NaOH solution. This linear relationship between Cox,na and surface area is suggested to be applicable for the measurement of real surface area of Ti specimen.