Correlation between amount of bound water and stability of passive film on Ti during passivation time in sulfuric acid solution

Abstract

We have tried to detect the bound water in the passive film sensitively using thermal desorption gas spectroscopy (TDS) equipped with a quadrupole mass spectrometer and investigated the effect of bound water on stability of the passive film formed on Ti. Ti was electrochemically passivated in a dilute sulfuric acid solution for several periods. The passivated specimens were subjected to two methods for evaluating properties of the passive film: One was the TDS method to determine an amount of bound water in the film, and the other was a conventional electrochemical potentiokinetic method in a sodium bromide solution to determine a pitting potential corresponding to stability of the film. As a result, the TDS successfully and quantitatively detected three states of bound water from the passive film on Ti. As a passivation time increased, a pitting potential of Ti shifted to more positive direction and an amount of bound water increased. In other words, improvement to stability of the passive film was achieved by increasing the amount of bound water in the film. The finding was the opposite result from stainless steels.