The effect of film formation conditions on the structure and composition of anodic oxide films on titanium

Abstract

Anodic oxide films on titanium which were potentiostatically formed in 0.5 M H 2SO 4 solution at various temperatures from 303 to 353 K and different potentials have been examined by transmission electron microscopy, ex situ Raman spectroscopy, together with X-ray photo-electron spectroscopy. The structure and composition of the anodic oxide films were found to be strongly dependent on film formation temperature and potential. At temperatures higher than 333 K or at potentials more noble than 6 V, film crystallization occurs. After film crystallization, the film growth rate increases greatly. During anodic film growth, the electric field within the film was found to be of the order of 10 6 V cm −2. This electric field exerts significant electrostriction on the film and yields high internal compressive stresses in the film. The internal compressive stresses increase with temperature, particularly, at 323 K. The film crystallization at high temperatures or at high potentials is considered to be attributed to the high compressive stresses. The amount of bound water was found to increase markedly above 343 K, and the presence of bound water in the film plays an important role in stabilizing the passive film.