CORROSION-RESISTANCE FOR BIOMATERIAL APPLICATIONS OF TIO2 FILMS DEPOSITED ON TITANIUM AND STAINLESS-STEEL BY ION-BEAM-ASSISTED SPUTTERING

The high corrosion resistance and good biocompatibility of titanium an d its alloys are due to a thin passive film that consists essentially of titanium dioxide. There is increasing evidence, however, that under certain conditions extensive titanium release may occur in vivo. An i on-beam-assisted sputtering deposition technique has been used to depo sit thick and dense TiO2 films on titanium and stainless steel surface s. In this study, using the following measurements these TiO2 films ha ve been investigated in a phosphate-buffered saline solution: (1) open -circuit potential versus time of exposure, (2) electrochemical impeda nce spectroscopy, (3) potentiodynamic polarization, and (4) Mott-Schot tky plot. A higher electrical film resistance, lower passive current d ensity, and lower donor density (in the order of 10(15) cm(-3)) have b een measured for the sputter-deposited oxide film on titanium in contr ast to the naturally formed passive oxide film on titanium (donor dens ity in the order of 10(20) cm(-3)). The improved corrosion protection of the sputter-deposited oxide film can be explained by a low defect c oncentration and, consequently, by a slow mass transport process acros s the film. As opposed to TiO2 on titanium, a deviation from normal n- type semiconducting Mott-Schottky behavior was observed for TiO2 on st ainless steel. (C) 1997 John Wiley & Sons, Inc.