Electrochemical studies on the stability and corrosion resistance of titanium-based implant materials

The corrosion susceptibility of Ti, Ti-6Al-4V and Ti-45Ni was studied in a buffered saline solution using anodic polarisation and electrochemical impe dance measurements. Fitting potentials as low as +250 mV(SCE) were recorded for Ti-45Ni and once initiated pits continued to propagate at potentials a s low as -150 mV(SCE). It was possible to increase the pitting potential of Ti-45Ni to values greater than +800 mV(SCE) using a H2O2 surface treatment procedure; however, this surface modification process had no beneficial ef fect on the rate of pit repassivation. Impedance spectra, recorded under op en-circuit conditions, were modelled using a dual oxide film model a porous outer layer and an inner barrier oxide layer. The nature of this porous ou ter layer was found to depend on the nature of the electrode material and t he presence of phosphate anions in the saline-buffered solution. The porous layers formed on Ti-45Ni and Ti-6Al-4V in the presence of phosphate anions had low resistances typically between 10 and 70 Omega cm(2). Much higher p orous layer resistances were recorded for Ti and also for Ti-45Ni and Ti-6A l-4V in the absence of the phosphate anions. (C) 2001 Elsevier Science Ltd. All rights reserved.