Anodic dissolution of Ti in acidic fluoride media

Anodic dissolution kinetics of Ti in HF medium was investigated using potentiodynamic polarization experiments. The concentration of HF was varied and the effect of changing the H+ and F- ions independently by the addition H2SO4 and KF was also investigated. In all the cases, a clear active and passive regions were observed, and the peak current and potential exhibiting a systematic trend with increasing HF concentration. Scanning electron micrographs of electrodes held in the active and passive regions were acquired to characterize the surface morphology. Several mechanisms were evaluated to model the polarization data. A mechanism involving an chemical dissolution step in parallel with an electrochemical dissolution step was proposed to explain the results. The model captures all the major characteristics of the polarization curves. Based on the results, it is proposed that HF2- is the key species which impacts the electrochemical dissolution and HF is the one which impacts the chemical dissolution process.