In Situ Monitoring of Ionic Metal Dissolution During Anodization of Titanium and Quantification of Parallel Electronic Oxygen Evolution

This study reports an in situ investigation of the metal dissolution during anodization of titanium. A combination of an electrochemical flow cell that is directly coupled to an ICP-MS was used for the investigation. The oxide film was grown through potentiodynamic anodization (CV with 10 mVs-1) between 0 and 8 V. A rather constant dissolution rate of approximately 1.5 ngs-1 cm-2 was observed during the entire oxide formation although the current, as measured by the potentiostat, increased from 58 mAcm-2 (1 V) up to 290 mAcm-2 (8 V). Controversially, the dissolution rate was not affected by the additional electronic currents, which become relevant for potentials higher than 3.5 V. The metal dissolution is triggered by the ionic species (Ti4+ and O2-) crossing the oxide layer (ionic currents) under the applied high-field conditions. No reduction of the oxide during the reverse scan could be observed. The fraction of charge carriers used for metal dissolution stayed rather constant (ca. 21%) up 3.5 V, and then continuously decreased to 4% for the highest applied anodization potential (8.0 V), reflecting the increased oxygen evolution rate at a rather constant dissolution rate.