STEADY-STATE ANODIC BEHAVIOR OF TITANIUM IN CONCENTRATED HYDROCHLORIC-ACID

Titanium dissolves in concentrated hydrochloric acid forming Ti(III) and Ti(IV). The steady state current-potential curve is consistent with a reaction model similar to that proposed for fluorinated sulfuric acid media in which there is one bifuraction leading to tervalent and tetravalent titanium in solution. Nevertheless, this model is insufficient to account for the variation of the dissolution valence with potential. This variation implies that the passivation phenomenon results from the progressive coverage of the electrode surface by two tetravalent titanium species: the first, which is slightly soluble, is formed at low potentials, whereas the second, which is of an oxide type and very slightly soluble, is formed at high potentials.