Influence of pH and fluoride concentration on titanium passivating layer: stability of titanium dioxide

Titanium and titanium alloy biomaterials are considered as being corrosion resistant, because of the formation of a titanium oxide passivating layer, which is not easily soluble even in acid media. In odontology, using dental preparations containing fluorides could alter the behaviour of titanium. After a review of the experimental works dealing with the effects of fluoride ions at different pH on titanium salts in solution, it was proceeded to a thermodynamic investigation at 25°C in the range of concentrations and pH corresponding to the solutions commonly used. Such a study gives a possibility to specify which species could be involved in the corrosion reaction to calculate the corresponding potentials, and lastly to define the domain of insolubility of TiO2. From these results, the reaction of titanium in laboratory spontaneous corrosion and voltammetric experiments was interpreted. From the recent experiments described and discussed in this article, it becomes evident that the close connection with the results obtained in this study contributes to support our thermodynamic model.