Reactivity between titanium dioxide and water at elevated temperatures

The present work considers the reactivity of titanium dioxide with oxygen at elevated temperatures and the related defect disorder in the presence and absence of water. The reactivity is discussed in terms of adsorption and chemisorption of several species at the surface of TiO2 and the interaction of these species with the TiO2 lattice. The effects of both oxygen and water activities on defect disorder at elevated temperatures are considered in terms of defect diagrams including protons. These diagrams allow assessment of the concentrations of both ionic and electronic defects as a function of oxygen and water activities, respectively. It is shown that in extremely reduced conditions, protons result in reduction of the concentration of titanium vacancies by 3 orders of magnitude. In oxidized conditions, the predominant defects in TiO2 being in contact with water are protons. Then their concentration is larger than that of oxygen vacancies.