The investigation of sodium titanates by the hydrothermal reactions of TiO2 with NaOH

The hydrothermal reactions of TiO₂ with NaOH were performed in the molar range of Na₂O from 0 to 30% between 250 and 530°C. The compounds obtained were TiO₂ (rutile, brookite, and anatase), Na₂O·nTiO₂ (n = 3, 4, 6, and 9) and Na_xTiO₂, the formation ranges for which are shown in a reaction diagram. The roles of water in this hydrothermal system are investigated, to discuss the differences among the known and the present reaction diagrams and to raise a reliability of diagrams. From the present reaction diagram, phase relations in the system TiO₂Na₂O are estimated taking account of direct or indirect actions of hydrothermal water on solid phases.