Dissolution reaction of TiO2 in molten 6.58NaF-AlF3: A Raman spectroscopy and computational simulation study

Abstract

The NaF-AlF3-TiO2 ternary system is often used in the molten salt electrolysis process to produce Al-Ti alloys. In order to explore the dissolution reaction of TiO2 in NaF-AlF3 melts, the ionic structure of (6.58NaF-AlF3)-TiO2 molten salts was examined by Raman spectroscopy combined with computational simulation in the present study. The results indicated that when TiO2 was added to 6.58NaF-AlF3 molten salt, it first reacted with F- or AlF63- with the following reactions: 2F-+2TiO2 = Ti2O4F22-, 4AlF63-+6TiO2 = 2Al2O3 + 3Ti2O2F62-+6F-, and then the generated Al2O3 reacted with TiO2 and F- or AlF63- with the following reactions: Al2O3 + 3TiO2 + 21F-=3TiO3F35-+2AlF63-, Al2O3 + 4AlF63-=3Al2OF84-, Al2O3 + 4AlF63-=3Al2OF62-+6F-. In addition, Ti2O2F62-, TiO3F35- and Ti2O4F22- clusters belonged to Cs, C2v and C1 point group, and the main characteristic Raman bands of these clusters were due to the stretching vibration of O1-Ti3-O2-Ti4, Ti1-O7 and O6-Ti2-O5 and/or O7-Ti1-O8, respectively. What’ more, the main characteristic Raman bands of Ti2O2F62-, TiO3F35- and Ti2O4F22- were located at 790, 850 and 900 cm−1, respectively.