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

The NaF-AlF 3 -TiO 2 ternary system is often used in the molten salt electrolysis process to produce Al-Ti alloys. In order to explore the dissolution reaction of TiO 2 in NaF-AlF 3 melts, the ionic structure of (6.58NaF-AlF 3 )-TiO 2 molten salts was examined by Raman spectroscopy combined with computational simulation in the present study. The results indicated that when TiO 2 was added to 6.58NaF-AlF 3 molten salt, it first reacted with F - or AlF 6 3- with the following reactions: 2F - +2TiO 2  = Ti 2 O 4 F 2 2- , 4AlF 6 3- +6TiO 2  = 2Al 2 O 3  + 3Ti 2 O 2 F 6 2- +6F - , and then the generated Al 2 O 3 reacted with TiO 2 and F - or AlF 6 3- with the following reactions: Al 2 O 3  + 3TiO 2  + 21F - =3TiO 3 F 3 5- +2AlF 6 3- , Al 2 O 3  + 4AlF 6 3- =3Al 2 OF 8 4- , Al 2 O 3  + 4AlF 6 3- =3Al 2 OF 6 2- +6F - . In addition, Ti 2 O 2 F 6 2- , TiO 3 F 3 5- and Ti 2 O 4 F 2 2- 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 O 1 -Ti 3 -O 2 -Ti 4 , Ti 1 -O 7 and O 6 -Ti 2 -O 5 and/or O 7 -Ti 1 -O 8 , respectively. What’ more, the main characteristic Raman bands of Ti 2 O 2 F 6 2- , TiO 3 F 3 5- and Ti 2 O 4 F 2 2- were located at 790, 850 and 900 cm −1 , respectively.