Shuai Tang,Xianwei Hu,Jiangyu Yu,Aimin Liu,Zhongning Shi,Zhuo Li,Yifan Zhang,Zhaowen Wang
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.
This study investigated the effect of TiO 2 dissolution behavior in NaF–K 2 TiF 6 molten salts and subsequent electrolysis on the production of dense titanium powder. Under isothermal saturation conditions at molar ratios of 1.3–1.9 and temperatures of 800°C–890°C, TiO 2 solubility increased with temperature, reaching 9.75 wt% at 890°C and a 1.3 molar ratio. Dissolution kinetics revealed a two-stage process: an initial zero-order reaction during the first 5 min, followed by a first-order reaction for approximately 90 min. The dissolved TiO 2 formed TiOF n 2−n complexes, leading to K 2 NaTiOF 5 precipitation. Higher saturation of TiOF n 2−n resulted in finer particles, while lower saturation promoted the formation of coarser particles. Electrolysis experiments were conducted at 800°C with a NaF–K 2 TiF 6 molar ratio of 1.3:1. The results revealed that an increase in cathode current density reduced both the specific surface area and oxygen content of the titanium powder. At cathode and anode current densities of 1.9 and 0.31 A/cm 2 , dense spherical titanium powder with 0.22 wt% oxygen was obtained after 4 h of electrolysis. These findings confirm the feasibility of producing dense titanium powder via fluoride-based molten salt electrolysis.
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