Abstract:

The Raman spectroscopy and quantum chemistry calculations were employed to analyze the ionic structure and variation rule of the LiF-ZrF₄ molten salt system with the molar fraction of ZrF₄ ranging from 10% to 60% at 803~1 086 K. The study identified four complex ions in the molten salts： ZrF{}_{\mathrm{5}}^{-}， ZrF{}_{\mathrm{6}}^{\mathrm{2}-}， ZrF{}_{\mathrm{7}}^{\mathrm{3}-}， and ZrF{}_{\mathrm{8}}^{\mathrm{4}-}. In the molten salts， ZrF{}_{\mathrm{7}}^{\mathrm{3}-} and ZrF{}_{\mathrm{8}}^{\mathrm{4}-} are the major components， accounting for 90%~94%， while ZrF{}_{\mathrm{5}}^{-} and ZrF{}_{\mathrm{6}}^{\mathrm{2}-} are present in lower amounts. At the initial stage of temperature increase， a reaction between ZrF{}_{\mathrm{7}}^{\mathrm{3}-} and ZrF{}_{\mathrm{6}}^{\mathrm{2}-} occurs， producing ZrF{}_{\mathrm{8}}^{\mathrm{4}-} and ZrF{}_{\mathrm{5}}^{-} （\mathrm{Z}\mathrm{r}{\mathrm{F}}_{\mathrm{7}}^{\mathrm{3}-}+\mathrm{Z}\mathrm{r}{\mathrm{F}}_{\mathrm{6}}^{\mathrm{2}-}\to \mathrm{Z}\mathrm{r}{\mathrm{F}}_{\mathrm{8}}^{\mathrm{4}-}+\mathrm{Z}\mathrm{r}{\mathrm{F}}_{\mathrm{5}}^{-}）. At a certain temperature， a reaction between ZrF{}_{\mathrm{8}}^{\mathrm{4}-} and ZrF{}_{\mathrm{6}}^{\mathrm{2}-} takes place and produces ZrF{}_{\mathrm{7}}^{\mathrm{3}-}， ZrF{}_{\mathrm{5}}^{-}， and F^- （\mathrm{Z}\mathrm{r}{\mathrm{F}}_{\mathrm{8}}^{\mathrm{4}-}+\mathrm{Z}\mathrm{r}{\mathrm{F}}_{\mathrm{6}}^{\mathrm{2}-}\to \mathrm{Z}\mathrm{r}{\mathrm{F}}_{\mathrm{7}}^{\mathrm{3}-}+\mathrm{Z}\mathrm{r}{\mathrm{F}}_{\mathrm{5}}^{-}+\mathrm{2}{\mathrm{F}}^{-}）. With the increase of ZrF₄， the amount of ZrF{}_{\mathrm{5}}^{-} increases， while the amounts of ZrF{}_{\mathrm{6}}^{\mathrm{2}-}， ZrF{}_{\mathrm{7}}^{\mathrm{3}-}， and ZrF{}_{\mathrm{8}}^{\mathrm{4}-} decrease.

Key words: LiF-ZrF₄, complex ions, ionic structure, Raman spectroscopy, quantum chemical calculation