Investigation of the Ionic Structure of Molten 1.5-8 KF-AlF3 Salts with Raman Spectroscopy

The form and concentration distribution of anions in a molten KF-AlF3 system with different molar ratios (1.5-8) at different temperatures were analyzed with Raman spectroscopy. The results indicate that for molar ratios in the range of 1.5-5, AlF63-, AlF52-, AlF4-, and F-, were all present in the system, while for molar ratios in the range of 6-8, only AlF63-, AlF52-, and F-, were present. For molar ratios in the range of 1.5-2.5, the AlF52- ion content was the most sensitive to temperature among all the complex ions in the system, whereas for molar ratios in the range of 4-8, minor variations in the constituent anion contents were observed as a function of temperature. The Al3+ ions in the system with the molar ratios of 1.5-5, 6, and 7 or 8 tended to form AlF4-, AlF52-, and AlF63-, respectively, as the temperature increased.