INFLUENSE OF KI ADDITION ON THE INTERACTIONSIN KF–KCl CONTAINING K<sub>2</sub>SiF<sub>6</sub> AND SiO<sub>2</sub>
The interaction of KI with the KF–KCl–K<sub>2</sub>SiF<sub>6</sub> and KF–KCl–K<sub>2</sub>SiF<sub>6</sub>–SiO<sub>2</sub> salt systems was studied. The KF–KCl and KF–KCl–KI systems containing both K<sub>2</sub>SiF<sub>6</sub> and SiO<sub>2</sub> were studied by Raman spectroscopy. It was shown that the addition of KI to the KF–KCl–K<sub>2</sub>SiF<sub>6</sub> and KF–KCl–K<sub>2</sub>SiF<sub>6</sub>–SiO<sub>2</sub> melts leads to the appearance of groups containing Si–I bonds in the solid samples. It was established that a significant part of silicon dioxide from the KF–KCl–K<sub>2</sub>SiF<sub>6</sub>–SiO<sub>2</sub> and KF–KCl–KI–K<sub>2</sub>SiF<sub>6</sub>–SiO<sub>2</sub> melts crystallizes in the form of silicate structures characteristic of the K<sub>2</sub>SiO<sub>3</sub> phase (K<sub>2</sub>O · SiO<sub>2</sub>). The Raman spectroscopy data are consistent with the data of X–ray phase analysis of KF–KCl and KF–KCl–KI melts containing both K<sub>2</sub>SiF<sub>6</sub> and SiO<sub>2</sub>. It was found that the crystallization field of K<sub>3</sub>SiF<sub>7</sub> is retained when KI is added to the KF–KCl–K<sub>2</sub>SiF<sub>6</sub> and KF–KCl–K<sub>2</sub>SiF<sub>6</sub>–SiO<sub>2</sub> melts. When KI is introduced into the melt, it is characteristic to precipitate it into a separate phase during crystallization. Low–intensity peaks corresponding to the crystallization of the α-SiO<sub>2</sub> phase were recorded for the KF–KCl–K<sub>2</sub>SiF<sub>6</sub>–SiO<sub>2</sub> and KF–KCl–KI–K<sub>2</sub>SiF<sub>6</sub>–SiO<sub>2</sub> systems. The study of KF–KCl–KI–K<sub>2</sub>SiF<sub>6</sub> and KF–KCl–KI–K<sub>2</sub>SiF<sub>6</sub>–SiO<sub>2</sub> melts by the method of synchronous thermal analysis was carried out. It was found that at temperatures up to 473 K, phase transitions are observed, which are probably associated with the transformation of \[{\text{Si}}{{{\text{I}}}_{x}}{\text{F}}_{y}^{{z - }}\ structures into structures containing \[{\text{SiF}}_{{\text{6}}}^{{{\text{2}} - }},\ which is consistent with information on the thermal stability of mixed silicon halide.