Influence of KI on the Reactions in the KF–KCl Systems Containing K2SiF6 and SiO2.

The reactions of KI with the KF–KCl–K₂SiF₆ and KF–KCl–K₂SiF₆–SiO₂ salt systems are studied. The KF–KCl and KF–KCl–KI systems containing both K₂SiF₆ and SiO₂ are studied by Raman spectroscopy. The addition of KI to the KF–KCl–K₂SiF₆ and KF–KCl–K₂SiF₆–SiO₂ melts induces groups containing Si–I bonds in the molten solid samples. A significant portion of silicon dioxide from the KF–KCl–K₂SiF₆–SiO₂ and KF–KCl–KI–K₂SiF₆–SiO₂ melts crystallizes in the form of silicate structures characteristic of the K₂SiO₃ phase (K₂O·SiO₂). The results of Raman spectroscopy are consistent with the X-ray diffraction data for the KF–KCl and KF–KCl–KI melts containing both K₂SiF₆ and SiO₂. The crystallization field of K₃SiF₇ is retained upon the addition of KI to the KF–KCl–K₂SiF₆ and KF–KCl–K₂SiF₆–SiO₂ melts. KI introduced into the melt precipitates to form an individual phase during crystallization. Low-intensity peaks corresponding to the crystallization of the α-SiO₂ phase are detected for the KF–KCl–K₂SiF₆–SiO₂ and KF–KCl–KI–K₂SiF₆–SiO₂ systems. The KF–KCl–KI–K₂SiF₆ and KF–KCl–KI–K₂SiF₆–SiO₂ melts are studied by synchronous thermal analysis. Phase transitions probably associated with the transformation of -structures into structures containing are observed at temperatures up to 473 K, which is consistent with the data on the thermal stability of mixed silicon halides. [ABSTRACT FROM AUTHOR]