The solubility mechanism of silica in a fluoride-chloride melt has been determined in situ using Raman spectroscopy. The spectroscopy data revealed that the silica solubility process involved Si-O bond breakage and Si-F bond formation. The process results in the formation of silicate complexes, fluorine-bearing silicate complexes, and silicon tetrafluoride in the melt. Mass spectrometry of the vapor phase over the KF-KCl-K2SiF6 and KF-KCl-K2SiF6-SiO2 melts and differential scanning calorimetry coupled with thermal gravimetric analysis of these melts were performed to verify the silica solubility mechanism.

The regularities of silicon electrodeposition from the KF-KCl (2:1)—75 mol% KI melt containing 0.075 or 0.5 mol% of K2SiF6 on glassy carbon and tungsten at 998 K were studied by the cyclic voltammetry, chronoamperometry and scanning electron microscopy methods. The silicon nucleation/growth processes on glassy carbon were analyzed in the framework of two theoretical models that imply diffusion controlled growth or kinetic (charge transfer) controlled growth. Continuous silicon nanofilms with good adhesion to the substrate were obtained by the electrodeposition under galvanostatic conditions. The reasons for the formation of Si films during electrodeposition from melts with potassium iodide were discussed.

The silicon electrodeposition from the KF-KCl-(10 mol%) K2SiF6 melt at 943–1103 K has been studied. The polycrystalline continuous single-phase silicon coatings (∼99.9 wt% Si) have been obtained on the graphite, glassy carbon, silver, and tungsten substrates. The Raman spectroscopic study of the Si/C and Si/Ag interfaces has proved an absence of the intermediate phases. Two phases (Si and Ni2Si) were formed during the silicon electrodeposition on nickel.

Silicon electrodeposition on glassy carbon from the KF-KCl-K2SiF6, KF-KCl-K2SiF6-KOH and KF-KCl-K2SiF6-SiO2 melts was studied by the cyclic voltammetry. ?he electroreduction of Si(IV) to metallic Si was observed as a single 4-electron wave under all considered conditions. The reactions of cathode reduction of silicon from fluoride and oxyfluoride complexes were suggested. It was shown that the process can be controlled by the preliminary transformation of SiO44- to SiF62- and SiOxFyz-. The influence of the current density on structure and morphology of silicon deposits obtained during galvanostatic electrolysis of the KF-KCl-K2SiF6-SiO2 melt was studied.

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