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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. nema

The electrochemical behavior of rhenium ions in the molten KF-KBF4-B2O3 salt was systematically studied, and pure metallic rhenium was obtained at the cathode. The processes of rhenium ions reduction and diffusion in molten KF-KBF4-B2O3 were determined using cyclic voltammetry, stationary galvanostatic and polarization curves analyses. The values of diffusion coefficients were 3.15 × 10−5 cm2/s and 4.61 × 10−5 cm2/s for R1 and R2, respectively. Rhenium electrodeposition was carried out at a constant potential. The process of rhenium cathode reduction in KF-KBF4-B2O3 at 773 K was found to be a one-step reaction Re(VII) → Re, and rhenium electrodeposition presumably occurred from two types of complex rhenium ions (KReO4 and K3ReO5). Both processes are quasi-reversible and controlled by diffusion. The obtained cathode deposit was analyzed by SEM, EDX, ICP-OES and XRD methods. The obtained deposit had a thread structure and rhenium was the main component.

Methods of simultaneous thermal analysis (differential scanning calorimetry, thermogravimetry) and an analysis of cooling curves were used to study the melting of K2B2OF6–(0–15 wt. %) KReO4 melts. The synthesis of K2B2OF6 was performed by alloying KF, KBF4, and B2O3 components. The liquidus temperature dependence on the content of potassium perrhenate in the K2B2OF6–(0–15 wt. %) KReO4 melts was determined. It was found that the addition of up to 6 wt. % KReO4 caused an increase in the melt liquidus temperature to 733 K. Further increases in potassium perrhenate did not change the temperature of the primary crystallization (733 ± 5 K) of the K2B2OF6–KReO4 melt. This fact testifies to the presence of the monotectic reaction. It was found that the relative loss of mass of the K2B2OF6–(0–15 wt. %) KReO4 melts did not exceed 2.1%. The delamination of the K2B2OF6–KReO4 melt was revealed according to the values of the primary crystallization temperatures (liquidus temperatures) in different layers of the melt. The density of the K2B2OF6–KReO4 melts as a function of potassium perrhenate content (0–15 wt. %) was investigated at 628–933 K. The temperature dependence of the K2B2OF6–KReO4 melts’ densities was recorded. They are presented as linear functions. The curves of the density temperature dependence of the K2B2OF6–KReO4 melts were used to determine the critical temperatures, i.e., the boundaries of the miscibility gap. The miscibility gap of the K2B2OF6–KReO4 melts is limited to 1 wt. % and 15 wt. % KReO4 content.

Methods of simultaneous thermal analysis (differential scanning calorimetry, thermogravimetry) and an analysis of cooling curves were used to study the melting of K[sub.2]B[sub.2]OF[sub.6]–(0–15 wt. %) KReO[sub.4] melts. The synthesis of K[sub.2]B[sub.2]OF[sub.6] was performed by alloying KF, KBF[sub.4], and B[sub.2]O[sub.3] components. The liquidus temperature dependence on the content of potassium perrhenate in the K[sub.2]B[sub.2]OF[sub.6]–(0–15 wt. %) KReO[sub.4] melts was determined. It was found that the addition of up to 6 wt. % KReO[sub.4] caused an increase in the melt liquidus temperature to 733 K. Further increases in potassium perrhenate did not change the temperature of the primary crystallization (733 ± 5 K) of the K[sub.2]B[sub.2]OF[sub.6]–KReO[sub.4] melt. This fact testifies to the presence of the monotectic reaction. It was found that the relative loss of mass of the K[sub.2]B[sub.2]OF[sub.6]–(0–15 wt. %) KReO[sub.4] melts did not exceed 2.1%. The delamination of the K[sub.2]B[sub.2]OF[sub.6]–KReO[sub.4] melt was revealed according to the values of the primary crystallization temperatures (liquidus temperatures) in different layers of the melt. The density of the K[sub.2]B[sub.2]OF[sub.6]–KReO[sub.4] melts as a function of potassium perrhenate content (0–15 wt. %) was investigated at 628–933 K. The temperature dependence of the K[sub.2]B[sub.2]OF[sub.6]–KReO[sub.4] melts’ densities was recorded. They are presented as linear functions. The curves of the density temperature dependence of the K[sub.2]B[sub.2]OF[sub.6]–KReO[sub.4] melts were used to determine the critical temperatures, i.e., the boundaries of the miscibility gap. The miscibility gap of the K[sub.2]B[sub.2]OF[sub.6]–KReO[sub.4] melts is limited to 1 wt. % and 15 wt. % KReO[sub.4] content.

The electrochemical behavior of rhenium ions in the molten KF-KBF -B O salt was systematically studied, and pure metallic rhenium was obtained at the cathode. The processes of rhenium ions reduction and diffusion in molten KF-KBF -B O were determined using cyclic voltammetry, stationary galvanostatic and polarization curves analyses. The values of diffusion coefficients were 3.15 × 10 cm /s and 4.61 × 10 cm /s for R and R respectively. Rhenium electrodeposition was carried out at a constant potential. The process of rhenium cathode reduction in KF-KBF -B O at 773 K was found to be a one-step reaction Re(VII) → Re, and rhenium electrodeposition presumably occurred from two types of complex rhenium ions (KReO and K ReO ). Both processes are quasi-reversible and controlled by diffusion. The obtained cathode deposit was analyzed by SEM, EDX, ICP-OES and XRD methods. The obtained deposit had a thread structure and rhenium was the main component.

The electrochemical behavior of rhenium ions in the molten KF-KBF[sub.4]-B[sub.2]O[sub.3] salt was systematically studied, and pure metallic rhenium was obtained at the cathode. The processes of rhenium ions reduction and diffusion in molten KF-KBF[sub.4]-B[sub.2]O[sub.3] were determined using cyclic voltammetry, stationary galvanostatic and polarization curves analyses. The values of diffusion coefficients were 3.15 × 10[sup.−5] cm[sup.2]/s and 4.61 × 10[sup.−5] cm[sup.2]/s for R[sub.1] and R[sub.2,] respectively. Rhenium electrodeposition was carried out at a constant potential. The process of rhenium cathode reduction in KF-KBF[sub.4]-B[sub.2]O[sub.3] at 773 K was found to be a one-step reaction Re(VII) → Re, and rhenium electrodeposition presumably occurred from two types of complex rhenium ions (KReO[sub.4] and K[sub.3]ReO[sub.5]). Both processes are quasi-reversible and controlled by diffusion. The obtained cathode deposit was analyzed by SEM, EDX, ICP-OES and XRD methods. The obtained deposit had a thread structure and rhenium was the main component.

The general regression equations basic physical and chemical properties (liquidus temperature, conductivity, solubility of alumina) mixed potassium-sodium cryolite melts with cryolite ratio 1,3-1,5 with additives LiF and CaF2 are investigated and described. Based on the identified patterns the electrolyte composition, promising for low-temperature aluminum electrowinning are defined: KF-AlF3 and KF-NaF-AlF3, containing 12-15 wt.% NaF, with cryolite ratio of 1,3-1,5 and the liquidus temperature below 800 C. The solubility of alumina in electrolytes such is not less than 4.5 wt.% in the temperature range of 700-800 C. In order to increase the electrical conductivity supplements LiF in an amount of not more than 3 wt.% are recommended. CaF2 in the presence of the electrolyte is not desirable.