The study of electrode processes in LiF–NaF–KF–K2TaF7–KBF4 melt

Abstract

The electrode processes in the FLINAK–K₂TaF₇–KBF₄ melt were studied by the method of linear voltammetry with a silver working electrode at the temperature of 700–750$\text{°}$C. In order to eliminate possible errors, two approaches were used, namely KBF₄ addition to the FLINAK–K₂TaF₇ melt and K₂TaF₇ addition to the FLINAK–KBF₄ melt. During the experiment the oxygen content in the melt was constantly monitored by linear voltammetry with a glassy carbon electrode. It was shown that depending on the B/Ta molar ratio in the melt the voltammograms had at least one peak. So, at B/$\text{Ta}\text{=}\text{1}$ two cathodic peaks can be seen. Electrolysis of this melt at increasing current density leads to the formation of Ta_cub, then Ta_tetragon and a mixture of tantalum with borides. Further increase of B/Ta results in a greater number of cathodic peaks, as well as the appearance of TaB₂ and elemental boron in the cathodic deposit alongside with the aforementioned phases. In the electrolytes studied no corroboration of the existence of tantalum and boron heteronuclear complexes has been found. The addition of sodium oxide to the melt in question simplifies the shape of cyclic voltammograms of the FLINAK–K₂TaF₇–KBF₄ melt considerably.