The Redox Chemistry of Niobium(V) Fluoro and Oxofluoro Complexes in LiF‐NaF‐KF Melts

Abstract

The electrochemical behavior of niobium(V) fluoro and oxofluoro complexes in eutectic LiF-NaF-KF (FLINAK) melts at 700°C has been studied by cyclic voltammetry. The fluoro complexes NbF, introduced into the melt by the addition of K2NbF7, can be reduced to niobium metal in two reversible steps involving one and four electrons, respectively. At 700°C the diffusion constants of the fluoro niobate complexes involved in these reduction steps, i.e., NbF and were determined to be 8.3 X 106 and 3.4 X iO cm2/s, respectively. Titration with equivalent amounts of oxide ions, introduced as Na2O, leads to a conversion of NbF to oxofluoro complexes of the type NbOF3 and NbO2F. At 700°C the conversion of NbF to NbOF3 is not complete, and the degree of conversion is shown to depend stronly on temperature. Thus, at 645°C the conversion is more nearly complete than at 700°C, while the presence of NbOF complexes cannot be identified in cyclic voltammograms obtained at 795°C. It is concluded that the degree of conversion decreases with increasing temperature. At Na20/K2NbF7 molar ratios equal to three, electroactivity is still observed in the melt, indicating the presence of solute secies. The products of reduction of the oxofluoro complexes have not been identified because the reduction of NbOF,°i ons cannot be obtained without simultaneous reduction of Nb(IV)F°4 ions, and at Na2O/K2NbF7 molar ratios exceeding two, no deposits are obtained. The reduction of the oxofluoro complex NbO2F, and complexes formed at Na2O/K2NbF7 molar ratios exceeding two always proceed in one step.

Electrochemical behavior of hexafluoroniobate, heptafluorotungstate, and oxotetrafluorovanadate anions in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide room temperature ionic liquid

“…Although electrochemical data are available for some chloro-and bromo-metallate anions [17][18][19][20][21][22][23], there are not many reports on electrochemical data for fluorometallate and oxofluorometallate anions and, to our knowledge, no reports are available for the electrochemical behavior of Nb(V)F 6 À , W(VI)F 7 À , and V(V)OF 4 À at 298 K. In this paper, the electrochemical behavior of Nb(V)F 6 À , W(VI)F 7 À , and V(V)OF 4 À in BMPyrTFSA at 298 K is discussed in detail, where BMPyrTFSA was chosen as a medium because of its high electrochemical stability and easy handling. following relation holds [24]:…”

The effect of the microstructure on the corrosion behavior of N5 superalloy in a molten (Li,Na,K)F eutectic salt

“…Aer drying the analytical grade of LiF, NaF and KF (supplied by Sinopharm Chemical Reagent Co., Ltd, China) at 200 C for 24 h, respectively, a mixture of (Li,Na,K)F was prepared and then put into a high-density graphite crucible. The mixed uorides were further dried at 200 C in the reaction chamber under vacuum for 48 h, and then the furnace was heated to 700 C. 16,17 It was the fact that KF was hygroscopic and deliquescent and a certain concentration of water vapor would be carried by Ar ow, so the HF was generated at elevated temperatures by eqn (2.1):…”

Electrochemistry of refractory metals in molten salts: Application for the creation of new and functional materials

“…In recent years, the behavior of oxygen, especially of oxygen-containing niobium species, in electrochemical processes has drawn the attention of many researchers [28][29][30][31][32][33][34]. This fact is apparent: oxygen is one of the most harmful impurities in niobium and adversely affects the mechanical and electrophysical properties of all refractory metals.…”