The influence of fluoride ions on the equilibrium between titanium ions and titanium metal in fused alkali chloride melts

Abstract

KF is employed as a source of fluoride ions added to the melt to disclose the influence of fluoride on the disproportionation reactions of titanium ions, 3Ti(2+) = 2Ti(3+) + Ti, and 4Ti(3+) = 3Ti(4+) + Ti. The results reveal that the equilibrium transferred to the right direction for the first reaction and the apparent equilibrium constant increased sharply, mainly because of the formation of coordination compounds: TiFi(3-i). The accurate values of the equilibrium constants referring to the formation reactions of Ti(3+) + iF(-) = TiFi(3-i) (i = 1-6) in NaCl-KCl melt at 1023 K were evaluated with a best fit least squares method. It is also revealed that the stable states of the coordination compounds are TiF(2+), TiF2(+), TiF4(-) and TiF6(3-). Moreover, the Gibbs free energies for complex formation were estimated. Ti(2+) was undetectable when the concentration of fluoride ion was high enough. The equilibrium constant for the formation reaction, Ti(4-) + 6F(-) = TiF6(2-), was evaluated. The equilibrium constant, Kc2, for the disproportionation reaction 4Ti(3+) = 3Ti(4+) + Ti, in chloride melt was determined as 0.015.

Preparation of Titanium from TiCl₄ in a Molten Fluoride-chloride Salt

“…(6) and (7) were ¹0.12 and ¹0.46 V, respectively. 22 This may well explain why the potential of Eq. (6) was lower than that of Eq.…”

“…22 Therefore, NaF likely reacted with TiCl 4 to form Na 2 TiF 6 and Na 2 TiF 6 was decomposed to Na + and ½TiF 6 2À in the melts.…”

Electrochemical Deposition of Al-Ti Alloys from Equimolar AlCl3 + NaCl Containing Electrochemically Dissolved Titanium

“…In comparison to other molten salt electrolytes systems, the electrochemical behaviour of titanium ions in chloride melts is different because of the stability of various oxidation states of titanium ions, which is caused by the influence of electrolyte composition [12][13][14][15] and temperature [14,15].…”

“…The fundamental aspects of chemistry and electrochemistry of titanium ions in molten salt electrolytes have been investigated, but data on the electrochemical behaviour of titanium ions in molten chloride/fluoride salt electrolytes are scarce and contradictory. The main barrier for successful development of an electrochemical route for aluminium-titanium alloy production is associated with the existence of different oxidation states of dissolved titanium species, namely Ti(II), Ti(III) and Ti(IV) [9,[12][13][14][15].…”

Production of Ti–Fe alloys via molten oxide electrolysis at a liquid iron cathode

“…However, the cathodic process of TiO 2 could be inuenced by the composition of the electrolyte and the cathode metal activity. The published literature has reported that the cathodic process of Ti(III) ions will change from a two-step reduction (Ti 3+ + e À ¼ Ti 2+ and Ti 2+ + 2e À ¼ Ti) to a one-step reduction (Ti 3+ + 3e À ¼ Ti) with an increase in uoride ion concentration in molten chloride 23,24 and the underpotential deposition of Ti(III) ions will occur at an active cathode, including liquid metal cathodes. 25 Therefore, this work investigates the feasibility of the direct electrochemical preparation of Ti-Fe alloys by MOE at a liquid iron cathode in a CaO-Al 2 O 3 -MgO-TiO 2 melt.…”