Chloride fluoride melt

It was also announced that tantalum diboride can be successfully synthesized from chloride - fluoride melts using the electrochemical method [560]. 

The above equations have been verified experimentally for the system silicon/ chloride-fluoride melts at 660 °C [2]. The initial open circuit voltage of the cell... 

Figure 2.5 represents the data as a function CsiP on P. Good linear fit is observed with the plot intersecting the negative part of ordinate axis. Hence it follows that main species in equiUhrium with silicon metal are potassium subions and Si(l). This conclusion consists with the data available on chemical reactions of elementary silicon and nonstatiOTiaiy electroreduction of silicon (IV) in chloride-fluoride melts [14]. 

In particular, the formation of a blocking film was found to be responsible for the anode effect in mixed chloride-fluoride melts like MCI-MF-M2S1F6 [22]. The kinetics of gas evolution at the anode and its quantitative composition have been studied in [23]. In addition, the impact of natural hydrocarbon gas on the properties of the electrode under the anode effect was investigated [24]. 

ZIRCONIUM ELECTROLYSIS FROM A CHLORIDE-FLUORIDE MELT... 

Refractory metals and particularly niobium and tantalum are obtained by molten salt electrolysis. Several authors 71-6/ investigated the electrochemical reduction of niobium ions in chloride or chloride + fluoride melts. However the current efficiency during electrolysis is strongly dependent on the average valence of the bath. Different reduction steps are proposed with niobium valences ranging from V to I. This is supported by the existence of many stoichiometric compounds. However, very few if not nothing is known on thermodynamics. 

Electrochemical synthesis in melts is one of several promising methods of producing refractoiy metal borides. To develop this method one needs to be aware of the mechanism of the processes occurring both in the melt bulk and on the surface of electrodes. The evidence available is mainly concerned with production of titanium and zirconium borides. The data on electrochemical synthesis of tantalum borides are contradictory and limited by the area of chloride-fluoride melts [1-5]. 

Deviatkin, S.V., Taranenko, V.I., Kushkhov, Kh.B., and Shapoval V.I. (1992) High-temperature electrochemical synthesis of tantalum diboride in chloride-fluoride melts, Rasplavy (Russ.), 2, 70-73. 

Alimova, Z. A., Elizarova, I. R., Polyakov, E. G. and Polyakova, L. P. (1992) Anodic dissolution of niobium in chloride and mixed chloride-fluoride melts, Soviet Electrochem. 28, 962-966. 

Glagolevskaya,A.L., Kuznetsova, S.V and Kuznetsov, S.A. (1989) Corrosion of hafnium in chloride and mixed chloride-fluoride melts, Zh. Prikl. Khim 63,2673-2677. 

Zaikov, Y.P.,Khramov, A.P.,Batukhtin, V.P.,Ivanovskiy, L.E., Pazdnikov, I.P., Spitsin, P.E. (1995) Electrolytic production of tantalum from Ta205 dissolved in chloride-fluoride melt. Rare Earth Metals raw material processing, technology of compounds and realated products. International conference. Abstracts, Krasnojarsk, 157-160. 

Alimova, Z.A., Polyakov, E.G., Polyakova, L.P. (1988) Anodic Dissolution of Tantalum in Chloride and Chloride-Fluoride Melts, Elektrokhimiya.24, 205- 2 l(in Russian). 

For the investigation of the rhenium electrochemical behaviour in chloride-fluoride melts, we used NaCl-NaF electrolyte of eutectic composition. Rhenium was introduced into... 

Density of potassium-boron-titanium chloride-fluoride melts 92... 

Tantalum deposition on nickel in chloride, fluoride melts 205... 

Titanium oxide solubility in chloride-fluoride melts 197... 

According to references [8, 9], the reduction process involves one step Eq. 18 in mixed chloride-fluoride melts, while two steps in pure chloride melts as shown in Eqs. 8 and 9. 

For hafnium electrowinning, electrolysis process is readily preferred to Kroll process Cezus developed the process in pure chloride media from HfCl4, reduced in Hf in a one single step [24]. However, the mechanism is controversial, other authors proposing two steps in pure chloride and a single step in chloride-fluoride melts [25]. 

Polyakova LP, Taxil P, Polyakov EG (2003) Electrochemical behaviour and codeposition of titanium and niobium in chloride-fluoride melts. J Alloys Comp 359 244-255... 

Kuznetsov, S.A., Kremenetsky, V.G., Popova, A.V. et al. (2009) Unusual effect of the second coordination sphere on the standard charge transfer rate constants for the Nh(V)/Nh(fV) redox couple in chloride-fluoride melts. Dokl. Phys. Chem, 428(2), 209-212. 

Compact and uniform deposits of pure titanium were obtained from NaF-K2TiF at 950-1000 C and LiF-NaF-KF-K2TiFg at 700 and 800 C, by direct current (DC) electrolysis. Nevertheless, these coatings became rougher and sometime dendritic as the cathodic current density and/or the deposition time increased. In mixed chloride-fluoride melts, pure and compact titanium coatings as well as powdery and dendritic deposits can be obtained, depending on the [F ]/[C1 ] ratio. 

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