Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride

Chen, George; Fray, Derek J.; Farthing, T. W.

doi:10.1038/35030069

Cited by 1,375 publications

(939 citation statements)

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“…Unfortunately, high O 2− ion concentrations can bring about an inevitable technical issue. The O 2− ion can react with the CO 2 molecule generated at the anode to form the CO 3 2− ions, i.e. reaction (9), which then can dissolve in the molten salt and transport back to the cathode to be reduced to carbon, and contaminate the cathode product [18][19][20].…”

Section: Oxidation Of O 2− Ionsmentioning

confidence: 99%

“…reaction (9), which then can dissolve in the molten salt and transport back to the cathode to be reduced to carbon, and contaminate the cathode product [18][19][20]. In theory, at sufficiently high temperatures (>887°C), the CO 3 2− ion is unstable and hence does not exert a great impact. However, medium and low temperatures are preferred in practice for both energy and technical reasons.…”

Section: Oxidation Of O 2− Ionsmentioning

confidence: 99%

“…Electrochemical reduction of various solid metal oxides to the respective metals and alloys has been successfully carried out in CaCl 2 -based molten salts at mild temperatures (500~1000°C) by many researchers since 2000 [1][2][3][4][5]. This process, known as the Fray-Farthing-Chen (FFC) Cambridge Process, is usually brought about by applying a constant cell voltage between typically a cathode fabricated from the metal oxide or a mixture of two or more metal oxides and a carbon or graphite anode.…”

Section: Introductionmentioning

confidence: 99%

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Influences of graphite anode area on electrolysis of solid metal oxides in molten salts

Chen

Jin

2014

J Solid State Electrochem

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Laboratory studies of electrochemical reduction of refractory metal oxides, e.g. TiO 2 and Ta 2 O 5 , in molten CaCl 2 often involve a graphite anode and a cell voltage of 3.0 V or higher, which deviates significantly from thermodynamic predictions. The causes considered in the past have included mechanistic, kinetic and dynamic complications of cathode reactions, but little was considered on anodic processes. This paper shows that oxidation of the O 2− ion on the graphite anode is also a significant contributor to the high cell voltages applied. Cyclic voltammetry in molten CaCl 2 containing added CaO (up to 2.51 mol%) suggested that O 2− oxidation on graphite proceeds dominantly in two steps as previously observed on glassy carbon. With increasing CaO concentration, the second step became rate-limiting over a wide range of potentials before the processes reached at diffusion controlled high current density. This understanding led to the proposal and experimental confirmation of a "low anode current density strategy" in potentiostatic reduction of thin cylindrical pellets of TiO 2 and Ta 2 O 5 in molten CaCl 2 at 850°C. It was observed that a 10-fold increase of the graphite anode area could decrease the cell voltage by about 1.0 V, which should save energy consumption by up to one third.

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Section: Oxidation Of O 2− Ionsmentioning

confidence: 99%

Section: Oxidation Of O 2− Ionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Influences of graphite anode area on electrolysis of solid metal oxides in molten salts

Chen

Jin

2014

J Solid State Electrochem

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“…This pyroprocess has been developed by Chen et al [7], who first demonstrated the direct electroreduction of TiO 2 …”

Section: Introductionmentioning

confidence: 99%

Direct electrochemical reduction of solid uranium oxide in molten fluoride salts

Gibilaro¹,

Cassayre²,

Lemoine³

et al. 2011

Journal of Nuclear Materials

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International audienceThe direct electrochemical reduction of UO2 solid pellets was carried out in LiF-CaF2 (+ 2 mass. % Li2O) at 850°C. An inert gold anode was used instead of the usual reactive sacrificial carbon anode. In this case, oxidation of oxide ions present in the melt yields O2 gas evolution on the anode. Electrochemical characterisations of UO2 pellets were performed by linear sweep voltammetry at 10mV/s and reduction waves associated to oxide direct reduction were observed at a potential 150mV more positive in comparison to the solvent reduction. Subsequent, galvanostatic electrolyses runs were carried out and products were characterised by SEM-EDX, EPMA/WDS and XRD. In one of the runs, uranium oxide was partially reduced and three phases were observed: non reduced UO2 in the centre, pure metallic uranium on the external layer and an intermediate phase representing the initial stage of reduction taking place at the grain boundaries. In another run, the UO2 sample was fully reduced. Due to oxygen removal, the U matrix had a typical coral-like structure which is characteristic of the pattern observed after the electroreduction of solid oxides

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“…In addition, the electrochemical decomposition of carbon dioxide gas by an advanced OS process using a solid electrolyte anode has been reported [20,21]. Fray, Farthing, and Chen investigated the cathodic deoxidation of metal oxides in calcium chloride and calcium oxide mixture molten salts and reported the production of metallic titanium [22][23][24][25][26], iron [27], chromium [28], zirconium [29], hafnium [30], tantalum [31], and other alloys [32][33][34] through the FFC (Fray, Farthing, and Chen) Cambridge process. Several other research groups have also investigated the successive reduction of metal oxides based on electrolysis in molten calcium chloride [33][34][35][36][37][38][39][40][41].…”

Section: Introductionmentioning

confidence: 99%

Rapid reduction of titanium dioxide nano-particles by reduction with a calcium reductant

Kikuchi

Yoshida

Matsuura

et al. 2014

Journal of Physics and Chemistry of Solids

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Micro-, submicron-, and nano-scale titanium dioxide particles were reduced by reduction with a metallic calcium reductant in calcium chloride molten salt at 1173 K, and the reduction mechanism of the oxides by the calcium reductant was explored. These oxide particles, metallic calcium as a reducing agent, and calcium chloride as a molten salt were placed in a titanium crucible and heated under an argon atmosphere. Titanium dioxide was reduced to metallic titanium through a calcium titanate and lower titanium oxide, and the materials were sintered together to form a micro-porous titanium structure in molten salt at high temperature. The reduction rate of titanium dioxide was observed to increase with decreasing particle size; accordingly, the residual oxygen content in the reduced titanium decreases. The obtained micro-porous titanium appeared dark gray in color because of its low surface reflection. Micro-porous metallic titanium with a low oxygen content (0.42 wt%) and a large surface area (1.794 m 2 g -1 ) can be successfully obtained by reduction under optimal conditions. Key words: Titanium, Calcium, Calciothermic reduction, Nano-particles, Electrolytic capacitor IntroductionMetallic calcium can easily reduce a large number of metal oxides directly to metals because calcium has a strong reducing ability. The reduction of metal oxides with a calcium reductant in calcium chloride molten salt at high temperature, well known as the calciothermic reaction, has long been widely investigated by many researchers. During oxide reduction, calcium chloride molten salt acts as a suitable solvent and has a high solubility for calcium and calcium oxide as a byproduct formed by reduction. [11] are formed via reduction of these oxides with a calcium reductant in calcium chloride molten salt. The residual oxygen in the reduced metal decreases continuously by deoxidation with a calcium reductant [4]. Pure metals, alloys, and intermetallic compounds with a lower residual oxygen content can be successfully fabricated by a one-step reduction technique. Reduction with a calcium reductant is a simpler technique for the production of these metals without complicated processes such as the Kroll process, although reduction is a batch-type production method.In recent years, a method for the successive reduction of metal oxides was developed by electrolysis in calcium chloride and calcium oxide mixture molten salts. Ono and Suzuki reported that calcium oxide in molten calcium chloride becomes the reductant source for the reduction of metal oxides during constant-voltage electrolysis [12]. For example, metallic calcium formed electrochemically at a cathode reacts with metal oxides, and reduced metals with a low residual oxygen content can be formed (OS (Ono and Suzuki) Kyoto process). Metallic titanium [13][14][15], niobium [16], nickel [17], and other alloys and intermetallic compounds [18,19] can be formed via the OS process. In addition, the electrochemical decomposition of carbon dioxide gas by an advanced OS process using ...

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Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride

Cited by 1,375 publications

References 16 publications

Influences of graphite anode area on electrolysis of solid metal oxides in molten salts

Influences of graphite anode area on electrolysis of solid metal oxides in molten salts

Direct electrochemical reduction of solid uranium oxide in molten fluoride salts

Rapid reduction of titanium dioxide nano-particles by reduction with a calcium reductant

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