The ability to electrodeposit titanium at low temperatures would be an important breakthrough for making corrosion resistant layers on a variety of technically important materials. Ionic liquids have often been considered as suitable solvents for the electrodeposition of titanium. In the present paper we have extensively investigated whether titanium can be electrodeposited from its halides (TiCl4, TiF4, TiI4) in different ionic liquids, namely1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIm]Tf2N), 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl-sulfonyl)amide ([BMP]Tf2N), and trihexyltetradecyl-phosphonium bis(trifluoromethylsulfonyl)amide ([P14,6,6,6]Tf2N). Cyclic voltammetry and EQCM measurements show that, instead of elemental Ti, only non-stoichiometric halides are formed, for example with average stoichiometries of TiCl0.2, TiCl0.5 and TiCl1.1. In situSTM measurements show that—in the best case—an ultrathin layer of Ti or TiClx with thickness below 1 nm can be obtained. In addition, results from both electrochemical and chemical reduction experiments of TiCl4 in a number of these ionic liquids support the formation of insoluble titanium cation–chloride complex species often involving the solvent. Solubility studies suggest that TiCl3 and, particularly, TiCl2 have very limited solubility in these Tf2N based ionic liquids. Therefore it does not appear possible to reduce Ti4+ completely to the metal in the presence of chloride. Successful deposition processing for titanium in ionic liquids will require different maybe tailor-made titanium precursors that avoid these problems.

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On the electrodeposition of titanium in ionic liquids

A critical survey is given of the research and development studies on the electrodeposition of silicon Among several systems, three are given particular attention, using inorganic baths with SiO2 or K2SiF6 as the source of silicon respectively, or organic baths The former two appear capable of development to commercial production Conceptual designs of a commercial-scale cell for silicon production at temperatures above its melting point, and of a pilot plant for plating silicon from an all-fluoride bath are presented

Electrolytic production of silicon

The electrolytic reduction mechanisms of K2SiF6 and K2TiF6 solutions in LiF-KF and LiF-NaF-KF eutectic mixtures have been studied at temperatures between 550 and 850°C.

Electroplating silicon and titanium in molten fluoride media

A selective review of the anodic and cathodic processes associated with electroextraction, electrorefining and plating of refractory metals (Ti, Zr, Nb and Ta) from molten salt-based electrolytes is presented with regard to the results obtained during the last two decades. Special attention is paid to the mechanism of cathodic reduction and its rate-limiting steps, as well as to the parallel chemical reactions of disproportionation and complexing. The anodic processes in corrosion and electrodissolution of Ti, Zr, Nb and Ta in molten electrolytes are also discussed. As a conclusion, a few contradictory subject-related questions are outlined and some new trends of investigation are suggested.

Electrodeposition of refractory metals (Ti, Zr, Nb, Ta) from molten salt electrolytes

Electrodeposition of Si films from a Si-containing electrolyte is a cost-effective approach for the manufacturing of solar cells. Proposals relying on fluoride-based molten salts have suffered from low product quality due to difficulties in impurity control. Here we demonstrate the successful electrodeposition of high-quality Si films from a CaCl2-based molten salt. Soluble SiIV−O anions generated from solid SiO2 are electrodeposited onto a graphite substrate to form a dense film of crystalline Si. Impurities in the deposited Si film are controlled at low concentrations (both B and P are less than 1 ppm). In the photoelectrochemical measurements, the film shows p-type semiconductor character and large photocurrent. A p–n junction fabricated from the deposited Si film exhibits clear photovoltaic effects. This study represents the first step to the ultimate goal of developing a cost-effective manufacturing process for Si solar cells based on electrodeposition.

Toward Cost-Effective Manufacturing of Silicon Solar Cells: Electrodeposition of High-Quality Si Films in a CaCl2 -based Molten Salt.

Premiere etape de reduction du fluoro titanate de potassium dissous dans les fluorures alcalins fondus

Les coefficients de diffusion des ions TiF 6 3− dans l'eutectique LiF−NaF−KF ont ete determines de 600 a 900° C a l'aide de la semi-integration des voltamperogrammes de reduction sur electrode de fer et d'oxydation sur electrode d'argent. Les interferences de la reduction de l'eutectique et d'un menisque a la surface du bain ont ete eliminees. Le coefficient de diffusion des ions TiF 6 3− obeit a la loi d'Arrhenius selon:D=1.4×10−2 exp (−6154/T) cm2 s−1.

Application de la voltampérométrie convolutionnele à la détermination du coefficient de diffusion des ions TiF 6 3− dans l'eutectique LiF−NaF−KF de 600°C a 900°C

Voltammetric and chronopotentiometric methods were used to study the electrochemical behaviour of copper in the NaF-AlF3-BaCl2 ternary melt at 750° C. Copper, graphite and platinum were used as electrode materials. It was shown that the electrochemical reduction of copper ions is a single step process, with the reversible exchange of one electron at a copper electrode. The value of the diffusion coefficient of the cuprous ion, determined by means of chronopotentiometry, isD =(2.8±0.3)× 10−5 cm2 s−1.

J. de Lepinay

Papers

Electroplating silicon and titanium in molten fluoride media

Premiere etape de reduction du fluoro titanate de potassium dissous dans les fluorures alcalins fondus

Application de la voltampérométrie convolutionnele à la détermination du coefficient de diffusion des ions TiF 6 3− dans l'eutectique LiF−NaF−KF de 600°C a 900°C

Electrochemical behaviour of copper in a NaF-AlF3-BaCl2 ternary melt at 750° C