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A new method was proposed for the preparation of carbon powders based on the electrochemical reduction of a fused eutectic mixture of lithium-sodium-potassium carbonates at 450°C. Transmission electron microscopy observations have revealed the presence of three forms of carbon in the powder samples depending on the deposition potential values: amorphous carbon, graphite, and fibers. The presence of graphite and amorphous carbon was confirmed by X-ray diffraction measurements. The d002 values were rather constant whatever the sample and close to 0.34 nm. Moreover, surface analyses by X-ray photoelectron spectroscopy revealed the presence of nearly metallic and ionic lithium belonging to lithium oxides. The specific areas were measured by the Brunauer-Emmett-Teller (BET) method. Whatever the deposit potential values, the total BET specific surface area is much higher than that corresponding to external one because of the pore walls contribution. It has been shown that, for carbon powder dried at 400°C under vacuum, the specific surface area decreased as the deposition potential became more cathodic: from about 850 m2 g−1 at −2.4 V vs. CO2­O2 to about 500 m2 g−1 at −6.0 V vs. CO2­O2. With increasing negative values of the potential, the nucleation and the growth of carbon competes with the formation of nearly metallic lithium and/or lithium oxides. The presence of the latter induces the closure of some nanopores. © 2002 The Electrochemical Society. All rights reserved.

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The electrochemical behavior of Zr 4+ in potassium-free fused alkali fluorides has been studied in the temperature range of 773-1123 K. With an inert tungsten or molybdenum electrode, a well-defined oxydo-reduction wave was observed during cyclic voltammetry experiments. The reduction of Zr 4+ is a single four-electron reversible step, and the process is diffusion controlled. Chronopotentiometry measurements give rise to the diffusion coefficient values of Zr 4+ ions. For instance, a value 2.92 ϫ 10 −5 cm 2 s −1 was found at 1010 K. The reduction of Zr 4+ ions was also studied using a nickel electrode for which Ni-Zr alloys formation was pointed out as revealed by cyclic voltammetry. The analysis of these deposits by scanning electron microscopy ͑SEM͒ and energy dispersive X-ray showed the presence of a multilayered Ni-Zr alloy with different Zr contents. On graphite electrodes, zirconium carbides have been evidenced on cyclic voltammograms and the formation of Zr metal was observed by SEM.The pyroelectrochemical route is considered as one of the most promising options in an innovative nuclear fuel cycle. 1 Indeed, this process allows the separation of actinides from lanthanides by electrorefining in fused electrolytes. 2-7 For instance, Lantelme et al. 5 have performed the extraction of lanthanum in fused alkali chlorides via the formation of La-Ni alloys using Ni and Ni-Ti alloyed electrodes. Recently, Massot et al. have reported the formation of Sm-Ni alloys in molten LiF-CaF 2 . 6 Several studies have also been devoted to the electrochemical behavior of Zr ions in fused LiClKCl due to the electrorefining of binary U-Zr Experimental Breeder Reactor II driver fuel. 8,9 In this refining process, Zr is commonly considered as a nuisance 10 due to its slightly higher potential than uranium. 9,11,12 Consequently, the current efficiency for the actinides recovering is significantly decreased by the Zr dissolution and, thus, the electrochemical behavior of Zr in such a medium was widely studied.The interest devoted to the preparation of Zr and Zr-based alloys is also because these materials can be used for various applications, such as corrosion-resistant materials or as catalysts in various processes, such as for example, for the hydrogen evolution reaction. 13 For example, when H 2 is used as a fuel in small fuel cells, it is a convenient way to store it is as a hydride because it is compact and easy to operate. A typical metal hydride uses an AB 2 -type alloy, where A is, for example, Zr or Zr-Ti alloys and B is a mixture of transition metals. 14 Another original use of stainless steel-zirconium alloys was proposed by Argonne National Laboratory 15 for the express purpose of immobilizing radioactive metal fuel components left behind following the electrometallurgical treatment of spent nuclear fuel. 16 Such materials have been proposed for the consolidation and the disposal of waste stainless steel, Zr, and noble metalfission products, such as Nb, Mo, Tc, Ru, Pd, and Ag recovered from spent nuclear fuel assemblies....