Beneficial influence of nanocarbon on the aryliminopyridylnickel chloride catalyzed ethylene polymerization

A series of 1-aryliminoethylpyridine ligands (L1―L3) was synthesized by condensation of 2-acetylpyridine with 1-aminonaphthalene, 2-aminoanthracene or 1-aminopyrene, respectively. Reaction with nickel dichloride afforded the corresponding nickel (II) chloride complexes (Ni1–Ni3). All compounds were fully characterized and the molecular structures of Ni1 and Ni3 are reported. Upon activation with methylaluminoxane (MAO), all nickel complexes exhibit high activities for ethylene polymerization, producing waxes of low molecular weight and narrow polydispersity. The presence of multi-walled carbon nanotubes (MWCNTs) or few layer graphene (FLG) in the catalytic medium can lead to an increase of productivity associated to a modification of the polymer structure

Thermochemical Properties of Lanthanides (Ln = La, Nd) and Actinides (An = U, Np, Pu, Am) in the Molten LiCl-KCl Eutectic

The electrochemical reduction of actinides (U, Pu, Np and Am) and lanthanides (La and Nd) chlorides was investigated by cyclic voltammetry and chronopotentiometry at different temperatures in LiCl¿KCl eutectic. The diffusion coeffcients of these metallic cations were estimated as well as their apparent standard potentials. These values of potentials are compared with existing data measured also by transient electrochemical techniques or e.m.f. measurements.JRC.E.2-Hot cell

Electrochemical Behaviour of Neptunium in the Molten LiCL-KCl Eutetic

The electrochemical properties of neptunium, dissolved in the LiCl KCl eutectic, were investigated by transient electrochemical techniques, such as cyclic voltammetry (CV) and chronopotentiometry on inert tungsten electrodes. It was shown that Np4+ is reduced to Np0 by a two-step mechanism corresponding to the transitions of Np4+/Np3+ and Np3+/Np0. In the 400 550 C (673 823 K) temperature range, the diffusion coefficients of Np3+ and Np4+ were found to be of similar magnitude and equal to DNp3þ ¼ 9:47 104 exp23:6 103=RT ðKÞÞ and DNp4þ ¼ 2:14 104 expð14:1 103=RT ðKÞÞ cm2 s1, respectively. The apparent standard potentials of Np4+/Np3+ and Np3+/Np0 redox systems were determined to be E(Np4+/Np3+) = 1.250 + 6.637 · 104 T (K) V versus Cl2/Cl and E(Np3+/Np0) = 3.250 + 7.251 · 104 T (K) V versus Cl2/Cl, respectively. The Gibbs free energies of formation in diluted solutions of NpCl3 and NpCl4 in the LiCl KCl eutectic were determined to be DG = 936.54 + 0.20654 T (K) and 120.61 + 0.06405 T (K) kJ mol1, respectively. Between 400 C and 550 C, the activity coefficients cNpCl3 and cNpCl4 range between 9 125 · 106 and 2 10 · 10 3, respectively.JRC.E.2-Hot cell

Separation of Plutonium from Lanthanum by Electrolysis in LiCl-KCl onto Molten Bismuth Electrode

This work presents a study on the electroseparation of plutonium from lanthanum using molten bismuth electrodes in LiCl–KCl eutectic at 733 K. The reduction potentials of Pu3+ and La3+ ions were measured on a Bi thin film electrode using cyclic voltammetry (CV). A difference between the peak potentials for the formation of PuBi2 and LaBi2 of approximately 100 mV was found. Separation tests were then carried out using different current densities and salt phase compositions between a plutonium rod anode and an unstirred molten Bi cathode in order to evaluate the efficiency of an electrolytic separation process. At a current density of 12 mA:cm2:wt (Pu3), only Pu3 ions are reduced into the molten Bi electrode, leaving La3 ions in the salt melt. Similar results were found at two different Pu/La concentration ratios ((Pu):(La) = 4 and 10). At a current density of 26 mA:cm2:wt (Pu3), co-reduction of Pu and La was observed as expected by the large negative potential of the Bi cathode during the separation test.JRC.E.2-Hot cell

Electroseparation of Actinides from Lanthanides on Solid Aluminum Electrode in LiCl-KCl Eutectic Melts

This work presents a study on Ibe electrochemical behavior of actinides (An = Am and Pu) and lanthanides (Ln = La and Nd) onto solid aluminum cathodes in a molten LiCI-KCl eutectic at 733 K. Cyclic voltammetiy of these elements onto A! woridog electrode is carried out to estimate the reduction potentials of An and Ln and to predict the efficiency of an An:Ln separation by eleclrolysis. Results show that the reduction of Am3 1, Pu3, LaJ, and Nd3 ions leads to the formation of An-Al or Ln-Al surface alloys. Moreover, the difference in reduction potentials between An and Ln elements was found to be larger than on the classical molten cadmium or bismuth electrodes. Pu:Nd and Am:Nd electroseparauons were carried out using Al foam as cathode and a plutonium rod as anode. Efficient and feradaic reduction of actinides was achieved at a cathodic potential preventing Nd coreduction. After electrolysis, a compact and adherent deposit covered the cathode surface, and scanning electron microscopy, energy-dispersive X-ray analysis of the deposit indicated the existence of Ai-Pu or mixed Am-Pu-Al alloys. Analysis of the dissolved Al cathodes, after electrolytic separation of Am from Nd, showed that 536 mg of An (94 of the total Am present in the initial salt phase) had been deposited compared to less than 3 mg Nd. This work represents a breakthrough in the selective partitioning of An by electrorefming methods.JRC.E.2-Hot cell

Promising Pyrochemical Actinides / Lanthanides Separation Processes Using Aluminium

Thermodynamic calculations have shown that aluminum is the most promising metallic solvent or support for the separation of actinides (An) from lanthanides (Ln). In molten fluoride salt, the technique of reductive extraction is under development in which the separation is based on different distributions of An and Ln between the salt and metallic Al phases. In this process molten aluminum alloy acts as both a reductant and a solvent into which the actinides are selectively extracted. It was demonstrated that a one-stage reductive extraction process, using a concentrated solution, allows a recovery of more than 99.3% of Pu and Am. In addition excellent separation factors between Pu and Ln well above 103 were obtained. In molten chloride media similar separations are developed by constant current electrorefining between a metallic alloy fuel (U60Pu20-Zr10 Am2Nd3.5Y0.5Ce0.5Gd0.5) and an Al solid cathode. In a series of demonstration experiments, almost 25 g of metallic fuel was reprocessed and actinides collected as An-Al alloys on the cathode. Analysis of the An-Al deposits confirmed that an excellent An/Ln separation (An/Ln mass ratio_ 2400) had been obtained. These results show that Al is a very promising material to be used in pyrochemical reprocessing of actinides.JRC.E.4-Nuclear fuel

Electrochemistry of Uranium in the Molten LiCl-KCl Eutectic

The Institute for Transuranium Elements ITU is building up an accurate database of actinide behavior in chloride melts in support of its nuclear fuel reprocessing development program. The electrochemical properties of uranium, dissolved in LiCl-KCl eutectic melt, were investigated by transient electrochemical techniques, such as cyclic voltammetry CV and chronopotentiometry on an inert tungsten electrode. It was shown that U4+ is reduced to U0 by a two-step mechanism corresponding to U4+/U3+ and U3+/U0 transitions. In the 400-550 C s673-823 Kd range, the diffusion coefficients of U3+ and U4+ were similar and equal to: DsU3+d = 13.7 3 10−4 exph−24.2 3 103/RTsKdj and DsU4+d = 5.25 3 10−4 exph−19.8 3 103/RTsKdj cm2 s−1. The apparent standard potentials of U4+/U3+ and U3+/U0 redox systems were Eo sU4+/U3+dsVd = −1.902 + 0.0006104T sKd vs. Cl2/Cl− and Eo sU3+/U0dsVd = −3.099 + 0.0007689T sKd vs. Cl2/Cl−, respectively. Some thermochemical properties sDG,gd of uranium solutions were also derived from the electrochemical measurements. The Gibbs free energies of dilute solution of UCl3 and UCl4 in the LiCl-KCl were determined to be: DG = −897.09 + 0.226T sKd and −183.53 + 0.0589T sKd in kJ mol−1, respectively. In the 400-550C s673-823 Kd range, the activity coefficients g of UCl3 and UCl4 range between 0.3 − 4.5 3 10−3 and 17.1 − 12.7 3 10−3, respectively.JRC.E.2-Hot cell

Production of Metallic Titanium by Electrowinning in Molten Salts of Titanium Oxycarbide Anode

The electrochemical behavior of Ti3+ in LiCl-LiF-TiF3 salt was investigated by cyclic and square wave voltammetries at 853 K. Both methods confirm the presence of a single reduction wave of Ti3+ ions to metal, at a potential of −2.3 V vs. Cl2/Cl−. The closeness of the potentials of TiCxOy dissolution and Ti3+/Ti4+ wave is an issue during the electrorefining of the anode. A low current density has to be applied to stay within the titanium oxycarbide dissolution and avoid the formation of Ti4+. The titanium deposition was studied by electrorefining of a titanium metal plate in LiCl-LiF-TiF3 (0.62 mol/kg). The cathodic deposit analysis by XRD and SEM confirms the formation of titanium metal with an average grain size of 150 µm. The faradic deposition yields are above 85% and constant between 60 and 160 mA/cm2

Actinide Electrochemistry in Low Temperature Ionic Liquids

Low Temperature or Room Temperature Ionic Liquids (RTILs) are viscous media entirely made up of ionic species but in contrast to traditional ionic media such as high temperature molten salts (LiCL/KCl, LiF/AIf3...), the melting pount is typially under 373K instead of over 600K.JRC.E.6-Actinides researc

Corrosion in molten chlorides - CEA developments and research program

International audienceA French R&D program (CEA, CNRS, Orano) has been launched on molten salts cooled reactors which aims at assessing the feasibility of fast MSRs and confirm their potential assets. Chloride salts have been selected and in the French context (closed cycle, transmutation, Pu multirecycling), we focus on chlorides fast MSR with a focus on actinides conversion (reducing ultimate wastes). One of the major constraints on the use of molten chlorides is the corrosion behaviour of structural materials. To overcome this constraint, different approaches are performed with different time scales:- Evaluation of already available and /or qualified materials such as nickel base alloys but also high entropy alloys or ceramics.- Evaluation of different corrosion protection strategies: protective coatings, electrochemical potential control, chemistry control…- Evaluation of more innovative solutions: advanced manufacturing processes, smart materials, architectured materials…In the same time a large French research program has been launched together with CEA and CNRS to work on the global acceleration of materials discovery, the DIADEM (DIscovery Acceleration for the Deployment of Emerging Materials) project. In the frame of this large project which will be launched in 2022 for 8 years, shorter targeted projects have been already selected (duration of 3 years), as the A-DREAM project which is dedicated to the acceleration of the development of corrosion resistant materials in molten chlorides. For this, the A-DREAM project proposes an integrated approach implementing: (i) the digital design of materials/coatings, (ii) the high throughput synthesis of these materials and (iii) the implementation of an accelerated corrosion methodology. In this presentation, the French corrosion strategy for MSR will be presented together with results obtained