Search Results

You are looking at 1 - 10 of 14 items for

  • Author or Editor: L. Martinot x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

We report on chronopotentiometric investigations of the UFe, UCu and UNi alloys. The experimental procedure is based on the control of the pO2– of the liquid melt and that allows to avoid undesirable chemical side-reactions. The capability of the method to prove the existence of two different metallic phases either of similar compositions or of non-stoichiometric composition is discussed.

Restricted access

Abstract  

We report voltammetric and chronoamperometric investigations on the reduction of Np/III/ in the /Li–K/Cl melt. The electrode reaction is nearly reversible and a nucleation phenomenon appears in the early deposition of neptunium metal. The Tafel equation corresponding to that deposition indicates that the charge transfer is the rate-determining step of the overall electrode process.

Restricted access

Abstract  

The electrochemical reduction of Th/IV/ in the /Li–K/Cl eutectic between 400 and 500 °C proceeds according to a four electron process without any intermediate step. The reduction is quasi-reversible and the diffusion coefficient deduced from the peak current of the voltammetric reduction equals 2.7×10–6 cm2 sec–1 at 400°C.

Restricted access

Abstract  

Electrochemical properties of hexavalent and tetravalent uranium were investigated in various molten organic ionic mixtures. Kinetic parameters and reaction mechanisms were defined by voltammetry, chronoamperometry and sampled polarography. Long-term electrolyses in the mixture phenanthrene/TBABF4 allowed the preparation of both metallic uranium and crystallized uranium dioxide.

Restricted access

Abstract  

The feasibility of the reaction Np4++2Ni0 Np0+2Ni2+ in organic liquids is reported. This reaction, which is impossible to carry out in water, has been achieved in acetonitrile, while it remained impossible in dimethylformamide. This behavior in the two liquids is determined by solvent effects on the ions (Np4+, Ni2+) and we demonstrate that the classical Bom equation, as modified by Tanaka, is capable to foresee these different behaviors.

Restricted access

Abstract  

AmO2 can be dissolved in molten (K−Na)OH in the presence of gaseous oxygen. The chronopotentiometric investigation of the dissolved species indicates that hexavalent americium is formed after oxidation. The diffusion coefficient of this species is about 6·10−6 cm2 sec−1 at 250 °C.

Restricted access

Abstract  

In this paper, the values of the solubility products of UO2 and MgUO4 in the (K–Na–Mg 1/2)Cl eutectic and the solubility products of UO2 and (K,Na)UO3 in the (K–Na)Cl eutectic are reported. The complete potential/pO2– diagram of uranium is set up in these liquid melts and a method of separation UO2/PuO2 is discussed in the molten chlorides media.

Restricted access

Abstract  

We have investigated the separation of uranium from lanthanum in two molecular organic liquids (sulfolane, TMSO2; ethylene carbonate, EC) and in one organic ionic melt: ethylammonium nitrate (EAN). A separation is achieved by chemical oxidation and precipitation of oxides in TMSO2; in this medium, the part of uranium remaining in solution may be recovered by an electrochemical reduction. In EAN, it is required to add Li2O to initiate the oxides precipitation: the separation corresponds to the difference between the solubility products of UO3(s) and La2O3(s). Best results are obtained in EC where the insoluble phase corresponds to an U/La ratio equal to 186 instead of 1.7 in the initial conditions.

Restricted access

Abstract  

The ability to electrochemically control the binding of uranium ions by redox active polypyrrole resins has been studied. The optimization of the conditions for the fixation of uranium has been defined while taking in account the nature of the fixed species, the nature of the resin and the nature of the solutions.

Restricted access

Abstract  

The electrochemical reduction of hexavalent and tetravalent uranium is investigated in ethylammonium nitrate at 298 K and in the acetamide-KSCN eutectic at 400 K. The transient techniques describe a two-step reduction of UO 2 2+ in acetamide-KSCN while only one step is observed in ethylammonium nitrate. The reduction of tetravalent uranium proceeds in one step giving trivalent uranium in the two media. In any cases, additional kinetic phenomena are the source of difficulties for the understanding of the reactions. In controlled potential electrolysis, side-reactions between the reduced species and the solvent impede completely the mechanism foreseen by transient methods.

Restricted access