G. Duyckaerts

Some recent observations on curium sesquioxide

Abstract We have studied as a function of temperature the rate of the radiation induced transformation of the cubic form of curium sesquioxide into the hexagonal form. The rate of destruction of the cubic lattice, as shown by X ray diffraction, is much greater at low temperature than at room temperature, while at 300°C, it is essentially negligible. Whereas the monoclinic form of Cm2O3 has been obtained on heating the cubic phase under vacuum, or by reduction of the dioxide, both reactions at temperatures higher than 850°C, we have shown that it can be produced by heating the hexagonal form to 500°C. We have observed an expansion in the lattice parameter of the cubic sesquioxide samples during the very first hours following their preparation. This expansion rapidly reaches a saturation value. We also noted a contraction of the hexagonal lattice during the time of its spontaneous formation from the cubic lattice.

Chronopotentiometric determination of U(III), U(IV), UO2(VI) and Np(IV) in molten LiCl-KCl eutectic*

Summary The use of chronopotentiometry for the quantitative analysis of uranium and neptunium in a molten LiCl-KCl eutectic has been investigated: U(IV) or Np(IV) may be determined with an accuracy of ±4% and U(III) or UO 2 (VI) with an accuracy of ±6% in the temperature range 400–550°. U(III) and U(IV) may be determined in the same solution with the accuracies given above.

Electrochemical and spectroscopic studies of the lanthanides in the AlCl3+1-n-butylpyridinium chloride melt at 40°C: Part I. The Yb(III-II), Sm(III-II) systems

Abstract The behaviour of Yb(III-II) and Sm(III-II) couples has been investigated in AlCl3+1-n-butylpyridinium chloride (BPC) mixtures at 40°C, by voltammetric and spectrophotometric methods. In very acidic melts, the two trivalent lanthanides can be reduced reversibly and solutions of divalent oxidation states are stable. The E1/2 potentials measured with respect to an Al electrode dipping in a melt containing 57 mol% of AlCl3 are constant and located respectively at +1.230 V (Yb) and +0.660 V (Sm). If the acidity of the melt is decreased, the lanthanide cations precipitate and the half-wave potentials exhibit a cathodic shift. These phenomena are explained in terms of cationic chlorocomplexes, depending on the pCl, the oxidation state and the atomic number. Species such as YbCl2+, YbCl+ and SmCl2+, Sm3+, Sm2+ are proposed.

Electrochemical and spectroscopic studies of the lanthanides in the AlCl3+1-n-butylpyridinium chloride melt at 40°C: Part II. The Tm(III-II), Eu(III-II) systems, application of Nugent's linearization method

The possibility of obtaining stable solutions of Eu(II) and especially Tm(II) in the acidic side of 1-n-butylpyridinium chloride-AlCl3 melts at 40°C is presented. It is based on the Refined Electron Spin Pairing Energy Theory proposed by Jorgensen and improved by Nugent. The behaviour of Tm(III-II) and Eu(III-II) has been qualitatively investigated by voltammetry and spectrophotometry, in order to confirm the predictions of Nugents theory. Tm(III) and Eu(III) have been reversibly reduced to the divalent state in very acidic melts. The E1/2 potentials measured with respect to the potential of an Al electrode in a 57 mol % of AlCl3 melt are respectively +0.020 V(Tm) and +1.855 V (Eu). From the experimental E1/2 values of Tm and Eu and those previously reported for Yb and Sm, it has been possible to obtain the two parameters of Nugents equation in room temperature melt and to compare their values with those reported in several other solvents. This comparison suggests that one of them could be related to the solvating power of the solvent.

Electrochemistry of lanthanides in molten chloroaluminates: Part I. The electrochemical behaviour of Eu(III), Yb(III) and Sm(III)

Abstract The electrochemical behaviour of Eu(III), Yb(III,II) and Sm(III,II) has been investigated in NaCl-AlCl 3 mixtures, in a temperature range between 150 and 250°C. Principal investigation methods are cyclic voltammetry, pulse polarography and chronoamperometry. The three tervalent lanthanides can be reduced reversibly and solutions of divalent oxidation states are stable. E 1/2 potentials measured with respect to an Al electrode in a saturated melt are located respectively at 2.295 V (Eu), 1.630 V (Yb) and 1.080 V (Sm). In acidic chloroaluminates, the three investigated lanthanides are more oxidizing than in other more complexing solvents. If the acidity of the melt is decreased, precipitation of the trichloride (or the dichloride) occurs and the solubility product of the different species is directly related to the cationic size.

Comportement polarographique et solvatation de quelques cations dans le mélange binaire diméthylsulfoxyde-carbonate de propylène

Summary We have studied the polarographic reduction of trifluoromethane sulfonates of Pb2+, Cd2+, Tl+ in anhydrous binary solvents of dimethylsulfoxyde-propylene carbonate in the range 0 to 1.0 molar fraction. The reduction waves are reversible except for lead and cadmium in solvents containing less than 0.2% of dimethylsulfoxyde (% in volume). Strehlows hypothesis (measurement of half-wave potential of the ion against that of the couple cobaltocene/cobalticinium) was used for obtaining the transfer activity coefficients. Our results in the pure constituents are compared with the values in the literature. In binary solvents, we observe an important half-wave potential shift towards negative potentials and a drastic reduction of the transfer coefficients when the concentration of DMSO increases. These effects are especially important for lead and cadmium and are due to the great solvation power of dimethylsulfoxyde as compared with that of propylene carbonate.

Comportement polarographique du cadmium dans le carbonate de propylenè en présence de diverses substances organiques à pouvoir solvatant élevé

Abstract The stoechiometry and the stability of Cd 2+ complexes with various neutral organic molecules (cosolvent) in propylene carbonate (solvent) have been determined. The experimental data were interpreted with the help of the theory of Cox et al. This theory accounts for the solvation by relying on the complexation equilibria. The free enthalpies of transfer of Cd 2+ from propylene carbonate to the pure cosolvents were calculated and compared with experimental measurements. From this comparison, it is concluded that the method of Cox et al. is a convenient procedure to assess the Δ G t o values if the solvent and the cosolvent form an ideal mixture and if their solvating power towards the cation under study is very different.

Electrochemical study of thorium in dimethylsulfoxide and propylene carbonate

Abstract Solutions of ThCl4 in anhydrous dimethylsulfoxide or propylene carbonate have been investigated by dc polarography and controlled potential chronoamperometry on a hanging mercury drop electrode. The results are interpreted by assuming that the cathodic reduction of thorium on mercury proceeds through one step Th(IV)+4 e→Th(0) (E1/2⋍−1.65V vs. SCE in DMSO); however, the results obtained indicate that the reduction gives rise to the the formation of an autoinhibiting monoatomic layer of thorium; further reduction of thorium on this requires an overpotential (E1/2⋍−2.15 V vs. SCE in DMSO). The mean value for the maximal superficial concentration of thorium in the film deduced from these experiments equals 1.25×10−9 mol cm−2, whereas the value for a hexagonal close-packed layer is 1.5×10−9 mol cm−2.