Hrudananda Jena

Combustion synthesis and thermal expansion measurements of the rare earth-uranium ternary oxides RE6UO12 (Re = La, Nd and Sm)

Abstract Rare earth–uranium ternary oxides were synthesized by a solution combustion route. The starting materials were the corresponding metal nitrates and urea. In these preparations, the metal nitrates act as oxidizer and urea as fuel. Highly exothermic decomposition of the metal nitrate–urea complexes on heating at about 500 K leads to a combustion process yielding RE 6 UO 12 fine powders. Thermal expansion measurements of these compounds were carried out in the temperature range of 298–1173 K by high temperature X-ray powder diffractometry. The observed axial thermal expansion behaviour is explained on the basis of the crystal chemistry of the compounds.

Studies on the structural and ionic transport properties at elevated temperatures of La1−xMnO3±δ synthesized by a wet chemical method

Abstract Structural transformation and ionic transport properties are investigated on wet-chemically synthesized La 1− x MnO 3 ( x =0.0–0.18) compositions. Powders annealed in oxygen/air at 1000–1080 K exhibit cubic symmetry and transform to rhombohedral on annealing at 1173–1573 K in air/oxygen. Annealing above 1773 K in air or in argon/helium at 1473 K stabilized distorted rhombohedral or orthorhombic symmetry. Structural transformations are confirmed from XRD and TEM studies. The total conductivity of sintered disks, measured by four-probe technique, ranges from 5 S cm −1 at 298 K to 105 S cm −1 at 1273 K. The ionic conductivity measured by blocking electrode technique ranges from 1.0×10 −6 S cm −1 at 700 K to 2.0×10 −3 S cm −1 at 1273 K. The ionic transference number of these compositions ranges from 3.0×10 −5 to 5.0×10 −5 at 1273 K. The activation energy deduced from experimental data for ionic conduction and ionic migration is 1.03–1.10 and 0.80–1.00 eV, respectively. The activation energy of formation, association and migration of vacancies ranges from 1.07 to 1.44 eV.

An electrochemical investigation of the thermodynamic properties of cerium stannide (CeSn3) and liquid tincerium alloys

Abstract The thermodynamic properties of the intermetallic compound CeSn 3 and the tin-rich liquid tincerium alloys in equilibrium with CeSn 3 were studied by a high-temperature galvanic cell technique using the reversible concentration cell Ta, Ce∥CeCl 3 , LiClKCl (eutectic)∥CeSn (two-phase alloy), Ta in the temperature range 723–873 K. The standard Gibbs energy of formation of CeSn 3 from pure solid cerium and pure liquid tin varies with temperature according to the equation ΔG f(CeSn 3 ) 0 = −260.08 + 0.0476 T (±2) kJ mol −1 The activity coefficients, excess partial molar free energies, enthalpies and entropies of cerium in the saturated liquid alloys have been computed from the e.m.f. data obtained in this study and the data for the solubility of cerium in liquid tin. The activity coefficients of cerium in liquid tin with reference to solid cerium can be expressed as G Ce xs = RT ln τ Ce = −249 + 0.059 T (±2) kJ mol −1

Feasibility Studies on Pd Removal from Molten BSG Containing Simulated Nuclear Waste Using Lead or Aluminum as a Solvent Metal

AbstractExperiments were conducted to remove palladium (Pd) from molten borosilicate glass (BSG) containing simulated nuclear waste using lead (Pb) or aluminum (Al) as solvent metal. The removal of Pd from molten BSG could be carried out successfully when lead was used as the solvent metal, and the percentage extraction fraction was nearly 100%. Significant quantities of Ni, Mo, and Fe also settled into the solvent metal phase along with Pd. The metal phase found to contain intermetallic compounds of Pb2Pd and Pb9Pd13. However, when Al was used as the collecting metal separation of metal and glass phase did not occur. The results of the experiments are interpreted based on the thermodynamic stabilities of the oxides of the collecting metals and the constituent elements in the molten BSG. Even though the experiments were conducted in argon atmosphere, the traces of oxygen present in the Ar are sufficient to oxidize Al metal powder to its oxide, leading to the formation of alumino-silicates (mullites) in mo...