[en] Enthalpy and Gibbs energy of formation of SmC₂ have been determined between 1420 and 1650 K by measuring the CO(g) partial pressure over the invariant SmC₂(s)-SmO_1.5(s)-C(s) three-phase field. The equilibrium CO pressure over the three-phase field was deduced from the effusion pressure by the dynamic effusion MS method. The Gibbs energy of formation of SmC₂(s) in the entire temperature range was deduced from the Gibbs energy of the reaction, SmO_1.5(s) + 3.5 C(s)=SmC₂(s) + 1.5 CO(g), and by taking the Gibbs energy functions of the other constituents from literature. The recommended Gibbs energy of formation of SmC₂ at 298 K is -(98 ± 7) kJ mol^-1. The enthalpy of formation of SmC₂(s) was derived from the enthalpy of reaction and the enthalpies of formation of SmO_1.5(s) and CO(g) taken from literature. The third-law enthalpy of formation of SmC₂(s) at 298 K is -(85 ± 8) kJ mol^-1

[en] Highlights: • Normal boiling points of dialkylalkyl phosphonates measured by using GC technique. • Retention times have been determined by using temperature programmed technique. • Topological indices derived to encode the structural aspects of phosphonates. • QSPR discipline have been developed for predicting normal boiling points. • Statistical characteristics were used for validity of the QSPR discipline. - Abstract: The normal boiling point of twelve dialkylalkyl phosphonates has been determined using gas chromatographic technique. Dibutylhydrogen phosphonate has been used as reference for computing normal boiling point of dialkylalkyl phosphonates. Retention times of dialkylalkyl phosphonates have been measured by using temperature programmed technique. The topological indices namely, odd–even index, atom type index and steric effect index have been designed to capture surface interaction parameters. It was found to exhibit excellent correlation of the topological indices to the normal boiling point of dialkylalkyl phosphonates. Multiple linear regression analysis has been performed for development of quantitative structure property relationships discipline. It exhibited good predictive power (R"2 = 0.998)

[en] CO partial pressures over the univariant three-phase region containing NdO_1.5(s), C(s) and NdC₂(s) were measured by using a quadrupole mass spectrometer (QMS) between 1403 and 1588 K. The NdC₂(s) phase was generated in situ starting from a mixture of NdO_1.5(s) and C(s). The second-law and third-law enthalpies of the reaction NdO_1.5(s)+3.5 C(s)=NdC₂(s)+1.5 CO(g) at 298 K were calculated. The enthalpy of formation of NdC₂(s) was derived from the enthalpy of reaction and the enthalpies of formation of NdO_1.5(s) and CO(g) taken from the literature. The Gibbs energy of formation of NdC₂(s) was derived from the Gibbs energy of formation of NdO_1.5(s) and CO(g) from the literature. The third-law enthalpy of the reaction is (648.1±1.0) and (647.6±1.0) kJ mol^-1 based on thermal functions of NdC₂(s) derived from those of UC_1.94 and ThC_1.94, respectively. The recommended enthalpy and Gibbs energy of formation of NdC₂(s) at 298 K are -(90.8±6.0) and -(122.2±6.0) kJ mol^-1, respectively

[en] Equilibrium CO partial pressures over the phase field LaO_1.5(s)-C(s)-LaC₂(s) between 1343 and 1638 K were obtained by employing a quadrupole mass spectrometer. The LaC₂(s) phase was generated in situ starting from a mixture of LaO_1.5(s) and C(s). The enthalpy of the reaction LaO_1.5(s)+3.5C(s)=LaC₂(s)+1.5CO(g) at 298 K derived by the second-law and third-law methods using thermal functions of LaC₂(s) derived from those of UC_1.94 and ThC_1.94 was found to be (656.6±8.4) kJ mol^-1 and (636.3±8.4) kJ mol^-1 (second-law), and (673.0±3.6) kJ mol^-1 (third-law), respectively. The enthalpy of formation of LaC₂(s) was derived from the enthalpy of reaction and the enthalpies of formation of LaO_1.5(s) and CO(g) taken from the literature. The Gibbs energy of formation of LaC₂(s) was derived from the enthalpy of formation at 298 K and the standard entropies of LaC₂(s), La(s) and C(s) from the literature. The enthalpy and Gibbs energy of formation of LaC₂(s) at 298 K (based on thermal functions of LaC₂(s) derived from those of UC_1.94 and ThC_1.94) are -(58.6±10.1) and -(62.4±10.1) kJ mol^-1, respectively

[en] The equilibrium CO pressure over the condensed phase region of CeO₂(s)-CeC₂(s)-C(s) was determined by adopting a method termed as the dynamic effusion MS method, which involves the measurement of the CO effusing out from the sample using a quadrupole mass spectrometer, even during carbothermic reduction of the oxide. The formation of oxicarbide has been ruled out. The Gibbs energies of the reaction CeO₂(s)+4C(s)=CeC₂(s)+2CO(g), at various temperatures in the rang 1350-1550 K were then determined from the equilibrium CO pressures. From the Gibbs energies of the reaction, the Gibbs energy of formation of CeC₂(s) at 298 K was derived. Similarly, from the data on the second and third-law enthalpies of the above reaction, the enthalpy of formation of CeC₂(s) at 298 K was calculated. The recommended Gibbs energy and enthalpy of formation of CeC₂(s) at 298 K are (103.0±6.0) and (120.1±11.0) kJ mol^-1, respectively

[en] Full text: A highly homogeneous Th_1-xSm_xO₂; 0 ≤ x ≤ 0.8 solid solutions were synthesized by co-precipitation technique and the co-precipitated samples were sintered at 1473 K. Compositions of the solid solutions were characterized by standard wet-chemical analysis. X-ray diffraction measurements were performed in the sintered pellets for structural analysis, lattice parameter calculation and determination of solid solubility of SmO_1.5 in ThO₂ matrix. Bulk and theoretical densities of solid solutions were also determined. A fluorite structure was observed for ThO₂-SmO_1.5 solid solutions with 0-55.2 mol % SmO_1.5. Their thermal expansion coefficients were measured using high temperature X-ray diffraction technique. The mean linear thermal expansivity, αm for ThO₂-SmO_1.5 solid solutions containing 17.9, 41.7 and 52.0 mole percent of SmO_1.5 were determined in the temperature range 298 to 2000 K for the first time. The mean linear thermal expansion coefficients for ThO₂-SmO_1.5 solid solutions are 10.47x10^-6 K^-1, 11.16x10^-6 K^-1 and 11.45x10^-6 K^-1, respectively. The percentage linear thermal expansion in this temperature range, for ThO₂-SmO_1.5 solid solutions containing 17.9, 41.7 and 52.0 mol % SmO_1.5 are 1.82,1.94 and 1.99 respectively. It is suggested that the solid solutions are stable up to 2000 K. It is also suggested that the effect and nature of the dopant are the important parameters influenced in the thermal expansion of the ThO₂

[en] An unsymmetrical diglycolamide namely N,N, didodecyl-N',N'-dioctyl diglycolamide developed in our laboratory is evaluated for its hydrodynamic suitability by determining the changes in its physical properties such as density and viscosity as a function of temperature and compared with those of tri n-butyl phosphate and N,N,N',N'-tetraoctyl diglycolamide. The effect of irradiation on density, viscosity and interfacial tension, up to a dose of 1000 kGy are also measured. In addition, the activation energy for the viscous flow (E_vis) were obtained for these pure solvents and their binary mixtures with n-dodecane in the temperature range 20-65 deg C using the Andrade's equation. (author)

[en] Uranium–europium mixed oxides (U_1_−_yEu_y)O_2_−_x (y = 0.2, 0.4, 0.6, 0.65, 0.7, 0.75, 0.8) were prepared by citrate gel-combustion synthesis and characterized by using X-ray diffraction (XRD). The terminal solid solubility of EuO_1_._5 in UO_2 is in the composition range 60–65 mol% EuO_1_._5. The coefficients of thermal expansions at 1973 K for (U_1_−_yEu_y)O_2_−_x (y = 0.2, 0.4, 0.6) measured by using high-temperature X-ray diffraction (HTXRD) were found to be 15.80, 14.81 and 14.30 × 10"−"6 K"−"1 respectively.

[en] The lattice thermal expansion characteristics of lanthanum oxide (La₂O₃) have been studied by high temperature x-ray diffraction technique (HT-XRD) in the temperature range 298-1773K. Lattice dimensions α and c were calculated from measured 2θ values. Instantaneous and mean linear thermal expansions were computed from the lattice parameter data. The mean linear thermal expansivities along the basal plane and in directions perpendicular to it are found to be of the order of, α_a (α-axis) =1.416; α_c (c-axis) =2.241. The thermal expansion values estimated in the present study are in reasonable agreement with existing dilatometry-based bulk thermal expansion data. (author)

[en] An experimental facility for out-of-pile simulation of thermal gradients in operating fuel pins was set up. Experiments were conducted at various linear power rating for evaluating operational limit of the Fast Breeder Test Reactor (FBTR) fuel pins. Above 1300 C the fuel pellets were found to show remarkable restructuring. The fuel-clad gap was fully closed at 400 W/cm linear power without any sign of fuel melting. (author). 2 refs., 2 figs