[en] Ternary oxides in the systems Ln-Co-O (where Ln = Eu, Gd, Tb) have been prepared by citrate-nitrate gel combustion method and characterized by X-ray powder diffraction method. Appropriate equilibrium phase mixtures were prepared, sintered in high purity argon gas and used for e.m.f. measurement using solid oxide galvanic cell with yttria-stabilized zirconia (YSZ) electrolyte. The e.m.f. values were measured as a function of temperature in the range of 1000-1200 K. The standard molar Gibbs energy of formation of the ternary oxides were calculated from the e.m.f. data

[en] Gibbs energy of formation of UPd₃(s) has been determined by measuring the equilibrium CO(g) pressure over {UO₂(s) + C(s) + UPd₃(s) + UPd₄(s)} and is given as (Δ_fG⁰_m(UPd₃,s,T) kJ mol^-1±4.1=-526.9+0.1259 T (K), (1175≤T (K)≤1333) Using the required literature data, Δ_fH⁰_m(UPd₃, s, 298.15 K) has been calculated as -(502.3 ± 5.1) kJ mol^-1

[en] The ternary alloys, Al_0.9749U_0.0216Zr_0.0035, Al_0.9607U_0.0316Zr_0.0077, Al_0.940U_0.0472Zr_0.0088 and Al_0.8933U_0.0911Zr_0.0156, were prepared by induction melting and casting. The enthalpy increment measurements were carried out using Calvet calorimetry. The enthalpy increment values as a function of temperature are least squares fitted to polynomial expressions using the constraint that H⁰(T)-H⁰(298.15 K)=0 at 298.15 K. The specific heat capacity expressions for these alloys have been derived and it is observed that C⁰_p(T) of U-Al-Zr alloy decreases with increasing U content

[en] Highlights: • Synthesis, characterization and heat capacities of TiNb_2O_7, Ti_2Nb_1_0O_2_9 and TiNb_2_4O_6_2. • Heat capacity by differential scanning calorimetry. • Smoothed heat capacities data for temperature range 0–850 K using Debye and Einstein functions. • Thermodynamic data tables for all three oxides. - Abstract: Three different ternary oxides TiNb_2O_7, Ti_2Nb_1_0O_2_9 and TiNb_2_4O_6_2 were prepared by solid-state reaction route and characterized by X-ray powder diffraction method. The standard molar heat capacities of these oxides were measured in the temperature range 125–850 K using differential scanning calorimetry. Since, the deviation from additive oxide was found to be insignificant, the low temperature values were extrapolated to 0 K using Debye extrapolation method and smoothed heat capacities data for temperature range 0–850 K were generated using a six-term fitting equation based on Debye and Einstein functions. By employing these smoothed heat capacities data the thermodynamic data tables were generated for all three oxides

[en] The Gibbs energy of formation of SrThO₃(s) has been determined using e.m.f. and manometric techniques. In the e.m.f. method, two fluoride cells have been constructed to determine Δ_fG⁰_m(SrThO₃,s,T) using CaF₂(s) as a solid electrolyte. The cells used are:(((-)O₂(g),Pt/SrO(s)+SrF₂(s)//CaF₂//(SrThO₃(s)+ThO₂(s)+SrF₂(s)/Pt, O₂(g)(+), (I) (-)O₂(g),Pt/SrThO₃(s)+SrF₂(s)+ThO₂(s)//CaF₂(s)//CaO(s)+CaF₂(s)/Pt,O₂(g)(+). (II)) The observed e.m.f. values are represented by following respective expressions: E (V)±0.0001=0.0998+3.254x10^-5T (K), (Cell I) E (V)±0.0001=0.0285-6.37x10^-5T (K). (Cell II) From the measured e.m.f. values of the cells and the Δ_fG⁰_m(T) values from the literature, Δ_fG⁰_m(SrThO₃,s,T) have been calculated and are respectively given as Δ_fG⁰_m(SrThO₃,s,T)±10 kJ mol^-1=-1829.2+0.2735T (K) (978≤T (K)≤1154), (Cell I)) Δ_fG⁰(SrThO₃,s,T)±20 kJ mol^-1=-1853.5+0.2867T (K) (1008≤T (K)≤1168). (Cell II) In the manometric technique, equilibrium CO₂(g) pressures are measured over the three phase mixture: SrThO₃(s)+SrCO₃(s)+ThO₂(s) using a mercury manometer from 1075 to 1197 K. The corresponding Gibbs energy as a function of temperature is given by Δ_fG⁰_m(SrThO₃,s,T)(kJ mol^-1)±14=-1865.4+0.3086T (K).))

[en] High temperature X-ray diffraction measurements were carried out for pure palladium and palladium-rich alloys of compositions Pd_0_._7_7Ag_0_._2_3 and Pd_0_._7_7Ag_0_._1_0Cu_0_._1_3 in the temperature range of 298–1023 K at an interval of 50 K. The lattice parameters, coefficient of thermal expansion and X-ray Debye temperature of these materials were calculated as a function of temperature from the XRD data. The lattice parameter of Pd_0_._7_7Ag_0_._2_3 alloy was found to be higher than that of palladium, whereas the lattice parameter of Pd_0_._7_7Ag_0_._1_0Cu_0_._1_3 was found to be lower than that of palladium in the temperature range of investigation. Further, the lattice parameters of both the palladium alloys show negative deviation from Vegard's law and the deviation was found to increase with increase in temperature. The average value of coefficient of linear thermal expansion was found to follow the trend: α_T (Pd)>α_T (Pd_0_._7_7Ag_0_._2_3)>α_T (Pd_0_._7_7Ag_0_._1_0Cu_0_._1_3). The X-ray Debye temperatures of Pd_0_._7_7Ag_0_._2_3 and Pd_0_._7_7Ag_0_._1_0Cu_0_._1_3 alloys were calculated and found to be 225±10 and 165±10 K, respectively.

[en] Nuclear technology involves the use of a wide range of materials. In a fission reactor, the most important materials are the fuel, the cladding, the coolant and the control rods. The fuel in most of the operating fission reactors are in the solid state which includes a variety of alloys, oxides, carbides and nitrides of uranium and plutonium whereas in a molten salt reactor, the fuel is in the form of low melting eutectic melts of fluoride salts. The claddings which encapsulate the solid fuel and provide mechanical strength and prevent direct contact of fuel with the coolant include mostly alloys of zirconium or different types of steel, depending on the type of nuclear reactors. The coolants in most of the operating thermal reactors are either light water or heavy water, whereas in a fast reactor, it is mostly liquid sodium. In a molten salt reactor, the fuel salt itself serves as a heat transfer medium and secondary coolants of inactive molten salts are used. Controls rods are materials having high neutron absorption cross section which are used to control the chain reaction in a sustained manner and to shut down the reactor. In addition, moderators are used in thermal reactors to thermalize the neutrons whereas fast reactors do not use any moderators

[en] The permeation of hydrogen isotopes especially tritium through structural materials at high temperature is a technological problem. Metal tritides are primarily contained in vessel made of SS316L vessel and these will undergo several thermal cycles during the processing and hydrogen isotopes can permeate out of the SS vessel. Accurate determination of permeation values, is therefore essential for designing of vessel for metal hydrides. With this aim, a study on permeation of hydrogen through SS316 L material was carried out in SS316L specimens of thickness 2,4 and 6mm. Measurements are done using time-dependent permeation method over temperature range of 573-823 K and over hydrogen pressure range of 1-3 bar(a). An experimental set-up for measurement of hydrogen permeation was designed and used for this study. The results indicate that the hydrogen permeation obey Arrhenius type relationship over experimental temperature range and is influenced by wall thickness and feed pressure

[en] The standard molar Gibbs energies of formation of LnFeO₃(s) and Ln₃Fe₅O₁₂(s) where Ln=Eu and Gd have been determined using solid-state electrochemical technique employing different solid electrolytes. The reversible e.m.f.s of the following solid-state electrochemical cells have been measured in the temperature range from 1050 to 1255 K. Cell (I): (-)Pt / {LnFeO₃(s)+Ln 2O₃(s)+Fe(s)} // YDT/CSZ // {Fe(s)+Fe_0.95O(s)} / Pt(+); Cell (II): (-)Pt/{Fe(s)+Fe_0.95O(s)}//CSZ//{LnFeO₃(s)+Ln₃Fe₅O₁₂(s)+Fe₃O₄(s)}/Pt(+); Cell (III): (-)Pt/{LnFeO (s)+Ln₃Fe₅O₁₂(s)+Fe₃O₄(s)}//YSZ//{Ni(s)+NiO(s)}/Pt(+); and Cell(IV):(-)Pt/{Fe(s)+Fe_0.95O(s)}//YDT/CSZ//{LnFeO₃(s)+Ln₃Fe₅O₁₂(s)+Fe₃₄(s) }/Pt(+). The oxygen chemical potentials corresponding to the three-phase equilibria involving the ternary oxides have been computed from the e.m.f. data. The standard Gibbs energies of formation of solid EuFeO₃, Eu₃Fe₅O₁₂, GdFeO₃ and Gd₃Fe₅O₁₂ calculated by the least-squares regression analysis of the data obtained in the present study are given by Δ fG deg. m(EuFeO₃, s) /kJ mol^-1 (± 3.2)=-1265.5+0.2687(T/K) (1050 ≤ T/K ≤ 1570), Δ fG deg. m(Eu₃Fe₅O₁₂, s)/kJ mol^-1 (± 3.5)=-4626.2+1.0474(T/K) (1050 ≤ T/K ≤ 1255), Δ fG deg. m(GdFeO 3, s) /kJ mol^-1 (± 3.2)=-1342.5+0.2539(T/K) (1050 ≤ T/K ≤ 1570), and Δ fG deg. m(Gd₃Fe₅O₁₂, s)/kJ·mol^-1 (± 3.5)=-4856.0+1.0021(T/K) (1050 ≤ T/K ≤ 1255). The uncertainty estimates for Δ fG deg. m include the standard deviation in the e.m.f. and uncertainty in the data taken from the literature. Based on the thermodynamic information, oxygen potential diagrams for the systems Eu-Fe-O and Gd-Fe-O and chemical potential diagrams for the system Gd-Fe-O were computed at 1250 K

[en] The standard molar Gibbs free energies of formation of TbFeO₃(s) and Tb₃Fe₅O₁₂(s) have been determined using solid-state electrochemical cell employing different solid electrolytes. The reversible emfs of the following solid-state electrochemical cells have been measured in the temperature range 1050≤T/K≤1250. Cell (I):(-)Pt/{TbFeO₃(s)+Tb₂O₃(s)+Fe(s)}//YDT/CSZ//{Fe(s)+Fe_0.95O(s)}/Pt(+))) (Cell (II):(-)Pt/{Fe(s)+Fe_0.95O(s)}//CSZ//{TbFeO₃(s)+Tb₃Fe₅O₁₂(s)+Fe₃O₄(s)}/Pt(+) The oxygen chemical potentials corresponding to the three-phase equilibria involving the ternary oxides have been computed from the emf data. The standard molar Gibbs free energies of formation of solid TbFeO₃ and Tb₃Fe₅O₁₂ calculated by the least-squares regression analysis of the data obtained in the present study are given by {Δ_fG^compfn_m(TbFeO₃,s)/(kJ·mol^-1)±3.2}=-1357.5+0.2531·(T/K); (1050≤T/K≤1548);))and({Δ_fG^compfn_m(Tb₃Fe₅O₁₂,s)/(kJ·mol^-1)±3.5}=-4901.7+ 0.9997·(T/K); (1050≤T/K≤1250).)) The uncertainty estimates for Δ_fG^compfn_m include the standard deviation in the emf and uncertainty in the data taken from the literature. Based on the thermodynamic information, oxygen potential diagram and chemical potential diagrams were computed for the system Tb-Fe-O at T=1250 K