D Das

Thermodynamic stability of barium thorate, BaThO3, from a Knudsen effusion study

Abstract The Gibbs energy of formation of barium thorate was determined using the Knudsen effusion forward collection technique. The evaporation process could be represented by the equation BaThO 3 (s)=ThO 2 (s)+BaO(g) The vapour pressure of BaO(g) over the two-phase mixture of BaThO3(s) and ThO2(s) was obtained from the rate of effusion of BaO(g) and could be represented as ln (p/ Pa ) (±0.39)=−50526.5/T/ K +26.95 (1770≤T/ K ≤2136) The Gibbs energy of formation of BaThO3(s) could be derived from this data and represented as Δ f G°( BaThO 3 (s) )/ kJ mol −1 ±8.0=−1801.75+0.276T/ K

Gibbs energy of formation of barium thorate (BaThO3) by reactive carrier gas technique

Abstract The Gibbs energy of formation of BaThO3 was determined employing the heterogeneous reaction between the compound and water vapour involving the formation of gaseous barium hydroxide species according to the reaction BaThO3(s)xa0+xa0H2O(g)=ThO2(s)xa0+xa0Ba(OH)2(g). The vapour pressure of barium bearing species over the univariant mixture containing barium thorate and thorium dioxide as the condensed phases in equilibrium with a controlled pressure of water vapour was measured in the temperature range 1548–1683 K employing the automatic recording transpiration apparatus. The vaporization of BaThO3 was studied in the presence of flowing argon saturated with water vapour. The equilibrium constant of the above reaction could be expressed by the equation ln Kp (±0.03)=−20306/Txa0+xa05.37 (1548⩽T/K⩽1683). The Gibbs energy of formation for BaThO3 derived from these data could be expressed as ΔfG°〈BaThO3〉 (±38 kJ/mol)=−1775.8xa0+xa00.266T between 1548 and 1683 K.

Thermodynamic stability of solid SrThO3

Abstract The Gibbs energy of formation of strontium thorate was determined by the Knudsen effusion forward collection technique. The evaporation process from a mixture of tungsten and strontium thorate in the Knudsen cell could be represented by the following heterogeneous equilibria: 5SrThO3(s)+W(s)=Sr2WO5(s)+5ThO2(s)+3Sr(g), 1670 Δ f G 0 ( SrThO 3 ( s )) (±5.0 kJ mol −1 )=−1953.6+0.367·T , (1670 Δ f G 0 ( SrThO 3 ( s )) (±7.0 kJ mol −1 )=−1960.2+0.369·T , (2135

Gibbs energy of formation of solid Ni3TeO6 from transpiration studies

Abstract The thermodynamic stability of nickel tellurate was established by studying the heterogeneous equilibrium Ni 3 TeO 6 ( s )=3 NiO ( s )+ TeO 2 ( g )+ 1 2 O 2 ( g ) . Using the transpiration technique, the equilibrium constant of the reaction was obtained from the vapor pressure measurement of TeO2(g) over the biphasic mixture of Ni3TeO6(s) and NiO(s) under 1 bar oxygen pressure. From the equilibrium data the second-law value of ΔfH° (Ni3TeO6(s), 298.15 K) was found to be −1216(±14) kJxa0mol−1. The energy change of the heterogeneous reaction derived from the equilibrium constant was used to calculate the Gibbs energy of formation of Ni3TeO6 as could be expressed by ΔfG° (Ni3TeO6(s)) (±13 kJ mol −1 )=−1307+0.64· T , ( 1122 K ⩽T⩽1202 K ). The above Gibbs energy data were found to be consistent with the available thermodynamic information of the Ni–Te–O ternary system.

Transport properties of iodine and tellurium in a thoria-2 mol% urania matrix

Abstract Diffusion properties of the volatile fission products iodine and tellurium inside the thoria based fuel matrix (ThO2-2 mol% UO2) were obtained by studying the release kinetics of the species from trace-irradiated fuel samples at different temperatures (1290–1790 K) in post-irradiation annealing experiments. Analysis of the kinetic data shows that the release through bulk diffusion is too low to be measurable below 1273 K. The apparent bulk diffusion coefficients for the two volatile species could be evaluated at higher temperatures in a well-defined powder sample (37–45 μm particle size, 24 m2xa0kg−1 BET surface area) of the high-density fuel (>95% T.D.). Temperature dependences of the diffusion coefficients of iodine and tellurium derived from this study could be expressed in the form of Arrhenius equations as log D ′ I ( s −1 )=−(15 000±1000)/T−1.19±0.63 , and, log D ′ Te ( s −1 )=−(25 600±1200)/T+6.14±0.77 . Activation energies and frequency factors for diffusion of the two species as obtained from the Arrhenius equations are 286 kJxa0mol−1 and 6.4xa0×xa010−2 s−1 for I and 491 kJxa0mol−1 and 1.38xa0×xa0106 s−1 for Te. The two sets of kinetic data are quite different and they suggest that the two species have different mechanisms of their transport in the fuel matrix. The results were compared with reported data in pure urania and thoria matrices.

Thermodynamics of liquid uranium vaporization

Abstract The vaporization of liquid uranium contained in single crystal cups of tantalum and tungsten was studied up to 3000 K using Knudsen effusion assembly. The flux of U(g) vapours effusing through the K-cell orifice was corrected for the solubility of Ta (or W) in liquid uranium and the equilibrium vapour pressure of liquid uranium was determined as: Log (P° u /aim) = (6.295 ± 0.164) - (2.642 ± 0.041) × 10 4 /T The sublimation enthalpy of uranium at 298.15 K was evaluated to be 126.3 ± 0.3 kcal/mol.

Vaporization behavior and Gibbs energy of formation of Cs2ThO3

Abstract The thermodynamic stability of rubidium thorate, Rb2ThO3(s), was determined from vaporization studies using the Knudsen effusion forward collection technique. Rb2ThO3(s) vaporized incongruently and predominantly as Rb2ThO3(s)=ThO2(s)xa0+xa02Rb(g)xa0+xa01/2xa0O2(g). The equilibrium constant K=pRb2·pO21/2 was evaluated from the measurement of the effusive flux due to Rb vapor species under the oxygen potential governed by the stoichiometric loss of the chemical component Rb2O from the thorate phase. The Gibbs energy of formation of Rb2ThO3 derived from the measurement and other auxiliary data could be given by the equation, ΔfG°(Rb2ThO3,s)=−1794.7+0.42Txa0±xa0 5.0 kJ mol −1 (1058⩽T/K⩽1187) .

Gibbs energy of formation of Ba(OH)2 vapor species using the transpiration technique

Abstract The Gibbs energy of formation of Ba(OH) 2 was determined employing the heterogeneous reaction between solid BaO and water vapor and generating gaseous barium hydroxide species according to the reactions BaO(s)+H 2 O(g)=Ba(OH) 2 (g). The equilibrium vapor pressure of Ba(OH) 2 species under a controlled pressure of water vapor was measured using an automatic recording transpiration apparatus. From the vapor pressure results, the equilibrium constant of the reaction obtained could be represented as ln K p (±0.04)=−16792.3/T+4.94 , K p = p (Ba(OH) 2 )/ p (H 2 O) (1346⩽ T /K⩽1451). The Gibbs energy of formation of Ba(OH) 2 derived from these data could be expressed as Δ f G °( Ba ( OH ) 2 , g )(±2 kJ mol −1 )=−667.29+0.118 T (1346⩽T/ K ⩽1451) . From the study, the second-law and third-law values of Δ f H°(Ba(OH) 2 ,g, 298.15 K) were worked out to be −(645.1±8.0) kJ mol −1 and −(643.9±2.5) kJ mol −1 , respectively.

Thermodynamic stability of Cs2ZrO3 by Knudsen effusion technique

Abstract Thermodynamic stability of cesium zirconate was determined by measuring the vapour pressure of Cs2O using Knudsen effusion forward collection technique. Cs2ZrO3(s) vaporized incongruently according to the reaction Cs 2 ZrO 3 (s)= ZrO 2 (s)+ Cs 2 O (g) The Gibbs energy of formation of Cs2ZrO3 obtained from the vapour pressure of Cs2O and other auxiliary data could be given by the equation Δ f G° ( Cs 2 ZrO 3 , s) (±18.0 kJ/mol )=−1671.6+0.440T (1142≤T/K≤1273)

Gibbs energy of formation of the Rh–Te intermetallic compounds Rh3Te2 and RhTe0.9

Abstract The vaporization behavior of the intermetallic compounds Rh3Te2 and RhTe0.9 was studied in the temperature range 1151–1234 and 1026–1092 K, respectively, by Knudsen effusion mass loss technique. The phase analysis of partially evaporated samples of Rh3Te2 (s) and RhTe0.9 (s) together with the available information on Te bearing vapor species revealed that the compounds incongruently volatilize as Rh3Te2 (s) = 3Rh (s)xa0+xa02/nTen (g) and 3RhTe0.9 (s) = Rh3Te2 (s)xa0+xa00.7/nTen (g), (n=1,2), respectively. The equilibrium vapor pressures of Te2 (g) and Te (g) were derived from the total pressure p(Ten) measured over the mixtures Rh3Te2 (s) and Rh (s), and RhTe0.9 (s) and Rh3Te2 (s) in the respective cases. The standard Gibbs energy of formation of Rh3Te2 and RhTe0.9 derived using the above vapor pressure data and other auxiliary data could be expressed by the equations ΔfG°(Rh3Te2, s) (kJxa0mol−1) = −176.9xa0+xa00.039T±7.0 and ΔfG°(RhTe0.9, s) (kJxa0mol−1) = −74.7xa0+xa00.015T±3.0 kJxa0mol−1, respectively.