No abstract available

[en] The neptunium-hydrogen system has been investigated previously by Mulford and Wiewandt (1965) who found two hydride phases. One phase, NpHsub(2+x) (0 < x < 0.7) has a f.c.c. crystal structure and the other phase, NpHsub(3-x), has a h.c.p. structure. These authors found an anomalous behaviour of the cubic NpH₂ phase at the lower composition limit as the hydrogen content increases with increasing temperature. Another anomalous trend may be shown to exist in the thermodynamic values calculated from the pressure-composition isotherms. When partial molal enthalpies and entropies are calculated for the homogeneity range of the cubic, non-stoichiometric NpHsub(2+x) (by plotting log P vs. 1/T, for a fixed value of x), one finds that ΔH values are independent of hydrogen composition (x), whereas ΔS decreases (becomes more negative) with increasing x. Both results contradict conventional statistical-thermodynamic derivations which are applied to metal-hydrogen systems. The present note reinvestigates the neptunium-hydrogen system and establishes whether such anomalous thermodynamic behaviour really exists. (Auth.)

[en] Diagenesis of argillaceous sediments is dependent upon many factors, including depositional environment, types of clay minerals, amount of organic matter, pore water chemistry, geothermal gradient and burial history. The systematic loss of porosity recorded with increasing burial is related to gravitational compaction and chemical diagenesis, most importantly the progressive reaction from smectite to illite. Because diagenetic processes are linked to flowing fluids, which transport heat and ions, flow rates, duration of flow and fluid pathways are crucial. Fluid inclusions often reveal precipitation of diagenetic minerals into fractures at temperatures less than 50 deg C, as well as the presence of injected clay fillings. (author)

[en] Selected values are given for the thermochemical properties of the compounds of thorium. They are obtained from a computer-assisted least sums-least squares approach to the evaluation of thermodynamic data networks. The properties given, where data are available, are enthalpy of formation, Gibbs energy of formation, and entropy at 298.15 K (Δ Hf (298), Δ Gf (298), and S (298)). The values are consistent with the CODATA Key Values for Thermodynamics. The reaction catalog from which this self consistent set of values is generated is given with a statistical analysis. Some thermal functions are also given, as well as detailed comments when necessary

No abstract available

[en] The free energy, enthalpy and entropy of formation of the compounds Cs₃PuCl₆ and CsPu₂Cl₇ have been determined by measuring the sublimation pressures for the reactions CsCl(s)↔CsCl(g), 2/5 Cs₃PuCl₆(s)↔ 1/5 CsPu₂Cl₇(s)+CsCl(g), and CsPu₂Cl₇(s)↔PuCl₃(s)+CsCl(g). The pressures are measured using Knudsen effusion mass spectrometry over the temperature range 600 to 850 K. For the formation of Cs₃PuCl₆ from CsCl and PuCl₃, ΔG₂₉₈ =-77.3±8.5 kJ/mol, ΔH₂₉₈ =-82.1±7.8 kJ/mol, and ΔS₂₉₈ =-16.2±10.9 J/K mol. For CsPu₂Cl₇, ΔG₂₉₈ =-39.4±3.5kJ/mol, ΔH₂₉₈ =-40.8±3.2 kJ/mol, and ΔS₂₉₈ =-4.6±4.2 J/K mol. (orig.)

No abstract available

[en] The standard enthalpy of formation of tantalum (IV) bromide has been determined by solution calorimetry: ΔHsub(f)sup(0)(TaBr₄(c)298 K) = -125.6 +- 0.5 kcal mol^-1. Experimental estimates of the enthalpies of formation of tantalum (III) bromide and tantalum (II,III) bromide were also obtained. Estimates of the entropies and heat capacities of the compounds are also given. (auth)

[en] The enthalpies of solution of Nd(OH)₃ and of Nd₂O₃ have been measured in 6.00 mol·dm^-3 HCl(aq) at 298.15 and at 308.15 K. From these measurements Δ_fH_m⁰ {Nd(OH)₃, s, 298.15 K} has been calculated to be -(1403.7±1.0) kJ·mol^-1. When combined with S_m⁰{Nd(OH)₃, s, 298.15 K}, the molar Gibbs free energy of formation Δ_fG_m⁰{Nd(OH)₃ s, 298.15 K} is calculated to be -(1270.9±1.1) kJ·mol^-1 and the standard solubility-product constant for Nd(OH)₃ is calculated to be 5 x 10^-23 or pK_sp⁰ = (22.3±0.7). (author)

[en] Highlights: • A novel nanoparticle-enhanced supramolecular fracturing fluid was developed. • The nanoparticle andsurfactant improved the properties of the fracturing fluid. • Low damage and efficient imbibition were realized with this fracturing fluid. • Oil production of the test well without flowback was increased significantly. The oil production from the low-pressure tight reservoirs in China decreases sharply after fracturing under natural depletion. To supply the formation energy and displace oil through imbibition instead of flowback, a novel nanoparticle-enhanced supramolecular fracturing fluid (NESF) was developed. It consisted of 0.10 wt% hydrophobically modified hydroxypropyl guar (HMHPG), 1.00 wt% synthesized hydrophilic gemini surfactant (HGS), and 0.05 wt% hydrophobically fumed nanosilica (HNS). A series of experiments were conducted to characterize the molecular structure of HGS and evaluate the heat/shear resistance, rheological property, proppant suspension and transportation, formation damage, and imbibition efficiency of NESF. Finally, the oilfield practical application of NESF fracturing without flowback was carried out. The results showed that the heat resistance and the interfacial property of NESF were improved by HNS and HGS respectively. Besides the favorable common properties, a low oil permeability loss rate of 9.40%, a high fracture conductivity retainment rate of 95.11%, and a high imbibition recovery factor of 19.43% were realized by NESF. The accumulative oil production of the well stimulated by NESF without flowback was increased by 13.55% and the decline rate of oil production was reduced from 14.70% to 5.22% in the first 6 months.