Results 1 - 10 of 1535
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[en] Complexation of neptunium(V) with fluoride at elevated temperatures was studied by spectrophotometry and microcalorimetry. Two successive complexes, NpO2F(aq) and NpO2F2-, were identified by spectrophotometry in the temperature range of 10-70 C. Thermodynamic parameters, including the equilibrium constants and enthalpy of complexation between Np(V) and fluoride at 10-70 C were determined. Results show that the complexation of Np(V) with fluoride is endothermic and that the complexation is enhanced by the increase in temperature - a two-fold increase in the stability constants of NpO2F(aq) and more than five-fold increase in the stability constants of NpO2F2- as the temperature is increased from 10 to 70 C.
[en] Sulfate, one of the inorganic constituents in the groundwater of nuclear waste repository, could affect the migration of radioactive materials by forming complexes. Spectrophotometric and microcalorimetric titrations were performed to identify the Np(V)/sulfate complex and determine the equilibrium constants and enthalpy of complexation at 10-70 C. Results show that the complexation of Np(V) with sulfate is weak but slightly enhanced by the increase in temperature. The complexation is endothermic and becomes more endothermic with the increase in temperature. The enhanced complexation at elevated temperatures is due to the increasingly larger entropy of complexation that exceeds the increase in enthalpy, suggesting that the complexation of Np(V) with sulfate is entropy-driven.
[en] The molecular reorganization occurring in liquid crystalline polymer fiber during heat treatment is of great interest for many commercial reasons. Using thermal analysis techniques, WAXS and real time temperature dependent synchrotron SAXS, the structure and morphology of commercial LCP (liquid crystalline polymer), Vectran, HBA/HNA (p-hydroxybenzoic acid/6-hydroxy-2-naphthoic acid), and its variant polymer fiber COTBP, HBA/HNA/BP/TA (BP-benzophenone, TA-terephthalic acid), have been examined. Both fibers have the typical liquid crystalline polymer structure, i.e., highly aligned with aperiodic sequencing along the fiber axis. There is a three-fold increase in strength in both fibers with heat treatment; however, the modulus is observed to increase significantly in COTBP but not in Vectran. This paper reports on the changes and the differences on the structural and morphological behavior for both the as-spun and heat-treated LCP fibers. We propose an 'oriented entanglement' model to describe the differences between the two polymer fibers.
[en] The original version of the article was improperly published online. In the consequence, the update of the article title was provided, which primordial form is as follows: "Early hydration calorimetric study of the sewage sludge incinerated waste streams Portland cement-based binders: technological implications". The original article has been corrected.
[en] Thermal analysis combined with mass spectrometry was applied to radiocarbon dating procedures (age determination of carbon-containing samples). Experiments carried out under an oxygen atmosphere were used to determine carbon content and combustion range of soil and wood samples. Composition of the shell sample and its decomposition were investigated. The quantification of CO2 formed by the oxidation of carbon was done by the application of pulse thermal analysis. Experiments carried out under an inert atmosphere determined the combustion range of coal with CuO as an oxygen source. To eliminate a possible source of contamination in the radiocarbon dating procedures the adsorption of CO2 by CuO was investigated. (author)
[en] Chalcogenide glasses of (As50Se50)100−xAgx (0 ≤ x ≤ 25) were prepared using the melt quenching technique under non-isothermal conditions. Differential scanning calorimetry curves measured at different heating rates (5 ≤ β ≤ 40 K min−1) are used to characterize the as-quenched samples. The thermal stability was monitored through the calculation of the temperature difference Tc − Tg, stability parameter S and crystallization rate factor Kp. The glass-forming ability (GFA) was investigated on the basis of Hurby parameter Hr which is a strong indicator of GFA. In addition, the activation energy of glass transition Et, activation energy of crystallization Ec and Avrami exponent n of the studied compositions were determined. The mechanism of crystallization was found to be a combination of two- and three-dimensional crystal growth.
[en] The present paper is a numerical study on heat transfer and pressure drop of a nanofluid including water as base fluid with Al2O3 nanoparticles inside a square channel having an inner cylinder, with and without fin under constant heat flux condition using two-phase Euler–Lagrange approach. Numerical investigation has been carried out for various combinations of base fluid, nanoparticle size and concentration through a straight cylinder. Simulation has been performed in a laminar flow regime using finite volume method. Besides, the thermal boundary condition of constant uniform heat flux on the channel wall was applied. The results show that the increase in Reynolds number and nanoparticle volume concentration have considerable effects on heat transfer coefficient enhancement. The heat transfer coefficient decreases when nanoparticles diameter increases. The passive way used in this study, leads to higher pressure drops. For all fluids under consideration, pressure drop escalates with Reynolds number. Adding nanoparticles to the base fluid leads to rise in pressure drop, and this effect is more intensive for higher concentrations.
[en] The thulium–germanium binary system has been critically assessed by means of the CALculation of PHAse Diagram technique through Thermo-Calc software package. The thulium–germanium binary system contains nine phases based on eight compounds, the intermediate phases with no solubility ranges: Tm5Ge3, Tm5Ge4, Tm11Ge10, TmGe, Tm4Ge5, TmGe1.5, and Tm0.9Ge2 were treated as stoichiometric phases, while the compound with homogeneity range TmGe1.8 (TmGe1.8_LT and TmGe1.8_HT) was modeled using two sublattices model as (Ge,Tm)0.358(Ge)0.642. The liquid phase was modeled as substitutional solution phase, in which the excess Gibbs free energy was formulated with Redlich–Kister polynomial. The germanium (diamond_A4) and thulium (hcp_A3) were kept as pure element phases since no solubility of germanium in thulium and vice versa. The calculations based on the thermodynamic modeling agree well with the phase diagram data and few experimental thermodynamic values from the literature.
[en] Many standard thermodynamic data in the binary system Li–Sb can be found in literature; however, they are often derived from electrochemical measurements taken at higher temperatures. The uncertainties associated with the extrapolation of these high-temperature data to room temperature are, however, inherently large. Therefore, a comprehensive investigation of the thermodynamic properties in the Li–Sb system was conducted in this work to generate more reliable data. Four different experimental techniques were used for the investigations. The heat capacities for both binary compounds, Li2Sb and Li3Sb, were measured for the very first time. In addition, the enthalpies of formation for both compounds were determined by drop solution and direct reaction calorimetry. Furthermore, Knudsen effusion mass spectrometry was performed to measure partial enthalpies and activities of Sb.