Search Results
Abstract
A thermodynamic study of the influence of the thermal treatments (annealing), below the glass transition temperature, on the thermal behavior and enthalpy of maltitol glass was carried out by differential scanning calorimetry (DSC). An enthalpic effect (exothermal) produced by the isothermal treatment of the quenched glass was found and measured. The origin of the thermal effect was assigned to a physicochemical transformation of molecular associations in the solid (glass). To achieve a correct description of the thermodynamic functions of glasses, another parameter, in addition to T and P, is introduced, namely the degree of advance of the above mentioned transformation.
Abstract
The results of recent developments on modelling of supramolecular ordering and physicochemical properties of molecular mixtures have been reviewed. The main attention is paid to the unified approach based on a generalized quasichemical model for a set of thermodynamic, dielectric and optical properties of mixtures, self-organized by specific bonding. Interrelations between thermodynamic, as well as dielectric, and optical properties of liquid mixtures, reflecting different molecular parameters, and the characteristics of quasichemical processes are presented. Applications for thermodynamic functions of mixing, permittivity, coefficients Rayleigh light scattering in molecular mixtures are considered. Data on thermodynamics of aggregation in mixtures have been obtained.
Abstract
The i-butyldodecylsulfoxide (BDSO) was synthesized. The extraction of uranium(VI) has been carried out with BDSO in toluene from various HNO3 concentrations. It was found that the distribution ratio increases with increasing nitric acid concentration up to 3.0 mol/l and then decreases. The distribution ratios also increase with increasing extractant concentration. The extracted species appears to be UO2(NO3)2·2BDSO and the equilibrium constant value is 15.2. The influence of temperature, sodium nitrate and oxalate concentrations on the extraction was also investigated, and the thermodynamic functions of the extraction reaction were obtained.
Abstract
Phase diagrams of urea-α-naphthol and urea-benzoic acid systems, determined by the thaw-melt method, show the formation of simple eutectic in each case. The growth velocity data, determined at different undercooling (ΔT) by observing the rate of movement of interface in a capillary, obey the Hillig-Turnbull equation, v=u(ΔT)n, where u and n are constants depending on the nature of the materials. Using enthalpy of fusion, undercooling (ΔT) and melting point data, entropy of fusion, interfacial energy, enthalpy of mixing, critical radius size and excess thermodynamic functions were calculated. The microstructural investigations give characteristic features of the eutectics.
Enthalpies of dissolution of benzo-15-crown-5 ether (B15C5) in mixtures of acetonitrile with water and in solutions of NaI and NaBPh4 (I=0.05 mol dm−3) in these mixtures were measured at 298.15 K. From the obtained results and appropriate literature data, the thermodynamic functions of B15C5/Na+ complex formation in acetonitrile-water mixtures were determined. The enthalpies of transfer of the complex B15C5/Na+ from pure acetonitrile to the examined mixtures were calculated and are discussed.
The phase diagrams of binary organic systems of benzidine with pyrogallol andp-nitrophenol give a double simple eutectic type phase diagram showing formation of a 1∶1 molecular complex with congruent melting point and two eutectics. The growth data on the pure components, the eutectics and the molecular complexes, determined by measuring the rate of movement of growth front in a capillary, justify the square relationship between growth velocity and undercooling. While enthalpy of mixing values suggest intermolecular hydrogen bonding, the excess thermodynamic functions reveal strong interactions among the components forming eutectics and addition compounds.
Abstract
Synthetic enstatite MgSiO3 was crystallized from a melt, quenched into water, and then annealed at 873 K. The product is the monoclinic polymorph with the unit cell parameters of a=0.9619(7), b=0.8832(3), c=0.5177(4) nm, β=108.27(5)°. Heat capacity was measured from 6 to 305 K using an adiabatic vacuum calorimeter. Thermodynamic functions for clinoenstatite differ by about 5% from those predicted after a thermodynamic model in the literature, but are very close to those measured for orthorhombic enstatite.
Abstract
Heat capacity of stoichiometric homogeneous spinel MgFe2O4 was measured from 5 to 305 K and thermodynamic functions were derived for temperatures up to 725 K using our previous high-temperature experimental data for the same sample. Anomaly in C p was found at very low temperatures. Experimental data below 20 K contain large (up to 25% near 5 K) error arising from the difference in the thermal history between the experimental series. Magnetic contribution to the low-temperature heat capacity was tested, and the linear function was found to fit experimental data better than the three-halves power derived from the spin-wave theory.
Abstract
The molar heat capacity, C p,m, of a complex of holmium chloride coordinated with L-aspartic acid, Ho(Asp)Cl2·6H2O, was measured from 80 to 397 K with an automated adiabatic calorimeter. The thermodynamic functions H T-H 298.15 and S T-S 298.15 were derived from 80 to 395 K with temperature interval of 5 K. The thermal stability of the complex was investigated by differential scanning calorimeter (DSC) and thermogravimetric (TG) technique, and the mechanism of thermal decomposing of the complex was determined based on the structure and the thermal analysis experiment.
Summary
The sorption of 60Co2+, 115mCd2+ and 203Hg2+ from diluted solutions (as analogues for radioactive waste waters) on ETS-4 microporous titanosilicate was studied at 277, 293, 313 and 333 K by measuring the sorption kinetics using a batch-method. The sorption of these radiocations was compared by means of the distribution coefficient and of the sorption capacity. The maximum sorption capacities follow the order: 203Hg2+>115mCd2+³60Co2+. The thermodynamic functions of the sorption processes have been estimated. The increase of the absolute value of DG° with increasing temperatures shows that higher temperatures favor ionic exchange.
