The limiting partial molar volumes and isentropic compressibilities of 2-methylpyridine and 2,6-dimethylpyridine in aqueous and methanolic solutions were calculated from the densities and speeds of sound at 293.15 and 298.15 K. All the limiting functions are smaller than the respective functions for the pure amines, due to the hydrogen bonds O-H... N between the amine molecules and those of water or methanol. The standard functions of transfer of the amines from methanol to water are negative which results from different nature of interactions in the aqueous and methanolic solutions. Most probably, the hydrophobic effect contributes to the limiting partial volumes and compressibilities of the amines diluted in water. That makes them smaller than the respective functions for the amines in methanol.
The room temperature ^{57}Fe Mössbauer spectra for binary iron-based solid solutions Fe_{1-x}Al_x, with x in the range 0.03 ≤ x ≤ 0.05, were analysed in terms of binding energy E_b between two Al atoms in the Fe-Al system. The extrapolated values of E_b for x= 0 were used for computation of the dilute-limit heat of solution of aluminium in iron. The results were compared with that resulting from the Miedema's model of alloys as well as those derived from the heat of formation of the system, obtained with both calorimetric measurements and theoretical calculations. The comparison shows that our Mössbauer spectroscopy findings are in good agreement with all the other results mentioned above.
The performance of an isothermal endoreversible four-reservoir chemical potential transformer, in which the mass transfer between the mass reservoir and the working medium obeys diffusive law, is analyzed and optimized in this paper. The relation between the rate of energy pumping and the coefficient of performance of the isothermal chemical potential transformer is derived by using finite-time thermodynamics. Moreover, the optimal operating regions and the influences of some parameters on the performance of the cycle are studied. The results obtained herein can provide some new theoretical guidelines for the optimal design of a class of apparatus such as mass exchangers, as well as electrochemical, photochemical, and solid-state devices, and the fuel pumps for solar-energy conversion systems.
An attempt to describe excess molar functions of alkane + alcohol and alcohol + alcohol binary mixtures was made using the theoretical approach constructed on the basis of S-ERAS model and the chemical theory proposed by Campbell. The results obtained seem to be promising, however in order to complete the work, the procedure of determination of fitting parameters as well as relative magnitude of physical and chemical contributions to regarded excess molar quantities must be established.
The room temperature Mössbauer spectra of ^{57}Fe were measured for Fe_{1-x}Si_x solid solutions with x in the range 0.01 ≤ x ≤ 0.05. The obtained data were analysed in terms of the binding energy E_{b} between two silicon atoms in the studied materials using the extended Hrynkiewicz-Królas idea. The extrapolated value of E_{b} for x=0 was used to computation of an enthalpy of solution H_{FeSi} of Si in α-Fe matrix. It was found that the H_{FeSi} value is negative or Si atoms interact repulsively. The result was compared with corresponding values given in the literature which were derived from experimental calorimetric data as well as with the value resulting from the cellular atomic model of alloys by Miedema.
Density (ρ), refractive index (n), ultrasonic velocity (u), and viscosity (η) were measured for the binary mixtures formed by butylamine with 1-butanol and tert-butanol at temperatures 293, 303, and 313 K over the entire composition range. Excess molar volume V_m^E, molar refraction deviation ΔR_m, deviation in ultrasonic velocity Δu, viscosity deviation Δη, and excess Gibb's free energy of activation for viscous flow ΔG^{*E} were derived from the experimental data and the computed results were fitted to the Redlich-Kister polynomial equation. The values of V_m^E, ΔR_m, Δu, Δη, and ΔG^{*E} were plotted against the mole fraction of butylamine. The observed positive and negative values of excess parameters for both the mixtures were explained on the basis of intermolecular interactions present in these mixtures. The higher negative values of V_m^E and ΔR_m and positive values of Δu, Δη, and ΔG^{*E} for butylamine + 1-butanol mixture suggest that specific interactions are taking place in butylamine + 1-butanol mixture, while weak dipole-dipole induced forces and dispersive forces seem to be responsible for butylamine + tert-butanol mixture. Furthermore, different empirical relations were used to correlate the binary refractive indices. An excellent agreement was found between experimental and theoretical values.
The room temperature Mössbauer spectra of ^{57}Fe were measured for iron-based solid solutions Fe_{1-x}Co_{x} and Fe_{1-x}Ni_{x} with x in the range 0.01 ≤ x ≤ 0.05. The obtained data were analysed in terms of the binding energy E_{b} between two Co or Ni atoms in the studied materials using the extended Hrynkiewicz-Królas idea. It was found that the energy is positive or the non-iron atoms interact repulsively. The extrapolated value of E_{b} for x=0 was used for computation of the enthalpy of solution of cobalt and nickel in iron. The results were compared with our previous Mössbauer spectroscopy findings, the values resulting from the Miedema's model of alloys and the data derived from the enthalpy of formation of the Fe-Co and Fe-Ni systems, obtained with calorimetric methods. The comparison shows that the present results are in a qualitative agreement with the Miedema's model predictions and calorimetric measurements but they are at variance with the previous Mössbauer spectroscopy findings.
Specific heat ratio (γ), pseudo-Grüneisen parameter (Γ), heat capacity (C_p) and effective Debye temperature (θ_{D}) for binary system of tetrahydrofuran with o-cresol and methanol respectively, were calculated using the experimentally measured densities, velocities and viscosities of the pure liquids and their mixtures over the whole composition range and at T = 293, 303, 313 K. The excess pseudo-Grüneisen parameter (Γ ^{E}), excess molar isentropic compressibility (K_{s}^{E}) and excess acoustic impedance (Z^{E}) were also calculated. The excess deviation functions have been correlated using Redlich-Kister polynomial equation. The observed values of the excess parameters plotted against the mole fraction of tetrahydrofuran have been explained on the basis of intermolecular interaction suggesting strong interaction in tetrahydrofuran + o-cresol than in tetrahydrofuran + methanol. Partial molar isentropic compressibility at infinite dilution and their excess values were calculated for each component. Sanchez theory, Goldsach-Sarvas volume fraction statistics, Sudgen's relation, Flory-Patterson-Rastogi and Brock and Bird model were used with the Aurebach relation to compute theoretically the values of ultrasonic velocities at varying temperatures. The velocity deviations were estimated in terms of average percentage deviations. Internal pressure for both the systems were calculated theoretically and discussed on the basis of relative applicability of the models in theoretical estimations. The isothermal compressibility (k_T), for these binary mixtures were theoretically evaluated by using the Flory statistical theory and five hard sphere models and compared with the experimental values.
The aim of the study was to determine whether it is possible to correlate directly the barrier properties of elastomer materials assessed on the basis of the breakthrough time t_{p} with the thermodynamic affinity of the elastomer-solvent system, characterized by their solubility parameters δ. According to EN ISO 6529:2001 standard, breakthrough time is defined as the time elapsing from the moment that the tested material sample gets in contact with the chemical to the moment in that a specified amount of the substance appears on the other side of the sample. Cured butyl rubber (IIR) in the form of flat membranes were tested in the study. For the nonpolar rubber-polar or rubber-nonpolar solvent systems it has been found that significant differences in rubber and solvent solubility parameters not in every case leads to better resistance to permeation. The properties of the permeating chemical and the rubber, including its polarity, shape, and molecule dimension of the solvent, are of considerable importance. A marked disparity of breakthrough times were observed for the permeation of polar or nonpolar solvents despite similar values of their solvent solubility parameter. The breakthrough time of the solvent from the homologous series (pentane, hexane and heptane) is determined not only by the rubber and solvent solubility parameters but by the size of the chemical molecule as well. Therefore, for the assessment of material barrier properties the thermodynamic affinity or dissimilarity of the elastomer and the permeating solvent is only semiquantitative in character.
The refractive indices, densities and ultrasonic velocities of binary liquid mixtures of tetrahydrofuran (THF) with methanol and o-cresol over the entire composition range have been measured at 293, 303 and 313 K. Refractive index, density and ultrasonic velocity data have been used to evaluate the molar refraction deviation ΔR_{m}, deviation in ultrasonic velocity Δu, excess internal pressure π_{i}^{E}, excess molar enthalpy H_{m}^{E} and excess free volume V_{f}^{E}. The computed results of ΔR_{m}, Δu, π_{i}^{E}, H_{m}^{E} and V_{f}^{E} were fitted to the Redlich-Kister polynomial equation. These results suggest that specific strong interactions are taking place in THF + o-cresol mixture while dispersive forces seem to be responsible for behaviour of THF + methanol mixture. Further, experimental refractive index and density data of these mixtures were also used to test the validity of the empirical/semi-empirical relations and models for refractive index and density, respectively.
Due to high bonding energy of N_2 molecule, the III-V semiconducting nitrides, especially GaN and InN require high N_2 pressure to be stable at high temperatures necessary for growth of high quality single crystals. Physical properties of GaN-Ga(l)-N_2 system are discussed in the paper. On the basis of the experimental equilibrium p-T-x data and the quantum-mechanical modeling of interaction of N_2 molecule with liquid Ga surface, the conditions for crystallization of GaN were established. The crystals obtained under high pressure are of the best structural quality, having dislocation density as low as 10-100 cm^{-2} which is several orders of magnitude better than in any other crystals of GaN. The method allows to grow both n-type substrate crystals for optoelectronics and highly resistive crystals for electronic applications. The physical properties of the pressure grown GaN measured to characterize both point defects and extended defects in the crystal lattice are discussed in the paper. A special attention is paid to the application of high pressure to reveal the nature of the point defects in the crystals and electric fields in GaN-based quantum structures. Due to their very high structural quality, the pressure grown crystals are excellent substrates for epitaxial growth of quantum structures. It opens new possibilities for optoelectronic devices, especially short wavelength high power lasers and efficient UV light emitting diodes. This is due to the strong reduction in dislocation densities in relation to existing structures (10^6-10^8 cm^{-2}) which are grown on strongly mismatched sapphire and SiC substrates. The experimental results on the epitaxial growth and physical properties of GaN-based device structures supporting above conclusions are discussed in the paper. The current development of blue laser technology in High Pressure Research Center is shortly reviewed.
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