Papers by Keyword: Thermodynamic Property

Abstract: Since the emergence of van der Waals equation of state, several equations have been proposed to represent the behavior of pure compounds and mixtures, such as GEOS, which is a new generalized cubic equation of state form that employs a temperature function dependent on two or three adjustable parameters. Recently, multiobjective optimization has started to be applied in equations of state for parameters estimation, due to the conflicting nature of the objective functions. This methodology is attractive because it can be used to compare different models or variants of the same problem, through the trade-off analysis of the so-called Pareto front. In this context, the multiobjective PSO algorithm, based on the Pareto dominance principle, is used in this work for estimating the parameters of the generalized cubic equation of state, by fitting its results to synthetic experimental data of vapor pressure and saturated liquid volume. The performance of the new estimated parameters of the three temperature functions is investigated through the calculation of thermodynamic properties of interest in industry and academia. In addition, comparisons against real experimental data available in the literature are performed.

Abstract: The structural, mechanical, and thermodynamic properties of refractory metals Rh, Ir, W, Ta, Nb, Mo, Re, and Os have been systematically investigated by first-principles calculations based on density functional theory. Comparative studies reveal that Young's modulus (E = 636.42 GPa), shear modulus (G = 256.81 GPa), bulk modulus (B = 406.55 GPa), and microhardness (H = 44.69 GPa) of hexagonal Os are the highest, which reveals Os has the best overall mechanical properties. The body-centered cubic Nb has the smallest Young's modulus (E = 94.76 GPa), shear modulus (G = 33.62 GPa), bulk modulus (B = 174.50 GPa), and hardness (H = 2.04 GPa). Based on the ratio of bulk to shear modulus, it is judged that Rh, Ir, and Os are brittle materials (B/G < 1.75), and Nb, Ta, Mo, W, and Re exhibit ductile (B/G > 1.75). The elastic anisotropy has also been discussed by plotting both the 3D contours and the 2D planar projections of Young's modulus. For the face-centered cubic metals Rh and Ir and hexagonal close-packed metals Re and Os, the 3D contours of the Young's modulus are very similar, whereas body-centered cubic metals Ta, W, Nb, and Mo exhibit significant difference in elastic anisotropy. The thermodynamic calculations show that Debye temperature and minimum thermal conductivity decreases along Rh, Os, Mo, Ir, Re, W, Ta, Nb sequence. Furthermore, the results can be used as a general guidance for the design and development of high temperature refractory alloy system.

Abstract: We investigate the electronic, dynamic and thermodynamic properties of α-MnO₂ using first-principles calculations based on density functional theory (DFT) with the GGA+U method. The results of electronic structures show that α-MnO₂ is a semiconductor with a direct band gap of 1.4 eV at Γ point. The results of dynamic properties indicate that the structure of α-MnO₂ is dynamically unstable at ground-state. Several important thermodynamic quantities, such as entropy, enthalpy and Gibbs free energy, et al each as a function of temperature were presented.

Abstract: In the paper, the progresses on the thermodynamic properties of several alkalis borates including lithium borates, sodium borates, potassium borates, rubidium borates and cesium borates at present were summarized, and the new trend in the future was also pointed out.

Abstract: It is well known that the magnesium borates are important materials in all fields. In this paper, the process on synthesis and thermodynamic properties of several hydrated magnesium borates including MgO·2B₂O₃·9H₂O (hungchaoite), MgO·3B₂O₃·7.5H₂O (mcallisterite), MgO·3B₂O₃·7H₂O, 2MgO·3B₂O₃·17H₂O, MgO·3B₂O₃·5H₂O (aksaite) were summarized. The key problems existed and the new trends in the future were also carried out.

Abstract: The derivatives of HNS are optimized to obtain their molecular geometries and electronic structures at the DFT-B3LYP/ 6-31G^* level. Their IR spectra are obtained and assigned by vibrational analysis. Compared with the experimental results, all the calculated IR data are found to be reliable. Based on the frequencies scaled by 0.96 and the principle of statistic thermodynamics, the thermodynamic properties are evaluated, which are respectively linearly related with the number of methyl, azido and difluoramino groups as well as the temperature, obviously showing good group additivity.

Abstract: The fully optimized and vibrational analysis calculation of some silane compounds containing Si-Ph bonds were carried out at the B3LYP/6-31G* level, to obtain the thermodynamic parameters of the molecules in standard state 298.15K, 1.013 × 105 Pa. Based on the output file of the Gaussian 03 program, using the statistical thermodynamic program to calculate the molar constant pressure heat capacity (Cp, m)of phenyl substituted silane derivatives from 200K to 1800K, the correlation between the Cp, m and temperature (T, T-1 and T-2) was fitted with the least square method, and what was found was that the Cp, m of series of phenyl substituted silane derivatives had a very good correlation with T, T-1 and T-2.

Abstract: An investigation on electronic, elastic and thermodynamic properties of VN under high pressure has been conducted using first-principles calculations based on density functional theory (DFT) with the plane wave basis set as implemented in the CASTEP code. At elevated pressures VN is predicted to undergo a structural phase transition from the relatively open NaCl-type structure into the denser CsCl-type atomic arrangement. The predicted transition pressure is 189 GPa. The elastic constants, Debye temperature as a function of pressure and temperature of VN are presented.

Abstract: Potential energy scan for U2 was performed by density functional theory (DFT) method at the B3LYP level in combination with the (ECP80MWB_AVQZ + 2f) basis set. The dissociation energy of U2, after being corrected for the zero-point vibrational energy, is 2.482 eV, which is in good agreement with the experiment. The calculated energy was fit to the typical potential functions of Morse, Lennard-Jones (L-J) and Rydberg. Both the Morse and Rydberg functions are good representatives of the potentials, but the Lennard-Jones function is not. The anharmonicity constant is very small. The anharmonic frequency is 113.99 cm^–1. Thermodynamic properties of entropy and heat capacity at 298.2 K – 1500 K were calculated by using DFT-B3LYP computational results and Morse parameters, respectively. The relationship between entropy and temperature was established.

Abstract: 136 polychlorinated 5,10-dihydrophenarsazine (PCPhZ) in the ideal gas state at 298.15 K and 101.3 kPa have been calculated at the B3LYP/6-31G* level using Gaussian 03 program, and their thermodynamic parameters were obtained. The isodesmic reactions were designed to calculate standard enthalpy of formation (ΔfHө) and standard free energy of formation (ΔfGө) of PCPhZ congeners. The relations of these thermodynamic parameters with the number and position of Cl atom substitution (NPCS) were discussed, and it was found that there exist high correlation between thermodynamic parameters (heat capacity at constant volume (Cvө), entropy (Sө), ΔfHө and ΔfGө) and NPCS. On the basis of the relative magnitude of their ΔfGө, the order of relative stability of PCPhZ congeners was theoretically proposed.