Molecular dynamics comparative study of methane–nitrogen and methane–nitrogen–ethane systems

This work concerns the site–site interaction study of 256 particles using the Buckingham potential model. We have calculated the new parameters of the Buckingham potential using an iterative algorithm with a mean square method. This adapted model allows determining the characteristics for each state point. We have applied this model to study the liquefied natural gas LNG properties for methane-nitrogen and methane–nitrogen–ethane mixtures by molecular dynamics. We have calculated the thermodynamic, dynamic and structural properties for both the microcanonical NVT and the isothermal-isobaric NPT ensembles of binary and ternary systems from the SP₁ to SP₉ points. Then, we have compared the results between binary and ternary systems. We have obtained a good prediction on transport properties. From the calculated values of self-diffusion coefficient and viscosity, we have confirmed the liquid state of the liquefied natural gas LNG system.     

Densities and derived thermodynamic properties of ternary mixtures 1-butyl-3-methyl-imidazolium tetrafluoroborate + ethanol + water at seven pressures and two temperatures

This work is a continuation of our studies on experimental measurements of physical properties on binary mixtures of the ionic liquid (IL) family 1-alkyl-3-methyl imidazolium tetrafluoroborate (CnMIM-BF₄) with water and ethanol. Here, we present density for the ternary system Butyl-MIM-BF₄ + ethanol + water at two temperatures (298.15 K and 323.15 K) and seven pressures (from 0.1 to 30 MPa). It should be noted that BMIM-BF₄ is the only IL of the family CnMIM-BF₄ that can be mixed with water and ethanol in all range of concentrations at room conditions. From the density data measured in function of pressure and temperature other important derived thermodynamic properties can be calculated, such us excess molar volumes, isothermal compressibility, isobaric expansion and the thermal pressure coefficients. These properties for selected ternary mixtures will be discussed and compared with data from the scarce number of published results for similar ternary mixtures with this same IL.     

Experimental study and modeling of the thermodynamic properties of magnesium silicates

The thermodynamic properties of all MgO-SiO₂ system phases were studied by Knudsen mass spectrometry over a wide temperature range (1571–1873 K) and the whole range of compositions. An approach based on the generation of volatile interaction products formed in the reduction of oxide components was used. The reducing agents were Nb, Ta, and Mo. The observed ion current intensity ratios I(Mg⁺)/I(SiO⁺) were used to calculate the activities and partial thermodynamic functions of the components in liquid and crystalline MgO-SiO₂ mixtures and the integral thermodynamic functions of formation of magnesium ortho-and metasilicates. For the first time, direct and reliable information about the thermodynamic properties of all system phases at high temperatures was obtained. These results in combination with all the available data on the thermodynamic properties and phase equilibria in the MgO-SiO₂ system were used to develop a statistical-thermodynamic model of liquid magnesium silicates based on treating them as associated liquids. Simultaneously, the problem of obtaining self-consistent data on the thermodynamic functions of all phases and conditions of equilibria between them was solved. In addition to polymeric silicon-oxygen structures of arbitrary sizes and spatial configurations, heteromolecular complexes such as MS, M₂S, and M₃S (S=SiO₂ and M=MgO) were found to exist in liquid MgO-SiO₂ mixtures. The correctness of the results obtained was substantiated by the virtually complete coincidence of the calculated thermodynamic properties and phase equilibrium conditions with experimental data and their conformity to the general patterns characteristic of binary silicate systems.     

Thermodynamic properties in the molecular dynamics ensemble applied to the gaussian core model fluid

The thermodynamic properties of pressure, energy, isothermal pressure coefficient, thermal expansion coefficient, isothermal and adiabatic compressibilities, isobaric and isochoric heat capacities, Joule-Thomson coefficient, and speed of sound are considered in a classical molecular dynamics ensemble. These properties were obtained using the treatment of Lustig [J. Chem. Phys. 100, 3048 (1994)] and Meier and Kabelac [J. Chem. Phys. 124, 064104 (2006)], whereby thermodynamic state variables are expressible in terms of phase-space functions determined directly from molecular dynamics simulations. The complete thermodynamic information about an equilibrium system can be obtained from this general formalism. We apply this method to the gaussian core model fluid because the complex phase behavior of this simple model provides a severe test for this treatment. Waterlike and other anomalies are observed for some of the thermodynamic properties of the gaussian core model fluid.     

Thermodynamic Properties of silicate glasses and melts: VIII. System MgO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>

Vaporization of the system MgO-Al₂O₃-SiO₂ in the temperature range 1770–1890 K was studied and activities of MgO and SiO₂ were determined. Activities of the components, isothermal sections of the phase diagram, and the position of the liquidus line in the studied system were calculated using the Gay-Kapoor-Frohberg model. The correlation of the found values of thermodynamic properties and phase equilibriua in isothermal sections of the phase diagram of the studied system was illustrated.     

Application of Model of Ideal Solution of Interaction Products and Thermodynamic Modeling

The essence of the ideal solution of interaction products (ISIP) model for systems involving strong interactions of the components is described. With the help of this model and thermodynamic simulation methods, the activities of the components and partial and integral thermodynamic characteristics of Fe-Si solutions at 1873–2003 K in an initial Ar atmosphere and at a common pressure of 1 atm were calculated. The compositions and structures of Fe-Si solutions according to the ISIP model are determined as statistical mixtures of [Fe], [Si] and the clusters [FeSi], [FeSi₂], [Fe₃Si] and [Fe₅Si₃]. The calculated values of activities, thermodynamic characteristics, compositions and structures of Fe-Si solutions agree satisfactorily with reliable experimental data. The thermochemical and thermodynamic properties of the compounds FeSi, FeSi₂, Fe₃Si and Fe₅Si₃ were revised. The temperature dependences of the activities of the components, and also the influence of temperature elevation on the composition of Fe-Si melts are discussed.     

Analysis of the Glass-Forming Ability of Fe–Er Alloys,Based on Thermodynamic Modeling

The Fe–Er phase diagram and thermodynamic properties of all its phases are assessed by means of self-consistent analysis. To refine the data on phase equilibria in the Fe–Er system, an investigation is performed in the 10–40 at % range of Er concentrations. The temperature–concentration dependences of the thermodynamic properties of a melt are presented using the model of ideal associated solutions. Thermodynamic parameters of each phase are obtained, and the calculated results are in agreement with available experimental data. The correlation between the thermodynamic properties of liquid Fe–Er alloys and their tendency toward amorphization are studied. It is shown that compositions of amorphous alloys prepared by melt quenching coincide with the ranges of concentration with the predominance of Fe₃Er and FeEr₂ associative groups that have large negative entropies of formation.     

硝酸盐型卤水体系的综合热力学模型与多温相图预测

硝酸盐型卤水是盐湖卤水、 硝酸盐工业、 废水处理中普遍遇到的电解质溶液体系. 硝酸盐具有极高的溶解度, 实现硝酸盐型复杂电解质体系物性和相平衡的精准热力学表达依然具有挑战性. 以煤化工废水的典型体系Na⁺//NO₃^- , Cl^-, SO₄^{2 -} -H₂O为对象, 以改进的eNRTL模型为基础, 由活度系数模型、 溶液物性模型、 物种热力学模型和固液相平衡模型构成了电解质体系的综合热力学模型. 利用二元体系的冰点、 饱和蒸汽压、 等压摩尔热容、 活度系数和渗透压系数等物性数据和三元体系等温相平衡数据, 采用多目标优化方法, 获得了表达研究体系的多温特性的12组液相特征参数和7个固相物种的热力学参数. 据此完成了3个二元体系、 3个三元体系等温相平衡的准确计算和三元、 四元完整相图的预测, 适用温度达到实验所及的全部温度范围(254.65~543.15 K); 适用浓度达到饱和程度, 其中NaNO₃的浓度高达226.88 mol/kg. 三元、 四元体系的多温相图预测结果与实验数据相吻合, 并给出了9个三元、 5个四元体系零变点的完整信息.     

Water Activity and Solubility Measurements and Pitzer Model Simulation of the MgCl<Subscript>2</Subscript>–RbCl–H<Subscript>2</Subscript>O Ternary System at 298.15 K

Water activities for the MgCl₂–RbCl–H₂O ternary system and its sub-binary MgCl₂–H₂O and RbCl–H₂O systems at 298.15 K have been measured using the isopiestic method. The measured results for the binary systems agree well with literature data. The measured equal water activity lines for the MgCl₂–RbCl–H₂O ternary system deviate from Zdanovskii’s rule. The solubilities for the MgCl₂–RbCl–H₂O ternary system also have been measured using a isothermal visual first/last crystal method, and the results are consistent with one reported set of solubility data. Pitzer’s model was selected to correlate the measured water activity and solubility data and the parameters reported in the literature are re-examined by comparing the model-calculated equal water activity lines and solubilities with experimental values measured in this work. New and reasonable parameters are obtained by fitting the water activity and solubility data measured in this work and those reported in the literature. The water activities and solubilities were simulated with the new parameters and the results show that the Pitzer model can successfully represent the thermodynamic properties and be used to calculate the solubility isotherms.     

等温气液平衡盐效应的研究——有机溶剂-水-无机盐体系

本文报导了甲醇-水-氯化锂、乙醇-水-氯化锂、丙酮-水-氯化锂和丙酮-水-碳酸钾体系在298.15 K时的等温气液平衡数据, 以及用三参数Margules公式的关联结果。提出了由等温气液平衡数据计算混合溶剂中盐的溶剂化数的理论公式。     

Establishment of thermodynamic properties of pure solid substances by thermomechanical analysis

The combination of a DuPont 942 thermomechanical analyzer with a CBM computer allowed the establishment of thermodynamic properties such as isobars, isobaric volumetric expansions, isothermal compressibilities, and the equation of stateV=V(p, T) in a limited region ofpVT space.     

The thermodynamic properties of solutions and phase equilibria in the water-2-butanol-sodium chloride system

Fragments of the phase diagram of the H₂O-2-C₄H₉OH-NaCl system were studied experimentally at 298 and 313 K. The thermodynamic properties of sodium chloride in three-component solutions with ionic strengths up to 1.9 mol/kg and alcohol content in the solvent 4.97 and 10 wt % were measured at 298 and 323 K by the electromotive force method with ion-selective electrodes. The eNRTL (electrolyte Non-Random Two-Liquids) model parameters correctly describing the results of electrochemical measurements of the partial properties of NaCl and phase equilibria in the water-2-butanol-sodium chloride ternary system and binary subsystems constituting it were determined. The isothermal sections of the phase diagram of the H₂O-2-C₄H₉OH-NaCl system were calculated using the method of convex hulls implemented in the TernAPI package.     

Volumetric Properties of the {x 1[C4mim][MeSO4] + (1 − x 1)MeOH} System at Temperatures from (283.15 to 333.15) K and Pressures from (0.1 to 35) MPa

Densities of pure 1-butyl-3-methylimidazolium methylsulfate, [C₄mim][MeSO₄], and its mixtures with methanol have been measured. Measurements were made with an accuracy of ±0.2 kg·m^?3, using a vibrating-tube densimeter, over the temperature and pressure ranges (283.15–333.15) K and (0.1–35) MPa, respectively. The experimental densities for the pure ionic liquid and alcohol have been correlated by the Tait equation. The results for the {x ₁[C₄mim][MeSO₄] + (1 ? x ₁)MeOH} system have been correlated by a van Laar equation involving parameters that are dependent on temperature and pressure. Excess volumes have been obtained directly from the experimental densities, while isobaric expansivities, isothermal compressibilities, and related excess properties were calculated from the correlation equation. Exceptionally strong pressure and temperature influences on these properties were observed.     

Isobaric thermal expansivity of the binary system 1-hexanol + n-hexane as a function of temperature and pressure

The isobaric thermal expansivity against temperature and pressure for the system 1-hexanol + n-hexane was directly determined by means of a calorimetric method. From these data, the excess isobaric thermal expansivity is calculated at representative temperatures and pressures. The obtained results for this excess quantity are qualitatively discussed by applying well-known arguments often used for explaining the thermodynamic behavior of alcohol + alkane mixtures. In order to check the consistency of these data with those of literature, the derivative of excess molar volume against temperature and that of excess isobaric molar heat capacity against pressure are calculated and compared with those obtained from literature data. Very good coherence between both data sources is obtained.     

Thermodynamic analysis of LiF-BeF2 and KF-BeF2 melts by a structural model

An earlier structural model for binary silicate melts and glasses is extended to MF-BeF₂ (M = Li, K) systems. The evaluation of the thermodynamic properties as well as the phase diagrams for the binary LiF-BeF₂ system and the integral enthalpy of mixing of the KF-BeF₂ system are carried out with this model. This thermodynamic model is based on the assumption that each alkali fluoride produces the depolymerization of BeF₂ network with a characteristic free energy change. A least squares optimization program permits all available thermodynamic and phase diagram data to be optimized simultaneously. In this manner, data for these binary systems have been analysed and represented with a small number of parameters. The model predicts the chain-length distribution of polymeric ions, even though these are not explicitly treated as structural units of the model. The calculated fluoride polyanion chain-length distribution for the LiF-BeF₂ system is in quantitative agreement with the predictions reported in the literature.     

A novel non-intrusive microcell for sound-speed measurements in liquids. Speed of sound and thermodynamic properties of 2-propanone at pressures up to 160 MPa

A novel high-pressure, ultrasonic cell of extremely reduced internal dimensions (∼0.8 · 10⁻⁶ m³) and good precision for the determination of the speed of propagation of sound in liquids was conceived and built. It makes use of a non-intrusive methodology where the ultrasonic transducers are not in direct contact with the liquid sample under investigation. The new cell was used to carry out speed of sound measurements in 2-propanone (acetone) in broad ranges of temperature (265<T/K<340) and pressure (0.1<p/MPa<160). (p,ρ,T) data for acetone were also determined but in a narrower T,p range (298 to 333 K; 0.1 to 60 MPa). In this interval, several thermodynamic properties were thus calculated, such as: isentropic (κ_s) and isothermal (κ_T) compressibility, isobaric thermal expansivity (α_p), isobaric (c_p) and isochoric (c_v) specific heat capacity, and the thermal pressure coefficient (γ_v). Comparisons with values found in the literature generally show good agreement.     

Estimation of 2nd-order derivative thermodynamic properties using the crossover lattice equation of state

We apply the crossover lattice equation of state (xLF EOS) [M.S. Shin, Y. Lee, H. Kim, J. Chem. Thermodyn. 40 (2007) 174–179] to the calculations of thermodynamic 2nd-order derivative properties (isochoric heat capacity, isobaric heat capacity, isothermal compressibility, thermal expansion coefficient, Joule–Thompson coefficient, and sound speed). This equation of state is used to calculate the same properties of pure systems (carbon dioxide, normal alkanes from methane to propane). We show that, over a wide range of states, the equation of state yields properties with better accuracy than the lattice equation of state (LF EOS), and near the critical region, represents singular behavior well.     

Isothermal decomposition of γ-irradiated indium acetate

The isothermal decomposition of un-irradiated (pristine) and pre-γ-irradiated indium acetate was studied in the temperature range (298–1273 K) and in air using isothermal thermogravimetric technique. The data were analyzed using various solid-state reaction models. The results showed that the kinetic of isothermal decomposition of indium acetate was governed by random nucleation reaction (Erof’ev equation A₃). The kinetics and thermodynamic parameters of the main decomposition process for un-irradiated and γ-irradiated samples were calculated and evaluated.