The spectrum of atomic excess free volume in grain boundaries

The grain boundary (GB) excess volume is an important structural factor that is strongly correlated with various thermodynamic and kinetic properties of GBs such as GB energy, GB mobility, GB diffusivity, and GB segregation energy, etc. However, the excess volume is usually reported as an average value of the entire GB. Such simplification does not consider the spectral nature of the excess volume in a GB, which cannot be used to describe the atomic mechanisms of some kinetic process, such as GB migration, that involves only a few atoms at a time. Here, we explore the spectrum of atomic excess volume in representative nanocrystalline Ni and Al samples as well as 388 Ni bicrystals based on the Olmsted dataset by using atomistic simulations. It is found that the nanocrystalline Ni and Al models show a skew-normal distribution in the spectrum of both the atomic excess volume and the atomic excess energy in the GBs, which show a weak inverse correlation between them. This is in stark contrast to the widely reported positive correlation between GB energy and excess volume based on the average value. We further show based on the statistical analysis that the correlation between the atomic excess volume and excess energy strongly depends on the GB type and a universal trend between them does not exist. While low ∑ Ni GBs generally shows a strong inverse linear correlation between these two properties, such correlation is weak for high ∑ Ni GBs. Moreover, we find that the spectrum of the excess volume shows characteristics distribution in some special Ni GBs. For example, twist GBs generally show a symmetrical unimodal distribution while most surveyed ∑3 Ni GBs with anti-thermal behavior show an apparent bimodal distribution. Nevertheless, a strong correlation is found between the atomic excess volume and the segregation energy based on the nanocrystalline Al model with Mg impurity, which implies a possible universal trend between the two properties. The current study thus shows that the excess volume provides useful insights in revealing the elemental structure–property correlations in GBs, which may be used as a structural variable in future thermodynamic modeling of GBs.

     

Internal Pressure in Binary Mixtures of Methylpyridine Isomers with H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O

Internal pressures and their excesses were calculated in the strict thermodynamic way for binary mixtures of 2-,3-,4-methylpyridine, 2,6-dimethylpyridine, and 2,4,6-dimethylpyridine with water and heavy water at T =  296.15 K. The excess internal pressure approach proved to be useful in studies of relatively subtle thermodynamic effects. Positive correlation was found between the association energy of the 1:1 water–amine complexes and the maximum values of the excess internal pressure. It was shown that the differences caused by the exchange of H₂O by D₂O in the mixtures are evident in the excess internal pressure isotherms. The larger excesses for the D₂O mixtures may indicate that the difference in energy between the O–D· · ·N and O–D· · ·O bonds is higher than that between the O–H· · ·N and O–H· · ·O ones. That probably leads to different phase properties of the studied systems.     

Thermodynamic Properties of Nanograin Boundary and Thermal Stability of Nanograin Structure

The thermal features of the nanograin boundary were described by a developed thermodynamic model.Using the nanocrystalline Cu as an example,the pressure,the bulk modulus,and the volume thermal expansion coefficient were calculated to characterize the thermodynamic properties of the grain boundaries on the nanoscale.Based on the parabolatype relationship between the excess free energy and the excess volume of the nanograin boundary,the thermal stability,as well as its evolution characteristics,was analyzed.T...     

Thermodynamic and Acoustic Properties of Mixtures of Dibromomethane + Heptane

Densities and speeds of ultrasound in binary mixtures of dibromomethane with heptane have been measured within the temperature range from 288.15 K to 318.15 K. From the experimental data, the thermodynamic excess volume, molar isobaric expansion, molar isentropic compression, and ultrasonic speed were calculated. The excess volume and excess isentropic compression have opposite signs, whereas the excess isobaric expansion is an S-shaped function of the mole fraction. An explanation was suggested to account for the excesses in terms of intermolecular interactions. It involved energetic and steric factors. Moreover, it was shown that the positive excess sound speed results almost entirely from the negative excess compression.     

The effect of grain size on the nanocrystalline growth in metals and its simulation by Monte Carlo method

In this study, the thermodynamic stability of the grain boundaries and the grain growth of nanocrystalline Palladium (Pd) at 800 K were investigated. For this purpose, the Gibbs free energy curves of grain boundaries were plotted in terms of the excess volume by the use of Song’s, quasi-harmonic Debye approximation (QDA), and equation of state (EOS) thermodynamic models. The results of the two EOS and Song’s models showed that the excess volume increase up to values more than the critical excess volume, can result in the thermodynamic stability of nanocrystalline Pd. Therefore, according to the prediction of these two models, the nanocrystalline growth in metals was stopped at the grain sizes less than the critical grain size. But, according to the results of the QDA model there was no possibility for the stoppage of the grain growth and thermodynamic stability of the nanocrystalline Pd. To investigate the validity of the mentioned predictions, the Monte Carlo atomic simulation method was employed. The results obtained from the simulation confirmed the grain growth of nanocrystalline Pd within the size of the grains larger than the critical grain size and stoppage within the size of the grains less than the critical grain size.     

Excess infrared absorption spectroscopy and its applications in the studies of hydrogen bonds in alcohol-containing binary mixtures

Excess infrared (IR) absorption spectroscopy, a new concept brought forward by applying the idea of excess thermodynamic functions to infrared spectroscopy, is shown to be a potential method to study hydrogen bonds. It can be applied to enhance spectral resolution of complexed IR bands, to evaluate nonideality of liquid mixtures, and to estimate selective molecular interactions. The sign of the excess infrared absorption coefficient is also of importance in providing information on molecular interactions. The results demonstrate that excess infrared absorption spectroscopy can unveil new information on hydrogen bonding in condensed phases.     

A New Thermodynamic Calculation Method for Binary Alloys：Part I：Statistical Calculation of Excess Functions

The improved form of calculation formula for the activities of the components in binary liquids and solid alloys has been derived based on the free volume theory considering excess entropy and Miedemaˊs model for calculating the formation heat of binary alloys.A calculation method of excess thermodynamic functions for binary alloys,the formulas of intregral molar excess properties and partial molar excess properties for solid ordered or disordered binary alloys have been developed.The calculated results are in good agreement with the experimental values.     

Thermodynamic model of hardness: Particular case of boron-rich solids

A number of successful theoretical models of hardness have been developed recently. A thermodynamic model of hardness, which supposes the intrinsic character of correlation between hardness and thermodynamic properties of solids, allows one to predict hardness of known or even hypothetical solids from the data on Gibbs energy of atomization of the elements, which implicitly determine the energy density per chemical bonding. The only structural data needed is the coordination number of the atoms in a lattice. Using this approach, the hardness of known and hypothetical polymorphs of pure boron and a number of boron-rich solids has been calculated. The thermodynamic interpretation of the bonding energy allows one to predict the hardness as a function of thermodynamic parameters. In particular, the excellent agreement between experimental and calculated values has been observed not only for the room-temperature values of the Vickers hardness of stoichiometric compounds, but also for its temperature and concentration dependencies.     

Densities,viscosities, and excess properties of trifluoroethanol-water,tetraethylene glycol dimethylether-water,and trifluoroethanol-tetraethylene glycol dimethylether at 303.15 K

Densities and kinematic viscosities of trifluoroethanol + water, tetraethylene glycol dimethylether + water, and trifluoroethanol + tetraethylene glycol dimethylether have been measured at 303.15 K and atmospheric pressure over the entire range of composition. Dynamic viscosities, excess volumes, excess viscosities, and excess Gibbs energies of activation of flow were obtained from the experimental results. The excess volumes were negative, whereas excess viscosities and energies of activation were positive, presenting the three thermodynamic properties asymmetric composition dependence. The kinematic viscosities were used to test McAllister, Stephan, and Soliman and Marshall correlations.     

Phase relations between germanium,tin, and lead chalcogenides in pseudobinary systems containing orthorhombic phases

As an extension of our earlier studies of phase relations in pseudobinary systems of germanium, tin, and lead chalcogenides, we have calculated the T-x phase diagrams of all the pseudobinary systems formed by IV–VI compounds and containing orthorhombic phases: SnS-SnSe, SnS-SnTe, SnS-PbS, SnSe-SnTe, and SnSe-PbSe. In the calculations, we used a unified thermodynamic model and the same thermodynamic data for the end members of the pseudobinary systems. The interaction parameters were determined using the relationship, derived earlier for IV–VI compounds with cubic structures, between the excess Gibbs energy and the difference in chemical bonding between the end members of the systems, quantified by a combination of Simons-Bloch orbital radii.     

Temperature-concentration dependence of the correlation length of concentration fluctuations in liquid binary systems

An analysis is made of the correlation length of the concentration fluctuations in liquid binary systems over a wide range of temperature and composition. A quantitative relationship is obtained between the correlation length, the concentration, and the temperature. It is shown that the correlation length is determined by regions of different thermodynamic stability of a homogeneous solution, bounded by binodal and spinodal curves. Pis’ma Zh. Tekh. Fiz. 23, 84–88 (February 12, 1997)     

Estimation of the stability limit of metallic crystals under conditions of isothermal stretching

Based on the results of analysis of behavior of the thermodynamic properties of metals, a semiempirical method is suggested for calculating the limit of thermodynamic stability of crystalline state under conditions of isothermal stretching. The pressure and volume on the spinodal at temperatures of 0 and 300 K are estimated for a group of metals, and the stability limit of lead is calculated in the temperature range from 0 K to the melting point. The correlation between limiting pressures on the melting line and on the spinodal of crystal at T → 0 is revealed.     

新型吸收制冷工质对CO_2-[emim][Tf_2N]超额吉布斯自由能的预测

针对氨系、水系、氟利昂系等传统吸收式制冷工质对的缺陷,提出以[emim][Tf_2N]为吸收剂的二元混合体系CO_2-[emim][Tf_2N]作为新型吸收制冷工质对。通过将PR状态方程和NRTL活度系数模型结合为一体,并以立方型方程和超额自由能模型结合得到的WS混合规则为纽带,建立GE-EOS热力学模型,得到高温高压下二元混合体系的超额吉布斯自由能,计算结果表明:当温度为453.15 K,压力为13.374 MPa,CO_2液相摩尔分数为0.392时,CO_2-[emim][Tf_2N]二元混合体系的超额吉布斯自由能存在最大值。     

An intrinsic correlation between driving force and energy barrier upon grain boundary migration

The migration of grain boundary (GB), which plays a key role in the microstructural evolution of polycrystalline materials, remains mysterious due to the unknown relationship between GB mobility associated with specific geometry and external conditions (e.g. temperature, stress, etc., hence the thermodynamic driving force). Combining the rate equation of GB migration with molecular dynamics simulations, an intrinsic correlation between driving force and energy barrier for the migration of various types of GBs (i.e. twist, symmetric tilt, asymmetric tilt, and mixed twist-tilt) is herein explored, showing the decrease of energy barrier with increasing thermodynamic driving force.     

等压固结条件下湘江饱和砂土动力特性研究

在大量的动三轴试验基础上,研究了等压固结条件下湘江饱和砂土振动孔隙水压力、应力应变滞回圈以及应力路径的发展变化规律。研究结果表明:孔压发展变化过程与土体的剪胀、剪缩密切相关;孔压与轴向动应变之间的变化关系显示饱和砂土具有明显的各向异性;从孔压与滞回圈面积累积之和的关系看,孔压的增长伴随着能量的损失;对于围压较大的情形,用ExpAssoc函数进行拟合效果较好。隧振次增加应力应变滞回圈也在发生变化,第一阶段滞回圈呈倒置的帽子形,第二阶段呈菱角形状。在振动初始阶段,应力路径基本上呈倾斜的直线变化;随孔压的增加,加载和卸载两条应力路径逐渐分开,呈纺锤形。     

Thermodynamic effects of mixing in gases at moderate densities

A parameter is found that governs the magnitude of thermodynamic mixing effects in gases. Values are calculated for the excess second virial coefficient and its derivatives for a number of binary gas systems at 298.15°K.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 2, pp. 263–266, February, 1985.     

Influence of composition and particle size on spin dynamics and thermodynamic properties of magnetoresistive perovskites

The thermodynamic behavior and spin dynamics of the colossal magnetoresistive (CMR) perovskites of general formula La(1-x)(A)xMn(1-y)(B)yO3 (where A is an alkaline earth, and B = Al, In) have been studied in order to evidence the effect of composition and the influence of nanocrystallinity on the thermodynamic and magnetic characteristics. By using electron paramagnetic resonance (EPR) spectroscopy, the behavior of the exchange coupling integral (J) between Mn spins and the polaron activation energy (Ea) have been investigated. The thermodynamic properties represented by the relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the equilibrium partial pressures of oxygen have been obtained by using solid electrolyte electrochemical cells method. The influence of the oxygen stoichiometry change on the thermodynamic properties was examined using the data obtained by a coulometric titration technique coupled with measurements of the electromotive force (EMF). The results were correlated with the average Mn valence values as determined by redox titration. The properties of the rare-earth manganites are strongly affected by the A- and B-site substitution and by the oxygen nonstoichiometry. New features related to the modifications in properties connected with the nanocrystalline state were evidenced. The correlation existing between the magnetic and thermodynamic characteristics were discussed in relation to significant changes in the overall concentration of defects.     

Solubilization and determination of solution thermodynamic properties of itraconazole in different solvents at different temperatures

The solubility of itraconazole (ITRA) in thirteen pure solvents including water, dimethyl sulphoxide, acetonitrile, methanol, 1,4-butanediol, ethanol, isopropyl alcohol, n-butanol, octanol, ethyl acetate, toluene, benzene, 1,4-dioxane were estimated at the temperatures ranging from 293.15?K to 318.15?K under atmospheric pressure (0.1?MPa). The results reflected that the solubility of ITRA was a function of temperature and was increased with a rise in temperature in each solvent. Moreover, the solubility in polar solvents was less and found to be increased in non-polar solvents. Furthermore, the results of solubilization were correlated by the Van’t Hoff equation, the modified Apelblat equation, the Buchowski???Ksiazaczak λh equation, and the polynomial empirical equation. The polynomial empirical equation proved to be more accurate and suitable for the correlation of solubilities of ITRA in studied solvents at various temperatures. Besides, theoretical ideal solubilities, activity coefficients, and thermodynamic properties of the solution process including standard molar enthalpy, entropy, Gibbs free energy, and excess enthalpy were calculated from the experimental solubility data. These thermodynamic parameters indicated that the solubilization process was not spontaneous, endothermic, and enthalpy driven. Such thermodynamic based solubility data of ITRA will be of immense help in solubilization, synthesis, process development, preformualtion, and dosage form development in pharmaceuticals.     

Investigating the effect of filler types on thermodynamic parameters and their relationship with moisture sensitivity of asphalt mixes

Filler plays a significant role in mastic cohesion and adhesion between aggregate–asphalt binder in asphalt mixes. In the majority of research on investigating moisture damage based on thermodynamic concepts, little attention has been given to the role of filler. In the present study, 20 different combinations of asphalt mixes made with 4 filler types (stone powder, hydrated lime, calcium carbonate and portland cement), with two types of asphalt binder (60–70 and 85–100), and two types of aggregate (limestone and granite) were used. Then thermodynamic parameters (with and without considering the effect of filler) were calculated and the relationship between these parameters and test results of moisture sensitivity of asphalt mixes was investigated using statistical analyses. Results obtained by thermodynamic parameters show that only stone powder filler caused an increase in free energy of adhesion between base asphalt binder and aggregates, and other fillers reduced free energy of adhesion. The maximum amount of debonding energy in samples made by asphalt binder 60–70, was related to mastics containing calcium carbonate and hydrated lime fillers, and in asphalt binder 85–100, mastics containing portland cement and calcium carbonate had the maximum amount of debonding energy. However, the minimum amount of debonding energy was related to the mastic containing stone powder. In addition, the results of moisture sensitivity mechanical tests show that samples containing calcium carbonate and hydrated lime fillers had the maximum amount of tensile strength ratio. Finally, the amount of adjusted coefficient of correlation between debonding energy and modified Lottman test results increased from 0.553 in 4 base compounds (without filler) to 0.701 in 16 compounds with filler. The difference in correlation coefficients show the necessity to use the effect of filler on calculating thermodynamic parameters in investigating moisture sensitivity of various asphalt mixes.