Critical evaluation and thermodynamic optimization of the Si-RE systems: Part I. Si-RE system (RE = La,Ce, Pr,Nd and Sm)

A critical evaluation and optimization of all available phase diagrams and thermodynamic data of the binary Si-RE (RE = La, Ce, Pr, Nd and Sm) systems were conducted to obtain reliable thermodynamic functions of all the phases in the systems. In the thermodynamic modelling, a systematic analysis involving the similarity and periodicity observed in the lanthanide series was applied to resolve inconsistencies in the experimental data and to estimate the unknown thermodynamic properties and phase equilibria data. The phase diagram of the Si-Sm system was predicted using this approach.     

BSA denaturation in the absence and the presence of urea studied by the iso-conversional method and the master plots method

The effect of cure temperature and modifier proportion on the miscibility of an epoxy–amine system with a thermoplastic modifier was studied by analysis of phase diagrams, morphologies, and glass transitions. Phase diagrams for the system before and during reaction were obtained from a thermodynamic analysis of phase separation using a model based on Flory–Huggins theory. Different types of morphologies were observed and analyzed in function of cure temperature and modifier proportion. The validity of the thermodynamic model was checked by comparing with observed morphologies. Two glass transitions were observed for most of the modified systems indicating that a phase separation was occurred.     

One Setup, Three Systems

The system—surroundings concept is one of the most important in thermodynamics. Precisely defining a system is of critical importance to thermodynamic analysis. Even when studying the same problem, different individuals may opt to select different systems; therefore, choosing the correct system requires skill. In order to help students understand the various systems and their differences, a simple distillation setup is used to demonstrate the three thermodynamic systems: open, closed, and isolated.     

Comparative thermodynamic analysis of the binary system Bi−Sb

Results of the comparative thermodynamic analysis of the binary system Bi?Sb obtained by DTA measurements and predicting are presented in this paper. Activities, activity coefficients, partial and integral molar quantities for Bi and Sb at temperatures 973, 1073 and 1173 K in the investigated binary system Bi?Sb determined by DTA measurements and thermodynamic predicting are given. An excellent agreement between the experimental and predicted results is reached. Also, a phase diagram of the investigated system Bi?Sb obtained by DTA shows good agreement with literature and it can be concluded that DTA could be satisfactorily used for quantitative thermodynamic analysis of any binary system containing equilibrium between solid and liquid solutions. It was also determined that conclusion about linear dependence ofgKs constant for binary eutectic systems and systems with phase transformation is valid for binary system containing equilibrium between solid and liquid solutions too.     

尺寸效应对氧化锌微/纳体系热力学性质的影响

采用微乳液水热辅助法合成了三种不同尺寸的手榴弹状ZnO 微/纳结构. 通过设计热化学循环, 建立了纳米ZnO与块体ZnO体系热力学性质之间的关系. 并结合微量热技术对不同尺寸ZnO微/纳体系的热力学性质进行了计算. 结果表明, 尺寸效应对微/纳体系热力学性质有显著的影响: 随着反应物尺度的减小, 体系的标准摩尔反应焓、标准摩尔反应Gibbs 自由能、标准摩尔反应熵均降低, 而材料自身的标准摩尔生成焓、标准摩尔生成Gibbs 自由能、标准摩尔熵均增加.     

Thermodynamic efficiency of a finite gain laser

The thermodynamic limitations on the efficiency of a laser are considered with special reference to operation at a finite gain. An entropy cycle is used to determine both the thermodynamic threshold condition and to limit the entropy generated during lasing at a finite gain. A lower limit for the required number density of systems in the lasing level is derived. Comparison is also made with the rate equations analysis of the system thereby showing that the efficiency is always below the thermodynamic value, due to loss mechanisms. The results are given in a form equally applicable to physical and chemical pumping processes.     

Thermodynamics and viscosities of dilute polymer solutions in binary solvents

Experiments aimed at comparison of calculated and experimental intrinsic viscosities of PS and PMMA in some binary solvents used as eluents in chromatography are performed. The intrinsic viscosities are determined in mixed solvents of different thermodynamic qualities, including a θ solvent, in a wide composition range. The analysis of the thermodynamic and rheological theoretical equations for ternary systems allowed the interpretation of anomalies observed on the experimental curves of intrinsic viscosity versus solvent composition.     

Thermodynamic properties of lead–sodium–antimony liquid alloys

The thermodynamic properties of lead–sodium–antimony liquid alloys were determined by the emf method. The thermodynamic properties of the edge binary systems, sodium–lead, sodium–antimony, and lead–antimony, were analyzed. The possibility of approximately estimating the thermodynamic properties of the ternary system on the basis of data on the edge binary systems using the simplest geometric models was demonstrated. The sodium-containing alloys show significant negative deviations from the ideal behavior. All the data are given for 900 K.     

Chemical equilibrium in a heterogeneous fluid phase system: thermodynamic regularities and topology of phase diagrams

Singularities of the systems with simultaneous phase and chemical equilibria were examined. The thermodynamic regularities were revealed and topology of phase diagrams was presented for multicomponent heterogeneous systems including two or several equilibrium liquid phases (solution layering). The thermodynamic conditions for displacement of phase and chemical equilibrium are considered.     

High-temperature thermodynamics of chemical transport reactions in the tungsten-bromine system of halogen-incandescent lamps and its influence by hydrogen,oxygen and carbon

The simultaneous reaction equilibria in the heterogeneous system tungsten- bromine and its influence by hydrogen, oxygen and carbon can be evaluated on the basis of chemical thermodynamics. By an analysis of the temperature dependence of the mass-balance of tungsten the chemical transport reactions in these systems and the burning behaviour of halogen-incandescent lamps may be predicted.Using thermodynamic data as given in the JANAF Tables or evaluated by comparison with related systems computer-calculations have been made for temperatures 500–4000 K for the various reaction equilibria in the tungsten-bromine system including the influence of the additional constituents. Results for the chemical transport reactions are compared to lamp experiments. From the results of the thermodynamic analysis a scheme of the mechanism of the tungsten-bromine cycle in halogen-incandescent lamps is revealed.     

Thermodynamics of liquid-crystalline solutions of hydroxypropyl cellulose in water and ethanol

Phase diagrams were constructed and comprehensive thermodynamic analysis was performed for hydroxypropyl cellulose-water and hydroxypropyl cellulose-ethanol systems with the use of the static sorption, calorimetry, cloud-point, polarization microscopy, and X-ray diffraction analysis techniques and the measurement of transmitted polarized light intensity. The concentration dependences of the enthalpy, entropy, and Gibbs energy of the formation of liquid-crystalline phases in the systems were determined. It was found that the formation of liquid-crystalline solutions of hydroxypropyl cellulose in water is associated with the energy term of interaction between the components and that in ethanol solutions is due to changes in combinatorial entropy.     

Pulsed NMR method for determining the thermodynamic characteristics of adsorption processes in biopolymers

The efficiency of the pulsed NMR method in studying phenomena in the interphase layer of biopolymer-water systems within the framework of the Gibbs thermodynamic theory was examined. Relationships between the nuclear magnetic relaxation times and the chemical potential and surface tension coefficient at the interphase interface of the adsorption system were established. How the thermodynamic and relaxation parameters change during the formation of the adsorption Gibbs layer on various cellulose samples was demonstrated. An analysis of the state of the water in the adsorption layer was performed, and its mean thickness was determined.     

Small Systems and Limitations on the Use of Chemical Thermodynamics

Limitations on using chemical thermodynamics to describe small systems are formulated. These limitations follow from statistical mechanics for equilibrium and nonequilibrium processes and reflect (1) differences between characteristic relaxation times in momentum, energy, and mass transfer in different aggregate states of investigated systems; (2) achievements of statistical mechanics that allow us to determine criteria for the size of smallest region in which thermodynamics can be applied and the scale of the emergence of a new phase, along with criteria for the conditions of violating a local equilibrium. Based on this analysis, the main thermodynamic results are clarified: the phase rule for distorted interfaces, the sense and area of applicability of Gibbs’s concept of passive forces, and the artificiality of Kelvin’s equation as a result of limitations on the thermodynamic approach to considering small bodies. The wrongness of introducing molecular parameters into thermodynamic derivations, and the activity coefficient for an activated complex into the expression for a reaction rate constant, is demonstrated.     

Optimization and Calculation of the EuCl<Subscript>3</Subscript>–MCl (M = Na,K, Rb,Cs) Phase Diagrams

By using the CALPHAD technique, an optimization of the binary EuCl₃–MCl (M = Na, K, Rb, Cs) systems has been carried out. To describe the Gibbs energies of liquid phases in these systems the new modified quasi-chemical model was used in the pair-approximation for short-range ordering. From the measured phase equilibrium data and the experimental thermo-chemical properties, the EuCl₃–MCl phase diagrams were optimized and calculated. A set of thermodynamic functions has been optimized based on an interactive computer-assisted analysis. The calculated phase diagrams and thermodynamic data are self-consistent.     

Al-Fe-P三元系的热力学优化

采用CALPHAD方法对Al-Fe-P三元系进行了热力学评估, 并根据相关的实验数据对边际二元系Al-P进行了热力学再优化, Al-Fe和Fe-P边际二元系的热力学参数取自之前的研究并做了局部调整. 根据相图数据和热力学数据优化了Al-Fe-P三元系的热力学模型参数, 获得了体系中所有相的Gibbs自由能表达式. 所得参数之间自洽且能很好地重现Al-Fe-P体系的大部分实验相图信息. 通过驱动力判据和本文优化所得的模型参数,从热力学上解释了该体系非晶形成能力与组成之间的关系.     

Thermodynamic Evaluation of NaF-MFn(M=Be,U, Th) Systems for Molten Salt Reactor

The phase diagrams of NaF-BeF₂, NaF-ThF₄and NaF-UF₄systems were assessed based on thermodynamic principles, and diverse thermodynamic models were adapted to different systems. Associate solution model (ASM) was used to describe the Gibbs energies of liquid phase of the NaF-BeF₂system, whereas other systems(NaF-ThF₄and NaF-UF₄) were treated with the substitutional solution model(SSM) and intermediate compounds were described as stoichiometric compounds according to the Neumann-Kopp rule. All the thermodynamic model parameters were optimized by the least squares procedure until good coincidence was achieved between the calculated results and the experimental data. The derived thermodynamic parameters will be merged into the NaF-BeF₂-ThF₄-UF₄ database to develop the thorium molten salt reactor(TMSR) project.<     

Thermodynamics of polymer systems

This work gives an introduction into the thermodynamic modeling of polymer systems. After a short overview about the different basics of thermodynamic models, results obtained with the recently proposed PC-SAFT equation of state are discussed exemplarily for systems containing polymers as well as copolymers.     

"Kinetic NMR titration": including chemical shift information in the kinetic analysis of supramolecular reaction systems such as organic replicators

Efficient harvesting of kinetic and thermodynamic information in supramolecular reaction systems comes from kinetic NMR titration, that is, the combined analysis of NMR integrals and chemical shifts. The method is introduced using a minimal self-replicating system studied at various temperatures.