Viscous and thermodynamic behaviour of glass-forming organic liquids

The free energy difference (ΔG) between an undercooled liquid and its corresponding equilibrium solid has been evaluated on the basis of a method involving Taylor series expansion of ΔG around its value at the equilibrium melting temperature. The resultant expression is shown to be capable of correctly estimating ΔG at temperatures as low as the glass transition temperature. The method is then enlarged to obtain the configurational entropy and used in conjunction with the Adam and Gibbs model to derive a novel expression for the viscosity of undercooled liquids. Most commonly used expressions for the temperature dependence of viscosity are shown to be approximations of the equation obtained in this study.     

Thermodynamic behaviour of undercooled melts

The Gibbs free energy difference (ΔG) between the undercooled liquid and the equilibrium solid phases has been studied for the various kinds of glass forming melts such as metallic, molecular and oxides melts using the hole theory of liquids and an excellent agreement is found between calculated and experimental values of ΔG. The study is made for non-glass forming melts also. The temperature dependence of enthalpy difference (ΔH) and entropy difference (ΔS) between the two phases, liquid and solid, has also been studied. The Kauzmann temperature (T ₀) has been estimated using the expression for ΔS and a linear relation is found between the reduced glass transition temperature (T _g/T _m) and (T ₀)/T _m). The residual entropy (ΔS _R) has been estimated for glass forming melts and an attempt is made to correlate ΔS _R,T _g,T ₀, andT _m which play a very important role in the study of glass forming melts.     

Calculation of the thermodynamic parameters of helium in a centrifugal force field

The design of cooling systems for a cryoalternator's superconducting field windings must be based on the knowledge of the distribution of the thermodynamic parameters (primarily temperature) of the helium in both its liquid and gaseous phases in centrifugal force fields. This paper proposes a set of ordinary differential equations describing the distributions. By numerically solving the set, the effects of the angular velocity of rotation, filling factor and temperature (pressure) at the axis of rotation upon the pressure, temperature and density distributions in helium in rotating vessels have been studied. Formulee for the approximation of the distributions have been obtained, which are applicable to rotation axis temperatures from 3 to 4.6 K (corresponding to saturation pressures 0.24 × 10⁵ to 1.4 × 10⁵ Pa), angular velocities of rotation from 50 to 300 rad s^?1 and filling factors from 0.1 to 0.9.     

Energy and entropy of crystals,melts and glasses or what is wrong in Kauzmann's paradox?

In order to understand the thermodynamic properties of solids and melts one has to consider simultaneously their entropy and energy as a function of temperature. Therefore, the molar entropy, S, and enthalpy (energy), H, of crystals, glasses and melts of the same one‐component systems have been suitably depicted including the transformation from the melt into a solid, i. e. a glass or crystal. S and H of glasses correspond to a simple continuation of these functions from the molten state to lower temperatures. Since crystallisation occurs spontaneously such a process necessarily produces entropy causing the temperature to increase. Thus, the glassy and the crystalline state are not connected by an isothermal process, which is in contrast to the assumption in the classical nucleation and crystallisation theory as well as in the arguments causing Kauzmann's paradox. For the temperature T → 0K the enthalpy and entropy of the glass are larger by ΔH₀ and ΔS₀ as compared to the stable crystal. The calculations are illustrated using experimental data for quartz and silica glass from P. Richet, Y. Bottinga, L. Deniélou, J. P. Petitet and C. Téqui.     

Evaluation of the thermodynamic properties of tungsten

A new evaluation of the thermodynamic properties of tungsten has been made. A set of parameters describing the Gibbs energy of each individual phase as a function of temperature and pressure is given. The experimental information on the P, T phase diagram and the thermodynamic data are compared with calculations made using the presented set of parameters.     

Estimation and application of thermodynamic properties for a non-azeotropic refrigerant mixture

The use of an azeotropic refrigerant mixture of R 131B1 and R 152a to replace R 22 in an air-to-air heat pump with an accumulator and capillary tube expander is discussed. The Redlick-Kwong-Soave equation of state provides a convenient method for generating thermodynamic data needed for this mixture.     

基于吸气喷液的制冷系统热力性能理论研究

吸气喷液是降低压缩机排气温度的有效手段,通过建立制冷系统热力循环计算模型,研究基于吸气喷液的制冷系统热力学状态,以制冷剂R410A为工质,分析在不同工况下热力性能随喷液流量比例的变化趋势。计算结果表明,当喷液流量比例增加到5%时,排气温度平均降低幅度为9℃,功率、制冷量和COP值分别平均下降0.4%、0.6%和0.3%;若蒸发温度增加,功率呈先上升后下降的趋势,蒸发温度每增加5℃,排气温度平均降低幅度为4.5℃,制冷量、COP值分别平均增加17.6%、16.9%;冷凝温度每降低5℃,排气温度平均降低幅度为8℃,功率平均下降11.3%,制冷量、COP值分别平均增加6%、17.9%。     

Critical evaluation of the thermodynamic properties of molybdenum

The thermodynamic properties and the pressure-temperature phase diagram of pure Mo have been evaluated from experimental information using thermodynamic models for the Gibbs energy of the individual phases. A set of parameters describing the Gibbs energy of the various phases as a function of temperature and pressure is presented. The agreement between experimental data and calculated values is satisfactory.     

Rate-Dependent Large Strain Behavior of a Structural Adhesive

This paper describes the development of a nonlinear viscoelastic modelthat can account for rate dependence at large strains. The model wasbased on tensile and shear experiments on a urethane structuraladhesive. The most striking observation was that the stress-strainbehavior at large strains was rate dependent. As a result, a rate-dependent rubbery shear modulus was added to Popelars shear modifiedfree volume model. This was very effective in predicting ramp shearbehavior over a range of strain rates and temperatures. Thecorrespondence of model results and tensile data was reasonable below20% strain. At higher strains, the model over predicted the stresslevels for a given strain. This may have been due to the accumulation ofdamage, which has yet to be included in the model. The model was unableto capture the effect of salt water on the tensile behavior of theurethane.     

Predictive approach to thermodynamic properties of the metastable Cr3C carbide

In thermodynamic modeling of phase diagrams it is often necessary to deal with the properties of metastable compounds, which are not known from experiments. As an illustrative example, we choose the Cr₃C(oP16) carbide, which is involved in the modeling of the Me₃C(oP16) (cementite) structure of the Fe-Cr-C system but is metastable in the Cr-C system. We discuss in detail the estimation of its thermodynamic properties, relying on regularities in bonding properties of 3d-transition metal carbides, and an account of the vibrational entropy through the so-called entropy Debye temperature. Our predictions are compared with values derived in thermodynamic modeling of the Fe-Cr-C phase diagram. Relying on the present results, we perform calculations of metastable phase equilibria in the Cr-C system and use them in analyzing information about Cr₃C from splat-quenching experiments.     

Psychrometry, a microcomputer approach

Equations are presented, suitable for coding in BASIC for a microcomputer, by which the properties of moist air may be computed accurately at any prevailing barometric pressure. The equations cover relative humidity and wet and dry bulb temperatures together with specific humidity, specific volume and enthalpy. The method is suitable for graphical presentation.     

Isotherm,kinetic, and thermodynamic studies on the adsorption behavior of malachite green dye onto montmorillonite clay

ABSTRACT

Systematic batch mode studies of adsorption of malachite green (MG) on montmorillonite clay were carried out as a function of process parameters which include pH, adsorbent dosage, agitation speed, ionic strength, initial MG concentration, and temperature. Montmorillonite was found to have excellent adsorption capacity. Equilibrium adsorption isotherms were measured for the single-component system, and the experimental data were analyzed by using Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm equations. It was found that the Langmuir equation appears to fit the equilibrium data. The monolayer (maximum) adsorption capacity (q_m) was found to be 262.494 mg g^?1 for montmorillonite. The experimental kinetic data were analyzed using the first-order, second-order, Elovich, and intraparticle kinetic models and the second-order kinetic model described the adsorption kinetics accurately for MG. Thermodynamic activation parameters such as ΔG*, ΔS*, and ΔH* of the adsorption of MG on montmorillonite were also calculated.     

The interrelation between hardness and compressibility of substances and their structure and thermodynamic properties

A strong correlation relationship has been established between the structure and specific Gibbs free energy of the substance atomization on the one hand, and the substance hardness and volume compressibility on the other. In the framework of the model proposed hardness is directly proportional to the specific Gibbs free energy per bond in isodesmic crystals. An application of a correction coefficient to the ionic component of chemical bonds allows one to evaluate the hardness of compounds having both the covalent (polar and nonpolar) and ion bonds. In the framework of the suggested approach we have been the first to correctly calculate the temperature dependence of the hardness by the example for diamond and cubic boron nitride.     

Quantifying technological aspects of process sustainability: a thermodynamic approach

Thermodynamic analysis has greatly helped to compare and to improve the energy efficiency of all kinds of technological processes, and recently we have also attempted to analyse some important biochemical processes under intracellular conditions. This work has pointed to some key strategies on sustainable process operation, such as the exceptionally high thermodynamic efficiencies of chemical and solar energy conversion in living cells.From this it was expected that the sustainability strategies of specific biochemical processes and those of the ecosphere as a whole could be of guidance to current technological processes, especially now that there is a growing demand from government and industry to effectively deal with sustainability aspects in process analysis. Our focus on this issue has led to methodologies to quantify technological aspects of sustainability by making use of thermodynamic principles. Three indicators were constructed to express three technological aspects of process sustainability. First, an indicator for the sustainability of resource utilization considers the thermodynamic input and the availability the resources used in the process. Secondly, an efficiency indicator focuses on the conversion and loss of thermodynamic quantities in the process itself. Thirdly, an indicator for environmental compatibility takes into account the thermodynamic input required to prevent possible negative side effects of the process, such as global warming or water pollution. The three indicators are used to reflect on (un)sustainable characteristics of current technological processes compared to biochemical processes. Finally, we address the drawbacks of combining indicator values to express overall sustainability.     

Measurement of Gibbs energies of formation of CoF2 and MnF2 using a new composite dispersed solid electrolyte

Gibbs energies of formation of CoF₂ and MnF₂ have been measured in the temperature range from 700 to 1100 K using Al₂O₃-dispersed CaF₂ solid electrolyte and Ni+NiF₂ as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF₂ thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al₂O₃ in the solid electrolyte and NiF₂ (or CoF₂) at the electrode, the dispersed solid electrolyte was coated with pure CaF₂, thus creating a composite structure. The free energies of formation of CoF₂ and MnF₂ are (± 1700) J mol⁻¹; {fx37-1} The third law analysis gives the enthalpy of formation of solid CoF₂ as ΔH° (298·15 K) = −672·69 (± 0·1) kJ mol⁻¹, which compares with a value of −671·5 (± 4) kJ mol⁻¹ given in Janaf tables. For solid MnF₂, ΔH°(298·15 K) = − 854·97 (± 0·13) kJ mol⁻¹, which is significantly different from a value of −803·3 kJ mol⁻¹ given in the compilation by Barinet al.     

Impact behaviour of concrete: a computational approach

The purpose of this study is to examine the numerical simulation of concrete specimens under high loading rates in tension. The data found in the literature are described: they show an increase in compressive and tensile strength as a function of the loading rate. To study this behaviour, we focused our attention on the assessment of the consistency model through the simulation of many experimental results related to a wide range of strain rates. In particular, the tests on unnotched and notched specimens performed at Delft University in recent years are examined. The proposed model is able to describe the increase in strength due to a high loading rate by an appropriate choice of the viscosity parameter.     

Prediction of dynamic recrystallisation behaviour of AISI type 4140 medium carbon steel

Abstract

The aim of the present work was to establish quantitative relationships between the flow stress and the volume fraction of dynamic recrystallisation (DRX) as a function of processing variables such as strain rate, temperature, and strain for AISI type 4140 medium carbon steel, by means of torsion tests. Torsion tests were carried out in the temperature range 900-1100°C and the strain rate range 5·0 × 10­2 -5·0 × 10⁰ s^­1 to study the high temperature softening behaviour. For the exact prediction of flow stress, the effective stress—effective strain curves were divided into two regions, the work hardening and dynamic recovery region and the DRX region. The flow stress of the DRX region could be expressed in terms of the volume fraction of DRX. It was found that the calculated results were in agreement with the experimental flow stress and microstructure of the steel for any deformation condition.     

Critical evaluation of the thermodynamic properties of cobalt

The thermodynamic properties and the pressure-temperature phase diagram of Co have been evaluated from experimental information using thermodynamic models for the Gibbs energy of the various phases. For hcp and fcc Co the model describes the magnetic contribution to the molar volume, expansivity, and compressibility and the efect of pressure upon the Curie temperature. Experimental data of many different types are satisfactorily described by the evaluated model parameters.This work was supported by the Swedish Board for Technical Development, and by Sandvik Hard Materials, Stockholm, Sweden.     

Modeling the thermodynamic properties of sodium chloride in steam through extended corresponding states

Recent precise data on anomalous behavior of apparent molar properties of electrolyte solutions in near-critical steam have raised important questions as to how the thermodynamic properties of these systems should be described. Current Gibbs free energy models fail for highly compressible solutions. Here, a Helmholtz free energy formulation is presented as a first step in modeling compressible dilute aqueous electrolyte solutions. Comparisons are made with the known critical line, coexistence curves, apparent molar volumes, and heat capacities of NaCl in steam, and conclusions presented on improving the model.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.