Quasi-chemical Theory Research Articles

Thermodynamic analysis of ordered liquid solutions by a modified quasichemical approach—Application to silicate slags

A system of semi-empirical equations has been developed for the analysis of the thermodynamic properties of ordered liquid solutions such as slags. The equations, which are based upon modifications of the quasichemical theory, take into account the concentration and temperature dependence of the solution properties of ordered systems and thus enhance the reliability of interpolations and extrapolations of data. For binary systems, these equations have been coupled with an optimization computer program to analyze simultaneously all available thermodynamic data including phase diagrams, Gibbs energies and enthalpies of formation of compounds, activities, enthalpies of mixing, entropies of fusion, miscibility gaps,etc. In this manner, data for several binary slag systems have been analyzed. In the present article, analyses for the CaO-SiO2, FeO-SiO2, and CaO-FeO systems are presented. The resulting equations represent all the binary data, including the phase diagrams, essentially within experimental error limits. The calculations have been extended to ternary systems, thereby permitting ternary thermodynamic properties to be approximated solely from data from the subsidiary binary systems. Results for the SiO2-CaO-FeO system are in excellent agreement with measured ternary data.

Conditions of interaction of materials in gas thermal spraying of metallized oxide powders on AK-4 alloy

The analysis made from the viewpoints of thermodynamics and the quasichemical theory of the formation of bonds in gas thermal spraying indicates the unquestionable advantages of aluminum oxide composites and the significant role of surface oxide films in the creation of reliable thermal protection coatings on aluminum alloys. It is most desirable to obtain ZrO2 base coatings and a change in the nature of the oxide film on the surface of AK-4 alloy by preliminary formation of a NiO sublayer on it. The use for spraying of metallized oxide powders substantially increases the energy of contact interaction of the materials on the base. The components of the metallized powders interacts with the formation of types Zr-Al and Zr-Al-Ni oxidized phases. The depth of mutual diffusion of the elements of the coating and the base is 0.5–3 um. The adhesion strength of the optimum composition thermal protection coating with the surface of AK-4 alloy reaches 20–25 MPa.

Excess enthalpies of the liquid systems: 1,2-dichloroethane + n-alkanes or +2,2,4-trimethylpentane

Hahn, G. Svejda, P. and Kehiaian, H.V., 1986. Excess enthalpies of the liquid systems: 1,2-dichloroethane + n-alkanes or +2,2,4-trimethylpentane. Fluid Phase Equilibria, 28: 309-323. Molar excess enthalpies, h E, at 293.15 K and atmospheric pressure are reported for the binary liquid mixtures of 1,2-dichloroethane + haptane, + decane, + dodecane, + tetradecane, + hexadecane or + 2,2,4-trimethylpentane, all determined by means of a flow microcalorimeter of the Picker-type. These measurements could be reproduced within the experimental limits by calculations according to a quasi-chemical group contribution theory, using constant values for two interchange energy coefficients, C 1,ad (Gibbs energy) and C 2,ad (enthalpy). Fair agreement between the calculated excess heat capacities, e E p , and the experimental literature values could be obtained by adjusting a third coefficient, C 3,ad (heat capacity). However, C 3,ad decreases with increasing chain length of the n-alkane. Even with three C 1,ad coefficients the model cannot reproduce the exact shape of the c E p versus composition curves. Apparently, not only the terms of an interchange of group surface contacts, but also conformational changes occurring in n-alkanes on mixing, contribute to the excess functions. The set of C 1,ad coefficients reported in this paper should prove useful in predicting phase equilibria in liquid 1,2-dichloroethane + n-alkane mixtures.

Thermodynamics of 1-alkanol + N-ether mixtures

Recent vapor-liquid equilibrium data for four 1-alkanol+n-polyether mixtures are examined on the basis of DISQUAC model -an extension of the surface-interaction version of the quasichemical group contribution theory, to correlate and predict excess enthalpies and excess Gibbs energies for such mixtures at 298.15 K. Using the new data, revised interaction parameters are proposed, which provide a fairly consistent description of the properties of the mixtures as functions of composition.

Thermodynamic properties of binary mixtures containing chloroalkanes. I. Analysis of the excess enthalpies and excess gibbs energies of 1-chloroalkane + + cyclohexane mixtures in terms of an extended quasichemical group contribution model (DISQUAC)

The data available in the literature for the excess enthalpies of 1-chloropropane, 1-chlorobutane, 1-chloropentane, 1-chlorohexane, 1 -chlorododecane or 1-chlorohexadecane + cyclohexane and for the liquid-vapour equilibria of 1-chloropropane or 1-chlorobutane + cyclohexane are examined on the basis of DISQUAC, a very simple extension of the quasi-chemical group contribution theory applied previously to correlate and predict excess enthalpies and excess Gibbs energies of 1-chloroalkane + n-alkane mixtures. Using the same parameters as before and adjusted values for the Gibbs energy and enthalpy of interchange of the chlorine(Cl)-cyclohexane contact, the model provides a fairly consistent description of the excess enthalpies as functions of composition and 1-chloroalkane chain length. Molar excess Gibbs energies are estimated for higher 1-chloroalkane + cyclohexane mixtures.

Excess enthalpies of (diether + n-alkane) at 298.15 K

Excess enthalpies, determined at 298.15 K in an LKB flow microcalorimeter, are reported for (2,4-dioxapentane + n-hexane) and (2,5-dioxahexane + n-heptane). Interpretation of the results by the generalized quasichemical theory of mixtures in terms of group surface interactions is examined.

The quasi-chemical group solution theory for organic mixtures

The extension of Guggenheim's Quasi-Chemical Theory in terms of groups proposed by Kehiaian, Grolier and Benson is discussed in terms of the non-random factors defined by Panayiotou and Vera. It is shown that the non-random factors correspond to a first neighbor's approximation of a step function radial distribution with a square-well potential. The variation of the coordination number from system to system is removed and a new method for the evaluation of the structural parameters, based on group connectivity, is proposed. Group interaction parameters have been determined from g E and H E values for hydrocarbon—hydrocarbon and hydrocarbon—alcohol systems. Results of correlation and prediction are compared with those of ASOG, SIGMA and UNIFAC methods.

Thermodynamic properties of binary mixtures containing aldehydes. III. Analysis of the excess enthalpies and excess Gibbs energies of n-alkanal + cyclohexane mixtures in terms of an extended quasichemical group contribution model (DISQUAC)

The data available in the literature for the excess enthalpies of ethanal, propanal, butanal, or pentanal + cyclohexane and for the liquid—vapour equilibria of propanal + cyclohexane are examined on the basis of DISQUAC, a very simple extension of the quasi-chemical group contribution theory applied in Parts I and II to correlate and predict excess enthalpies and excess Gibbs energies of n-alkanal + n-alkane mixtures. Using the same four alkyl group increments as in Part II, to account for intramolecular effects in the n-alkanals, and adjusted values for the Gibbs energy and enthalpy of interchange of the formyl(CHO)-cyclohexane contact, the model provides a fairly consistent description of the excess enthalpies as functions of composition and n-alkanal chain length. Molar excess Gibbs energies are estimated for several n-alkanal + cyclohexane mixtures. The (CHO)-cyclohexane interchange parameters are slightly larger than the (CHO)-normal alkane parameters. Ketones (CO group) and esters (COO group) behave similarly.

Monte Carlo simulation of model amphiphile-oil–water systems

A square-lattice model of amphiphile-oil–water systems is developed in which oil and water molecules occupy single sites and amphiphiles occupy chains of sites. Energies and free energies estimated by Monte Carlo sampling of configuration space show that when the head, or water-loving portion, of the amphiphile has no tendency to hydrate or surround itself with water, as opposed to surrounding itself with other heads, the capability of even long amphiphiles to solubilize repellant oil and water into a single phase is weak. Although the Monte Carlo free energies deviate markedly from those given by quasichemical theory, the deviation of the phase behavior is modest. Computer drawings of typical equilibrium configurations show highly irregular interfaces, apparently caused by capillary waves which are pronounced in two dimensions.

Calorimetric study of molecular interactions in mixtures of substances containing carbonyl and dialkylamino groups

A Tian-Calvet type calorimeter has been used to determine molar excess enthalpies at 298.15 K as a function of concentration for mixtures ofN,N-dialkylated aminoketones or amides+n-heptane. These data are examined on the basis of a quasi-chemical theory using group-surface interactions. The occurrence of the “hetero-proximity effect” between -CO- and-N < groups is suggested by the variation of the interchange parameters.

Thermochemistry of binary liquid gold alloys: The systems gold-copper and gold-silver at 1379 K

The enthalpies of mixing of the binary liquid alloys of gold with copper and silver have been measured by high temperature reaction calorimetry. The experimental results are described by the following analytical expressions which were derived by a least squares treatment of the data: Au-Cu: ΔHmix = XAuXCu(-28,821 - 2,468 XAu + 9,541 XAu 2) J mol-1 Au-Ag: ΔHmix = XAuXAg(-15,820 - 529 XAu @#@) J mol-1 The results are compared with excess Gibbs energy data from the published literature to yield approximate excess entropies of mixing. For the gold-copper system the observed parabolic dependence of the enthalpy interaction parameter on composition is well accounted for by the quasi-chemical theory.

Thermodynamic properties of binary mixtures containing aldehydes. II. Liquid-vapor equilibria in normal or branched alkanal + normal alkane mixtures: Analysis in terms of a quasichemical group-contribution model

Recent liquid-vapor equilibrium data for three alkanal + n-alkane mixtures are examined on the basis of the surface-interaction version of the quasichemical group-contribution theory used in Part I to correlate and predict excess enthalpies and excess Gibbs energies for such mixtures. The predictions prove to be accurate to better than 10%. Using the new data, revised interaction parameters are proposed for the estimation of liquid-vapor equilibrium for normal or branched alkanal + normal alkane mixtures.

Thermodynamic properties of binary mixtures containing esters. I. Analysis of the properties of n-alkanoate + n-alkane and n-alkanoate + n-alkanoate mixtures in terms of a quasichemical group-contribution model

The thermodynamic properties of n-alkanoate + n-alkane and + n-alkanoate binary liquid mixtures are examined on the basis of the group-surface interaction version of the Guggenheim-Barker quasichemical pseudolattice theory. All the data available in the literature for liquid—vapor and liquid—liquid equilibria, excess enthalpies and activity coefficients at infinite dilution are taken into consideration. Using only four alkyl-group increments, in addition to the two group-interaction parameters for methyl ethanoate, the model provides a fairly consistent description of the properties of the mixtures as functions of composition, temperature and chain length. The results are discussed in comparison with other classes of systems investigated previously (alkanones and alkanals).

Thermodynamic properties of binary mixtures containing aldehydes. I. Excess enthalpies of some n-alkanal + n-alkane mixtures: Measurement and analysis in terms of a quasi-chemical group-contribution model and estimation of excess Gibbs Energies

A Tian—Calvet-type calorimeter has been used to determine molar excess enthalpies at 298.15 K as a function of concentration for the following binary mixtures: ethanal, propanal, butanal or pentanal + hexane, heptane, dodecane or hexadecane. These and the few data available in the literature for liquid—vapor equilibria are examined on the basis of a quasi-chemical theory using group-surface interactions. With two group-interaction parameters and three alkyl-group increments, the model provides a fairly consistent description of the excess enthalpies as functions of composition and n-alkane chain length. Molar excess Gibbs energies are estimated for the n-alkanal + n-alkane mixtures and the results discussed in comparison with the properties of n-alkanone + n-alkane mixtures.

A quasi-lattice quasi-chemical theory of preferential solvation of ions in mixed solvents

The quasi-lattice quasi-chemical theory is used with a single fitting parameter (Z, the number of nearest neighbours) and data independent of the transfer to solvent mixtures, to describe quantitatively the standard molar Gibbs free energy of transfer of ions from a reference solvent to solvent mixtures, ΔGt� (X, W → S1 + S2), as a function of the composition (mole fraction, x). The independent data include the ΔGt� to the two pure solvents and the excess Gibbs free energy of mixing of these solvents. A defined preferential solvation parameter, g(x), is a convenient measure that is obtained from this treatment. The advantages of employing volume fractions, �, and g(�) rather than mole fractions, x, and g(x), are examined. The theory is applied to the transfer from water of Cl- to ethanol, of Ag+ to acetonitrile or dimethyl sulfoxide, and of NaCl to methanol, and of Na+ from acetonitrile to dimethyl sulfoxide as illustrative examples, comparing the calculated values to experimental data.

Theory of formation of second-phase particles as a result of diffusive saturation of solid solutions

This chapter discusses the statistical thermodynamics of interacting surfaces. For the evaluation of the interaction energies, it is needed to know which piece of surface is an interaction partner of which, while in the usual 3D interaction models, complete information about the coordinates and distances of all particles is needed. This chapter discusses about the Flory-Huggins theory and the Quasichemical theory. The GEQUAC model of Egner and the Cosmospace approach are elaborated, and the equivalence between Cosmospace and Quasichemical approximation is established. It is concluded that the thermodynamic model of independently pairwise interacting surface segments can be exactly and efficiently solved by the COSMOSPACE equations. The surprising equivalence of the off-lattice model to the older lattice model of Guggenheim in his quasi-chemical approximation gives additional support to the reliability of the approximation suggested in the study. Also, the extremely good agreement of COSMOSPACE results with lattice MC simulations proves that the neglect of any kind of neighborhood information, and of steric constraints induced by the packing of molecules in a lattice, appear to be of surprisingly small importance over a wide range of thermodynamic conditions.

The coordination cluster theory—description of the activity coefficients of dilute solutions of oxygen and sulfur in binary alloys

The activity coefficients of dilute solutions of oxygen and sulfur in some binary alloys are analyzed in terms of three models—the quasi-chemical theory, the ideal solvent model, and the coordination cluster theory. The first theory does not give a satisfactory representation of a large fraction of the data. The ideal solvent model provides a good representation of a majority of the systems. However, the coordination cluster theory provides a consistently good description of the data. Only one unknown parameter is present in the analytical expressions of the activity coefficients of the solute in the latter two theories. This parameter is related to physical quantities and, in principle, can be independently determined experimentally or theoretically.

Application of first-order quasichemical theory to transformations in steels

There are several theoretical and empirical thermodynamic models which adequately describe the equilibrium properties of carbon in ferrite and in austenite (e.g. Refs. 1, 2). These models usually contain unknown parameters which have to be deduced by ‘curve-fitting’ to experimental thermodynamic data, and this has made it difficult to judge the validity of particular theories, since the curve-fitting procedure always seems to ensure good agreement with the known Fe–C phase diagram. However, the analysis of reactions occurring under metastable equilibrium conditions (such as the bainite and martensite transformations) requires the extrapolation of the free energy surfaces of austenite and ferrite; it is clearly desirable to base such extrapolations on physically meaningful laws.

Equations of state for strongly nonideal fluid mixtures: Application of local compositions toward density-dependent mixing rules

A local-composition, two-fluid model has been developed for equation-of-state calculations of fluid-phase equilibria for asymmetric mixtures; it is applicable to any equation of state of the van der Waals form. A modification of the quasichemical theory of Guggenheim is applied to mixtures at all fluid densities. Desirable boundary conditions are met at low densities, at high densities, and at high temperatures.

The structure of radiative and non-radiative recombination centres in activated CdS phosphors

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