Properties Of Solid Phases Research Articles

Solid–fluid phase equilibrium for single component and binary Lennard-Jones systems: A cell theory approach

We consider the application of the cell theory to single component and binary Lennard-Jones solids. We calculate solid phase properties and solid–fluid equilibrium using the cell theory for the solid phase and an equation of state for the fluid phase. In the single component case the thermodynamic properties as well as the solid–fluid phase diagram predicted by the theory are in quite good agreement with Monte Carlo simulation results. The introduction of correlations between the motions of nearest neighbor particles into the cell theory in a fashion suggested by Barker significantly improves the agreement. For binary Lennard-Jones 12-6 mixtures the predictions of the theory are compared with experimental data for mixtures forming substitutionally disordered solid solutions involving argon, krypton and methane. The theory correctly predicts the form of the phase diagram but the quantitative predictions are quite sensitive to the choice of potential parameters. The shape of the phase diagram is similar to that for a hard sphere mixture with the same diameter ratio.

Free energy computer simulation in solid state chemistry

A methodology of the free energy computer simulations in the application to realistic models of molecular crystals has been presented. It is based on the symmetry properties of solid phases and a definition of the reversible path between then. Examples of calculations for nitrogen and carbon dioxide solid states have been used to illustrate advantages of the approach.

Towards phase transferable potential functions: Methodology and application to nitrogen

We describe a generalizable approach to the development of phase transferable effective intermolecular potentials and apply the method to the study of N2. The method is based on a polarizable shell model description of the isolated molecule and uses experimental data to establish the parameters. Consideration of the Ne dimer shows this to be a conceptual advance over point polarizability descriptions of atomic interaction. Our parametrization of N2 accurately describes not only the molecule’s electrostatic field (i.e., a practical representation of the molecular charge distribution) but also its response to electrical and mechanical stress (polarization and deformation). The purely intermolecular terms in our potential reflect shell-shell interactions. These are parametrized by fitting properties of the low temperature solid phase of nitrogen. We derive a phase transferable potential able to account for the second virial coefficient of the gas phase, the pressure induced phase transition between nitrogen’s cubic and tetragonal phases, and a wide range of liquid properties (pair distribution function, heat of vaporization, self-diffusion coefficient and dielectric constant).

Effects of solid-phase properties on flames spreading over composite materials

The problem of downward flame spread over composite, thermally thick materials is theoretically investigated by means of a thermal, analytical model and a numerical model based on the reactive fully elliptic Navier-Stokes equations. The solid, made of a thermoplastic polymer and inert additives, undergoes in-depth endothermic pyrolysis, for the active part, with volatile monomer formation. The effective thermal conductivity of the composite material depends on the content of inert and the variable content of the active part, whose thermal conductivity varies between that of the polymer and that of the melted phase monomer. Even though surface regression is not taken into account, polymer consumption is modeled through a mass balance. The changes in the flame spread mechanisms with solid phase properties are investigated. The spread process is strongly affected by the solid perpendicular (to the spread direction) thermal conductivity which, when it decreases, causes a continuous increase in the spread rate. On the other hand, both numerical and analytical solutions give no dependence of the spread rate on the solid parallel (to the spread direction) thermal conductivity for a wide range of variation. In agreement with previous experimental results, at very large values of the latter, the finite-rate reaction model predicts a decrease in the spread rate. However, in contrast to certain experiments performed for non homogeneous composite samples, an increase of the spread rate with the effective solid parallel thermal conductivity or thermal capacity has not been found.

Influence of magnetic dilution on the spin transition in the complex of iron(II) nitrate with 4-amino-1,2,4-triazole

Influence of magnetic dilution with ZnII ions on the spin transition in the iron nitrate complex of 4-amino-1,2,4-triazole (AT) was studied by magnetochemistry, Mossbauer spectroscopy, and IR spectroscopy. In studies of the properties of solid phases of Fe x Zn 1−x (AT)3(NO3)2 (0.01≤x≤0.8), it was demonstrated that magnetic dilution results in a lowered spin transition temperature and an increased share of the high-spin form of the iron(II) complex.

Thermodynamic analysis and phase equilibria calculations of pb-zn, sn-zn, and pb-sn-zn systems

Thermodynamic properties of liquid and solid phases in the Pb-Zn, Sn-Zn, and Pb-Sn-Zn systems were assessed using a quasi sub-subregular solution model. The model parameters for different phases were obtained by simultaneous optimization with respect to the available thermodynamic and phase equilibrium data. Phase diagrams and thermodynamic data were then calculated and compared with the experimental/assessed data.

Stability and thermodynamic properties of supersaturated solid solution and amorphous phase formed by ball milling in the Zr- Al system

Zr100-xA1x (x ≤ 40) metastable alloys were synthesized by high- energy ball milling of elemental Zr and Al powders: supersaturated substitutional cph solid solution for x ≤ 15 and an amorphous phase for x ≥ 17.5. We performed a calorimetric study of the thermodynamics and kinetics of the metastable- to- equilibrium transformations of these phases. Their stability range (temperature/composition), as well as the apparent activation energies associated with the transformations, were determined. The transformation enthalpies were measured and used to determine the enthalpy of formation for these metastable phases. For both as- milled and relaxed amorphous phases, the measured enthalpy of crystallization is compared with those estimated for an undercooled liquid. Different amounts of retained entropy at the glass transition temperature were used to estimate the enthalpy loss upon undercooling due to the excess specific heat.

Alleviation of soil acidity in Ultisol and Oxisol for corn growth

Malaysian Ultisols and Oxisols are characterized by low pH, high soil solution Al concentration and Ca and/or Mg deficiencies, which are limiting to corn growth. An experiment was conducted to determine the changes in solid and soil solution phase properties of a representative Ultisol and Oxisol following applications of ground magnesium limestone (GML), gypsum and their combinations, and their effects on corn growth. A plot of pAl against lime potential (pH-1/2 pCa) showed that the points were mostly positioned between the theoretical lines for kaolinite-quartz and gibbsite equilibrium, reflecting the kaolinitic-oxidic mineralogy of the Ultisol and Oxisol. Gypsum application increased Al concentration in the soil solutions of the Ultisol, but had no significant effect on that of the Oxisol. The increase in Al concentration in the Ultisol was due to an increase in ionic strength. Gypsum application increased soil solution pH of the Oxisol due to release of OH as a result of ligand exchange between SO4 and OH ions on the oxides of Fe and/or Al. Exchangeable Al in both soils was reduced by gypsum application. The reduction was associated with solid phase immobilization through alunite formation; the soil solutions of soil samples treated with 2 and 4 t gypsum ha−1 were supersaturated with respect to alunite. Application of GML at 2 t ha−1 together with 1–2t gypsum ha−1 gave high top weight of corn. Relative top weight of corn was positively correlated with a soil solution Mg and Ca/Al concentration ratio, but negatively correlated with soil solution Al concentration. Foliar Al corn was positively correlated with soil solution Al concentration. Soil solution Al and Mg concentrations, and Ca/Al concentration ratio can be used as indices of soil acidity in Ultisols and Oxisols. ei]{gnB E}{fnClothier}

Wigner solid versus incompressible Fermi liquid: phase diagram derived from time-resolved photoluminescence

We have made the first measurements of the time-resolved luminescence of two-dimensional electrons confined in GaAs/AlGaAs heterojunctions in the regime of Wigner crystallization. We find that the recombination time for electrons in the pinned Wigner-solid phase is up to several orders of magnitude longer than for electrons in the liquid phase. The different time scales allow us to investigate the properties of liquid and solid phases independently and to derive a phase diagram for the Wigner crystallization.

The influence of physical properties on the operation of a three-phase fluidized-bed fermentor with yeast cells immobilized in Ca-alginate

A three-phase fluidized-bed bioreactor with Ca-alginate immobilized yeast cells in which an external air stream is introduced to promote and maintain fluidization was studied with respect to its characterization and air-flow optimization. The fluidization behavior is very strongly dependent on the physical properties of both liquid and solid phases (liquid viscosity, density, surface tension, and solid density). Satisfactory or unsatisfactory fluidization behavior could be determined in a graph on the basis of two parameters calculated with the values of the physical properties. A correlation on the minimum air-flow rate necessary to obtain acceptable fluidization of the immobilized yeast beads was developed using experimental data obtained in two fermentors with different L/D ratios.

Dielectric studies of orientational disorder in D- and L-systems of camphor and camphoric anhydride

Dielectric properties of low-temperature solid phases of mixtures of optical antipodes of camphor and camphoric anhydride have been measured and related to their phase diagrams determined calorimetrically. Two distinct mechanisms of dipolar relaxation emerge for camphor: one for mixtures with compositions around the pure optical isomer, and the other for those mixtures around the racemic composition. A composite relaxation process involving both orientational and substitutional disordering modified by short-range order effects applies in the case of compositions around the racemic mixture. A simple relaxation process associated with orientational disordering is dominant in the phase transition of mixtures around the optical isomer. The two relaxation processes account for the different patterns of dipolar relaxation phenomena observed. The overall disordering transition has a strong second-order character for compositions around the racemic mixture. In contrast, only one relaxation process involving orientational disordering is dominant for all compositions in binary mixtures D- and L-camphoric anhydride. The transition is predominantly first-order in character for all compositions of D- and L-camphoric anhydride and for mixtures around the pure isomer in camphor. Substitutional disordering appears to be responsible for much of the dielectric absorption observed in low-temperature phases of the binary systems studied. In camphoric anhydride, the presence of a large chirodiastaltic energy leads to phase separation and limited coupling between orientational and substitutional disordering processes.

The effect of radiative heat transfer on morphological stability during directional solidification of a binary melt

The influence of radiant heat transport and impurity distribution in a semi-transparent crystal-melt system on the morphological stability of a planar interface during the crystallization of semi-transparent binary dilute melt is studied in the framework of the linear theory. Our analysis shows that the influence of radiation on stability is complex. If radiant transport of heat is sufficiently strong, and the physical properties of liquid and solid phases differ considerably, radiation will influence the loss of stability of the crystal-melt interface. The loss iof stability can also occur when the impurity is absent. It is very evident in the case N S » N L α L >α S. In addition, radiation can enhance or reduce the stability of interface through the dependence on the relation between α S, α L and λ S, λ L for the case in which the values of N S,L are small. If λ S = λ L and λ S = λ L, the stability of interface is not influenced by radiation, though the radiation undercooling exists ( N S. L = 16 n 2 bT 3 m /(3 λ S. L α S, L. ), n is refractive index, b is Stefan-Boltzmann constant, T m is the equilibrium temperature of melting, α S.L is mean value of absorption coefficient, λ S.L is heat diffusivity and the indexes S, L correspond to the solid or liquid phases).

The chemical synthesis and physical characterization of [formula omitted], an important class of membrane glycolipids

Improved procedures for the preparation of 1,2- di-O- acyl-3-O-( α- d-glucopyranosyl )-sn- glycerols have been developed. The procedures are based on a halide ion condensation of a benzylated 1-bromo sugar with 1,2-di- O-butenyl- sn-glycerol and have enabled a relatively straightforward and inexpensive synthesis of 1,2- di-O- acyl-3-O-( α- d-Glucopyranosyl- and 1,2- di-O- acyl-3-O- d- galactopyranosyl)-sn- glcerols with a wide variety of acyl chain lengths and structure and in quantities suitable for detailed structural studies. The analytical data on these compounds are consistent with the expected structure and high sample purity. A physical characterization of the α-D-glycosyl diacylglycerols also indicates that the solid phase and solution properties of these glucolipids differ markedly from those previously reported for the β-anomers. Such differences should also be manifest in the polymorphic phase behavior of lipid bilayers composed of these lipids.

Chirality and the thermophysical properties of molecular solid phases under pressure: (+)- and (±)-camphor

Thermal conductivity λ, heat capacity per unit volume pcP and P-T phase diagrams are investigated for both (+)- and (±)-camphor. The transient hotwire method is used at temperatures in the range 100–430 K and at pressures up to 1·75 GPa. We detect solid phases I-IV for (+)-camphor and I′-V′ for (±)-camphor. We conclude that λ is independent of enantiomeric composition for plastic-crystal phase pairs I-I′, II-II′ and IV-IV′. Phase V′ also appears to be a plastic-crystal phase. Non-plastic phases III and III′ show a variation of λ with T that differ considerably from that expected for a simple crystal, with the greatest such difference being observed for the racemic compound III′. An unannealed specimen of the racemic compound III′ is probably chirally disordered and shows a variation of λ with T for T < 130 K, which may indicate phonon-assisted fracton hopping.

A Defect Equilibrium Treatment of Selected Transport Phenomena in Solids

AbstractSome aspects of the thermodynamic and transport - related properties of binary solid electrolyte phases are discussed in terms of the associated defect behaviour. In particular, the close relationship between results obtained from an asymmetric polarization experiment and the relevant defect equilibrium diagram for the phase under study, is emphasized.

Effect of storage medium on thermal properties of packed beds

The present paper is concerned with studying the effects of storage medium properties on the thermal behaviour of packed beds during charging. A transient one-dimensional two-phase model is used to describe the temperature fields in the air and solid media constituting the bed. The numerical solution of the resulting two-coupled partial differential equations is obtained, and the variation of thermal energy stored with time is computed. Solutions are obtained for a wide range of storage media (the solid phase) properties, namely density, thermal conductivity and specific heat. The results show that increasing either the density or specific heat increases the rate and capacity of energy storage, and decreases the rate of temperature rise throughout the storage medium. On the other hand, increasing the thermal conductivity is found to markedly increase the rate of temperature rise and energy stored inside the bed up to a certain time during charging, beyond which this trend completely reverses. In addition, the thermal storage properties of aluminum, steel and rock-packed beds are computed and compared.

Interactions between HCl, NOx and H2O ice in the Antarctic stratosphere: Implications for ozone

Thermodynamic properties of solid phases containing H2O and HCl are examined for conditions expected over Antarctica in winter. It is shown that solid solutions with 0.02–0.035 mole fraction HCl in H2O ice will form in the stratosphere at temperatures between 193° and 190°K. Crystalline HNO3·H2O and/or HNO3·3H2O form in the same temperature range. Thus condensation of small quantities of H2O (&lt;1 ppm) leads to nearly complete removal of both HCl and HNO3 from the gas phase. Formation of ice‐HCl solid solutions provides a favorable setting for the heterogeneous reaction of HCl with ClNO3, initiating a rapid sequence of reactions that converts solid‐phase HCl into gaseous ClNO3 or chlorine oxide radicals. Odd nitrogen species are simultaneously converted into solid‐phase nitrates. The cycle producing reactive chlorine gases is likely to be completed before particles grow large enough to fall from the stratosphere. Hence precipitation of particles from the polar stratospheric clouds is expected to remove odd nitrogen from the stratosphere efficiently, leaving chlorine gases behind. High concentrations of reactive chlorine oxide radicals are rapidly produced by heterogeneous reactions if the initial concentration of HCl exceeds a critical value, 0.5 times the concentration of NOx before onset of condensation. Production of unreactive ClNO3 and HOCl is favored if HCl levels are lower than this value. The onset of Antarctic ozone depletion in the late 1970s may in part reflect growth of HCl levels beyond this threshold.

Atomic anisotropy and the structure of liquid chlorine

An anisotropic atom–atom potential for chlorine that can explain the static properties of both solid and liquid phases is presented. Molecular dynamics simulations with this potential show that the anisotropies in the repulsive interactions introduce significant changes into the behaviour of the liquid, and are especially important in determining the liquid structure factor. Some aspects of the implementation of orientation-dependent pair potentials in molecular dynamics calculations are discussed. In particular, the use of an anisotropic instead of an isotropic atom–atom potential was found to require only a modest increase in computation time.

Effect of variable solid phase thermal properties on propellant combustion

Mathematical models derived for describing the combustion of solid rocket propellants have in the past assumed that the thermal properties, specific heat, and thermal conductivity are constant throughout the solid phase portion of the combustion zone. The values for specific heat and thermal conductivity can vary as much as 50–100 percent for the temperatures in the solid phase combustion wave, values from about 250 to 1100 K. Thus, the variation in solid phase properties due to the temperature variation in the solid phase have significant effects on the burning rate, the temperature sensitivity and the pressure coupled response. The paper is concerned with predicting the effect of the variable solid phase properties on the combustion properties. Parametric calculations were made to illustrate the effect of the magnitude of the variation of solid phase properties with temperature. The results indicate that significant differences exist between the values for the combustion parameters calculated using variable thermal properties as compared to those calculated using constant thermal properties.

Statistical mechanics of the Xe/Ag(111) monolayer

Calculations are reported of properties of solid and fluid phases of the Xe/Ag(111) monolayer. The thermal expansion of the solid at its sublimation curve is calculated and the monolayer triple point is estimated. Anharmonic effects in the solid are discussed and mean field approximations to the adsorption dipoles in the dense fluid are introduced. The interaction model reproduces the low temperature properties of the monolayer solid, but there are small departures from the experimental data for the thermal expansion above 60 K. The calculated triple point temperature is significantly lower than the values reported for other monolayer xenon systems.