Mars Z. Faizullin

Crystal-Liquid-Gas Phase Transitions and Thermodynamic Similarity: SKRIPOV: CRYSTAL-LIQUID-GAS PHASE TRANSITIONS AND THERMODYNAMIC SIMILARITY O-BK

Foreword. 1 Introduction. 1.1 Basic Aims and Methods. 1.2 States of Aggregation. Phase Diagrams and the Clausius-Clapeyron Equation. 1.3 Metastable States. Relaxation via Nucleation. 1.4 Phase Transformations in a Metastable Phase. Homogeneous Nucleation. 2 Liquid-Gas Phase Transitions. 2.1 BasicFact: ExistenceofaCriticalPoint. 2.2 Method of Thermodynamic Similarity. 2.3 Similarity Near the Critical Point: The Change of Critical Indices. 2.4 New Universal Relationships for Liquid-Vapor Phase Coexistence in One-Component Systems. 2.4.1 Correlation Between Pressure and Densities of Liquid and Vapor Along the Saturation Curve. 2.4.2 Correlation Between Caloric Properties and Densities of Liquid and VaporAlongtheSaturationCurve. 2.4.3 Correlation Between Surface Tension and Heat of Evaporation of Nonassociated Liquids. 2.4.4 One-Parameter Correlation for the Heat of Evaporation of NonassociatedLiquids. 3 Crystal-Liquid Phase Transitions. 3.1 The Behavior of the Crystal-Liquid Equilibrium Curve at High Pressures. 3.2 Experimental Methods of Investigation of Melting of Substances at High Pressure. 3.3 Application of Similarity Methods for a Description of Melting. 3.4 The Extension of the Melting Curve into the Range of Negative Pressures and the Scaling of Thermodynamic Parameters. 3.5 Internal Pressure in a Liquid Along the Equilibrium Curves with Crystal and Vapor. 3.6 Stability of Thermodynamic States and the Metastable Continuation of the Melting Curves. 3.7 The Behavior of the Viscosity of a Liquid Along the Coexistence Curve with the Crystalline Phase. 3.8 The Behavior of Volume and Entropy Jumps Along the Melting Curve. 3.9 The Surface Tension of Simple Liquids Along the Melting Curve. 3.10 Correlations Between Thermodynamic Properties Characterizing Melting. 3.11 Melting and Crystallization of Small Particles. 3.11.1 Thermodynamic Aspects. 3.11.2 KineticAspects. 4 Phase Transitions in Solutions. 4.1 Generalized Clausius-Clapeyron Equation for Solutions. 4.2 Application of the Generalized Clausius-Clapeyron Equation for the Plot of thePhaseDiagrams. 4.3 Thermodynamic Correlations for Phase-Separating Solutions. 4.4 Experimental Studies of Phase-Separating Solutions. 4.5 Thermodynamic Similarity of Phase-Separating Binary Solutions with Upper Critical Dissolution Temperature. 4.6 Thermodynamic Similarity of Phase-Separating Binary Solutions with Lower Critical Dissolution Temperature. 4.7 Concluding Remarks. A Appendices. A.1 List of Symbols. A.2 SuperscriptsandSubscripts. References. Index.

New universal relationships for surface tension and vaporization enthalpy of non-associated liquids

The methodology of thermodynamic similarity has been used to study the relation between the surface tension of a liquid and the vaporization enthalpy calculated per unit volume of the liquid phase. Simple reliable relationships that do not contain substance dependent parameters have been found. A new universal one-parameter relationship for the temperature dependence of the vaporization enthalpy has been suggested. The results of calculations with the use of these relationships are compared with experimental data.

Glass transition and crystallization of low-temperature amorphous condensates of the water-propane mixture

Interest in gas hydrates stems from the existence of vast reserves of hydrocarbons on the earth in the form of gas hydrates, prospects for using them as a fuel source, and the possibility of storage and transporta� tion of gas in the gas hydrate state. The known meth� ods of production of gas hydrates are based on rela� tively small deviations from the equilibrium condi� tions of gas dissolution. They require the use of high pressures in laboratory or manufacturing equipment. For example, the pressure corresponding to the for� mation conditions of methane hydrate at temperatures near 0°С amounts to tens of bars. In addition, forma� tion of the crystal hydrate requires dispersion of water, which is afforded by longterm and vigorous stirring of the water-gas mixture. In this work, we have proposed another approach implying that hydrates are formed under conditions far from thermodynamic equilibrium. The approach is based on lowtemperature molecularbeam deposi� tion in a vacuum onto a surface cooled by liquid nitro� gen. During this process, amorphous (glassy) layers of the water-gas mixture are initially formed, which are stabilized by high viscosity. Heating of the amorphous layers is accompanied by avalanchetype nucleation and growth of gas hydrate crystallization sites. This method requires neither high pressures nor stirring of the water-gas system. Its advantage is that it is univer� sal and can be used for producing various gas hydrates. This work deals with studying the glass transition and crystallization of amorphous condensates of the binary water-propane system obtained by lowtem� perature condensation to determine the conditions of crystal hydrate formation. Amorphous solid (glassy) layers of lowmolecular� weight substances can be obtained by molecularbeam deposition onto a cooled surface. At low temperatures, the amorphous state of these substances is stabilized by the high viscosity. Molecularbeam deposition onto a copper substrate cooled by liquid nitrogen affords amorphous layers of water and simple molecular com� pounds (1), as well as of aqueous solutions of organic liquids (2). Cooling rates under these conditions are as high as 10 5 -10 7 K/s. On heating, the condensates undergo glass transition (softening) and subsequent spontaneous crystallization. In the course of the latter, a decisive role for phase transformation is played by homogeneous nucleation. The crystallization of amorphous water-gas condensates can result in the formation of gas hydrates (3-5). Hydrate formation is facilitated by the low chemical affinity of the hydrate� forming substance, as well as by the size and shape of its molecules corresponding to the geometry of cavi� ties in the arising clathrate framework. Among such substances, there are light hydrocarbons of the meth� ane series. Experiments with lowtemperature con� densates of the water-methane mixture showed the possibility of producing massive samples of crystal hydrates with high gas content capable of sustained burning (5).

Properties of gas hydrates formed by nonequilibrium condensation of molecular beams

Low-temperature crystallization of amorphous materials has been analyzed theoretically taking into account nonstationary nucleation. The kinetics of crystallization of amorphous water layers, formed by depositing molecular beams on a substrate cooled by liquid nitrogen, has been investigated by differential thermal analysis. The conditions of gas hydrate formation in low-temperature amorphous-ice layers saturated with carbon dioxide have been studied. The glass-transition and crystallization temperatures of the gas hydrates have been determined from the change in dielectric properties upon heating. Under the deep-metastability conditions, crystallization of water-gas layers leads to the formation of crystallohydrates. Gas molecules are captured by the avalanche-like nucleation of crystallization centers and, therefore, are not displaced by the moving crystal-melt interface. Gas-hydrate samples formed in nonequilibrium water-gas layers are convenient for studying their thermophysical properties.

Heat capacities and thermal diffusivities of n-alkane acid ethyl esters—biodiesel fuel components

The heat capacities and thermal diffusivities of ethyl esters of liquid n-alkane acids CnH2n–1O2C2H5 with the number of carbon atoms in the parent acid n = 10, 11, 12, 14, and 16 are measured. The heat capacities are measured using a DSC 204 F1 Phoenix heat flux differential scanning calorimeter (Netzsch, Germany) in the temperature range of 305–375 K. Thermal diffusivities are measured by means of laser flash method on an LFA-457 instrument (Netzsch, Germany) at temperatures of 305–400 K. An equation is derived for the dependence of the molar heat capacities of the investigated esters on temperature. It is shown that the dependence of molar heat capacity Cp,m(298.15 K) on n (n = 1–6) is close to linear. The dependence of thermal diffusivity on temperature in the investigated temperature range is described by a first-degree polynomial, but thermal diffusivity a (298.15 K) as a function of n has a minimum at n = 5.

Formation of gas hydrate during crystallization of ethane-saturated amorphous ice

Layers of ethane-saturated amorphous ice were prepared by depositing molecular beams of water and gas on a substrate cooled with liquid nitrogen. The heating of the layers was accompanied by vitrification (softening) followed by spontaneous crystallization. Crystallization of condensates under the conditions of deep metastability proceeded with gas hydrate formation. The vitrification and crystallization temperatures of the condensates were determined from the changes in their dielectric properties on heating. The thermal effects of transformations were recorded by differential thermal analysis. The crystallization of the amorphous water layers was studied by electron diffraction. Formation of a metastable packing with elements of a cubic diamond-like structure was noted.

Preparation of Gas Hydrates by Nonequilibrium Condensation of Molecular Beams

Layers of amorphous ice saturated with carbon dioxide were prepared by the deposition of molecular beams of water and gas onto a substrate cooled with liquid nitrogen. Their heating is accompanied by glass transition (softening) and subsequent spontaneous crystallization. The glass transition and crystallization temperatures were determined from the change in dielectric properties during heating. The heat effects of the transformations were detected using differential thermal analysis. The crystallization of amorphous layers under conditions of deep metastability leads to the formation of crystalline hydrates. The avalanche nucleation of crystallization sites captures the gas molecules; therefore, they are not displaced by the movement of the crystallization front.

Unsteady nucleation in layers of amorphous ice in the presence of artificially injected crystalline centers

The role of thermal conditions under which crystallization of an amorphous substance occurs is analyzed theoretically with allowance for unsteady nucleation.