Metastable phase equilibria in a Lennard-Jones system

A method of molecular dynamics is used to calculate the pressure, internal energy, and isochoric heat capacity in a system of 2048 Lennard-Jones particles in the range of reduced temperatures from 0.1 to 2.0 and the range of densities from 0.001 to 1.15. Local equations of state for the gas, liquid, and crystalline phases are derived. The spinodals of a superheated (extended) liquid, supersaturated vapor, and superheated (extended) crystal are determined. It is shown that the spinodal of a supercooled liquid is nonexistent. An algorithm to calculate the lines of phase equilibria is constructed. The lines of liquid-gas, liquid-crystal, crystal-gas phase equilibria, and their metastable extensions are determined. It is shown that the metastable extensions of the melting and sublimation lines terminate at the spinodals of the liquid and crystal, respectively. The properties of final critical points in the lines of melting and sublimation are considered.     

Phase equilibria,metastable states,and critical points in a simple one-component system

Stability of metastable phase states against infinitesimal perturbations in a simple one-component system is considered. The method of molecular dynamics simulation was used to determine the boundaries of essential instability of supersaturated vapor, a superheated liquid, and a superheated crystal. The absence of a spinodal from a supercooled liquid and the dependence of the boundary of essential instability of a superheated crystal on the character of deformation were established. It is shown that each of the three lines of phase equilibria in a one-component system has an endpoint of termination of phase coexistence. As distinct from the liquid–gas critical point, which is the point of phase identity and is located in the region of stable states, the endpoints of melting and sublimation lines are located in the region ofmetastable states. At these points, a critical (spinodal) state is achieved only for one of the coexisting phases.     

Singular point of a system of Lennard-Jones particles at negative pressures

The method of molecular dynamics is used in a system of 2048 Lennard-Jones particles to determine the spinodal of a stretched liquid and crystal and the lines of their phase equilibrium at negative pressures. It is shown that a metastable extension of the melting line does not reach the zero isotherm, and ends on the spinodal of a stretched liquid. The point of termination of metastable liquid-crystal phase equilibrium is the singular point at a thermodynamic surface of states.     

Melting line, spinodal and the endpoint of the melting line in the system with a modified Lennard—Jones potential

A molecular dynamics method was used to calculate the pressure p* and the internal energy e* of a liquid and a crystal in stable and metastable states in a system of 2048 particles, which interaction is described by a modified Lennard—Jones potential. For the liquid phase, calculations were performed along 13 isotherms from the range of reduced temperature T* = 0.35–3.0, and for the crystal phase, along 16 isotherms from the range T* =0.1–3.0. The thermal p* = p*(ρ*,T*) and caloric e* = e*(ρ*,T*) equations of state for liquids and crystals have been constructed. The parameters of crystal-liquid phase equilibrium have been determined from the conditions of phases coexistence at positive pressures and in the region of negative pressures, where the coexistent phases are metastable. The spinodal of a stretched liquid has been approximated. It has been found that with a temperature decrease the metastable extension of the melting line meets the spinodal of the liquid phase. The point of their meeting, the endpoint of the melting curve, is the point of termination of crystal-liquid phase equilibrium without the onset of identity of the phases.     

Specifics of nucleation in superheated water and supersaturated vapor

This work is dedicated to the experimental studying of the nucleation kinetics in superheated water and supersaturated water vapor. A percolation model for the liquid water structure that explains a number of anomalous thermophysical properties of water and water vapor in the metastable region is proposed.     

Experimental testing of liquid boiling-up homogeneity near the boundary of the attainable superheating

Results of measured average expectancy time of n-pentane and n-hexane boiling-up to the boundary of attainable superheating are presented. Experiments have been carried out in glass capillaries with substantially decreasing value of the superheated liquid volume for the preset metastable state (p, T = const). Obtained data fail to prove correlation 1 JVῑ = following from the condition of homogeneity and stationarity of the random process resulting in the superheated liquid boiling-up (J is the frequency of homogenous nucleation, V is the volume of the superheated liquid, ῑ is the average life time). Thus, experiments on superheated liquid boiling-up kinetics bound with measurements of average life time in glass capillaries cannot serve a proof of the validity of classical theory of nucleation for superheated liquids since one of the ground conditions — boiling-up homogeneity — is not met.     

Studies of thermal resistance of mixtures in a wide temperature range. 1. Experimental techniques

Experimental techniques for investigation of heat transfer in liquid mixtures of different types complimenting each other have been presented. The main attention is focused on the measurements under conditions of pulse heating. The paper opens the set of papers dealing with the elucidation of features characteristic of the heat transfer in pulse superheated mixtures, including metastable states with respect to the liquid-vapor and liquid-liquid equilibriums.     

Collective Motion of Atoms in a Superheated Crystal and a Supercooled Melt of a Simple Metal

JETP Letters - Stable and metastable states of a crystal and a melt have been studied near the equilibrium crystal–melt phase transition point using a four-point correlation coefficient...     

Metastable states and their disintegration at pulse liquid heating and electrical explosion of conductors

The regularities of formation of metastable states and their disintegration under pulse liquid heating and electrical heating and explosion of conductors are studied. With a high energy flux density, the phase transitions occur with a high intensity of heat and mass fluxes, leading to spontaneous generation of a new phase and to phase explosion. The basic features of bubble-like disintegration in not uniformly superheated water and alcohol layers on the microheater are found. Regularities of matter disintegration with electrically exploded conductors are obtained. The metastable liquid disintegration is experimentally investigated for characteristic times of matter transfer to a metastable state of 1 to 4 μs; phase transitions during electric conductor explosion are studied at characteristic times of transfer to a metastable state to 200 ns. A common approach to describing the effects with radically different characteristic times of transfer of the matter to a metastable state is developed.     

Melting,freezing and other peculiarities in small systems

The theory of solid-liquid phase changes in small systems implies that such systems may—but need not—exhibit sharp but unequal freezing and melting temperatures. The origin of this conclusion is reviewed and its implications for the theory of first-order phase transitions in bulk matter are discussed. The logical separation is made of the two temperatures as limits of stable existence, each of its own ‘phase’; and the convergence, with increasing size of cluster, of the observable coexistence to a sharp transition temperature is discussed. The equilibrium ratios of concentrations for such a coexistence are discontinuous functions of temperature at the limits of stability. The possibility of observing coexisting forms in equilibrium depends on there being a time scale separability, who validity lies outside the realm of thermodynamics. It is conjectured that spinodals are the loci of the same kind of locally stable states responsible for coexisting solid and liquid forms of clusters, and that the limits of spinodals are the points of discontinuity in the equilibrium concentration ratios, the chemical ‘equilibrium constants’.     

亚稳相的高压暴露

 很久以前,便有人指出,气态冷凝成固态时,要连续经历液相及各种高温相,才达到平衡结晶相。但是,液态及高温相往往需靠很大的冷却速度才能冻结下来,这在当时对绝大多数合金,是不可能的。近些年,随着超急冷等技术的进步,关于非晶等亚稳相得研究十分活跃。当超过一定临界冷却速度时,液态合金可固化为非晶态。虽然,亚稳结晶相较非晶应更容易冻结,但是,由于产生各种亚稳相所需的过冷条件各不相同,以及对冷却速度的选择不能是任意的,因此有时它们较非晶还难于形成。与液相凝固过程相似,非晶合金的晶化也服从构型最小重排原理,即在晶化完成之前,存在某些亚稳相变态阶段。但是,限于热力学上的不稳定性及动力学因素,在常压下这些亚稳相同样是难以发现的。作者根据对多种合金系的研究,提出高压暴露亚稳相的设想,并利用非晶等亚稳相的高压变态过程,将进行液态急冷时的速度控制方式,改为便于掌握的高压退火方式,来获得新亚稳相。本文对压力暴露亚稳相的原理和实践,加以论述。     

Superheated ice

Ice single crystals are superheated by a pressure jump. Their optical homogeneity is examined by elastic light scattering in order to obtain information about the thermodynamic state in the bulk of the sample. The intensity of the scattered light after the pressure jump remains first unchanged. Only after a time lag a steep intensity increase is observed. The dependence of on the superheating, on sample size, on the position of the scattering volume in the sample, on crystal orientation, on the scattering angle and on the crystal quality is examined. depends only on superheating and crystal quality within experimental sensitivity. After a superheating of more than 5°C the optical appearance of ice is like opalescent glass. The observations are compatible with the assumption that the ice has been superheated with respect to the melt and that homogeneous nucleation occurs in the metastable state. The equilibrium curve iceI _h —water has been determined.     

Interdiffusion in condensed solutions

Expressions for the coefficient of interdiffusion of components in a binary condensed vacancy-free alloy and a diffusion coefficient matrix for the same alloy with equilibrium and nonequilibrium vacancies are studied. In the first alloy, metastable states may appear if the mixing energy is positive. In the case of the second alloy, closed spinodals may arise under certain conditions. In binary systems with a constant concentration of particles having close atomic volumes, a vacancy stationary nonequilibrium distribution is observed, which may generate vacancy “channels” through which atoms diffuse much more rapidly than in the regular lattice.     

Evaporation of atoms from femtosecond laser-heated gallium arsenide

The surface temperature of a GaAs crystal irradiated with 150 fs laser pulses is determined from the Maxwell velocity distribution of the evaporated atoms. The crystal is strongly superheated, and melting is observed to occur at a temperature 600–1000 K above the equilibrium melting point.     

Superheating and supercooling of vortex matter in a Nb single crystal: direct evidence for a phase transition at the peak effect from neutron diffraction

We report the first observation of a striking history dependence of the structure function of vortex matter in the peak effect regime in a Nb single crystal by using small angle neutron scattering combined with in situ magnetic susceptibility measurements. Metastable phases of vortex matter, supercooled vortex liquid and superheated vortex solid, have been identified. We interpret our results as direct structural evidence for a first-order vortex solid-liquid transition at the peak effect.     

On the size dependence of the melting temperature of nanoparticles

The size dependence of the melting temperature of nanocrystals has been investigated within the thermodynamic approach. A formula is obtained, which, in contrast to the classical Thomson formula, takes into account the metastable character of equilibrium between the crystal core and melt shell. Comparative investigation of the size dependence of the melting temperature, disregarding and taking into account the size dependences of the surface tension of the solid and liquid phases and the interface tension, has been performed by the example of aluminum, tin, and copper nanoparticles.     

Metastable states and coexistence of phases in scaling theory

The methods of scaling theory are used to investigate the physical properties of matter in a large neighborhood of the stability boundary (spinodal), including metastable states and lines of phase equilibrium. Expressions are obtained for the pressure isotherms in metastable gas and liquid phases, a phase equilibrium equation, and an expression for the width of the metastable region.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 73–77, March, 1981.We thank V. M. Sysoev and Yu. I. Shimanskii for valuable comments and for discussing the results.     

Thermodynamic model of crystallization and melting of small particles

The size dependence of the nanocrystal melting temperature has been investigated based on a nonequilibrium thermodynamics approach. An expression has been derived for the melting temperature that, contrary to the classical Tomson formula, takes into account the metastable character of the crystal nucleus-melt shell equilibrium. Quantitative estimations have been carried out for small spherical particles of aluminum, tin, and lead.     

Dispersion transition and the nonergodicity of the disordered nanoporous medium-nonwetting liquid system

The experiments in which a nonwetting liquid does not flow from a disordered nanoporous medium are described. The outflow is shown to depend on the degree of filling of the porous medium and its temperature in a critical manner. A physical mechanism is proposed where the transition of a system of liquid nanoclusters in a confinement into a metastable state in narrow filling and temperature ranges results from the appearance of a potential barrier due to the fluctuations of the collective “multiparticle” interaction of liquid nanoclusters in neighboring pores of different sizes at the shell of a percolation cluster of filled pores. The energy of a metastable state forms a potential relief with numerous maxima and minima in the space of a porous medium. The dispersed liquid volume in a metastable state is calculated with an analytical percolation theory for a ground state with an infinite percolation cluster. The outflow time distribution function of pores is calculated, and a power law is obtained for the decrease in nonwetting liquid volume retained in a porous medium with increasing time. The relaxation of the system under study is a multistage process accompanied by discontinuous equilibrium and overcoming of numerous local maxima of a potential relief. The formation of the metastable state of retained nonwetting liquid results from the nonergodicity properties of a disordered porous medium. The proposed model can describe the detected dependences of dispersed liquid volume on the degree of filling and temperature.