Model Of Nonequilibrium Phase Transition Research Articles

Investigation on wave system matching of two-phase pressure oscillation tube

Non-equilibrium phase transition will take place in the pressure oscillation tube if the intake of wave rotor refrigerator (WRR) contains condensable components, which will affect intensity and speed of the wave system in the tube, and further affect the port matching of WRR. In this paper, numerical model of non-equilibrium phase transition is established and the effects on intensity of the wave system and the port matching is studied. The properties of polar gas are described by the cubic-plus-association (CPA) gas state equation, improving the accuracy of computational fluid dynamics (CFD) calculations. By using the model, the design precision of two-phase WRR is improved. Besides, the results of numerical simulation are verified by experiments.

Radiation damage thin coating of silicon carbide

This paper presents computer experiments studies interaction of radiation (ions Xe++ gas with keV energy) with crystal lattice of "SiC/metal" substrate. Properties of substrate are altered due to porosity and stresses formation into thin layers covering silicon carbide as a result of inert gas flux penetration. First, the stochastic model of non-equilibrium phase transitions (or nucleation of defects) in nanomaterials is presented. Behavior of gaseous bubbles in thin layers are tested and corresponding details computer modeling are discussed. Secondly, the analytical models of Gibbs free energy implanted microdefects as well as their Brownian motion in long-range potentials of indirect interaction between gaseous bubbles into lattice through acoustic phonons are concretized. These models predict stress from gas penetration as a result of damaging in form of gaseous bubbles (named here "blisters"). New emphasis is on numerical modeling includes stochastic model clustering of defects as the diffusion of Markov processes. Finally, the mechanism of porosity formation in materials such as silicon carbide can be accounted as the ways to improve solidity and fracture toughness and hardening of materials.

Thermodynamic model of nonequilibrium phase transitions

Within the scope of a thermodynamic description using the maximum entropy production principle, transitions from one nonequilibrium (kinetic) regime to another are considered. It is shown that in the case when power-law dependencies of thermodynamic flux on force are similar for two regimes, only a transition accompanied by a positive jump of thermodynamic flux is possible between them. It is found that the difference in powers of the dependencies of thermodynamic fluxes on forces results in a number of interesting nonequilibrium transitions between kinetic regimes, including the reentrant one with a negative jump of thermodynamic flux.

Nonequilibrium phase transitions and S-shaped current-voltage characteristics in a model semiconductor-metal system

A model of nonequilibrium phase transition in a semiconductor-metal system was considered using a finite-element method. It is shown that, beginning with a certain fraction of the metal component in the heterophase system, the S-shaped current-voltage characteristics exhibit a change: the system features a hysteresis but possesses no singular points.

Computational model of nonequilibrium phase transitions in a Si-Ge system

A computational model of a Si-Ge system melting and solidification induced by pulsed-laser irradiation is presented in the paper. Phase transitions in the system are modeled using the theory of transition states so that undercooling or overheating of the interface and kinetic phase diagrams are taken into account. The computational solution of the mathematical model is performed using the Galerkin finite element method in a one-dimensional approximation and the moving boundary problem is solved by a front-fixing technique. In a practical application of the model, the melting and solidification of both Si-Ge alloys of various composition and thin Ge layers on the Si bulk induced by ArF excimer laser are simulated. The results of numerical simulations are compared with the available experimental data.

The structure of the phase transformation wave in the discrete model of a non-equilibrium phase transition

The structure of the wave of the phase transformation in the deterministic discrete model of non-equilibrium phase transitions is investigated. In this model each of the cells forming a two-dimensional lattice can be in one of three states: stable, metastable or excited. The transition into the stable state is allowed only through an intermediate excited state. The change of the phase state of each cell is initiated by the variation of a continuous parameter, the 'temperature', taking into account the energy exchange between cells, the phase stability regions and local rules in the neighbourhood of the cell. Taking the square and hexagonal lattices as examples, it is shown that this model possesses the following fundamental property: when the lifetime of the excited states is increased beyond a certain threshold, an abrupt change of the dynamics of the phase transition occurs. The wavefront then acquires a beam-like or fractal-like structure and, in the latter case, the system of cells has a quasicontinuous frequency spectrum of white or coloured noise. The application of this model to the description of non-equilibrium (explosive) crystallization in amorphous metals and semiconductors is discussed.

Critical phenomena at surfaces in a model of nonequilibrium phase transitions

Critical phenomena at surfaces are studied in a simple two-dimensional model of non-equilibrium phase transitions belonging to the class of interacting particle systems. The mean field renormalization group approach and numerical simulations are used to determine the phase diagram for this system and some of the critical exponents associated with ordinary, special, extraordinary and surface phase transitions.