Model of non-ideal lattice gas

Abstract. A phase equilibriums in intermetallic compounds hydrides in the area of disordered a-, (3-phase in the framework of the model of non-ideal lattice gas are description. LaNi5 hydride was chosen as the subject for the model verification. Position of the critical point of the P—w.-transition in the LaNi5-hydrogen system was definite. 

Keywords Hydrogen, metal hydrides, intermetallic compounds, phase equilibriums, model of non-ideal lattice gas. 

Chapter 8 provides a unified view of the different kinetic problems in condensed phases on the basis of the lattice-gas model. This approach extends the famous Eyring s theory of absolute reaction rates to a wide range of elementary stages including adsorption, desorption, catalytic reactions, diffusion, surface and bulk reconstruction, etc., taking into consideration the non-ideal behavior of the medium. The Master equation is used to generate the kinetic equations for local concentrations and pair correlation functions. The many-particle problem and closing procedure for kinetic equations are discussed. Application to various surface and gas-solid interface processes is also considered. 

The lattice-gas model allows to use it for studying the effect of the lateral interactions between the adspecies on the surface process rate or, in other words, to consider the non-ideality of the reaction system in the surface process kinetics. In the lattice-gas model the interaction of adspecies / and j in sites / and g at the distance r is set by the energy parameter sjg(r). In the homogeneous lattice systems such distances can be conveniently determined with the use of the numbers of the (c.s.) where site g is located relative to site /. In this case in the parameter y(r) the index r runs a discrete series of values from 1 to R, where R is the interaction radius 1 1) = 0, one deals with the nearest-neighbors... 

We shall deal here with a Lattice Gas (LG) model and a model of Unified Gas-Adsorbate Layer (UGAL). These two models correspond to two alternative approaches in the statistical theory of equilibrium adsorbates (Flood 1967) and can be considered as mutually complementary ones. Which of them should be used depends on the adsorbate properties (ideal, weakly non-ideal, liquid, polycrystalline, localized, partially localized, delocalized), external conditions (isothermaJ, non-isothermal), meclianisms of elementai y processes (adiabatic, non-adiabatic), etc. 

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