Dynamic equilibrium alloys

It should be realized that unlike the study of equilibrium thermodynamics for which a model is often mapped onto Ising system, elementary mechanism of atomic motion plays a deterministic role in the kinetic study. In an actual alloy system, diffusion of an atomic species is mainly driven by vacancy mechanism. The incorporation of the vacancy mechanism into PPM formalism, however, is not readily achieved, since the abundant freedom of microscopic path of atomic movement demands intractable number of variational parameters. The present study is, therefore, limited to a simple spin kinetics, known as Glauber dynamics [14] for which flipping events at fixed lattice points drive the phase transition. Hence, the present study for a spin system is regarded as a precursor to an alloy kinetics. The limitation of the model is critically examined and pointed out in the subsequent sections. 

MOS] Chemical analysis for determination of equilibrium carbon concentrations in the alloys. Dynamic method for equihbration of alloys with gas mixtures of type H2-H2O-CO-CO2-CH4 Alloys with Cu contents from 1.95 to 7.4 mass%. Calculation of carbon activity at 950, 1000, 1050, 1100°C. 

The binary alloy of platinum and rhodium is especially known for the catalytic properties of its surfaces [123-126]. Therefore, various publications have already attended to this system for example. Refs [125-130] discuss the relevancy of Pt-Rh in three-way catalysts, and some empirical models about the catalytic process are developed in Refs [131-133]. Here, we take two steps back first, because the whole alloy Pt-Rh will be brought down to its atomic constituents, and second, because not the dynamics of the catalytic process itself wiU be under investigation but, more fundamentally, the equilibrium properties of a Pt-Rh surface. This approach joins other atomistic works on Pt-Rh surfaces, experimental papers such as Refs [1, 134], as well as numerous theoretical surveys such as Refs [2,106, 135-137]. 

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