Inhomogeneous surface approach

Non-compliance with the simple Langmuir adsorption model is indicative of violation under experimental conditions of certain assumptions used to derive the model. Therefore, while developing the theoretical models adequately describing experimental data one usually resorts to one of two approaches either introduces the notion of a inhomogeneous surface [36, 37] or accounts for various types of interaction developing between the particles absorbed [4, 38]. 

To a certain extent one can consider an approach to describe non-Langmuir features accounting for probable interaction between adsorption particles as an alternate theory of inhomogeneous surface. Moreover... 

Doyen [158] was one who theoretically examined the reflection of metastable atoms from a solid surface within the framework of a quantum- mechanical model based on the general properties of the solid body symmetry. From the author s viewpoint the probability of metastable atom reflection should be negligibly small, regardless of the chemical nature of the surface involved. However, presence of defects and inhomogeneities of a surface formed by adsorbed layers should lead to an abrupt increase in the reflection coefficient, so that its value can approach the relevant gaseous phase parameter on a very inhomogeneous surface. 

The second approach is based on the different activation energies of separate particles. However, if at the adsorption on the inhomogeneity surface this approach is physically grounded, then under consideration of processes in the liquid phase the assumption about activation energy dependence upon time looks unconvincingly. In spite of this fact, the mathematical description of problem practically does not differ from the previous one [10-12]. 

The first, most simple approach describing corrosion on an inhomogeneous surface can be expressed by the following transfer function introduced by Mansfeld, Kendig, and co-workers (Jiittner et al., 1985 Kendig et al., 1984 Mansfeld et al., 1984)... 

M) were typically used for such a comparison to eliminate the influence of possible differences in the inner-layer capacities. However, C of different solid metals, as well as of liquid Ga, In(Ga), and Tl(Ga) alloys have shown such a large variation that this approach can hardly be considered as appropriate. It should be noted that the error in C, which for solid electrodes is much higher than for liquid electrodes, increases with the decrease ofcei further, as shown later (Section II.2 (iv)), the effects of surface crystallographic inhomogeneity also prove especially appreciable.24 67 74... 

A highly detailed picture of a reaction mechanism evolves in-situ studies. It is now known that the adsorption of molecules from the gas phase can seriously influence the reactivity of adsorbed species at oxide surfaces[24]. In-situ observation of adsorbed molecules on metal-oxide surfaces is a crucial issue in molecular-scale understanding of catalysis. The transport of adsorbed species often controls the rate of surface reactions. In practice the inherent compositional and structural inhomogeneity of oxide surfaces makes the problem of identifying the essential issues for their catalytic performance extremely difficult. In order to reduce the level of complexity, a common approach is to study model catalysts such as single crystal oxide surfaces and epitaxial oxide flat surfaces. 

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