Heterogeneity of surface

Safety in use of x-ray equipment, 332 Sample, errors due to heterogeneity of surface, 172, 175... 

Lochmuller, C.H., Marshall, D.B., and Harris, J.M., Room temperature, excitation wavelength dependent fluorescence at surfaces a potential method for studying the micro heterogeneity of surface environments. Anal Chim. Acta, 131, 263, 1981. 

As was already mentioned in the introduction, we have to assume that adatoms of hydrogen adsorbed on a metal surface with a high heat of adsorption must be mobile so that they either can find the sites of highest surface energy or can move as far apart from each other as possible if the heterogeneity of surface energy of the sites is due to interaction of adsorbed atoms on neighboring sites. A rapid redistribution of adsorbed atoms by evaporation and readsorption is out of the question... 

The discovery of the heterogeneity of surfaces, and in particular of dislocations (see Section 7.12.12), was made in the 1930s (Taylor, 1936), but there had been theoretical work on metal deposition at an earlier time. The model of the surface employed by these earlier workers (Kossel, 1927 Stranski, 1928 Erdey-Gruz, and Volmer, 193 l)was a flat plane without steps and edges to which the adions produced by ion transfer from the double layer could surface diffuse. The only way a metal could grow on a perfect planar surface without growth sites was by nucleation of the deposited atoms, rather than diffusion to the growth sites shown in Fig. 7.134. 

A simple model approach to the heterogeneity of surface reactivity in soils can be developed by assuming that Eq. 4.3 [without the dissociable species Q(aq)] applies to each member of a set of parallel adsorption-desorption react ions involving the same reactant aqueous species, but with differing ail sorbent and adsorbate species. A rate law for each of the parallel reactions can be postulated in the following form (cf. Eq. 1.34) ... 

In the Monte Carlo simulations of the chromatographic and related processes we should also account for the new knowledge about the deep heterogeneity of surfaces, about the role of localized adsorption and about the occurrence of surface diffusion. Evidently, now the molecular desorption energy accepted for a concrete simulation is to be understood as the effective value over the spectrum of possible energies in the sense of Eq. 5.71. As such, it is related to a concrete form of the p(E ). The... 

Mamleev, V. Sh. and Bekturov, E.A. (1996). Improved method for analysis of energetic heterogeneity of surfaces from adsorption isotherms. Langmuir, 12, 441-9. 

One other factor contributed to the desirability for the re-examination of the concept of active centers. The development of a distinction between van der Waals adsorption and chemisorption only occurred after the interest in heterogeneous surfaces had somewhat waned. A return to the study of heterogeneity of surfaces in the postwar years could be assisted by the sharper differentiation between the two types of adsorption that resulted from the development of the concept of and criteria for chemisorption. 

This aspect of heterogeneity of surface which the desorption-readsorption phenomena reveal is worthy of a more detailed analysis. Consider, for example, a hypothetical adsorbent, having two distinct adsorbent areas A and B, characterized by two distinct activation energies Ea. and Eb, and two characteristic heats of adsorption and X . It is possible to conceive two temperatures Ti and T such that, at the lower temperature... 

Adivalion Energy of Chemisorption on Heterogeneous Surfaces. A further consequence of a heterogeneity of surface such as is indicated in... 

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