Sorbents structural density

The SAW hydrogen responses measured for four different crystal structures involving a Pd sorbent film [50] is given in Table 4.1. Find the relative variations in the elastic constant and the density of the film using perturbation theory approach. The values of film density and elastic constants are p =11000 kg/m Cn=190 GPa, and C44=40 GPa. The perturbation expansion derived [50,51] on the basis of Equation 4.37 is given by... 

Co(II) sorption complexes on rutile surfaces appear to form extensions of the bulk structure, with EXAFS-derived Co-Ti distances very similar to Ti-Ti distances in rutile. The small number of Ti second neighbors detected by EXAFS spectroscopy indicates that Co occurs dominantly in Ti-equivalent sites at the rutile surface (21). A bond-valence analysis of Co(II) sorption on rutile also indicates that Co(II) can bond stably to a variety of surface oxygen sites (26). When the sorption density of Co is high on rutile, O Day et al (21) found Co-Ti distances characteristic of anatase. The observed differences in the style of Co sorption on quartz, rutile, and alumina under similar conditions and sorption densities are consistent with structural differences among the three sorbents that result in different reactivities of available surface sites. 

Here (Po ) is an approximation for the average density (p) of the sorptive layer, cp. Fig. 1.20, a quantity which at least for technical porous sorbents with a complicated, fractal-like surface structure cannot be measured up to date, cp. Figure 1.21, [1.3]. Actually, there are two possibilities so far to get physically reasonable numerical values for (Po) ... 

The density of the free active centers per unit of the sorbent surface area also depends on the chemical structure of the sorbent, and additionally on the number of molecules other than those of the solute or mobile phase occupying sorbent active centers. These are mostly water molecules, which block (deactivate) active centers on a sorbent surface, and the degree of deactivation usually depends on the storage conditions of the precoated chromatographic plates. The density of the free active centers can also be measured and expressed numerically. 

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