Mercury structural data

Table VI summarizes the structural data on mercury chalcogenide halides.

From the mercury porosimetry data, porosity can be calculated. A higher porosity means a more open pore structure, thus generally providing a higher permeability of the membrane. Porous inorganic membranes typically show a porosity of 20 to 60% in the separative layer. The porous support layers may have higher porosities. 

Fig. 2.1.14 Mercury porosimetry data for ordered silica packing structures.

An alternative explanation of the data presented in Figure 3 is that the majority of the macropore structure is available for reaction, and by breaking up the coal one is simply opening up hitherto sealed pores. However, this does not seem likely since—to explain the results in Figure 3— one would have to assume that from 2% to 90 mesh the exposed internal area of the coal increases by a factor of 12. Mercury penetration data on Coal C indicates that the macropore area increased only 7% going from 2% to 90 mesh (see Discussions). Also, Malherbe (16) found for three bituminous coals that in going from 5 to 270 mesh the BET area only increased by a factor of 2. Furthermore, the helium density of coal is independent of particle size indicating no sealed pores exist at least in respect to the accessibility of helium (14). 

Recently cluster compounds of mercury with an Hg3 ring, an Hg4 ring and an H octahedron with four capped tetrahedrally correlated faces have been described.29 413 1 18 Structural data are listed in Table 1. 

Table 15 Structural Data of Mercury(II) Sulfur Complexes...

Lovenberg, Buchanan, and Rabinowitz found that treatment of ferredoxin with iodoacetate or N-ethylmaleimide in either the presence or absence of 8 M urea had no effect on its spectral characteristics. Less than 1 mole of carboxymethyl cysteine was formed per mole of protein when native ferredoxin was treated with iodoacetate-1-C14 (Table 10). Sobel and Lovenberg (96) showed recently that C14-iodoacetate did not react appreciably with reduced ferredoxin. However, Table 10 shows that if ferredoxin was treated with 2-mercaptoethanol in 8 M urea, it was alkylated with iodoacetate. This demonstrated that the half-cystine residues of native ferredoxin were not present as free sulfhydryls, and the mercurial titration data given above showed that they were not present as disulfides. The two observations were consistent, therefore, with a structure in which the half-cystine residues are present as cysteine and are bonded with the iron by a sulfide bridge. 

We are not going to deal with all these examples of application of percolation theory to catalysis in this paper. Although the physics of these problems are different the basic numerical and mathematical techniques are very similar. For the deactivation problem discussed here, for example, one starts with a three-dimensional network representation of the catalyst porous structure. Systematic procedures of how to map any disordered porous medium onto an equivalent random network of pore bodies and throats have been developed and detailed accounts can be found in a number of publications ( 8). For the purposes of this discussion it suffices to say that the success of the mapping techniques strongly depends on the availability of quality structural data, such as mercury porosimetry, BET and direct microscopic observations. Of equal importance, however, is the correct interpretation of this data. It serves no purpose to perform careful mercury porosimetry and BET experiments and then use the wrong model (like the bundle of pores) for data analysis and interpretation. 

A kinetic study of the reaction was also performed in which NMR-obtained rate data were correlated with mercurial structure changes (12). This study revealed a quite distinct reactivity order which, coupled with a 1 1 reactant stoichiometry, indicates a 1,3-dipolar electrophilic attack by ozone via a SE2 or four-center process. Although the exact mechanism was not conclusively proved, it is certain that neither the SE1 or SEi processes were operative during these reactions. 

Figure 4.10 shows the pore size distribution data of an alumina membrane by mercury porosimetry. This particular sample has a three-layered structure. The support has a relatively narrow pore size distribution but the membrane layer and the intermediate support layer do not show a clear distinction on the mercury porosimetry data. Typical mercury porosimetry analysis involves intrusion and extrusion of mercury. The intrusion data are normally used because the intrusion step precedes the extrusion step and complete extrusion of mercury out of the pores during the de-pressurization step may... 

Many commercial ceramic membranes have two three or even four layers in structure and their pore size distributions are similar to that shown in Figure 4.12. It should be noted, however, that determination of those multi-layered, broad pore size distributions is not suaightforward. The major reason for this is the overwhelmingly small pore volume of the thin, fine pore membrane layer compared to those of the support layer(s) of the structure. It is possible, although very tedious, to remove most of the bulk support layer to increase the relative percentage of the pore volumes of the membrane and other thin support layers. Provided the amount of bulk support layer removed is known and the mercury porosimeu data of the "shaved" membrane/support sample is determined, it is feasible to construct a composite pore size distribution such as the one shown in Figure 4.12. 

The macropore size distributions of C8-C18 obtained from mercury porosimetry data had two peaks however, the peak observed at very high pressures of mercury is not considered because of the possible collapse of the structure at high pressures. The macropore diameter decreases in going from C8 to C16, with exception of C12 whose pore diameter is higher than that of C8. The pore diameter of C18 is also found to be higher than that all other samples except C12. 

In order to quantify this pore-gradient structure, the corresponding mercury-porosimetry data have been shown in Fig. 4(a-c). From (a) to (c) in Fig. 4, a pore-gradient can be observed. This pore-gradient shows the largest pores with d 250 nm in the bottom layer and the smallest pores with d w 40 nm in the top layer. According to Kruyer [10] and Mason [11] (see 2.1), the particles which contribute to this pore size of d 40 nm, have a... 

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