Irregular pore structure

Equation 71 is the basic equation that relates permeability of a porous medium to its other properties. However, equation 71 contains the hydraulic diameter of the passage (pore), tortuosity, and areal porosity of the medium, which may not be easily accessible. For example, sandstones or rock formations have irregular pore structure and often have inconsistent pore size measurement values (see previous section). It is rather difficult to measure the average hydraulic pore diameter. On the other... 

In the calculation of the diffusion in a porous media the effective diffusion coefficient is applied, because the diffusional cross section is smaller than the geometric cross section (porosity e) and the catalyst has irregular pore structure (expressed via tortuosity x) as illustrated in Figure 9.9. 

Porous coating, irregular pore structure of, 41-11 Porous composite biomaterials,... 

Due to large specific surface area and irregular pore structure, nanofibers have the potential to increase the interactions between the fibers and the polymer matrix [86-87], Dzenis and Reneker [88] investigated unidirectional laminated composites using polybenzimidazole (PBI) nanofibers. They discovered that energy release rate of the material was improved. 

With the experimental results about the wetting ability and the fractal dimension of four kinds of anode electrodes, we could conclude the following. The addition of NisAl could make the electrolyte wet the electrode very well. The pore structures of all the electrodes prepared in this study were highly irregular and rough. Finally, the chemical properties of the surfaces were as important as the physical properties in determining the wetting ability of the electrodes in this study. 

On the other hand, the surface fractal dimension characterizes the pore surface irregularity the larger the value of surface fractal dimension is, the more irregular and the rougher is the pore surface. Since the pore structure is closely related to the electroactive surface area which plays a key role in the increase of capacity in practical viewpoint, many researchers have investigated the microstructure of the pores by using fractal geometry. 

Band broadening due to resistance to diffusion of a molecule within the mobiie phase, contained within the pores of a stationary phase and due to irregularities in stationary phase pore structure. 

This is liquid-solid chromatography in which the surface of microparticulate silica or other adsorbent constitutes the polar stationary phase. The silica particles are characterized by their shape (irregular or spherical), size and size distribution, and pore structure (mean pore diameter,... 

McBain s term Sorption applies to all cases when a gas or solute is taken up by a solid. Adsorption means strictly the formation of a layer on an impermeable surface a sorption to penetration, or solution, into the interior. With the zeolites, there are pores of quite regular shape and size, only a few A. across. With charcoal there are irregular pores of similar size, as well as larger ones. Foreign substances, finding their way into these very fine pores may be said to be adsorbed on the walls of the pores, but as they permeate the whole structure of the solid more or less uniformly, they may equally be said to be absorbed by the solid. McBain avoids this difficulty simply by omission of the prefix. 

The fact that the shape of the isotherms in Figure 10.7 has remained almost unchanged after the acid treatment is an indication that the mesopore structure was not altered to any signifiant extent. However, as pointed out in Chapter 7, this form of H2 hysteresis loop is not easy to interpret since it is associated with pronounced percolation effects in an irregular pore network. 

Fig. 2. Spongy porous solids with regular (a) and irregular (b) structures. The pore volume (white areas) is primarily concentrated in voids, whereas the necks do not possess volumes of their own. 

Figure 1. Electron microphotograph of membrane surface showing irregularity in pore structure...

Chemistry and material sciences are key disciplines for the development of advanced and more specific adsorbents. The stability and reproducibility of chromatographic columns was significantly increased by the introduction of spherical instead of irregular stationary phases. Recently, another step forward was made by the development of high efficiency monolithic columns with a rather low pressure drop. Future, further improvements, which include surface activation and internal pore structures of stationary phases, should help to tailor stationary phases for certain applications. But, besides the need for more specific and efficient solid phases, their cost is often a major problem for the widespread application of preparative chromatography. 

The surface atomic structure of silica gel was also simulated in Refs. [17, 18]. Silica gel is another form of amorphous silica which is formed not in the process of cooling of the liquid but as a result of coagulation at room temperature. Its surface is the surface of small microspheres which together form an irregular porous structure. We consider here only the simulation of the surface atomic structure presented in Refs. [17, 18]. The pore structure of such a material clearly depends on the arrangement of the microspheres in space. Together with the surface atomic structure, the pore structure determines the adsorption properties of silica gel and we consider it in this context in the next section. 

Once the correlation functions have been solved, adsorption isotherms can be obtained from the Fourier transform of the direct correlation function Cc(r) [55]. The ROZ integral equation approach is noteworthy in that it yields model adsorption isotherms for disordered porous materials that have irregular pore geometries without resort to molecular simulation. In contrast, most other disordered structural models of porous solids implement GCMC or other simulation techniques to compute the adsorption isothem. However, no method has yet been demonstrated for determining the pore structure of model disordered or templated structures from experimental isotherm measurements using integral equation theory. 

Pore structures of typical polymeric ultrafiltration membranes, produced by so called "phase inversion methods," consist of interconnected, irregular, three-dimensional networks of pores, interstices and voids in their skin layers. 

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