Specific internal surface area

Shea et al. [281] have also succeeded in making a low-density aerogel from tetramethoxysilane and p-di(triethoxysilyl)benzene in one step using supercritical CO2 as a solvent. The highly porous monolithic samples exhibited a specific internal surface area over 700 m g. 

To be able to model the processes of diffusion and reaction, one needs to know some parameters describing the porous catalyst structure. One characteristic parameter is the internal surface area, that can be determined with adsorption experiments. This is frequently expressed as units of area per gram of catalyst. In this text the specific internal surface area a. is used, with dimension m/tti or m ... 

Mesri and Olson (1971) measured the permeability of pure clay (see Revil and Cathles, 1999). Permeabilities show a correlation with the specific internal surface area of the clay minerals with increasing surface area, a larger amount of water does not take part at the fluid flow and reduces permeability. 

Surface relaxation term of T2 directly depends on the surface-to-volume ratio of the pore or specific internal surface area 5por (Eq. 3.8). As discussed in Section 2.3, internal surface area is related to pore size, permeability, and capillary pressure. On this basis, an estimate of these pore properties is possible. However, it must be noted that the NMR-derived pore geometric properties and the properties like permeability and capillary pressure are controlled by two different pore size measures ... 

NMR-derived properties are referred to the specific internal surface area, which is controlled by the pore body size. 

Experimental results (Bomer et al., 1996) for the imaginaiy component of conductivity show a similar dependence on the specific internal surface area to porosity ratio as a result of interface effects ... 

Activated carbon is an amorphous solid with a large internal surface area/pore strucmre that adsorbs molecules from both the liquid and gas phase [11]. It has been manufactured from a number of raw materials mcluding wood, coconut shell, and coal [11,12]. Specific processes have been developed to produce activated carbon in powdered, granular, and specially shaped (pellet) forms. The key to development of activated carbon products has been the selection of the manufacturing process, raw material, and an understanding of the basic adsorption process to tailor the product to a specific adsorption application. 

Specific surface area (square meters per gram or square centimeters per gram) the sum of the external and the internal surface areas. 

The specific surface area also represents a mean of the pigment particle size distribution. It can be used to calculate the mean diameter of the surface distribution. Care must be taken that the effect of the internal surface area is taken into account. If the product has an internal surface area which cannot be neglected in comparison to the external surface area, then the measured specific surface area no longer gives a true measure of the mean diameter. This applies, for instance, to aftertreated pigments because the treatment material is often very porous. 

Specifically, this volume focuses on the synthesis, processing, and structural tailoring of nanocrystalline and nanoporous materials. Nanocrystalline materials possess unique hybrid properties characteristic of neither the molecular nor the bulk solid-state limits and may be confined in nanometersized domains in one, two, or three dimensions for unusual size-dependent behavior. Nanoporous materials, characterized by well-defined pores or cavities in the nanometer size regime and controlled pore diameter and structure, give rise to unique molecular sieving capabilities and ultrahigh internal surface areas. Nanoporous structures also act as hosts and templates for the fabrication of quantum dots and quantum wires. 

Fumed silica is typically available with sizes of 7 to 40 nm and surface areas ranging from 50 to 380 m2/g. Unlike precipitated silica, fumed silica has no internal surface area. The specific gravity of fumed silica is approximately 2.2. Because of its high surface area to weight ratio, formulations generally require only a minor amount of fumed silica (1 to 5 percent by weight) to achieve thixotropic properties. 

The main features of this technique are the absence of contact between the foam and the ambient space (i.e. no foam/gas interface) and constant capillary pressure along the whole foam height. This technique allows to study the kinetics of internal foam destruction at various capillary pressures, i.e. decrease in the specific foam surface area without destruction of the foam column. Thus, the influence of surface foam films on foam lifetime and the character of foam destruction can be estimated. 

Fig. 6.1 depicts the experimental time dependence of foam expansion ratio, surfactant concentration in the flowing out solution as well as the rate of internal foam collapse. Within the whole time interval the rate of diminishing of specific foam surface area for a sulphonol foam is less than that for a NP20 foam, though the difference is not significant. Probably this is related to the fact that in the initial stage of internal foam collapse the rate deF/dx is determined by the gas mass-transfer that does not depend considerably on the surfactant kind. 

The reaction rate per unit volume of catalyst as well as its selectivity depend on both the specific catalytic activity and the surface area of the active component per unit catalyst volume, as well as on its pore structure. These characteristics are determined by the conditions of catalyst preparation. Therefore, when developing a new catalyst, it is extremely important to be able to determine in advance the required internal surface area and the most suitable pore structure of the catalyst for the given reaction. 

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