Pore size distribution determination

Adsoiptive molecules transport through macropores to the mesopores and finally enter the micropores. The micropores usually constitute the largest portion of the internal surface and contribute the most to the total pore volume. The attractive forces are stronger and the pores are filled at low relative pressures in the microporosity, and therefore, most of the adsorption of gaseous adsoiptives occurs within that region. Thus, the total pore volume and the pore size distribution determine the adsorption capacity. 

Comparison of the pore size distribution determined by the present method with that from the classical methods such as the BJH, the Broekhoff-de Boer and the Saito-Foley methods is shown in Figure 4. Figure 5 shows a close resemblance of the results of our method with those from the recent NLDFT of Niemark et al. [16], and XRD pore diameter for their sample AMI. The results clearly indicate the utility of our method and accuracy comparable to the much more computationally demanding density functional theory. There are several other methods published recently (e. g. [21]), however space limitations do not permit comparison with these results here. It is hoped to discuss these in a future publication. 

The pore size distribution determination is illustrated in Figure 10. Again, the pore size distribution determination method does not result in the actual membrane pore size and pore size determination. It does, however, give a means of comparing different fdter media. A narrow pore size distribution is required for effective filtration and filtration validation. 

Figure 10 Pore size distribution determination example. (From Ref. 59.)...

Comparison of Pore Size Distributions Determined by Mercury Injection and Gas Breakthrough Experiments... 

Molecular Probes Used in Reverse Gel Permeation Techniques for Pore Size Distribution Determination... 

McGuire, K.S., Lawson, K.W., and Lloyd, D.R. Pore size distribution determination from liquid permeation through microporous membranes, J. Membr. Sci., 99, 127, 1995. 

Another possibility is to fill some pores by capillary condensation and to determine the counter-current diffusion flux of an inert gas pair through the unblocked pores [9-11]. By changing the partial pressure or temperature of the condensable vapor different groups of pores can be blocked and the pore-size distribution determined. 

Lindstrom and Boersma (1971) pioneered the prediction of breakthrough curves from equivalent cylindrical pore size distributions, determined by either the water retention or mercury porosimetry methods. The model developed by these authors includes the effects of bothintra- and interpore dispersion. In general, dispersion due to differences in tube size has a much greater influence on the shape and position of the breakthrough curve than mixing within tubes due to microscopic velocity profiles (Rao et al., 1976). For completeness, however, it is preferable to include both effects. Lindstrom and Boersma (1971) defined a CDE for each tube, so that C/C0 for the bundle as a whole is given by ... 

Fig. 7. Power spectrum determined by TEM analysis and pore size distribution determined by gas adsorption for three ACFs. Courtesy of Prof K. Oshida of Nagano Nat, Coll. Technol.

Fig. 10. Pore size distributions determined by the DFT method for three ACFs. Courtesy of Prof. K. Kaneko of Chiba Univ.

Gregory, R. B., Free volume and pore size distributions determine by numerical Laplace inversion of positron annihilation lifetime data, J. Appl. Phys., 70, 4665-4670 (1991). 

It is clear that the permeability of material to water depends mainly on the volume of capillary pores. It is not linked with total porosity but depends rather on the pore size distribution. However, Marsh [133] gives attention to a fairly good correlation between the total porosity, determined by means of helium method, and permeability. This relation is shown inFig. 5.60 [133]. The diying of samples by substitution of water with propan-2-ol and -pentane was applied. Porosity and pore size distribution determined with mercuiy porosimeter do not correspond to the real stmcture, because the intmsion of mercury under a high pressure, causes the destmction of hydrates plugging the pores, particularly in the pastes of cements with fly ash. 

Except for nonporous particles, all packing materials contain a variation of pore sizes around a mean value. This pore size distribution determines the range of... 

In Chapter 2, we discussed the fundamentals of adsorption equilibria for pure component, and in Chapter 3 we presented various empirical equations, practical for the calculation of adsorption kinetics and adsorber design, the BET theory and its varieties for the description of multilayer adsorption used as the yardstick for the surface area determination, and the capillary condensation for the pore size distribution determination. Here, we present another important adsorption mechanism applicable for microporous solids only, called micropore filling. In this class of solids, micropore walls are in proximity to each other, providing an enhanced adsorption potential within the micropores. This strong potential is due to the dispersive forces. Theories based on this force include that of Polanyi and particularly that of Dubinin, who coined the term micropore filling. This Dubinin theory forms the basis for many equations which are currently used for the description of equilibria in microporous solids. 

A. Pore size distribution determined from adsorption isotherm of water vapor on collagen fiber... 

A. Pore Size Distribution Determined from Adsorption Isotherm of Water Vapor on Collagen Fiber... 

Telkki, V.-V, LounUa, J., and Jokisaari, J. 2006b. Influence of diffusion on pore size distributions determined by xenon porometry. Phys. Chem. Chem. Phys. 8 2072-2076. 

PSD pore size distribution determined from the C values... 

F1g. 3 Partition coefficient, Ksec (not normalized), of four silica gel packings (B-E) having sharp pore size distributions. Determined with standard polystyrene fractions in tetrahydrofuran. The broken line shows the calculated curve, with the wall effect being ignored, for the sample D from its pore size distribution determined by mercury intrusion. Observed discrepancy shows the significance of the wall effect. (Reproduced from ref. 22 with permission.)... 

The pore size distributions determined by the BJH method show that, as expected, the non-pelletized zeolite HY has no mesopore. The non-pelletized zeolite HDaY has mesopores in the range 5-30 nm. As far as the pelletized samples are concerned, it appears that the binder has a drastic effect since it adds a large amount of mesopores centered at about 7 nm. Note that the peaks at about 4 nm are an artefact of the BJH method [4]. 

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