Most probable pore radius

For this pellet the distribution is seen to be reasonably symmetrical with most of the volume in pores from 300 to 8,000 A and with a most probable pore radius of 1,200 A. Note that the flatness of the penetration curve at low pore radii justifies neglecting the pores smaller than 250 A. 

The actual pore has different sizes and distributions. Sometimes catalysts with near average pore have different activities because they have different pore distributions. As a result, another important parameter of solid catalysts is the data of pore distribution and the most probable pore radius. 

The radius ro corresponding to the maximum value of curve in Fig. 7.9 is known as the most probable pore radius. It means that the proportion of the pore whose radius ro is the highest in the porous catalyst. In order to obtain the curve of pore size distribution, it needs to detect the contribution of a variety pore on the adsorption quantity, and then use the following ways to calculate the relationship of pore size distribution according to the scope of pore size of a variety of materials. 

In order to obtain a pore size distribution and an average (or most probable) pore size directly from the material stmeture, we proceed by considering the sub-volumes of the system accessible to spheres of different radii [5. Let Vporc(r) be the volume of the void space coverable" by spheres of radius r or smaller a point x is in Vp<,re(r) if and only if we can constiuct a sphere... 

Figure 8-10 shows that this is an approximate value for the average pore radius in the micropore region. Note that the micropore distribution is asymmetrical in such a way that the average radius is greater than the most probable value (20 A). 

Probably the most used experimental technique is the one that involves solvent permeation measurements through brush-coated membranes [7,27,35]. The rate of solvent permeation through a membrane of cylindrical pores depends on the pore size and may be related to their radius by the Hagen-Poiseuille equahon ... 

Such structures are known as porous electrodes and they behave quite differently from the effectively planar electrodes used in most other areas of applied electrochemistry. The porous electrode is a mass of particulate reactants (sometimes with additives) with many random and tortuous electrolyte channels between. Real porous electrodes cannot be modelled but their behaviour can be understood qualitatively using a simplified model shown in Fig. M.5 in fact, there are two distinct situations which arise. In the first (Fig. 11.5(a)) the electroactive species is a good electronic conductor (e.g. a metal or lead dioxide here, the electrode reaction will occur initially on the face of the porous electrode in contact with the electrolyte but at the same time, and probably contributing more to the total current, the reaction will occur inside the pore not, however, along the whole depth of the pore because of the fR drop in solution. The potential and current distribution will depend on both the kinetics of electron transfer and the resistance of the electrolyte phase. A quantitative treatment of the straight, circular pore approximation allows a calculation of the penetration depth (the distance down the pore where reaction occurs to a significant extent) and it is found to increase linearly with electrolyte conductivity and the radius of... 

While SEC and CZE are capable of physically resolving components, and FIA is not, the point made in Table I is that at a given Mi the reliability of a molecular weight determination improves with increasing resolution per time, Rs/t (equations 1 and 2). In addition, SEC is limited by pore size for the molecular weight resolution of analytes, as well as polymer/solvent interactions that will affect the hydrodynamic radius of the polymer, while CZE experiences the artifact of non-ideal flow rate. However, FIA-based methods operate at zero back pressure, with a lower probability of clogging than most sample modulated analyzers such as S. Further, IA with G detection provides a means for the analysis of mixtures using multivariate statistical techniques (24). 

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