Open ends Pore diameter

Further, for open-ended pores, the bootstrap relation given by equation (1-106) for constant total pressure applies throughout the transition range for solids whose pore diameters are on the order of 10 pm or less (Treybal, 1980). 

If a large number of open-ended cylindrical pore segments (like the one in Fig. 2) are interconnected such that the diameter of any pore is independent of the size of neighbor pores, a so-called randomized, or stochastic, pore network is formed. Such a set can be assembled from a cohort obeying any stipulated pore diameter distribution function. If all the pore segments are of equal length with a connectivity of 4, a square network... 

With respect to the absolute values of porosity parameters, the data from adsorption isotherms are much less reliable. When considering these data, one has to remember that they actually characterize an equivalent model system composed of an ensemble of open-ended, independent cylindrical capillaries of constant width. This model is far from the real structure of a polymeric adsorbent. Another serious drawback is the rather arbitrary choice between the adsorption and the desorption branches of the hysteresis loop for the calculations. If, indeed, open-ended channels are anticipated in the material, the desorption branch should give more representative results. On the other hand, if closed ink-bottle-type pores are present, the adsorption branch could be used. Filling of a bottle-type pore starts at a low p/p value corresponding to the diameter of the neck and ends at a higher relative pressure corresponding to the size of the bottle s interior, whereas evaporation proceeds at a single p/p value determined by the meniscus in the neck. Partially for this reason, the... 

Vessels of relatively large diameter are also known as pores. These cells form the main conduits for sap flow. A vessel is built up by several vessel elements, with more or less open end plates, aligned in the longitudinal direction. 

Enzymes can be coupled to the surface of a very open-pored silica gel to obtain a relatively stable fixed enzymatic catalyst (282). Porous silica with a pore diameter of 51 nm was used as a carrier to the surface of which the enzyme B. subtilic protease was attached, a bifunctional diazonium salt-was reacted with the surface of the silica, followed by reaction of enzyme with the other end of the diazonium molecule. The silica-supported enzyme hydrolyzed casein and had a half-life of more than 7 months whereas that of enzyme simply adsorbed on the silica was 2.5 months. 

We examined the field emission properties 29) of the carbon nanotubes prepared in the pores of an alumina membrane whose pore diameter was 230 nm. The wall thickness and the length of the carbon tubes obtained were 15 nm and 60 pm, respectively. The emitting ends of the tubes were open, while the other ends were connected to the same carbonized film formed on the surface of the membrane. As shown in Figure 12, we utilized the gold-coated indium / tin oxide (ITO) as the anode and the carbon tubes as cathode. The gap between the tube ends and the anode was 130 pm. According to the measured results given in Figure 12, the turn on applied electric field is 3 V / pm, which is comparable to... 

Because the tenn miCTo pores may incorrectly be associated with micrometer sized pores, some authors have preferred the term nanopores for pore diameters smaller than 2 nm (e.g., Ref. 86). It is important to note that the lUPAC classification is independent of the choice of the porous material (carbon, metal, metal oxide. ..), the kind of pores (closed-pore, open pore. ..), or where the pore is actually located (inside a particle versus between particles). As schematically shown in Figure 15.12, open pores may be dead-end-pores (also called semi-open that is a pore with only one open end which cannot contribute to percolation), interconnected (i.e., connected with another pore but not necessarily to the entire pore volume), or passing—and only closed pores cannot contribute to desalination. 

Ultrafiltration hollow-fiber modules are usually made with a shell and tube configuration. The fibers are potted at both ends of the module with the fiber lumen open for recirculation of the process stream (Figure 21). Naturally, strainers or prefilters must be utilized to eliminate plugging of the fibers. At Nude-pore, it has been shown that larger diameter hollow fibers, 1.5 to 3mm in i.d., are much less prone to fouling. Fortunately, all UF hollow fiber systems can be back-washed and are amenable to a number of cleaning techniques. 

The single cylindrical pore is of course not the geometry we are interested in for porouS catalysts, which may be spheres, cylinders, slabs, or flakes. Let us consider first a honeycomb catalyst of thickness It with equal-sized pores of diameter cfp, as shown in Figure 7-14. The centers of the pores may be either open or closed because by symmetry there is no net flux across the center of the slab. (If the end of the pore were catalytically active, the rate would of course be sHghtly different, but we will ignore this case.) Thus the porous slab is just a collection of many cylindrical pores so the solution is exactly the same as we have just worked out for a single pore. 

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