Interconnected cavity channels

Figure 5.24a shows a typical pore structure of a C-9 membrane in which large pores exist throughout the whole membrane surface. On the other hand. Fig. 5.24b shows a nodular structure with interconnected cavity channels between the a lom-erated nodules for a C-11 membrane. It is beheved that the cellulose concentration affects the chain entanglement. A higher cellulose concentration results in a membrane with a smaller pore size, lower flux, and higher solute rejection. 

A new dimension to acid-base systems has been developed with the use of zeolites. As illustrated in Fig. XVIII-21, the alumino-silicate faujasite has an open structure of interconnected cavities. By exchanging for alkali metal (or NH4 and then driving off ammonia), acid zeolites can be obtained whose acidity is comparable to that of sulfuric acid and having excellent catalytic properties (see Section XVIII-9D). Using spectral shifts, zeolites can be put on a relative acidity scale [195]. An important added feature is that the size of the channels and cavities, which can be controlled, gives selectivity in that only... 

Zeolites have an open, three-dimensional framework structure with pores (channels) and interconnecting cavities in the alumosilicate lattice. In Table 4.8, the basic characteristics of the most important zeolite species of commercial use are presented. 

There are four interconnected cavities in the unit cell, each of c. 0.8 nm width. Each of the four interconnecting straight channels is 0.46 nm long and each of the four sinusoidal channels is 0.66 nm long. 

Pressure testing of the finned oil cooler in Fig. 15.29 revealed leaks. Examination of the interior of the cooler after sectioning in the vicinity of the leaks revealed a small cavity in the weld zone in the corner of some fins (Fig. 15.14) and porous areas inside the channel in the welded zone in other fins. Microstructural examinations of specimens cut through the sites revealed interconnected voids resulting from either shrinkage during solidification of the weld or lack of fusion of the base metal and weld metal. 

This is an interconnected network of flattened or spherical vesicles and tubules found in the cytoplasm of eukaryotic cells. These structures are enveloped by a membrane that separates the endoplasmic reticulum cavities or cisternae. The cisternae constitute a network of channels that go through the cytoplasm and regulate the transport of various cell products, generally to the exterior environment. In some cells the cisternae also serve as a storage area. There are two types of endoplasmic reticulum granular (or rough) and smooth. 

The mechanism of this process is the same as was discussed in the previous section for SPG membranes, only here no interconnected pores are needed. The micro-channels that gave these effects end in a region that consists of a slit-shaped cavity in between two plates. The oil coming out of the pore has to squeeze between the two plates, and therefore will not form a droplet but a disk. The Laplace pressure... 

This is the area of zeolitic materials, which can be characterized as crystalline, porous materials built predominantly of oxygen, silica, and alumina (or phosphor) [1,2]. These crystals contain straight or sinusoidal channels that can be interconnected, resulting in a one-, two-, or three-dimensional pore network. At the intersections, small or large cavities may exist. Due to the crystallinity, the pores are uniform and can be prepared with great reproducibility, which is the biggest advantage over attempts to produce amorphous membranes with pores of molecular dimensions. Therefore, in the last decade much research effort has been put into the development of zeolitic membranes, and with success [3-29]. 

The catalytic activity of zeolites also involves shape complementarity. The cavities of zeolites are interconnected by various channels, consequently, in a strict sense, a cavity does not fully surround a molecule that enters the zeolite. As a result, for high density zeolite MIDCO s only local shape complementarity is possible. Nevertheless, the low density MIDCO s of zeolites contain closed internal contour surfaces corresponding to the cavities and for these parts of MIDCO s global shape complementarity is relevant. The shapes of these MIDCO s may approximately complement the shapes of the MIDCO s of a molecule inside the cavity. 

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