Channel pore

Directed Oxidation of a Molten Metal. Directed oxidation of a molten metal or the Lanxide process (45,68,91) involves the reaction of a molten metal with a gaseous oxidant, eg, A1 with O2 in air, to form a porous three-dimensional oxide that grows outward from the metal/ceramic surface. The process proceeds via capillary action as the molten metal wicks into open pore channels in the oxide scale growth. Reinforced ceramic matrix composites can be formed by positioning inert filler materials, eg, fibers, whiskers, and/or particulates, in the path of the oxide scale growth. The resultant composite is comprised of both interconnected metal and ceramic. Typically 5—30 vol % metal remains after processing. The composite product maintains many of the desirable properties of a ceramic however, the presence of the metal serves to increase the fracture toughness of the composite. 

When a dilute solution of a polymer (c << c ) is equilibrated with a porous medium, some polymer chains are partitioned to the pore channels. The partition coefficient K, defined as the ratio of the polymer concentration in the pore to the one in the exterior solution, decreases with increasing MW of the polymer (7). This size exclusion principle has been used successfully in SEC to characterize the MW distribution of polymer samples (8). 

The partitioning principle is different at high concentrations c > c . Strong repulsions between solvated polymer chains increase the osmotic pressure of the solution to a level much higher when compared to an ideal solution of the same concentration (5). The high osmotic pressure of the solution exterior to the pore drives polymer chains into the pore channels at a higher proportion (4,9). Thus K increases as c increases. For a solution of monodisperse polymer, K approaches unity at sufficiently high concentrations, but never exceeds unity. 

Glaser and Litt (G4) have proposed, in an extension of the above study, a model for gas-liquid flow through a b d of porous particles. The bed is assumed to consist of two basic structures which influence the fluid flow patterns (1) Void channels external to the packing, with which are associated dead-ended pockets that can hold stagnant pools of liquid and (2) pore channels and pockets, i.e., continuous and dead-ended pockets in the interior of the particles. On this basis, a theoretical model of liquid-phase dispersion in mixed-phase flow is developed. The model uses three bed parameters for the description of axial dispersion (1) Dispersion due to the mixing of streams from various channels of different residence times (2) dispersion from axial diffusion in the void channels and (3) dispersion from diffusion into the pores. The model is not applicable to turbulent flow nor to such low flow rates that molecular diffusion is comparable to Taylor diffusion. The latter region is unlikely to be of practical interest. The model predicts that the reciprocal Peclet number should be directly proportional to nominal liquid velocity, a prediction that has been confirmed by a few determinations of residence-time distribution for a wax desulfurization pilot reactor of 1-in. diameter packed with 10-14 mesh particles. 

Veratridine appears to act at a different part of pore channel from DDT or pyrethroids Act as agonists causing desensitization of receptor Inhibitor of GABA receptors... 

In one example (Lawrence and Casida 1984, Abalis et al. 1985) rat brain microsacs were used to test the action of cyclodiene insecticides such as dieldrin and endrin on the GABA receptors contained therein. The influx of radiolabeled CL into the microsacs via the pore channel of the receptor was inhibited by these chemicals. A similar assay was developed using microsacs from cockroach nerve. Assays with this preparation showed again the inhibitory effect of a cyclodiene (this time heptachlor epoxide) on CL influx. Also, that microsacs from cyclodiene resistant cockroaches were insensitive to the inhibitory effect of picrotoxinin, which binds to the same site on the GABA receptor (Kadous et al. 1983). 

In the field, such effects as are observed in the laboratory may be mitigated due to the existence of very high shear rates at and near the well bore. Far away from the well bore, the polymer sees a larger flow area and this may preclude agglomeration and blocking of pore channels. Thus, extrapolation to the field has to be done very carefully. 

By using other templates, the size of metal nanoparticles can be also controlled. Chen et al. reported the sonochemical reduction of Au(III), Ag(I) and Pd(II) and synthesis of Au, Ag and Pd nanoparticles loaded within mesoporous silica [48,49]. Zhu et al. also reported the sonochemical reduction of Mn04 to Mn02 and synthesis of Mn02 nanoparticles inside the pore channels of ordered mesoporous cabon [50]. Taking into account these reports, the rigid pore of inorganic materials can be used as a template for the size controlled metal nanoparticle synthesis even in the presence of ultrasound. 

The mean pore diameter and the pore volume decrease respectively from 67 A and 0.46 cm7g for calcined SBA-15 to 56 A and 0.32 cm3/g for GFP/SBA-15. A decrease of SSA was also observed from 648 m2/g for SBA-15 to 456 m2/g for the hybrid material. These values suggest that GFP molecules can be embedded within the SBA-15 pores/channels and not simply adsorbed on the external surface of the mesoporous silica. 

Crystal habit (or morphology) is an important property for the industrial use of zeolites. Manipulating habit can be used to tailor the number of pores exposed to the surface of a crystal, as well as the length of pore channels. The shape of a crystal can vary because the different faces grow at different rates relative to one another. 

The results collected in Table 2 show that the average activity is also dependent on the architectural system of channels. Thus, samples with close pore size, Ni and acid sites density, but with different topology showed very different catalytic behavior Ni-MCM-48 (with a 3D pore system) was more active than Ni-MCM-41 (with a ID pore system). In fact, the three-dimensional interconnecting mesopore system is very beneficial with respect to the molecular diffusion of heavy products in the pore channels. 

These microporous crystalline materials possess a framework consisting of AIO4 and SiC>4 tetrahedra linked to each other by the oxygen atoms at the comer points of each tetrahedron. The tetrahedral connections lead to the formation of a three-dimensional structure having pores, channels, and cavities of uniform size and dimensions that are similar to those of small molecules. Depending on the arrangement of the tetrahedral connections, which is influenced by the method used for their preparation, several predictable structures may be obtained. The most commonly used zeolites for synthetic transformations include large-pore zeolites, such as zeolites X, Y, Beta, or mordenite, medium-pore zeolites, such as ZSM-5, and small-pore zeolites such as zeolite A (Table I). The latter, whose pore diameters are between 0.3... 

Figure 8.7 Structural changes of ReOx species in HZcvd catalyst preparation and the catalytic reaction conditions, and a proposed structure of active [Re6017] cluster in the ZSM-5 pore channel, where the [Re6013] cluster is bound to the pentagonal rings of the zeolite inner wall via three lattice oxygen atoms, and the oxygen atoms are tentatively arranged on the Re6 octahedron.

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