Through-pores

Another important distinction relating to pore geometry is that between "through" pores, with two open ends, and "dead-end" pores with only one. 

Case (a). The through pores are of uniform radius a and isotropic... 

A second form of desolvation chamber relies on diffusion of small vapor molecules through pores in a Teflon membrane in preference to the much larger droplets (molecular agglomerations), which are held back. These devices have proved popular with thermospray and ultrasonic nebulizers, both of which produce large quantities of solvent and droplets in a short space of time. Bundles of heated hollow polyimide or Naflon fibers have been introduced as short, high-surface-area membranes for efficient desolvation. 

Under severe conditions and at high temperatures, noble metal films may fail by oxidation of the substrate base metal through pores in the film. Improved life may be achieved by first imposing a harder noble metal film, eg, rhodium or platinum—iridium, on the substrate metal. For maximum adhesion, the metal of the intermediate film should ahoy both with the substrate metal and the soft noble-metal lubricating film. This sometimes requires more than one intermediate layer. For example, silver does not ahoy to steel and tends to lack adhesion. A flash of hard nickel bonds weh to the steel but the nickel tends to oxidize and should be coated with rhodium before applying shver of 1—5 p.m thickness. This triplex film then provides better adhesion and gready increased corrosion protection. 

A fundamental difference exists between the assumptions of the homogeneous and porous membrane models. For the homogeneous models, it is assumed that the membrane is nonporous, that is, transport takes place between the interstitial spaces of the polymer chains or polymer nodules, usually by diffusion. For the porous models, it is assumed that transport takes place through pores that mn the length of the membrane barrier layer. As a result, transport can occur by both diffusion and convection through the pores. Whereas both conceptual models have had some success in predicting RO separations, the question of whether an RO membrane is truly homogeneous, ie, has no pores, or is porous, is still a point of debate. No available technique can definitively answer this question. Two models, one nonporous and diffusion-based, the other pore-based, are discussed herein. 

Global uranium flux calculations have typically been based on the following two assumptions (a) riverine-end member concentrations of dissolved uranium are relatively constant, and (b) no significant input or removal of uranium occurs in coastal environments. Other sources of uranium to the ocean may include mantle emanations, diffusion through pore waters of deep-sea sediments, leaching of river-borne sediments by seawater," and remobilization through reduction of a Fe-Mn carrier phase. However, there is still considerable debate... 

Figure 2. Simplified capillary view of flow through pores.

Membranes are applied directly to the metal or concrete surface to protect from corrosion by any liquor that penetrates the brick lining through pores and cracks. Membranes consist of sheet material bonded to the metal or concrete, e.g., flexible PVC sheet, or it may be formed in situ (e.g., polyester resin reinforced with glass fiber, or synthetic rubber sheet, lead, polyisobutylene, polyethylene and asphalt). 

Passivation According to Fig. 1.15 (top) all the Fe will be converted to Fe2 03, whilst the rust originally present will be unaffected. According to Fig. 1.15 (bottom) the rust will be unaffected, whilst the iron surface exposed to the solution through pores in the rust will be passivated by a protective film of Fe203. Water will be stable except at high potentials where it will be oxidised to O2. 

Studies suggested that under certain conditions platinum would become mechanically detached from titanium anodes owing to attack of the substrate through pores in the coating. Anodes became available with a... 

Equation 1 has as its basis the concept that diffusion, either through pores or to the gross surface of the catalyst particle, controls the reaction rate. When the control is strictly by the gas film surrounding the catalyst, one would have to convert Equation 1 to... 

Long-chain fatty acids (e.g., palmitate Cig) diffuse through pores in the outer mitochondrial membrane, and then form long-chain acyl-CoA esters catalyzed reversibly by palmitoyl-CoA synthase (assumed to be on the inner face of the outer membrane). 

Evapotranspiration (ET) is the collective term for land surface evaporation and plant transpiration, which are difficult to isolate in practice. Transpiration refers to the process in which water is transported through plants and returned to the atmosphere through pores in the leaves called stomata, and is distinct from direct evaporation of intercepted precipitation from leaf surfaces. Some land surface processes and the roles of vegetation in the water and energy balances are illustrated in Fig. 6-5. Due to... 

In a series of papers, Gupta et al. (109-112) studied the in vitro release properties of heat-stabilized BSA microspheres containing adriamycin. The biphasic release of drug was attributed to its location in the microsphere. The initial release results from surface desorption and diffusion through pores, while the later release arises from drug within the microsphere, which becomes available as the microsphere hydrates. 

FIG. 20-92 SEM image of a poly(styrene-co-divinylbenzene) gigaporous particle synthesized from suspension polymerization and schematic of a gigaporous particle showing through-pores and diffusion pores [Gu et al., China Partic-uology, 3, 349 (2005)]. 

Efforts to overcome the limitations of the fragile membranes (as delicate as soap bubbles) have evolved with the use of membrane supports, such as polycarbonate filters (straight-through pores) [543] or other more porous microfilters (sponge-like pore structure) [545-548]. 

Depending on their structure, membranes can be separated into porous, where matter is transported through pores in the membrane, and compact, where the substance is transported either through the entire homogeneous membrane phase or its homogeneous parts. 

Flow properties of macroemulsions are different from those of non-emulsified phases 19,44). When water droplets are dispersed in a non-wetting oil phase, the relative permeability of the formation to the non-wetting phase decreases. Viscous energy must be expended to deform the emulsified water droplets so that they will pass through pore throats. If viscous forces are insufficient to overcome the capillary forces which hold the water droplet within the pore body, flow channels will become blocked with persistent, non-draining water droplets. As a result, the flow of oil to the wellbore will also be blocked. 

Other experiments are planned to study the location, distribution and resuscitation of ultramicrobacteria in large three-dimensional sandpacks. Such studies will allow a more realistic approximation of reservoir conditions than the unidirectional core studies. We do not consider that the ultramicrobacteria will reach or grow in areas where residual oil is located. Selective plugging involves blocking the high permeability zones already drained of oil. We consider that the injection of ultramicrobacteria will be carried, like waterflood operations, to the areas of the strata already drained of oil and permit them to disperse through pore spaces and resuscitate in these areas. 

The monomers commonly used for the preparation of polymer monoliths are either hydrophobic, for example, styrene/divinylbenzene and alkyl methacrylates, or hydrophilic, for example, acrylamides. The polymerization is usually accomplished by radical chain mechanisms with thermal or photochemical initiation, as detailed in the reviews (Eeltink et al., 2004 Svec, 2004a and b). Internal structures of polymer monoliths are described to be corpuscular rather than spongy this means through-pores were found to be interstices of agglomerated globular skeletons as shown in Fig. 7.1 (Ivanov et al., 2003). Porosity is presumably predetermined by the preparation... 

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