Porosity effects pore size

Among the separator varieties described, the phenol-formaldehyde-resorcinol separator (DARAK 2000) [60] as well as the microporous PVC separator [86] have proven effective for this construction. For applications without deep discharges, concessions may be made with the respect to porosity and pore sizes of the separator therefore polyethylene separators or a spe-... 

This model (known as the SDR model) uses the log mean relaxation of 100% brine saturated rock as the estimator of the effective pore size [32]. This limits the method to rocks in the absence of hydrocarbons, which models permeability to be proportional to the porosity to the fourth power and log mean T2 to the second power, Eq. (3.6.6). Variations of this method use different exponents or the formation resistivity factor rather than porosity [2] ... 

The catalyst activity depends not only on the chemical composition but also on the diffusion properties of the catalyst material and on the size and shape of the catalyst pellets because transport limitations through the gas boundary layer around the pellets and through the porous material reduce the overall reaction rate. The influence of gas film restrictions, which depends on the pellet size and gas velocity, is usually low in sulphuric acid converters. The effective diffusivity in the catalyst depends on the porosity, the pore size distribution, and the tortuosity of the pore system. It may be improved in the design of the carrier by e.g. increasing the porosity or the pore size, but usually such improvements will also lead to a reduction of mechanical strength. The effect of transport restrictions is normally expressed as an effectiveness factor q defined as the ratio between observed reaction rate for a catalyst pellet and the intrinsic reaction rate, i.e. the hypothetical reaction rate if bulk or surface conditions (temperature, pressure, concentrations) prevailed throughout the pellet [11], For particles with the same intrinsic reaction rate and the same pore system, the surface effectiveness factor only depends on an equivalent particle diameter given by... 

The best answer to the permeability/permselectivity optimization would be to synthesize very thin layers of materials having a comparatively high porosity and pore sizes in the range 5-8 A so as to achieve molecular sieving effects. Instead of the modification of already available membranes, the synthesis of new membranes seems more appropriate to reach the above goal. The two most promising candidates in this context are carbon and zeolite membranes. 

Anhydrous ammonia was purchased from Matheson Canada Ltd., Whitby, Ontario. The substrate materials used were polypropylene membrane (Celgard-2400, Celanese Corp., Summit, NJ) and polypropylene beads (Hercules Canada Ltd., Montreal, Quebec). The Celgard-2400 was a 25.4 pm thick porous membrane with an effective pore size of 0.02 pm with a 38% porosity. The beads as purchased were slightly flattened spheres having a diameter of about 2.5-3 mm and being about 3.5 ran thick. The membranes and the beads were washed with distilled water, then with absolute ethanol in an ultrasonic cleaner and were finally dried in a vacuum oven, at about 70° C. These substrate materials were ready for use as a control or for further treatment. The further treatment involved the attachment of NH2 groups onto the surface of the substrate material in an ammonia plasma reactor, perhaps by free-radical reaction, as reported in our previous report (2). 

One of the most commonly used terms to explain drug targeting is the EPR effect. The porosity and pore size of tumor blood vessels has been amenable to nanocarriers for tumor-targeting therapy, imaging, and diagnosis. The porosity facilitates the supply of adequate nutrients to the developing area in tumors. When tumor growth is inhibited or when the tumor size is decreased by any... 

Plasticizers and superplasticizers improve radically the pore stmcture (effect of w/c) and concrete becomes less permeable to air and water [159], Collepardi and Massida [159] found a capillary porosity and pore size lowering with decreasing permeability of concretes in which water reducers were used. The resistance to the sulphate attack was also improved [159]. 

Characteristics of the mold, such as porosity and pore size, have significant effects on the consolidation rate of the casting. According to Eqs. (4.66) and (4.69),... 

S. Ghosh, et al.. Dynamic mechanical behavior of starch-based scaffolds in dry and physiologically simulated conditions effect of porosity and pore size, Acta Biomaterialia 4 (4) (2008) 950-959. 

By these means it is possible to prepare carbon sieves with effective micropore diameters ranging from about 4 to 9 A. The micropore size distribution of such sieves is much narrower than in a typical activated carbon and the porosity and therefore the adsorptive capacity are generally very much smaller, as may be seen from Figure 1.2. The ability to modify the effective pore size by adjusting the conditions of the manufacturing process makes it relatively easy to tailor a carbon sieve to achieve a particular separation. However, it is difficult to achieve absolute reproducibility between different batches, and the existence of a distribution of pore size, even if narrow, means that the molecular sieving selectivity of a carbon sieve seldom approaches the almost perfect separation achievable under fav orable circumstances with a zeolite sieve. Nevertheless, the kinetic selectivities which may be attained with a well-prepared carbon sieve are remarkably high. 

Activated carbons have a spread of pore sizes. Consequently the possibility that they can show a partial molecular sieve effect cannot be overlooked when the components of the binary solution are not of the similar molecular dimensions. This factor would add a degree of preferential adsorption of the components of smaller size molecules irrespective of the competitive adsorption due to other factors. The composite isotherms would, therefore, be of the type obtained on heterogeneous surfaces. This competitive adsorption effect wiU be more prominent and visible when carbons are produced from the same source raw materials by different procedure or post preparation treatments. For example, carbons that have been produced after varying degrees of activation or carbons that are heat treated at varying temperatures after activation will have different porosities and pore size distribution. The extremely fine micropores get partially blocked as the final heat treatment temperature exceeds 800°C to 900°C, due to the calcinations of the pores. This will produce molecular sieve effect depending upon the heat treatment temperature. 

These SEM piioiographs clearly show that ihc porosity and pore size distribution differ substantially for the various membranes depicted. Table Vl.S summarises the effect of the preparation method on the porosity and the pore size distribution. 

The porosity (ie, pore size and amount of pores) of microparticles is also an important characteristic to take into consideration when fabricating microparticles because it plays an essential role in controlling the release of payloads. The porosity and morphology of particles are usually determined by scanning electron microscopy (SEM). For the emulsification solvent extraction/evaporation method of fabrication, the rate of solvent extraction, which depends on the flow in the stirred vessel the droplet size the temperature and the dispersed phase hold-up in the 0/W emulsion have an effect on porosity [87]. The porosity usually increases with a decrease in solvent extraction rate. The porosity of microparticles results in initial burst release due to pore diffusion [78,88]. Mao et al. studied the influence of different W/O/W emulsification solvent extraction/evaporation process parameters on internal and external porosity of PLGA microparticles [78]. The surface morphology of the microparticles can be influenced by the type of polymer, internal aqueous phase voliune (Wi), volume of continuous phase (W2), polymer concentration, homogenization speed, and equipment used for the primary emulsion [78,79]. 

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