Fill of Pores

PS in nonoxidizing electrolyte such as acetonitrile (MeCN), whereas they are not filled in oxidizing electrolytes such as DMF. However, it has been reported that the PS on p-Si (13 Qcm) formed in anhydrous HF-MeCN solution has only the macropore layer with no nanometer PS covering the surface of the macropore walls and the sample surface.  

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Figure 9.41 The relative changes of the surface area after gradual deposition of an additional component on the surface of monodisperse spherical particles depending on the degree of filling of pore volume, U, and initial porosity of a support s0.

Following the convention in gas adsorption-desorption isotherms, the mercury isotherm, illustrated in Fig. 12.5, is plotted as volume versus relative pressure so that the radius increases from left to right. Curve I in Fig. 12.5 represents the condensation isotherm from the extrusion curve and curve II is the evaporation isotherm from the intrusion data. Since no adsorption takes place on the pore walls prior to the filling of pores in mercury porosimetry as occurs in gas adsorption, the usual knee of the isotherm is absent. However, condensation-evaporation isotherms from mercury porosimetry are strikingly similar to adsorption-desorption... 

In an apparatus based on Figure 6.16b, the volume of mercury forced into the pores of the solid can be measured as a function of the applied pressure. Equation (86) shows that higher pressures are required for smaller pores. Therefore incremental increases in p will result in the filling of pores of progressively smaller radii. The volume V that has intruded a porous solid at a pressure p gives the cumulative volume of all pores larger than the size associated with p. Since plots of V versus p give information about the cumulative pore distribution, it is the derivative of such data that measures the increment in pore volume associated with an increment in Rc. Written as a formula, dV/dp oc dV/(—dRc) since Fincreases as R( decreases. 

It has therefore been assumed that a virial type of equation can relate the concentration C of the intracrystalline guest to the osmotic pressure (solution thermodynamics) or mean hydrostatic stress intensity (volume filling of pores) (9)... 

This classification is certainly not perfect because the filling of pores is also determined by their shape (cylinders, slits, cones, irregular) and pores may be separate or connected. 

Metals accumulate more slowly on the catalyst surfaces because the inlet concentrations of metals are lower than for coke precursors. The accumulation of metals can be even greater than coke, for example the vanadium concentration can reach 30-50 wt% of the catalyst on a fresh catalyst basis (Thakur and Thomas, 1985). Demetallization reactions can be considered autocatalytic in the sense that once the surface of the catalyst is covered with metal sulfides the catalyst remains quite active and continues to accumulate metal sulfides. The final loss of catalyst activity is usually associated with the filling of pore mouths in the catalyst by metal sulfide deposits. 

It is unlikely, however, that the lithification of chalk will go on without consolidation, in which the volume of chalk material is reduced in response to a load on the chalk. Consolidation can lead to a reduction in porosity up to about 40%, and an increase in the effective stress (Jones et al., 1984). The increased effective stress is required to instigate the process of pressure solution. Pressure solution provides Ca2+ and HCO3 for early precipitation of calcite cement in the chalk. However, the inherently low permeability of chalk would inhibit the processes of consolidation and pressure solution/cementation unless some permeable pathways are opened up to permit the dissipation of excess pore pressure created by the filling of pore space by calcite cement. Pressure solution will cease if the permeable pathways are blocked by cement. Thus, it appears that the development of fractures, open stylolites and microstylolitic seams (Ekdale et al., 1988) is necessary to permit pressure solution to continue and lead to large rates of Ca2+ and HC03 mobilization. 

The limiting dimensions of micropores are difficult to specify exactly, but the concept of micropore filling is especially useful when it is applied to the primary filling of pore space as distinct from the secondary process of capillary condensation in mesopores. 

The increase in the amount of mercury forced into the porous material upon a pressure increase corresponds to filling of pores of a size given by Equation 3.10. The... 

Issue (1) includes aspects of surface structure and composition, (il) surface area, porosity and heterogeneity. Regarding (iii), there was a certain emphasis on monolayer adsorption (which prevails for adsorption from solution) filling of pores by molecules has its analogies with the stacking of colloidal particles under certain confinements. 

In this case the permeation is proportional to the average pore radius r and inversely proportional to but is independent of the mean pressure P that is an important difference from viscous flow. The separation selectivity between two gases will be proportional to M2/M-[f. In the case of vapor transport in mesopores, another mechanism that may occur is the capillary condensation leading to selective filling of pores by a molecule and preferential transport of this molecule. 

Figure 1. SEM image of polycarbone membranes surface (a) - pores 4.8 pm (b) - burl FeNi(P) formed after filling of pores with d=4.8 pm.

The sharp decrease in surface area at very high water contents is clearly attributable to the filling of pores in the fibre and sheet structure by liquid water. The reason for the decrease in surface area at lower relative humidities is less obvious. One may speculate that fibrillation occurs at the fibre-fibre bond during bond formation, because of the stresses induced by drying under tension. On subsequent re-exposure to a moist atmosphere, the hydrogen-bonded network may relax, and the fibrillated areas may collapse onto the fibre surfaces, causing the observed loss of surface area. 

Densification results from particle rearrangement under the influence of capillary forces and the filling of pores by the liquid phase. This process is very rapid, and if during the early stages of sintering, the liquid flows and completely fills the finer pores between the particles, 100 percent densification can result almost instantaneously. 

Gradual filling of pores, leaving no appreciable area and so a negligible heat effect at high relative pressures. Methanol on charcoal [21]. Benzene on graphitized black [19]... 

Keeping of this regime provides bottom-up filling of pores during the pulse electrodeposition. 

Latex-modified mortar and concrete have improved resistance to freezing and thawing, i.e., frost attack, over conventional mortar and concrete. This is due to the reduction of porosity as a result of decreased water-cement ratio and filling of pores by polymers, and the air entrainment introduced by polymers and surfactants. Figures 4.66 and 4.67 represent the freeze-thaw durability in water (-18 to 4°C) of combined water and dry-cured SBR-, PAE-, and EVA-modified mortars.The frost resistance of SBR-, PAE-, and EVA-modified mortars is improved markedly at polymer-cement ratios of 5% or more. As the degree of expansion by frost (calculated... 

Fig. 3.12 The scheme of cement hydration (according to [20]) (a) cement grains in water, (b) gel layer formed on cement grains, (c) break-up of gel layer under the osmotic pressure and the growth of secondary C-S-H gel, (d) filling of pores in the paste after longer period of time, caused by gel formation...

Parrott et al. [153] found an exact relationship between the rate of water replacement by methanol and the ratio of pores greater than 50 nm. With lowering of this ratio to the level of about 0.4, the diffusion becomes extremely low (Fig. 5.71) the authors attribute this to the filling of pore chaimels by some amount of hydration products. However, Feldman [138] remarks that there are some questions as the water replacement by methanol is concerned. The reactivity of methanol towards Ca(OH)2 and C-S-H, resulting in the formation of calcium methoxide or a methylated complex compounds was reported by some authors [138,156]. These reactions occur very quickly and a substantial amount of products appears, modifying the paste microstracture. The swelling of paste, observed by Feldman [138] was about 0.1 % after 14 days when the paste absorbed 85 % methanol as water replacement. This effect can be attributed to the intrasion of methanol between the layers in C-S-H structure and the calcium methoxide formatioa At extended distance between C-S-H layers the specific surface of paste markedly increases, as it has been proved by Winslow and Diamond [ 13 5]. In turn, the water replacement by propan-2-ol, re-... 

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