Porosities and pore size distributions

Studies on the pore structures of pastes of composite cements have presented 

Uchikawa et al. (U18) studied pastes of Portland and composite cements by N2 sorption. In all cases, the pore size distributions peaked at 2 nm. Partial replacement of cement by slag increased the height of the peak, and partial replacement by pfa decreased it. 

Calculations based on reaction stoichiometry and densities of phases support the conclusions from experimental observations that mature pastes of composite cements are more porous than comparable pastes of Portland cements. This is indicated by the results in Table 7.3, 9.4 and 9.6. Similar calculations for 180-day-old pastes of w/s 0.45 indicate free water porosities of about 24% for a typical Portland cement, 35% for a cement with 40% slag, 35% for one with 40% pfa and 32% for one with 30% microsilica. The calculated values are in all cases somewhat higher than observed mercury porosities (F34,F41). 

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The erosion of graphite in nozzle appHcations is a result of both chemical and mechanical factors. Changes in temperature, pressure, or fuel-oxidizing ratio markedly affect erosion rates. Graphite properties affecting its resistance to erosion include density, porosity, and pore size distribution... 

Porosity and pore-size distribution usually are measured by mercury porosimetry, which also can provide a good estimate of the surface area (17). In this technique, the sample is placed under vacuum and mercury is forced into the pore stmcture by the appHcation of external pressure. By recording the extent of mercury intmsion as a function of the pressure appHed, it is possible to calculate the total pore volume and obtain the population of the various pore sizes in the range 2 nm to 10 nm. 

S. Anferova, V. Anferov, D. G. Rata, B. Bliimich, J. Arnold, C. Clauser, P. Blunder, H. Raich 2004, (A mobile NMR device for measurements of porosity and pore size distribution of drilled core samples), Concepts Magn. Reson. Part B 23B (1), 26-32. 

Hydraulic conductivity is one of the characteristic properties of a soil relating to water flow. The movement of water in soil depends on the soil structure, in particular its porosity and pore size distribution. A soil containing more void space usually has a higher permeability. Most consolidated bedrocks are low in permeability. However, rock fractures could create a path for water movement. 

The pore structure of a solid can contribute to the disintegration, dissolution, adsorption, and diffusion of a drug material [26,27]. Because of this, porosity and pore size distribution measurements have been used extensively to study tablets [28-30], granules [31,32], and excipients [33]. The following classification system of pore sizes has been developed based on the average pore radii [6] ... 

In the main body, this sechon presents recently employed mesoscale computational methods that can be uhlized to evaluate structural factors during fabrication of PEMs. These simulations provide density distributions or maps and structural correlahon functions that can be employed to analyze the sizes, shapes, and connectivihes of phase domains of water and polymer the internal porosity and pore size distributions and the abundance and wetting properties of polymer-water interfaces. 

The specific area is measured in m2/gramme. Its value can vary from 1-5 m2/g in the case of, for example, coarse kaolin to about 100 m2/ g for certain plastic clay types. The measurement for example takes place by adsorption of gases like nitrogen. The adsorbed amount is measured as a function of the pressure. At a certain N2 pressure nitrogen molecules at the surface of the solid particles are adsorbed and pressed into the pores. Consequently, this method is also suitable for measuring porosity and pore size distribution. 

Table 4. Porosities and pore size distributions derived from mercury intrusion porosimetry.

Porosity and pore size distributions, both before and after surface modification, are analyzed from N2 adsorption data. Both capacity as well as adsorption free energies are obtained from metal ion adsorption isotherms from aqueous solution as described in the experimental section. 

Porosity and pore size distribution from small-angle X-ray scattering... 

The density of granules used in tablet production is influenced by the densification of the slugs or compacted ribbon (7-9). To determine the porosity and pore size distribution of a ribbon or granules, mercury intrusion porosimetry may be used. This technique can also be used to evaluate the homogeneity of density/pressure distribution on a compact or granule which in turn affects the characteristics of the final granulation. In addition, gas... 

R. Herino, G. Romchil, K. Boala, and C. Bertrand, Porosity and pore size distribution of porous silicon layers, J. Electrochem. Soc. 134, 1994, 1987. 

An important barrier to rapid development of supported microporous membranes is also the lack of direct measurement methods to determine porosity and pore size (distribution) of the (supported) separation layer. 

Porosities of membrane components vary widely and values are reported ranging from 20 to 60%. Commonly, values of 30-40% are used. Pore sizes range from macropores (>500 nm) via mesopores (20-500 nm) to micropores (<2 nm). A great problem is the lack of reliable measurement methods to measure the porosity and pore size distribution of supported membranes (see Chapter 4). 

Work by Elferink et al. [59b] has shown that further optimisation of the microstructure can be obtained by lowering the temperature of the hydrolysis-condensation reaction. This results in better control of porosity and pore size distribution. 

Ngadi, M. O., Rassama, L. S., and Raghavan, G. S. V. (2001). Porosity and pore size distribution in cooked meat patties containing soy protein. Canadian Biosystems Engineering, 43(3), 17-24. 

Porosity and pore size distribution for catalyst coating application (30-35% open porosity and 4-15 micron median pore size). 

The particular concepts of stmcture models of cement paste are based mainly upon the speciQc surface area measurements and the sorption properties of this material, as well as on the smdies of porosity and pore size distribution. 

It is clear that the permeability of material to water depends mainly on the volume of capillary pores. It is not linked with total porosity but depends rather on the pore size distribution. However, Marsh [133] gives attention to a fairly good correlation between the total porosity, determined by means of helium method, and permeability. This relation is shown inFig. 5.60 [133]. The diying of samples by substitution of water with propan-2-ol and -pentane was applied. Porosity and pore size distribution determined with mercuiy porosimeter do not correspond to the real stmcture, because the intmsion of mercury under a high pressure, causes the destmction of hydrates plugging the pores, particularly in the pastes of cements with fly ash. 

The density of a green body can be direcfly measured from its mass and volume. Porosity and pore size distribution are normally measured by using mercury... 

Fig. 4 Porous monoliths with different porosities and pore size distributions created by the photopolymerization of a blend of acrylate monomers and porogens...

A very detailed fuel cell-related TEM study of CB and CB corrosion can be found in Eiu et al. [15]. Gas adsorption, Hg intrusion porosimetry, and small-angle X-ray scattering (SAXS) provide information on porosity and pore size distribution, each of them having its own advantages and limitations. Methods that can be used to probe the functional groups at the carbon surface are X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption spectroscopy (NEXAES). Table 7.1 gives an overview of characterization techniques applied... 

Nevertheless, the overall diliiisivity of hydrogen through nanocrystalhne-based membranes is commonly 10 times higher than a membrane based on polycrystalline material. Furthermore, a composite membrane based on a thin noble metal layer deposited onto a porous support makes possible the necessary mechanical strength, however superior to dense and self-standing Pd-membranes. In particular, porosity and pore size distribution of the porous support can have some influence on hydrogen flux as well as on the membrane stabUity elevated temperatures. 

The pores are for the transport of fuel cell reactants and product(s). Optimal porosity and pore size distribution can facilitate the mass transport process to minimize the fuel cell performance loss due to concentration overpotential. If some pores are more hydrophobic than others, what is the relative distribution Is the distribution of pore sizes and hydrophobicity within the allowable range ... 

Sol-gel techniques are being employed to fabricate components not only for mainstream applications such as photonics, thermal insulation, electronics and microfluidics, but also for more exotic applications such as space dust and radiation collectors [1]. Methods have been developed to tailor the physical properties of sol-gel materials to the requirements of a specific application. For example, porosity and pore size distribution can be controlled by forming micelles in a sol [2-4-] gels can be made hydrophobic by derivatizing the otherwise hydrophilic pore walls with hydrophobic moieties [5] superhydrophilicity can be obtained by ultraviolet irradiation [6, 7] mechanical strength can be increased by cross-linking the oxide nanoparticles that make up the gel [1, 8, 9], and optical properties can be controlled by adding chromophores and nanoparticles to control index of refraction, absorption and luminescence [10-12]. 

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. 

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