Pore fraction

The effect of varying the mean pore size and number of pores on the predicted strength distributions of grade H-451 graphite are shown in Fig. 25. In this instance, both the mean size (SJ and number (N) of pores per unit volume was varied in the "SIFTING" code. This was necessary because the density was held constant, i.e., the pore fraction remains unchanged, and therefore a decrease of the mean pore size must be accompanied by an increase in the number of pores per unit... 

D = relative density P = pressure (1 — D) = pore fraction K= proportionality constant... 

When volume V is occupied by a porous solid, eq 11 is generally made to include a tortuosity coefficient [), the pore fraction e (fraction of the support grain volume occupied by the pore space) and an interaction coefficient K between the precursor and the support (K = 1 if there is no interaction) ... 

Frequently we define a porous medium as a solid material that contains voids and pores. The notion of pore requires some observations for an accurate description and characterization. If we consider the connection between two faces of a porous body we can have opened and closed or blind pores between these two faces we can have pores which are not interconnected or with simple or multiple connections with respect to other pores placed in their neighborhood. In terms of manufacturing a porous solid, certain pores can be obtained without special preparation of the raw materials whereas designed pores require special material synthesis and processing technology. We frequently characterize a porous structure by simplified models (Darcy s law model for example) where parameters such as volumetric pore fraction, mean pore size or distribution of pore radius are obtained experimentally. Some porous synthetic structures such as zeolites have an apparently random internal arrangement where we can easily identify one or more cavities the connection between these cavities gives a trajectory for the flow inside the porous body (see Fig. 4.30). 

Based on the simple expression obtained by Zhang and Seaton [8] upon fitting simulation results for a cubic lattice (Z=6), subsequently generalized by Lopez-Ramon et al. [3], the actual accessible pore fraction for an arbitrary coordination number Z can be written as follows ... 

Heckel considered the compaction of powders analogous to that of a first-order chemical reaction. The pores were the reactant and the densification of the material the product. The proportionality between the change of density with pressure and the pore fraction was the process kinetics.Heckel explained mathematical constants that described the compaction behavior of a given powder and developed a mathematical relationship, Eq. (2). ... 

Heckel concluded that density-pressure data indicate the rate of the change of density with pressure, at any pressure, is proportional to the pore fraction in the compact at that pressure. Additionally, density-pressure curves may be described by two parameters. He theorized that one was related to low pressure densification by interparticle motion. The second measured the ability of the compact to densify by plastic deformation after appreciable interparticle bonding. 

Figure 2a. Relative permeability vs adsorbate Figure 2b. Relative permeability vs open volume, for 3D network and EMA models pores fraction, fh, for 3D network and EMA...

The solute rejection is then given as a function of the total water flux, of the solute diffusion coefficient Dg and of the pore fraction e permeable to the solute ... 

If a pore fraction, , can be determined for a particular support, then these equations may be further refined ... 

This can also be expressed in terms of the partition coeflident and the interstitial and pore fraction in the column ... 

The ratio of the pore fraction to the interstitial fraction has been used as a measure of quality of a size-exclusion column. It is the ratio of the useful volume to the unused volume in a column. However, a better measure is the pore fiaction itself. 

The open porosity of the PAlCs-derived ceramic samples shows a weak dependence from the amount of aluminum and falls in the range f 8-13%. It increases up to w20% for the PCS-derived component. Such low values of open porosity have been already reported in the literature for similar polymer-derived ceramics [56] and indicate that this processing route is suitable for the fabrication of dense (up to 92% of theoretical density) covalent ceramics at low temperature. The porosity values measured for the ceramic products are comparable with the starting pre-ceramic samples. Indeed, results of the mercury infiltration experiments indicate that the pyrolysis process leads to the removal of the finer pore fraction (below lOnm) leaving almost unchanged the amount and the size of the coarser pores. 

At the mesoscopic scale (size of single agglomerate, 50 — 100 nm), the accessibility of catalyst surface sites to protons is critical, and it is determined by the water-filled pore fraction. 

Internal wetted pore fraction (nomalized) Volumetric Faradaic current density Effective Volumetric Faradaic current density including effectiveness factor of agglomerates... 

However, when the concretes are partially exposed to sulfate solutions, the situation may be different. V.T. Ngala i ] studied the effect of carbonation on the ratio of capillary to total porosity of cement paste. The results showed that the capillary pore fraction greatly was improved after carbonation (shown in Fig. 24). This will promote the capillary suction of concrete, forming a more severe sulfate pore solution in the concrete and resulting more severer concrete damage. 

From Fig. 24, compared to cement paste, the ratios of capillary pores fraction of cement + 30% FA and cement + 65% BFS were higher than cement paste after carbonation. Some research showed that blended concrete has high carbonation rate [s l, high degree of carbonation [S7] or large carbonation depth [ss] compared to the ordinary cement concrete. The carbonation susceptibility of blended concrete may be another reason for the negative effect of mineral addition on sulfate resistance of partially exposed concrete. 

The pores may be separated or interconnected by channels or microcracks in the matrix and the overall pore fraction is an important material characteristic. However, more precise information may be needed, e.g. pore diameter distribution and average distance between pores are often required to evaluate the material s frost resistance see. Section 6.5.2. In addition, aggregate grains themselves contain pores. 

Niger hydrophilic pore fraction leading to film formation larger front - liquid water slug and higher flooding (txjbble point)... 

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