Porosity and density

The real density of molded graphite, that is the density exclusive of open porosity (measured with a pycnometer) but including closed-internal porosity, is 2.20 - 2.23 g/cm. This value is near the theoretical density of the graphite crystal (2.25 g/cm, indicating that the amount of internal porosity is small and the structure of the material is well ordered. 

Typical pore-size distribution of several molded graphite materials is shown in Fig. 5.5.t l 

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Fibers of different diameters, lengths, shapes, and densities fractionate, or break up, when processed together in airstreams. This fractionation results in the formation of webs with different top and bottom surface characteristics, as well as varying density and porosity gradients. Such stmctures ate well suited for many filtration appHcations. 

Bulk density is easily measured from the volume occupied by the bulk solid and is a strong func tion of sample preparation. True density is measured by standard techniques using liquid or gas picnometry Apparent (agglomerate) density is difficult to measure directly. Hink-ley et al. [Int. ]. Min. Proc., 41, 53-69 (1994)] describe a method for measuring the apparent density of wet granules by kerosene displacement. Agglomerate density may also be inferred from direcl measurement of true density and porosity using Eq. (20-42). 

Winters and Lee134 describe a physically based model for adsorption kinetics for hydrophobic organic chemicals to and from suspended sediment and soil particles. The model requires determination of a single effective dififusivity parameter, which is predictable from compound solution diffusivity, the octanol-water partition coefficient, and the adsorbent organic content, density, and porosity. 

Porosity calculations from density measurements have also been applied to granulations prepared using different processes. The method of granulation, such as the type of adjuvant used [64] or the amount of granulation liquid [74], was found to change the bulk density and porosity of the material. Consequently, the compression and flow properties of the materials were also different. 

Characteristics of a catalyst particle include its chemical composition, which primarily determines its catalytic activity, and its physical properties, such as size, shape, density, and porosity or voidage, which determine its diffusion characteristics. We do not consider in this book the design of catalyst particles as such, but we need to know these characteristics to establish rate of reaction at the surface and particle levels (corresponding to levels (1) and (2) in Section 1.3). This is treated in Section 8.5 for catalyst particles. Equations 8.5-1 to -3 relate particle density pp and intraparticle voidage or porosity p. 

In general, the structure of sol gel materials evolves sequentially as the product of successive and/or simultaneous hydrolysis and condensation and their reverse reactions (esterification and depolymerization). Thus, in principle, by chemical control of the mechanisms and kinetics of these reactions, namely the catalytic conditions, it is possible to tailor the structure (and properties) of the gels over a wide range. For example, stable silica xerogels of tailored particle dimensions, pore morphology, density and porosity, from relatively... 

MORPHO-INDEPENDENT TEXTURAL PARAMETERS 9.4.1 Density and Porosity... 

The apparent density 5 (g/cm3) is usually measured using mercury as a pycnometric fluid. Mercury does not wet most of the solids and, thus, does not penetrate pores until pressure is applied. Mercury is not the only choice highly dispersed powders can serve as a guest fluid with the same penetration properties as well [55], Reciprocal to S is the specific apparent volume of PS, which is equal to the sum of the volumes of the pores and solid phase (e.g., the total volume of a granule shown in Figure 9.17a), and is obviously related to the mass of a PS. Relation between true and apparent density and porosity was considered in Problem 4. 

As it has been discussed in previous section, from a practical point of view1, and also for comparison between adsorbents, hydrogen adsorption capacities should be reported in a volumetric basis, which makes necessary to know the sample density. Unfortunately, papers reporting hydrogen adsorption capacities of MOFs in volumetric basis use the crystal density of the materials, which is not realistic for this application because it does not include the inter-particle space. Crystal densities of MOFs can vary between 0.2 and 1.3 g cm 3 36 39, and similar to what happens with tap and packing densities of carbon materials, crystal densities of MOFs decreases when porosity increases. Therefore, as in the case of carbon materials (see Figure 5) a maximum is observed when the hydrogen uptake in volumetric basis is plotted versus the porosity of the MOFs samples, and a compromise between density and porosity is necessary from a practical point of view. 

The pore diameter on the abscissa is calculated by employing a particular pore model, usually to the intrusion branch. As a matter of convenience, a cylindrical pore model is traditionally applied. On the ordinate, steep changes in the cumulative diagram are reflected as peak maxima in the incremental curve. From several possible representations (incremental, differential, log differential), the log differential plot seems to be the most revealing, since the areas under the peaks are proportional to the pore volume [79]. Data that can easily derived from mercury intrusion are the pore size distribution, median or average pore size, pore volume, pore area, bulk and skeletal density, and porosity. 

Wang,N., Brerman, J. G. (1995). Changes in structure, density and porosity of potato during dehydration. Journal of Food Engineering, 24,61-76. 

The mechanical properties of cancellous bone are dependent upon the bone density and porosity, and the strength and modulus are therefore much lower than those for cortical bone. The axial and compressive strength are proportional to the square of the bone density, and moduli can range from 1 to 3 GPa. 

As discussed later, compression and densification during compaction can be followed by monitoring and measuring density and porosity. The monitoring of the consolidation, i.e., the bonding process to create the tablet strength, is more difficult. It should be clear, and can be emphasized again, that the important parameters in this operation are the physicochemical properties of the powder and the equipment used to perform this operation. 

The most important characteristics of the final formulation to be compacted are particle size and particle size distribution, density and/or porosity, powder flow, cohesiveness, and lubrication. Particle size, particle size distribution, and density and porosity of the formula will not be addressed here because they are the result of other operations in the scale-up sequence, such as granulation and milling. They should be evaluated as part of those specific operations. It should be noted, however, that the influence of particle size on powder flow and, therefore, on uniform die fill is very important to the compaction operation, but is not a result of it. The one consideration to keep in mind during scale-up is the speed of the press, which will directly affect the time available for the die filling to occur. This is an important parameter to observe carefully. 

Coal density is a useful parameter not only for deducing the spatial structure of coal molecules, but the relationship between the density and porosity suggests that emphasis must be given to density and its determination. Porosity measurement, in turn, provides useful information on the technical behavior of coal toward its end use. Particle density is required for calculating the porosity of individual coal particles. 

For each raw material, basic physical properties such as specific and bulk densities, and porosity were determined. For bulk density, two values were determined each time for loose material pbi and for material condensed to its minimum volume on a riddle pbc-... 

BS EN 623-2 (1993), Advanced technical ceramics - monolithic ceramics - general and textural properties. Part 2 Determination of density and porosity. 

Void [52] developed a variety of ballistic deposition models to simulate sedimentation processes. Void used ballistic models to determine deposition densities for spherical particles which traveled via vertical paths and were deposited on horizontal surfaces. Recently, Schmitz et al. [53] used a ballistic aggregation model to describe particle aggregation at the surface of a crossflow microfiltration membrane. Schmitz and co-workers were able to account for interfacial forces empirically, and demonstrated the influence of physical and chemical variables on the resulting morphology of the fouling deposits (such as aggregate density variation with depth, and influence of shear flow and re-entrainment properties on fouling deposit density and porosity). 

The problems of defining and determining densities of finely porous solids, indicated in Section 5.3.3, apply to hep. A determination of the density of such a material is also one of porosity, since both properties are related to the solid volume the porosity per unit volume of material is equal to 1 -[mJ D X V)], where tn and are, respectively, the mass and density of the solid and V is the total volume. The density and porosity determined by any method entailing contact with a fluid can vary with the extent to which the solid has been dried, how it has been dried and the fluid employed. Fluids may differ in their abilities to penetrate the pore system, and the pore structure may be altered both during drying and by the action of the fluid subsequently introduced. 

The properties of a powder can be subdivided into those related to the particle itself and those of the ensemble of particles (bulk properties). The major particle properties include particle size and size distribution, shape, density and porosity, surface properties (van der Waals attractions, electrostatic charge), moisture content and composition. Particle properties influence the bulk properties of powders/particulates. There are a vast number of bulk properties including moisture content, bulk density, bed porosity, compressibility, flowability, permeability, sinkability, wettability and dispersibility, among others. 

The BET cell is then flooded with helium for the determination of the sample volume, which allows the determination of its real density and porosity since we already know both its weight and its apparent volume. 

S 11. — — Ion exchange resin matrices. IV. Densities and porosity of ion exchange matrices on the basis of styrene-divinylbenzene copolymers. Chem. prtimysl 13, 100 (1963). 

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