Characteristics apparent density

The characteristics of a powder that determine its apparent density are rather complex, but some general statements with respect to powder variables and their effect on the density of the loose powder can be made. (/) The smaller the particles, the greater the specific surface area of the powder. This increases the friction between the particles and lowers the apparent density but enhances the rate of sintering. (2) Powders having very irregular-shaped particles are usually characterized by a lower apparent density than more regular or spherical ones. This is shown in Table 4 for three different types of copper powders having identical particle size distribution but different particle shape. These data illustrate the decisive influence of particle shape on apparent density. (J) In any mixture of coarse and fine powder particles, an optimum mixture results in maximum apparent density. This optimum mixture is reached when the fine particles fill the voids between the coarse particles. 

Inasmuch as friction conditions determine the flow characteristics of a powder, coarser powder particles of spherical shape flow fastest and powder particles of identical diameter but irregular shape flow more slowly. Finer particles may start to flow, but stop after a short time. Tapping is needed in order to start the flow again. Very fine powders (fine powder particles to coarser ones may increase the apparent density, but usually decreases the flow quality. Metal powders having a thin oxide film may flow well. When the oxide film is removed and the friction between the particles therefore increases, these powders may flow poorly. 

Refining and Fractionation. These processes are used to alter and select cellulose properties so the final sheet has the desired properties (51). Properties of recycled fibers differ from those of fibers prepared directly from wood. For example, recovered chemical fibers have lower freeness, an apparent viscosity leading to different water drainage characteristics on paper machines. Recovered fibers also have iacreased apparent density, lower sheet strength, iacreased sheet opacity, inferior fiber—fiber bonding properties, lower fiber sweUiag, lower fiber flexibiUty, lower water reteatioa, reduced fiber fibrillatioa, and much lower internal fiber delamination. 

Unsaturated polyester syntactic foams are cheaper than epoxy foams, although the latter are stronger, more water resistant, and shrink less if cured at room or high temperatures 83,136). One merit of polyester syntactic foams is the low apparent density that can be obtained. But the mechanical characteristics depend upon the apparent density e.g. for the Soviet polyester syntactic foams (SPB), using phenolic microspheres (BV-01)1 ... 

Fig. 3. Main characteristic of silica product powders (S denotes specific surface area, p represents apparent density).

The resin beads used in most columnar operations range in size from 0.3 to 0.9 mm in diameter, which is a compromise based on the effect of ion-exchange rates, capacities, and hydraulic characteristics. The especially made resins used in resin-in-pulp operations range in size from 0.8 to 1.6 mm in diameter. The apparent density of a resin is defined as that weight of backwashed and settled wet resin per cubic foot, which for resins used in the uranium industry is about 38-45 Ib/ft . In column operations, the attrition losses due to swelling and contraction of resin, abrasion of resin-resin surfaces, and abrasion of resin-equipment surfaces are negligible. In resin-in-pulp operations, an appreciable amount of attrition loss is encountered. 

This technique is used to determine two characteristic values of a porous solid the true density and the apparent density from which it is possible to determine the total porous volume... 

Kozlov compared Eqs. (1) and (6) for tensile tests of 56 specimens of phenolic foams ba d on resol oligomers (FRP-1 grade). In order to exclude the effect of differences in the apparent density of samples which were cut from the same panel, specific strength characteristics were used, i,e. the ratio of strei h to specific gravity. 

Other physical characteristics such as refractive index and apparent density of the oil are as given in Table 3.7. 

The mean apparent density depends on both the porosity of the parent limestone and the degree of burning of the lime. Thus, a quicklime produced from a porous limestone may have a similar reactivity to one made from a dense limestone, but different hydration characteristics. 

Bulk density and real density Apparent density For estimation of the filter packing volume Important for flow characteristics of the activated ... 

Activity of the unit of a catalytic layer volume is very important characteristics of the catalyst, which depends on the activity per the weight unit as well as on apparent density of the layer. For bulk ZrFe intermetallides (fraction 2-3 mm), the apparent density ( 3 g/cm ) is much higher than that for composite catalysts ( 1 g/cm ). However, enhancement of AC specific activity due to... 

According to DIN 7726, a foam is a material with cells (open, closed or both) distributed throughout its entire mass with an apparent density lower than the density of the skeletal substance. Table 8 shows the main characteristics and classifications of this material ... 

Powders are finely divided solids, smaller than 1000 in its maximum dimension. A particle is defined as the smallest unit of a powder. The particles of powder may assume various forms and sizes, whereas the powders, as an association of such particles, exhibit, more or less, the same characteristics as if they were formed under identical conditions and if the manipulation of the deposits after removal from the electrode was the same [1,2]. The size of particles of many metal powders can vary in a quite wide range from a few nanometers to several hundreds of micrometers. The most important properties of a metal powder are the specific surface, the apparent density, the flowability, and the particle grain size distribution. These properties, called decisive properties, characterize the behavior of a metal powder. 

All these properties have a strong influence on the thermal characteristics. For example, as previously described in this handbook by H.-P. Ebert (Chap. 23) and already underlined in the previous paragraphs of this chapter, the effective thermal conductivity is strongly dependent on the aerogel s apparent density [27]. Indeed superinsulating samples (e.g., X <0.020 W m K ) can only be found within a rather short range of densities (Figure 26.6), usually located between 0.10 and 0.20 g cm . ... 

Figure 19 Compression characteristics of recipe I. The second v-axis shows the influence of the nitrogen pressure on the porosity. Porosity was calculated by the quotient of upward pressure of the coated granules in silicon oil as a measure of the apparent density and the true density. The three different charts display the compression characteristics for three compression forces (5-15 kN).

In spite of the efficacy of exogenous interferon, the major search has been for Interferon inducers. Synthetic polymers have been effective inducers and some of the characteristics apparently necessary for activity are as follows a large molecule with a high density of free anionic groups, not readily degradable and not readily eliminated. Agents with these characteristics include polymers of maleic anhydrides, polyacrylates and carboxylates. Polyacrylic acid (PAA) and polymethacrylic acid (PMAA) have induced Interferon in tissue culture and protected mice infected with Mengo virus and vaccinia and vesicular stomatitis viruses,76. Salts of polyvinyl sulfate appear to have dual activity since they induce interferon activity in mice but not in tissue culture, and the antiviral activity exerted is not correlated with virus interferon sensitivity. ... 

Apparent density also known as particle or mercury density, is defined as the mass of unit volume of the carbon particle, including its pore system. From this value it is possible to obtain the bed porosity. This bed porosity, or void volume is an important value with respect to the flow characteristics of the activated carbon bed. The method uses a pycnometer. If both apparent and real densities are known, the difference of their inverses will provide the total pore volume of the activated carbon. 

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