Packings apparent density

Apparent Density. This term refers to the weight of a unit volume of loose powder, usually expressed in g/cm (l )- The apparent density of a powder depends on the friction conditions between the powder particles, which are a function of the relative surface area of the particles and the surface conditions. It depends, furthermore, on the packing arrangement of the particles, which depends on the particle size, but mainly on particle size distribution and the shape of the particles. 

Tap Density. Tapping a mass of loose powder, or more specifically, the appHcation of vibration to the powder mass, separates the powder particles intermittently, and thus overcomes friction. This short-time lowering of friction results in an improved powder packing between particles and in a higher apparent density of the powder mass. Tap density is always higher than apparent density. The amount of increase from apparent to tap density depends mainly on particle size and shape (see Table 4). 

Potassium Methylate. Potassium methoxide [865-33-8] KOCH, mol wt 70.13, is a fine, free-flowing, yellowish-white, caustic, hygroscopic powder purity 96.5—99% powder density after loose shaking, 0.75 g/mL apparent density (packing weight), 1.00 g/mL medium grain size, 0.05 —0.8 mm easily soluble in alcohols (33% in methanol at 20°C), insoluble in hydrocarbons. 

The device described in USP 2541334(1951) of C.H- Carey D.R. Walton is intended primarily for expls contg a high proportion of AN and little or no NG. In expls of this kind, as the apparent density is increased (as by hard packing), there is reduction in sensitivity to detonation and decrease in sensitivity by influence. Introduction of an auxiliary expl (booster) compressed to a lesser degree than the main charge assures complete detonation. It also permits the use of insensitive expls (as main charges) which could not be detonated by the cap alone... 

Note 1 As was mentioned in Note 1 under item B the US MIL-STD-650 (Ref 21) does not make any distinction betw Bulk Apparent Densities. It defines them in Method 201.1 as "weight per unit of outside volume, which may include voids in Method 201.2 as "weight per unit of apparent volume and in Method 201.3 as "weight per unit of packed volume , which means that the specimen is dropped and tapped to dispel voids Note 2 Accdg to Ref 13, p 877, "It is not always possible to say whether a given measurement refers to bulk specific gravity, to apparent specific gravity, or to some intermediate value, since the determination of solid volume depends on the nature of the substance used to permeate the voids and on the nature of the pores in the solid ... 

V=Vol occupied by sample Note This density is called in Ref 21, Method 201.3 as "Bulk or Apparent Density , but actually it is "Packed Density", because it is detd after the material has been packed and tapped. Compare with "Bulk Density detn described in previous item (m) and with "packed density detn, described in the next item (o)... 

As mentioned above, the binder/filler ratio determines the fluidity and hence the process technology for a given syntactic composition. The solid line in Fig. 1 shows how the apparent density depends on the relative microsphere concentration in syntactic compounds, provided there are no air inclusions. The lower limit of apparent density is at the concentration at which the filler is most densily packed at this point the material has its highest specific strength (strength per unit apparent density). Experience has shown that the closest packing of the spheres within the binder is obtained when the material is mixed and cast or molded under vacuum 8 10). 

The lowest apparent density, without voids, should be obtained when monodisperse microspheres are packed in the closest possible way. Materials made from large mono disperse microspheres have lower apparent densities than those made from small ones, even though theory indicates that the void depends only on the packing arrangement and not on the particle dimensions. This enigma is resolved by the fact that larger spheres have lower apparent densities (Fig. 4) because they have thinner walls 78,79). If they could be made with thicker walls, the resultant syntactic material would be stronger75>. 

In order to obtain in practice the theoretical highest apparent density of the syntactic foam, the mixture has to be molded at the pressure at which the microspheres pack the closest. Several methods (mold vibration, high molding pressures, etc.) have been recommended as ways of obtaining a syntactic foam density close or equal to y by helping the microspheres pack more closely and thus approach the foam s maximum strength. It should be remembered that ideal packing is never actually achieved and there is always some disorder 80). 

Bulkiness of a packing is defined as the reciprocal of the apparent density, that is, in terms of Eq (6-10)... 

The whole problem of computing pressure distributions in particulate packings is one of great complexity. In addition to the fact that we are unable to deal with a material whose apparent density is not uniform, we must consider added difficulties such as diffusion, sliding friction, deformation of individual particles, cohesive forces, and perhaps others. The quantitative relationships of these factors to particle size must remain empirical for the time being. In the paragraphs to follow we shall be concerned only with a limited theory of the problem of particles under pressure. 

Patten studied the change on heat conductivity C, diffusivity C/Kpy and specific volume (the reciprocal of the apparent density) of various packings with varying moisture contents. Figure 58 shows some of the data obtained by Patten an coarse and line quartz. The curves, with the... 

Bulk density, or packing density, includes all pores and voids (interparticle spaces) in its calculation. It is determined by filling a graduated cylinder, with or without tapping. It follows that the value obtained is dependent upon the form of the catalyst (powder, tablets, extrudates) because of the different contribution of interparticle void space to the pore volume. Tap density is the apparent density of a bed of particles in a container of stated dimensions when a given amount of powder is vibrated or tapped under controlled conditions. The use of the term bulk density should be... 

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

Real Density, Poured (Apparent) Density and Packed Density... 

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