Packing density of powder

Size, Particle Size Distribution, and Packed Density of Powdered Materials , MIL-STD-1233 (March 1962) 3) Anon, EngDesHdbk, Pro-... 

MIL-STD-1233 — Procedure for Determining Particle Size Distribution and Packing Density of Powdered Material MIL-STD-1235 — Single and Multilevel Continuous Sampling Procedures and Tests for Inspection by Attributes 2.2 Other Publications See Spec, pp 1 2 3. REQUIREMENTS... 

Diffuse reflectance technique is used for powders and solid samples having rough surface such as paper, cloth. In diffuse reflectance technique, particles size, homogeneity, and packing density of powdered samples play important role on the quality of spectrum. A sample with smaller particle size having narrow size distribution is preferred. Thus, in order to obtain a qualified spectrum, the sample should be ground into smaller size. 

The bulk factor (i.e. ratio of the density of the moulding to the apparent powder density) of powder is usually about 2-3 but the high-shock grades may have bulk factors of 10-14 when loo.se, and still as high as 4-6 when packed in the mould. Powder grades are quite easy to pellet, but this is difficult with the fabric-filled grades. 

From isotherm measurements, usually earried out on small quantities of adsorbent, the methane uptake per unit mass of adsorbent is obtained. Sinee storage in a fixed volnme is dependent on the uptake per unit volume of adsorbent and not on the uptake per unit mass of adsorbent, it is neeessary to eonvert the mass uptake to a volume uptake. In this way an estimate of the possible storage capacity of an adsorbent can be made. To do this, the mass uptake has to be multiplied by the density of the adsorbent. Ihis density, for a powdered or granular material, should be the packing (bulk) density of the adsorbent, or the piece density if the adsorbent is in the form of a monolith. Thus a carbon adsorbent which adsorbs 150 mg methane per gram at 3.5 MPa and has a packed density of 0.50 g/ml, would store 75 g methane per liter plus any methane which is in the gas phase in the void or macropore volume. This can be multiplied by 1.5 to convert to the more popular unit, V/V. 

Brown et al. [494] developed a method for the production of hydrated niobium or tantalum pentoxide from fluoride-containing solutions. The essence of the method is that the fluorotantalic or oxyfluoroniobic acid solution is mixed in stages with aqueous ammonia at controlled pH, temperature, and precipitation time. The above conditions enable to produce tantalum or niobium hydroxides with a narrow particle size distribution. The precipitated hydroxides are calcinated at temperatures above 790°C, yielding tantalum oxide powder that is characterized by a pack density of approximately 3 g/cm3. Niobium oxide is obtained by thermal treatment of niobium hydroxide at temperatures above 650°C. The product obtained has a pack density of approximately 1.8 g/cm3. The specific surface area of tantalum oxide and niobium oxide is nominally about 3 or 2 m2/g, respectively. 

The bulk density of a powder is calculated by dividing its mass by the volume occupied by the powder (Abdullah Geldart, 1999). Tapped bulk density, or simply tapped density, is the maximum packing density of a powder achieved under the influence of well-defined, externally applied forces (Oliveira et al., 2010). Because the volume includes the spaces between particles as well as the envelope volumes of the particles themselves, the bulk and tapped density of a powder are highly dependent on how the particles are packed. This fact is related to the morphology of its particles and such parameters are able to predict the powder flow properties and its compressibility. 

Parallel investigations of amorphous silica and quartz were executed by Stober (173, 218, 219, 225) with many reactions. No essential difference in reaction behavior and in the packing density of the surface groups was observed. Of course, quantitative measurements were not as accurate with quartz powder as with high surface area Aerosil. 

The constitutive equation for a dry powder is a governing equation for the stress tensor, t, in terms of the time derivative of the displacement in the material, e (= v == dK/dt). This displacement often changes the density of the material, as can be followed by the continuity equation. The constitutive equation is different for each packing density of the dry ceramic powder. As a result this complex relation between the stress tensor and density complicates substantially the equation of motion. In addition, little is known in detail about the nature of the constitutive equation for the three-dimensional case for dry powders. The normal stress-strain relationship and the shear stress-strain relationship are often experimentally measured for dry ceramic powders because there are no known equations for their prediction. All this does not mean that the area is without fundamentals. In this chapter, we will not use the approach which solves the equation of motion but we will use the friction between particles to determine the force acting on a mass of dry powder. With this analysis, we can determine the force required to keep the powder in motion. 

Jenike developed the idea that no single line represents the yield but rather a curve called the yield locus. The yield behavior depends on the packing density of the powder when it is caused to flow under the action of normal and shear stress. Figure 12.36 shows a yield locus for a given porosity, e. A Mohr circle for the stage when yielding starts is characterized by the principal stresses i and 2-The points at the end of the yield locus lies on the Mohr circle pertains to... 

A 10% volume SiC ethanol suspension Dg = 0.3 pm cr = 2) is slip cast with a conical plaster of Paris mold to make a radome for an airplane. The pores in the mold are 50 pm in diameter and the permeability of the mold is negligible compared to that of the powder. Determine the time necessary to slip cast a conical green body with a wall thickness of 1.5 cm. Assume that the ultimate packing density of the SiC powder is 80% theoretical. Data for ethanol density 0.7893 gm/cc viscosity 1.2 cP and yi = 24 dynes/cm. 

These observations suggest that the powder is porous with two internal generations of abrogates, each with a packing density of 0.67. In addition, the scale factor S of the first generation of aggregates is... 

Wakeman, R. Packing densities of particles with log-normal size distribution. Powder Technol. 1975, 11, 297-299. 

The characterization of particulate matter and structures of particle systems is still at the beginning of becoming an exact and widely used science. However, a fast growing understanding of the requirements and recent rapid developments in the ability to (automatically) analyze particles and structures of particle systems have led to new insights into the mechanisms that form and modify particles or particle systems. As already indicated above, it may well be that, in the near future, from an automatic scan of a powder and subsequent shape analysis one may be able to compute the initial and final packing densities of that powder. 

Besides the packing density, the pore structures belong to the important properties of particulate structures. They constitute an useful aspect of packed particles, since they control properties such as filtration, permeability, fluid trapping, etc.. Packing structures of powders with continuous size distribution are very complex. The pores in ordered packings of monosized spheres would seem to be the simplest case to study. 

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