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Particles powder

One can see from the formulas (1) and (2) that PT sensitivity strongly depends on the thickness of a developer s layer. But during liquid s penetration into developer s layer the powder particles are sinking and more tightly packing each other. It results in decrease of layer thickness h Physical meaning of the influence of this process upon defect s detection is obvious as follows. [Pg.614]

The simplest way of introducing Che pore size distribution into the model is to permit just two possible sizes--Tnlcropores and macropotes--and this simple pore size distribution is not wholly unrealistic, since pelleted materials are prepared by compressing powder particles which are themselves porous on a much smaller scale. The small pores within the powder grains are then the micropores, while the interstices between adjacent grains form the macropores. An early and well known model due to Wakao and Smith [32] represents such a material by the Idealized structure shown in Figure 8,2,... [Pg.68]

To be specific let us have in mind a picture of a porous catalyst pellet as an assembly of powder particles compacted into a rigid structure which is seamed by a system of pores, comprising the spaces between adjacent particles. Such a pore network would be expected to be thoroughly cross-linked on the scale of the powder particles. It is useful to have some quantitative idea of the sizes of various features of the catalyst structur< so let us take the powder particles to be of the order of 50p, in diameter. Then it is unlikely that the macropore effective diameters are much less than 10,000 X, while the mean free path at atmospheric pressure and ambient temperature, even for small molecules such as nitrogen, does not exceed... [Pg.77]

In non-reactive conditions concentrations in the gaseous phase might be expected to vary significantly only over distances large compared with the powder particle size, and consequently it should be possible to define... [Pg.78]

There are three basic forms of abrasives grit (loose, granular, or powdered particles) bonded materials (particles are bonded iato wheels, segments, or stick shapes) and coated materials (particles are bonded to paper, plastic, cloth, or metal). [Pg.9]

All materials are white powders. Particle sizes range from 1—10 p.m. [Pg.459]

In sintering, the green compact is placed on a wide-mesh belt and slowly moves through a controlled atmosphere furnace (Fig. 3). The parts are heated to below the melting point of the base metal, held at the sintering temperature, and cooled. Basically a solid-state process, sintering transforms mechanical bonds, ie, contact points, between the powder particles in the compact into metallurgical bonds which provide the primary functional properties of the part. [Pg.178]

Shape. Metal powder particles are produced in a variety of shapes, as shown in Figure 4. The desked shape usually depends to a large extent on the method of fabrication. Shape can be expressed as a deviation from a sphere of identical volume, or as the ratio between length, width, and thickness of a particle, as weU as in terms of some shape factors. [Pg.179]

Fig. 4. Shapes of metal powder particles (a) spherical (b) rounded (c) angular (d) acicular (e) dendritic (f) kregular (g) porous and (h) fragmented. Density. The density of a metal powder particle is not necessarily identical to the density of the material from which it is produced because of... Fig. 4. Shapes of metal powder particles (a) spherical (b) rounded (c) angular (d) acicular (e) dendritic (f) kregular (g) porous and (h) fragmented. Density. The density of a metal powder particle is not necessarily identical to the density of the material from which it is produced because of...
Surfa.ce, Any reaction between two powder particles starts on the surface. The amount of surface area compared to the volume of the particle is, therefore, an important factor in powder technology. The particle—surface configuration, whether it is smooth or contains sharp angles, is another. The particle surface area depends strongly on the method of production, as shown in Table 1. The method of production usually determines the particle shape. [Pg.180]

Table 1. Particle Shapes and Surface Areas of Fabricated Powder Particles ... Table 1. Particle Shapes and Surface Areas of Fabricated Powder Particles ...
Particle Activity. Particle activity determines the type and rate of the reaction of a powder particle with its environment. [Pg.180]

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. [Pg.181]

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. [Pg.181]

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). [Pg.181]

Flow. The free flow of a powder through an orifice depends on the orifice which is standardized for the testing of the powder (14). Flow, therefore, depends not only on friction between powder particles, but also on friction between the particles and the wall of the orifice. Flow is usually expressed by the time necessary for a specific amount of powder (usually 50 g) to flow through the orifice. [Pg.181]

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. [Pg.181]

The manufacture of metal in powder form is a complex and highly engineered operation. It is dominated by the variables of the powder, namely those that are closely connected with an individual powder particle, those that refer to the mass of particles which form the powder, and those that refer to the voids in the particles themselves. In a mass of loosely piled powder, >60% of the volume consists of voids. The primary methods for the manufacture of metal powders are atomization, the reduction of metal oxides, and electrolytic deposition (15,16). Typical metal powder particle shapes are shown in Figure 5. [Pg.181]

Fig. 5. Metal powder particle shapes (a) atomized copper (b) sponge iron and (c) atomized iron. Fig. 5. Metal powder particle shapes (a) atomized copper (b) sponge iron and (c) atomized iron.
Lubricants protect die and punch surfaces from wear and bum-out of the compact during sintering without objectionable effects or residues. They must have small particle size, and overcome the main share of friction generated between tool surfaces and powder particles during compaction and ejection. They must mix easily with the powder, and must not excessively impede powder flow (see Lubrication and lubricants). [Pg.185]

Sintering. Basically a soHd-state process, sintering transforms compacted mechanical bonds between the powder particle into metallurgical bonds (23,34—38). [Pg.185]

Liquid-Ph se Sintering. Sintering ia the Hquid state refers to the sintering of a powder mixture of two or more components, of which at least one has a melting temperature lower than the others. The sintering temperature is then selected ia such a manner that a Hquid phase is formed ia which the soHd powder particles of the other components rearrange. A high density powder compact is the result. [Pg.186]

Another method for direct precipitation of cellulose acetate powder suitable for extmsion into plastics is described (90). The reaction solution is precipitated with dilute aqueous acetic acid at 80—85°C in the presence of a coagulant such as isopropyl acetate. The resulting powder particles have a higher bulk density and absorb plasticizers more readily than powders obtained by the usual methods. [Pg.254]


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See also in sourсe #XX -- [ Pg.153 , Pg.155 , Pg.206 , Pg.207 , Pg.208 , Pg.209 , Pg.212 , Pg.214 , Pg.217 , Pg.220 , Pg.221 , Pg.222 , Pg.223 , Pg.228 , Pg.229 , Pg.295 , Pg.319 , Pg.320 , Pg.323 , Pg.357 ]

See also in sourсe #XX -- [ Pg.1139 ]




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