Density pressure compaction

Fig. 9. Effect of density, where d is density as compacted and is density as siatered, for (a) particle size and (b) compacting pressure.

Fig. 6.4. At relatively low pressures the shock speeds observed for stress waves in low density powder compacts are dominated by the crush-up of the powder toward solid density. The figure shows measured wavespeeds for a range of densities and fits to the data based on Herrmann s P-a model on Fe. Note the unusually low wavespeeds compared to solid density (after Herrmann [69H02]).

Abnormal Formation Pressures Origin. Four main causes are attributed to abnormal formation pressures compaction effects, diagenetic effects, differential density effects and fluid migration. 

The density-pressure relationship for powder compaction at room temperature typically increases from the apparent density at zero pressnre to values that approach the theoretical density at high pressures, as illustrated in Figure 7.16. A compact with 100% theoretical density would indicate that it contains no porosity. Soft powders are more easily densified than hard powders at a given pressnre, and irregularly shaped powders have lower densities than spherical powders in the low-pressure regime. 

Nomenclature p = pressure applied to compact V = volume of compact at p V0 = volume of compact at zero pressure Vs = solid material volume (void-free) = V/Vs Pa = apparent or bulk density of compact ps = true density of solid material Pr =Pa/Ps my b, alf a2, k, k2 are constants ... 

Heckel, R. W. (1961), Density-pressure relationships in powder compaction, Trans. Met all. Soc. AIME, 221, 671-675. 

TABLE 13.1 Apparent Yield Pressures and Associated Densities for Compaction of Different Ceramic Powders... 

Heckel concluded that density-pressure data indicate the rate of the change of density with pressure, at any pressure, is proportional to the pore fraction in the compact at that pressure. Additionally, density-pressure curves may be described by two parameters. He theorized that one was related to low pressure densification by interparticle motion. The second measured the ability of the compact to densify by plastic deformation after appreciable interparticle bonding. 

Miller s experiments evaluated the effects of powder density, screw feed speed, roll speed, roll pressure, vacuum deaeration pressure, compaction rate, and... 

Typically, displacement measurements during compaction are used to define relationships between compaction force/pressure and the resulting tablet porosity/ density. Heckel plots have been derived from the density-pressure relationship and have been frequently presented in the literature. Fig. 18 is an example of a Heckel plot, where the tablet porosity values are plotted as a function of compaction pressure. The shape of the Heckel plot has been used to describe the type of... 

Comparatively soft powdered substances can be densified by compacting pressures of up to 100 MPa to a relative density of 0.75 at the most and talc materials under pressures of 400 MPa up to 0.94. With micron-sized powders of hard substances, the relative density of compacts is 0,50 - 0.70. These materials can be densified to... 

The density of granules used in tablet production is influenced by the densification of the slugs or compacted ribbon (7-9). To determine the porosity and pore size distribution of a ribbon or granules, mercury intrusion porosimetry may be used. This technique can also be used to evaluate the homogeneity of density/pressure distribution on a compact or granule which in turn affects the characteristics of the final granulation. In addition, gas... 

A new model was compared to known compaction equations, including Kawakita and Heckel, for some mineral salts. Panelli and Filho (2001) concluded that Equation 12 best represents the density-pressure relationship for powders, obtaining a linear correlation coefficient close to the unity. 

Plasma pressure compaction technique was successfully employed to produce a polycrystalline ZrB2-5wt%SiC composite, with a sintered density above 96% of theoretical density, at a temperature of 1750 C and at a pressure of 43 MPa over a short consolidation period of only 5 min. 

The mathematical description of the powder billet SSE cannot rely on the above conditions of plasticity, as they do not take the change in density of the extruded sample into account. Nor the conditions of plasticity used to model the compaction of metal powders are suitable for this case (48). They imply that with the increase in hydrostatic pressure the relative density of powder material tends to unity. However, in the case of hydrostatic compaction of polymer powders, the relative density of compacts tends to a value less than unity, which is typical of the polymer. The reason is in difference of compaction mechanisms for the metal and polymer powders. 

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