Particle density, compression/compaction

The foUowing variables can affect a material s bulk density. (/) Moisture higher moisture content often makes a material mote compressible. (2) Particle size and shape often, the finer the bulk soHd, the mote compressible it is. The shape of the particles can affect how they fit together and thein tendency to break while being compacted. (3) Temperature some materials become mote compressible as thein temperature increases. This could be due, for example, to softening of the particles. (4) Particle elasticity elastic materials tend to deform significantly when they ate compressed. 

The majority of active pharmaceutical agents are administered as tablets, and as a result the characterization of compact species is of great interest to formulators. During the compression step, a variety of particle-particle interactions take place, which ultimately lead to the formation of a stable entity. One may envision that the compaction process results in such consolidation of the input solids that the final density of the tablet approaches the true density of the component materials. 

For most ceramic pressing, a CR < 2.0 is desired since it rednces both the punch displacement and the compressed air in the compact. As indicated in Eq. (7.15), a high fill density leads to a low CR. For comparison, the CR in metal powder pressing is typically much greater than 2.0 dne to the dnctility of the particles. 

There are three definitions needed to accurately describe this process. (1) Compaction is the compression and consolidation of a two-phase (particulate solid/gas) system by the application of an external force (2) compression causes an increase in the apparent density (or a reduction in volume) by the displacement of air and (3) consolidation is defined as an increase in mechanical strength due to particle-particle interaction [1,2]. 

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