Particle fragmentation

Flow behavior of powders is also of interest in direct compression. It is generally accepted that the flow rate initially increases with particle size, achieves a maximum in the range of 100-400 /um, and then decreases [85]. An excipient that has been well characterized is lactose, which undergoes particle fragmentation when compacted. For a-lactose monohydrate, it has been shown that the... 

Particle fragmentation through collisions will increase surface area. 

Treatments in some gases that lead to the gross modification of particle structure. For example, treatments of supported platinum particles in oxygen lead to particle fragmentation. 

A.D. Salman, M.J. Hounslow, A. Verba, Particle fragmentation in dilute phase pneumatic conveying, Powder Technol. 126 (2002) 109— 115. 

The general tablet compaction process normally is described by a number of sequential phases rearrangement, deformation (elastic, plastic) of initial particles, fragmentation, and deformation of fragments. Particle-surfaces are brought into close proximity and interparticulate attraction or bonds will be formed. Similar conditions will prevail with the effervescent tablets. 

The degree of fragmentation was found to diminish with smaller sieve fractions at the same compression load when several sieve fractions of unmilled crystalline a-lactose monohydrate was used. The authors concluded that particle fragmentation would reduce as porosity approached zero and elastic behavior would start to dominate the consolidation process (43). With a decrease in particle size, yield pressure decreased and the strain rate sensitivity index increased (44) which suggested a reduction in the extent of fragmentation. The transition from brittle to ductile material was thought to occur for a median particle size of around 20 pm (45). 

Duberg M. Nysirom C. Studies on direct compression of tablets VI. Evaluation of methods for the estimation of particle fragmentation during compaction. Acta F arm Suec 1982 19 421-36. 

The narrowing effects could be due to particle fragmentation and the formation of ultrafine particles, with the observed spectral line narrowing being due to UFPNMR. This possibility was discounted as a narrowed spectrum could not be detected when studying the filtrate of a coarsely filtered (one which would allow only submicron particles through into the filtrate) SINNMR suspension. 

Eriksson M, Alderbom G. The effect of particle fragmentation and deformation on the interparticulate bond formation process during powder compaction. Pharm Res 1995 12 1031-1039. 

The fluid particle fragmentation phenomena in a highly turbulent flow are related to the fact that the velocity in a turbulent stream varies from one point to another (i.e., validated by two-point measurements [99]). Therefore, different dynamic normal stresses will be exerted at different points on the surface of the fluid particle. Under certain conditions, this will inevitably lead to deformation and breakage of the fluid particle. 

Particles within the supersaturated region develop in a two-step process nucleatton and growth. Nucleation may proceed spontaneously through the formation of M(OH) entities or be initiated with "seed materials. These are solid impurities such as dust, particle fragments, or rough edges on... 

The inherent ability of the powder to reduce its volume during compression could affect the amount of interparticulate attraction in the final compact. A decrease in compact porosity with increasing compression load is normally attributed to particle rearrangement elastic deformation, plastic deformation, and particle fragmentation. Scanning electron microscopy (SEM) for the qualitative study of volume-reduction mechanisms has been presented in the literature. 

The three attrition mechanisms are in turn governed by different failure modes brittle, semibrittle, and ductile (Ghadiri, 1997). Brittle failure occurs when internal or surface cracks already exist and is dominant at low elastic deformation at the powder contact surface (Shipway and Hutchings, 1993). Semibrittle failure, at limited plastic deformation, is responsible for flaw initiation and occurs when the impact forces surpass the yield point. In fact, median and radial cracks cause particle fragmentation, and lateral cracks cause chipping. Soft materials are usually ductile and the mechanisms for particulate solids under ductile mode have not yet been elucidated (Ghadiri, 1997). 

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