Powders particle formation

Maa Y-F, Prestrelski SJ. Biophannm cutical powders Particle formation and formulation considerations. Curr Pharm Biotech 2000 1 283-302. 

Maa, Y.F. and Prestrelski, S.J., Biopharmaceutical powders Particle formation and formulation considerations. Curt Pharm. BiotechnoL, 2000, 1, 283-302. 

Y-F. Maa and S. Prestrelski Biopharmaceutical powders particle formation and formulation considerations. Current Pharmaceutical Biotechnology, 1, 283-302 (2000). 

Increase adhesion tension. Maximize surface tension. Minimize contact angle. Alter surfactant concentration or type to maximize adhesion tension and minimize Marangoni effects. Precoat powder with wettahle monolayers, e.g., coatings or steam. Control impurity levels in particle formation. Alter crystal hahit in particle formation. Minimize surface roughness in milhng. 

Solids appear in one of two forms, either as crystals or powders. The difference is one of size, since many of the powders we use are in reality very fine crystals. This, of course, depends upon the manner in which the solid is prepared. Nevertheless, most solids that we encounter in the real world are in the form of powders. That is, they are in the form of discrete small particles of varying size. Each particle has its own unique diameter and size. Additionally, their physical proportions can vary in shape from spheres to needles. For a given powder, aU grains will be the same shape, but the particle shape and size can be eiltered by the method used to create them in the first place. Methods of particle formation include ... 

First, the breadth of the XRD peaks of p-MgH increases with increasing milling time. As discussed in Sect. 1.4.3, this is related to the formation of crystallites (nanograins) within the powder particles, which may be accompanied by the introduction of lattice strains. Table 2.8 lists nanograin size and lattice strain of P-MgH as a fnnction of milling time estimated from the procedure described in Sect. 1.4.3. 

B. Vigeholm, K. Jensen, B. Larsen, A.S. Pedersen, Elements of hydride formation mechanisms in nearly spherical magnesium powder particles, J. Less-Comm. Metals 131 (1987) 133-141. 

It should be noted that the procedure described in this chapter is strictly limited to the interactions of droplets with surrounding gases, with much emphasis on the conditions that would yield powders of narrow size distributions. However, no attempt is made to describe the literature on particle formation from a single levitated droplet (7). The technique used in these studies also differs from those in which the... 

Since the properties of these particulate materials are basically determined by their mean size, size distribution, external shape, internal structure, and chemical composition, the science in the mechanistic study of particle formation and the fundamental technology in their synthesis and characteristic control may constitute the background for the essential development of colloid science and pertinent industries. Scientists have now learned how to form monodispersed fine particles of different shapes of simple or mixed chemical compositions, and, as a result, it is now possible to design many powders of exact and reproducible characteristics for a variety of uses. These achievements are especially important in the manufacture of high-quality products requiring stringent specification of properties. 

Initial sintering involves rearrangement of the powder particles and formation of a strong bond or neck at the contact points between particles (see Figure 2.31). The relative density of the powder may increase from 0.5 to 0.6 due mostly to an increase in particle packing. 

Formation of free milk fat in DWM powder particles as a result of atomization and drying may also contribute significantly to poor solubility and dispersibility. Free milk fat, which is extractable from the powder by a 50 50 mixture (v/v) of ethyl and petroleum ether (Brunner, 1974), probably coats the powder particles and prevents their rehydration. The physical state of the milk fat, as controlled by the liquid-to-solid ratio and the presence of free milk fat on the particle surface, strongly influences DWM particle dispersibility. Spray coating of DWM particles with lecithin or other surfactants and dispersion in warm water improve their dispersibility. 

Example 12.5. The stabilizing effect of powders was impressively demonstrated by making liquid marbles in air [549], Liquid marbles (Fig. 12.11) are obtained by making a small amount of water (typically 1 mm3) roll on a very hydrophobic powder. The powder particles go into the interface and completely coat it so that, after spontaneous formation of the spherical drop, only the solid caps of powder particles come into contact with the solid support. 

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