Agglomeration processes powder compaction

The maltodextrin solids are amorphous, white, or off-white powders or granules, which are non-sweet and odorless. The materials are processed by spray drying, fluidized bed agglomeration, and roller compaction to improve their handling properties. Maltodextrins are hygroscopic above 50% RH and need to be stored below... 

The major variables which determine sinterability and the sintered microstructure of a powder compact may be divided into two categories material variables and process variables (Table 1.1). The variables related to raw materials (material variables) include chemical composition of powder compact, powder size, powder shape, powder size distribution, degree of powder agglomeration, etc. These variables influence the powder compressibility and sinterability (densification and grain growth). In particular, for compacts containing more than two kinds of powders, the homogeneity of the... 

Note that the fractal DLCA-like aggregates which are generated in the flame frequently agglomerate to large, micrometre-sized clusters. This may either occur during the combustion process or later when the pyrogenic powders are stored in silos or big packs (Kammler et al. 2004 Tsantilis and Pratsinis 2004 Ibaseta and Biscans 2010). These agglomerates are relatively compact with fractal dimensions of 2.5. 

This observation has important implications on the mechanism of agglomerate formation, since, during compaction, points of surface contact will increase together with interparticle attractive forces, and supports practical experience that more elastic agglomerates, such as those formed from phthalocyanines, are usually more difficult to disperse [3]. Powder compaction is relevant to many processing industries and has been considered with other material forms such as coal [4]. 

Kawashima Y, Imai M, Takeuchi H, Yamamoto H, Kamiya K, Hino T. Improved flowability and compactibility of spherically agglomerated crystals of ascorbic acid for direct tabletting designed by spherical crystallization process. Powder Technol. 2003 130,... 

A fundamental requirement in powder processing is characterization of the as-received powders (10—12). Many powder suppHers provide information on tap and pour densities, particle size distributions, specific surface areas, and chemical analyses. Characterization data provided by suppHers should be checked and further augmented where possible with in-house characterization. Uniaxial characterization compaction behavior, in particular, is easily measured and provides data on the nature of the agglomerates in a powder (13,14). 

Chemical engineers could also work to devise processes to improve the flow characteristics of powders after they are formed. Such research would help control agglomeration of particles in subsequent processing steps as well as facilitate the production of compacted ceramic preforms. For example, gas-solid chemical reactions might be used to tailor the chemical composition of powders. As another example, better methods of componnding powders with binders might be achieved by processes that mix powders with suitable binders in a liquid and then spray dry the resulting suspension. 

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