Solid bridge forces

In these methods of size enlargement, powders are densified and compacted by application of external force in a confined space. Forces involved to produce a stable agglomerate include solid bridges, immobile liquid bonds, surface forces and mechanical interlocking. The success of the operation depends in part on the effective utilization and transmission of the applied external force and in part on the physical properties of the particulate material. 

In other cases (Figure 14d), the particles in an agglomerate must not contact each other and solid bridges do not exist either. Then, bonding is caused by adhesion forces such as molecular forces, e.g. van der Waals or valence forces, and electrostatic or magnetic forces. 

With exception of capillary and matrix bonded structures of partiadate solids, it is unlikely that only one binding mechanism acts on all the coordination points within a mass. If molecular and electric forces as well as liquid bridges and the solid bridges, resulting from the latter by one or the other of the mechanisms that were discussed above, are considered, it must be assumed that the effect of each binding mechanism is different at essentially every coordination point due to varying microscopic surface structures and distances at each interaction point (see also Section 5.2.1). 

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