Melt agglomeration solid fine particles

Sintering is essentially a process in which fine particles, which are in contact with each other, agglomerate when heated to a suitable temperature roughly one-half to two-thirds of the melting temperature. At this temperature, the crystallite faces display disorder, which enables rapid surface diffusion. The body of the powder remains solid while the surfaces become slippery. This agglomeration is accompanied by a decrease in the porosity and an increase in the bulk density of the mass. Simultaneously, there is a reduction in surface area and surface free energy, and hence a reduction in the total free energy of the system itself. 

Often, the process is characterized by conversion of a liquid feed (solution, suspension, or melt) into a granular product whereby the liquid is sprayed on or into a fluidized layer of primary particles. Sometimes the liquid is only a binder and, therefore, is introduced in small amounts together with or without finely divided solids. While in the first case growth occurs chiefly by layering, random agglomeration by coalescence prevails in the second. 

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