Intermediate stage of sintering

The model of clusters or ensembles of sites and bonds (secondary supramolecular structure), whose size and structure are determined on the scale of a process under consideration. At this level, the local values of coordination numbers of the lattices of pores and particles, that is, number of bonds per one site, morphology of clusters, etc. are important. Examples of the problems at this level are capillary condensation or, in a general case, distribution of the condensed phase, entered into the porous space with limited filling of the pore volume, intermediate stages of sintering, drying, etc. 

During the intermediate stage of sintering, the porosity is eliminated by the diffusion of vacancies from porous areas to grain boundaries, free surfaces, or dislocations. The uniformity of particle packing and lack of agglomerates are important for the achievement of rapid densification. 

D. L. Johnson, A General Method for the Intermediate Stage of Sintering, J. Amer. 

This concept can also be applied to the intermediate stage of sintering. Coble s intermediate stage model also took the surface area of the pore into account. The kinetic equations based on the two models are, in fact, the same except for the numerical constants. 

Fig. 5.73 Alumina grain size as a function of density. Growth of the alumina grain is significantly impeded by addition of 5 % ztrconia only in the final stage of sintering. In the initial and intermediate stages of sintering, the zirconia particles do not have a measurable effect on grain growth [32]. With kind permission of John Wiley and Sons...

The structure shown in Fig. 8 (hereafter called the cylinder model) has been proposed [28] as a model for the intermediate stage of sintering, during which the pores are interconnected (open to the atmosphere). The structure is represented by a unit cell with edge length /. The relative density is... 

Figure 3.5. Diagram of the porosity in the form of inter-connected canals along the edges of a polyhedron with 14 faces, typical of the intermediate stage of sintering [GER 96]...

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