Final stage sintering

The elimination of pores comes about by the combined effects of grain growth and Ostwald ripening in the final stages of sintering. 

Figure 2.31 Development of ceramic microstructure during sintering (a) Loose powder particles (b) initial stage (c) intermediate stage and (d) final stage. From W. E. Lee and W. M. Rainforth, Ceramic Microstructures, p. 37. Copyright 1994 by William E. Lee and W. Mark Rainforth, with kind permission of Kluwer Academic Publishers.

Initial powder Initial stage Intermediate stage Final stage Dense polycrystal-compact of sintering of sintering of sintering line compact... 

Chen, I.W., and Wang, X.H., Sintering dense nanocrystalline ceramics without final-stage grain growth , Nature, 2000, 404, 168-71. 

FIGURE 162 Densification of two log-nonnal alumina powders (dg = 1.3 and 0.8 fan) showing the initial, intermediate, and final stages of sintering. Sintering is under constant heating rate conditions tf 7.3°C/min. Data from Reed [1]. 

Since the introduction of a mathematical model for sintering by Kuczynski [12] numerous other models have been proposed. Reviews of these sintering kinetic models are given in references [13—19]. This description of sintering kinetics is organized into initial, intermediate, and final stage kinetic models. 

Solid state sintering was discussed previously in this chapter. The sintering kinetics depend upon the rate determining step, which can be either viscous flow, grain boundary diffusion, or lattice diffusion. These sintering kinetics are summarized in Tables 16.4 and 16.6 for the initial and intermediate stage and Section 16.3.2.3 for the final stage. 

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