On the Theory of the Ceramic Densification Process and of Recrystallization in Colloidal Solutions*

In the theory of the ceramic densification process the starting point is that the material transport consists mainly of diffusion processes. At least three different contributions are however distingutshable : volume diffusion, grain boundary diffusion and surface difksionl. For volume diffusion it has been shown tbeorctica& that in ionic compounds an optimal delusion rate can bc obtained by appropriate controf of the crystal lattice defectz?. In these theories calculations are based upon equilibria and transport of the lattice defects rather than those of the real components. This has the advantage that the methods used are mathematically analogous to those applied to solutions of salts in water. lo demonstrate this we compare a porous crystal of Mg0 with AgCl crystallites in contact with 8 saturated solutionIn MgO we distinguish two types of lattice vacancies V,, and &, with concentrations in accordance with the Schottky equilibrium: _