1. Explain why the shrinkage equation derived from a two-particle model cannot be applicable to the prediction of the shrinkage of a real powder compact with a particle size distribution.
2. At the final stage of sintering, the densification of a powder compact occurs by both lattice and grain boundary diffusion. With an increased sintering time, which mechanism is more important for densification? Is it possible to get an answer from Herring's scaling law? Assume negligible grain growth.