DESIGN, ASSEMBLY AND CHARACTERIZATION OF COMPOSITE ...

Equation 2.3 indicates that the excessive energy per atom in the spherical particle
depends on the inverse of the particle size. Small particles are more energetic. For the flat
surface, however, the chemical potential difference is zero as the surface area remains the
same. In this sense, a concave solid surface tends to fill and a convex surface tends to
flatten, Figure 2.16. In a powder compact consisting of particles and interstitial pores,
sintering eliminates surface curvature. The particles are convex surfaces acting as the
mass sources to fill the interstitial pores that have concave curvature.
Figure 2.16 Effective curvature changes for both convex and concave surfaces with
convergence toward a flat surface. 38
Such mass flow requires high atom mobility, and only becomes significant at an
adequately high temperature, which means that sintering processes are thermally
activated. The Arrhenius equation applies to this process as