A continuum approach to sintering kinetics

Abstract

Sintering is the process by which an initially unconnected collection of particles form bonds at their points of contact resulting in a single, solid framework. As this process proceeds, the relative density increases from that of the initial loose particle stack to a density which may approach that of the solid material. The material rearrangement which is necessary for densification is driven by a surplus of energy associated with the excess of free surface area in the material and also by the particular arrangement of this free surface. A continuum theory for granular (or porous) materials is proposed to describe the kinetics of sintering. The stresses which promote densification of the material are quantified in terms of two microstructural parameters associated with a granular material: the specific surface area and the mean curvature of the void-solid interface. The theory was applied to two materials which can be sintered: copper and snow. In the case of copper, the microstructural data were available and the stresses induced in the material as it sintered could be evaluated. In the case of snow, the microstructural data were not available so only an estimate of the stresses induced in snow as it sinters was found. The application of the theory to copper gave very good results. This indicates that the proposed theory is an accurate representation of the processes that occur in a material as it sinters. The result of applying the theory to snow indicates that the stresses produced by sintering are of comparable magnitude to other stresses found in a natural snowpack.