Annealing of Fine Powders: Initial Shapes and Grain Boundary Motion

Abstract

This paper describes the evolution of shapes of powder particles during the first stage of sintering, assuming initial spherical shapes. Although this model has been proposed in 1949, it is solved exactly for the first time in the present paper. Several paradigmatic cases are considered, e.g. pure surface transport and pure grain boundary and volume transport, as well as the extensions of the original model to mixed transport. The influence of grain boundary tension forces on the shape of the sinter is also investigated. The new results differ substantially from earlier approximate ones for both small and large neck sizes. Based on these results we propose a new, experimentally testable mechanism for grain boundary annealing in second and third stage sinters.