Implications of Sintering Theories with Regard to Process Controls

Abstract

In sintering, powder compacts are consolidated into strong, dense products by heating at high temperatures. Changes in compact structure take place under force of surface tension with a rate determined by viscosity, volume-diffusion coefficient, vapour pressure, or surface-diffusion coefficient In cases where solid and liquid are present together, solution and reprecipitation may be the predominant process. For these cases, theoretical analyses and experimental data are compared. It is shown that for different systems (pottery and fireclay, pure oxides, basic refractories, cermets) different sintering-mechanisms predominate. For these mechanisms semiquantitative relationships are developed which confirm the proposed mechanisms and allow a rational analysis of the process kinetics. When different processes are predominant, variables such as temperature, sintering-time, atmosphere, composition, temperature uniformity, material preparation, rate of heating, etc., affect results in different ways. Examples illustrate how a theoretical analysis of the problem and an understanding of the kinetics can lead to better control of these process variables; critical variables in processing are indicated for particular applications.