An Origin for the Apparent Variety in Sintering Mechanisms

A general sintering equation for a single mechanism is developed with respect to ΔL according to Taylor's expansion method, where ΔL is the shrinkage of a powder compact during sintering. The resulting equations indicate that effective shrinkage of the green compact, ΔLi, influences the apparent time dependence, that is, the m-power dependence of ΔL. The n-power dependence of ΔL, defined using a conventional sintering model, appears only in the case where ΔLi<<ΔL. If ΔL<<ΔLi, sintering obeys a kinetic equation of m=1 irrespective of the n value, that is, regardless of the sintering mechanism that contributes to densification. The foregoing evaluation well explains the data that slight pre-sintering of a sinterable Al2O3 powder compact results in an appreciable decrease of the m value. The presently derived equations can be used to estimate the degree of neck growth in a green compact and thus evaluate the quality of sintering data.