Kinetics of Sintering at a Constant Rate of Heating By Yusuke Moriyoshi and Wazo Komatsu.

Abstract

Sintering is an extremely old technology, which has been used since prehistory. However, it is so complicated that a quantitative study just began to start in the 1950's. A theory for sintering in a simple model was separately derived by Frenkel, Kuczynski, Kingery, and Coble. They elucidated the mechanism of material transport in sintering by the rate of interface growth and distance between the centers of two spherical particles. The equation derived was successfully applied to the shrinkage data of powder compacts. Since then, these so-called log-log plots of data have been widely used by many researchers in order to elucidate the mechanisms of the sintering shrinkage.In such a situation, Moriyoshi and Komatsu pointed out that the log-log plot method was not necessarily suitable because of the effect of many factors such as the combined mechanisms of sintering, the size distribution of particles, particle shape, and so on. They reported this in a series of papers (Kinetics of Initial Sintering with Grain Growth, J. Am. Ceram. Soc., 53, No. 12, 621-675 (1970); Analysis of Initial Combined Sintering, Yogyo-Kyokai-Shi, 81 [3], 102-107 (1973); Initial Sintering of Glass, Yogyo-Kyokai-Shi, 82 [8], 426-429 (1974); A Method for Obtaining Surface Diffusion Coefficients from Initial Sintering Data, Yogyo-Kyokai-Shi, 86 [2], 130-136 (1978)), in which they suggested that various processes such as surface and volume diffusion, grain boundary and volume diffusion, and other processes proceeded concurrently during sintering. The above paper was the first one in the series, in which a different method was used to evaluate and to define a sintering mechanism. The paper also served as an important trial encouraging other sintering studies of ceramics.Moriyoshi and Komatsu pointed out that the method of log-log plots was not necessarily reliable and that the decision of a mechanism at the initial stage of sintering should be carried out by the comparison of activation energies obtained from sintering data with those obtained from the tracer diffusion of ions. From these viewpoints, they derived theoretically an equation to obtain activation energies from shrinkage data at a constant rate of heating. As a result, it was shown that activation energies of sintering shrinkage can be simply obtained with precision by using the equation derived. Then, they indicated that the activation energies obtained in the shrinkage data of ZnO, NiO, and Fe2O3 compacts were in good agreement with the values obtained from tracer measurements. Based on these results, they discussed the rate determining steps in the sintering process.This paper not only provides fundamental information to understand sintering processes such as sintering shrinkage, grain growth, and others, but also stimulates the studies concerning solid state reactions, erosion and corrosion of ceramics, creeps associated with ion diffusion, and so on. The study also gave basic information to fabricate ceramic materials.