Microstructure and densification mechanism of tabular corundum aggregates: Role of molding methods

Abstract

In this paper, tabular corundum aggregates were prepared using the rolling ball method and semi-dry pressing combined with the cold isostatic pressing method, using industrial alumina raw powder as the raw material and water as the binder, respectively. Then, the influence of various molding methods on phase composition, microstructure, pore characteristics, densification, and physical properties was investigated by X-ray diffraction, scanning electron microscopy, and Archimedes’ principle. The results revealed that tabular corundum aggregates prepared using the rolling ball method had higher bulk density and lower apparent porosity. It also rendered a relatively homogeneous grain size distribution and a high cylinder compressive strength retention rate of 68.0%. The grain size distribution and pore size distribution of tabular corundum aggregates prepared using semi-dry pressing combined with the cold isostatic pressing method were wide, and there were a few large pores, which decreased the strength and densification. Green density was a key factor influencing the sintering; the two molding methods minimized porosity and improved the green density through collision extrusion and external force, respectively. Meanwhile, the molding process also increased the contact points between particles and the material migration channels, which had an impact on the densification mechanism of tabular corundum aggregates.