Influence of Additives on the Microstructure of Sintered Al2O3

During an investigation to determine the effect of additives in inhibiting exaggerated grain growth, it was observed that several gave strikingly similar microstructures with pore clusters at grain centers surrounded by substantially pore-free annular regions. A few very large pores were found at the grain boundaries and occasionally in the small-pore-free annular regions. The development of this structure is explained as a sequence of exaggerated grain growth followed by normal grain growth. A discontinuous grain-boundary liquid phase facilitates the final grain-growth step and takes part in the coalescence of fine pores into coarse pores.