Highly dense and fine-grained SiC with a Sc-nitrate sintering additive

To explain the sintering behavior of 5 wt.% Sc-nitrate-added SiC, which showed a 99.3% density with the fine 156 nm-sized grains, a microstructural study using high resolution electron microscopy (HREM) was performed and the results were compared with those of Tm-added SiC, which had a mean grain size of 753 nm. Contact flattening was proposed as a governing sintering mechanism for Sc-added SiC based on the experimental observations of an inter-granular phase thinner than 1 nm along with the straight grain boundaries. On the other hand, the Tm-added SiC showed a several nm-thick inter-granular phase with a curved grain boundary morphology, which is the typical microstructure that can be obtained by a solution-reprecipitation mechanism combined with Ostwald ripening.