Abnormal shrinkage behavior and sintering mechanism of alumina nanoparticles

Abstract

High temperature and ultrafast heating rate, the characteristics of ultrafast high-temperature sintering (UHS) process, make it difficult to capture the evolution of sintering behavior and explore sintering mechanism of alumina ceramics. In this study, molecular dynamic simulations are adopted to describe the sintering behaviors of equal-sized and unequal-sized alumina nanoparticles, particularly about shrinkage behaviors, microstructure evolution and atomic migration. Results show that high temperature and ultrafast heating rate can yield two different abnormal shrinkage behaviors, accelerating the polymerization of the nanoparticles. The main mechanism for this phenomenon is that high temperature causes the amorphization of crystal structure of nanoparticles, and ultrafast heating rates retain larger sintering driving forces at high temperatures, leading to the reduction of diffusion activation entropy and migration barriers. In particular, the appearance of viscous flow further enhances the shrinkage of the nanoparticles. In addition, surface diffusion is found to dominate the growth of sintering neck during this period. These findings are expected to deepen the understanding of ultrafast high-temperature sintering mechanism.