Influence of SiO2 addition on the sintering behavior and kinetics of fine-sized α-Al2O3 nanoparticles

Abstract

Due to the low solubility of Si in Al2O3, SiO2 additives/impurities can segregate at grain boundaries, altering the grain boundary kinetic behaviors in Al2O3 and inducing the abnormal grain growth of Al2O3—which also makes preparing high-density SiO2-doped Al2O3 sintered samples with uniform microstructures difficult during free sintering. Almost all the work thus far has focused on analyzing the reason for the abnormal grain growth of Al2O3 induced by SiO2, while the effect of SiO2 on the sintering behaviors and/or grain boundary kinetics of Al2O3 is less studied. Here, using homemade 15 nm dispersed α-Al2O3 nanoparticles as a raw material, we systematically investigated the effect of SiO2 additives on the sintering behaviors (including densification and grain growth) and kinetics (including grain boundary diffusion and grain boundary migration) of high-purity α-Al2O3 nanoparticles. The kinetic results show that doping SiO2 does not change the enthalpic contribution (i.e., activation energy) of α-Al2O3 but significantly reduces its entropic contribution (i.e., preexponent term). Furthermore, based on the explored sintering behaviors combined with two-step free sintering, a dense SiO2-doped Al2O3 nanocrystalline ceramic with an average grain size of 43 nm and ultra-uniform microstructure (the standard deviation of the grain size distribution to the average grain size is only 0.33) was successfully obtained at the optimal sintering parameters.