Dual effects of amorphous SiO2 in ZrO2-SiO2 nanoceramics: Enable viscous flow sintering and inhibit grain coarsening

In this study, we investigated the effects of amorphous SiO 2 on the sintering mechanism and grain coarsening behavior of ZrO 2 nanograins in ZrO 2 –SiO 2 nanocrystalline ceramics (NCCs) during pressureless sintering (PLS). Two NCCs with different ZrO 2 /SiO 2 molar ratios (65%:35% and 50%:50%) were fabricated and subsequently sintered via PLS. Their densification behavior and phase composition were analyzed. The SiO 2 content had a significant effect on the activation of viscous flow sintering. The NCC containing 50 mol% SiO 2 achieved high densification after sintering at 1210 °C, whereas a higher temperature of 1250 °C was required to enable significant densification in the NCC with 35 mol% SiO 2 . The crystallization of ZrO 2 restricted the viscous flow of SiO 2 , thereby impeding the densification process. Hot isostatic pressing did not eliminate the residual pores remaining after PLS. The SiO 2 matrix was capable of inhibiting the coarsening of ZrO 2 nanograins by acting as a diffusion barrier. These findings reveal the dual effects of amorphous SiO 2 during PLS and provide guidance for the fabrication of dense NCCs with minimal grain coarsening.