The influence of magnesium compounds on the properties of silicon nitride ceramics
Yinghua Zhuang, Feng Sun, Lijuan Zhou, Changxi Jiang, Jianjun Wang, Shuang Li, Shengjun Liao
Abstract
Abstract Silicon nitride (Si 3 N 4 ) ceramics using four compound sintering aids Er 2 O 3 –MgO, Er 2 O 3 –MgF 3 , Er 2 O 3 –Mg 2 Si, and Er 2 O 3 –Mg 3 N 2 . The effects of binary sintering aid types and temperatures on the microstructure, mechanical properties, and thermal conductivity of Si 3 N 4 ceramics were investigated. The depolymerization effect of fluorine atoms introduced by MgF 2 sintering additives on the silicate melt structure reduced the viscosity of the liquid phase. However, the existence of volatile phase leads to low density of Si 3 N 4 ceramics. While the additional Si and N atoms increase the concentration of solute atoms, which was conducive to sintering densification of Si 3 N 4 ceramics. Although Mg 2 Si and Mg 3 N 2 sintering aids produced higher viscosity liquid phase compared with MgF 2 , denser Si 3 N 4 ceramics were obtained at 1900°C. The Si 3 N 4 ceramics doped with 5 mol% Er 2 O 3 and 2 mol% Mg 3 N 2 at 1900°C showed the excellent properties: including the highest Vickers hardness (16.8 GPa), flexural strength (912 MPa), and fracture toughness (8.1 MPa m 1/2 ), as well as the desirable thermal conductivity (83 W/(m K)).