The effect of the crystallization of oxidation-derived SiO2 on the properties of porous Si3N4–SiO2 ceramics synthesized by oxidation

Abstract The effect of the crystallization of oxidation-derived SiO 2 on the properties of porous Si 3 N 4 –SiO 2 ceramics synthesized by oxidation was studied over the range of oxidation temperature and time. The SiO 2 remains amorphous at the temperature lower than 1250 °C and starts to crystallize as the temperature rises to 1300 °C. At the temperature higher than 1300 °C, the crystallization of SiO 2 impacts greatly the flexural strength of porous Si 3 N 4 –SiO 2 ceramics. A rapid crystallization of SiO 2 at 1350 °C decreases the bonding strength of the necks between Si 3 N 4 particles, leading to a serious decrease of flexural strength. An appropriate crystallization of SiO 2 at 1300 °C strengthens the bonding necks between Si 3 N 4 particles. The porous Si 3 N 4 –SiO 2 ceramics oxidized at 1300 °C for 3 h show the highest flexural strength value of 82 MPa. The crystallization of SiO 2 has no effect on the dielectric property of porous Si 3 N 4 –SiO 2 ceramics. Porous Si 3 N 4 –SiO 2 ceramics demonstrate a low dielectric constant of 3.0–4.0 and dielectric loss of 3.0–4.0×10 –3 due to their high total porosity and SiO 2 content.