Effect of surface nano-modification on the antioxidation properties of Si3N4 ceramics

The application of Si3N4 ceramics is effectively limited due to the catastrophic failure which is caused by the oxidation weight gain. Nano-modification on the surface of Si3N4 micropowders is prepared to reduce the oxidation weight gain of Si3N4 ceramics. After modification, the Si3N4 particles are encapsulated completely by spherical nano-SiO2, which can obviously reduce the oxidation weight gain of the Si3N4 ceramics for the good sealing effect of dense SiO2 coatings. The finally oxidation weight gain rate of the Si3N4 ceramics reduces about 54.3% at 1580 °C. The nano-SiO2 coatings can also increase the surface area of Si3N4 particles, which can improve the sintering extent of the Si3N4 ceramics through accelerating the gradual strengthening of bonding necks between Si3N4 particles. The flexural strength of the Si3N4 ceramics without sintering additives is 78 MPa. The dielectric constant is 3.47 while the dielectric loss is 0.001, which satisfies the dielectric conditions of radomes.