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

Highlights: • Nano-modification on the surface of Si₃N₄ micro powders is prepared. • The oxidation weight gain reduces about 54.3% at 1580 °C after nano-modification. • The nano-modification can improve the sintering extent of the Si₃N₄ ceramics. • The Si₃N₄ ceramics appear good dielectric properties after nano-modification. 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.