Fabrication of c-axis oriented Si3N4 ceramics using multilayered-graphene-coated β-Si3N4 seeds and their orientation in an innovative low magnetic field

- c-axis oriented Si3N4 ceramic was fabricated by applying a magnetic field of 0.4 T.
- Multilayered-graphene was used for orienting rod-like β-Si3N4 particles.
- Multilayered-graphene was coated by using a mechanical treatment process.
- Thermal conductivity was higher in the c-axis oriented direction.

c-axis oriented Si3N4 ceramics were fabricated by applying a low static magnetic field. Conventionally, c-axis oriented Si3N4 ceramics are fabricated using a rotating magnetic field of over 10 T considering the anisotropy and the magnitude of diamagnetic susceptibility between c- and a-axes. In this work, multilayered-graphene was used for orienting rod-like β-Si3N4 particles as graphene exhibits a high diamagnetic anisotropy. The multilayered-graphene was coated with their orientation on the surface of rod-like β-Si3N4 particles by using a mechanical treatment process. As a result, the c-axis of multilayered-graphene-coated β-Si3N4 particles were oriented parallel direction to the applied magnetic field even at 0.4 T. In addition, c-axis oriented Si3N4 ceramics were fabricated successfully by adding a small quantity of multilayered-graphene-coated β-Si3N4 particles as seeds. The thermal conductivity of the c-axis oriented Si3N4 ceramics prepared with a magnetic field of 0.4 T exhibited anisotropy with a higher value achieved in the c-axis oriented direction.

Graphical AbstractMicrostructures of Si3N4 ceramics prepared at 1 T and sintered at 1900 °C for 6 h in 0.9 MPa N2 observed by using SEM. (a) Plane normal to the magnetic field. (b) Plane parallel to the magnetic field.182