Microstructure tailoring of high thermal conductive silicon nitride through addition of nuclei with spark plasma sintering and post-sintering heat treatment

High thermal conductive β-silicon nitride (β-Si₃N₄) ceramics were fabricated from fine α-Si₃N₄ powder as the raw material and coarse β-Si₃N₄ particles as the nuclei through spark plasma sintering (SPS) at 1650 °C for 5 min and post-sintering heat treatment at 1900 °C for 4 h. The microstructures of the sintered β-Si₃N₄ ceramics could be tailored with the nuclei. The mean sizes and frequencies of large grains increased and consequently decreased as the increased amount of coarse β-Si₃N₄ particles increased. The thermal conductivity of the sample with 10 mol% of β-Si₃N₄ nuclei reached a maximum value of 84.6 W m⁻¹ K⁻¹. These results revealed that the thermal conductivity of β-Si₃N₄ ceramics was independent of the grain size and controlled by the amount of reprecipitated large grains.