Bulk hexagonal boron nitride with a quasi-isotropic thermal conductivity

Hexagonal boron nitride (BN) is electrically insulating and has a high in-plane thermal conductivity. However, it has a very low cross-plane thermal conductivity which limits its application for efficient heat dissipation. Here, large BN pellets with a quasi-isotropic thermal conductivity are produced from BN nanosheets using a spark plasma sintering (SPS) technique. The BN pellets have the same thermal conductivity from both perpendicular and parallel directions to the pellet surface. The high quasi-isotropic thermal conductivity of the bulk BN is attributed to a quasi-isotropic structure formed during the SPS process in which the charged BN nanosheets form large sheets in all directions under two opposite forces of SPS compression and electric field. The pellet sintered at 2300 °C has a very high cross-section thermal conductivity of 280 W m−1K−1(parallel to the SPS pressing direction) and exhibits superior heat dissipation performance due to more efficient heat transfer in the vertical direction.