Thermally conductive hexagonal boron nitride/spherical aluminum oxide hybrid composites fabricated with epoxyorganosiloxane

Hexagonal boron nitrides (h-BNs) have received much attention as thermally conductive fillers because of their high thermal conductivity. However, their high aspect ratio hampers the realization of high filler loading by dramatically increasing viscosity and deteriorating the processability of the h-BN composites. To address this issue, an epoxyorganosiloxane with the viscosity of 250 mPa s was used to maximize h-BN loading in composites in this study. Although the BN-50 composite containing 50 wt% of h-BN achieved high in-plane thermal conductivity (5.25 W/m·K), its use was limited because of its low through-plane thermal conductivity (1.35 W/m·K) and high viscosity. To overcome this, spherical aluminum oxides (s-AOs) were incorporated into the h-BN composite with 40 wt% fillers. This increased the through-plane thermal conductivity of the h-BN/AO hybrid composites up to 2.47 W/m·K. Moreover, thanks to the spherical shape of AOs, the viscosity of the h-BN/AO hybrid composites was lower than that of the BN-50 composite despite higher filler loading.