Effect of Al2O3 with Different Nanostructures on the Insulating Properties of Epoxy-Based Composites.

High thermal conductivity insulating dielectrics with good electrical properties have received widespread attention due to the continuous development of power systems and power electronic technologies. In this paper, the effects of differently structured nano alumina fillers on the thermal conductivity and insulating properties of polymer-based composites were studied. It was found that all three types of Al2O3 nano-fillers enhanced the thermal conductivity of the composites, and the thermal conductivity increased more dramatically with increasing filler particle size. It is worth noting that Al2O3 nanowires (NWs) exhibited the most significant improvement in thermal conductivity. The volume resistivity of the composites first increased and then decreased with increasing mass fraction of fillers, and Al2O3 nanoplates (NPLs) showed the most significant improvement in the insulation performance of the composites. The dielectric constants of the composites increased with increasing mass fraction of fillers, while the dielectric losses first decreased and then increased with the same trend, yet the mass fractions of fillers for the three materials were different when the dielectric loss reached a minimum. In addition, all three types of filler increased the AC breakdown strength of the composites, but Al2O3-NPLs showed the most significant improvement on the breakdown performance of the composites.