Thermal conductivity and electrical properties of Al₂O₃-Sn₅₇Bi₄₃/epoxy composites

Constructing thermal conductive pathways in polymer matrix with interconnected high conductive thermal fillers is an effective strategy to enhance the thermal conductivity of the composites. In this paper, eutectic Sn-Bi alloy (Sn₅₇Bi₄₃) nanoparticles are deposited on the surface of Al₂O₃ microspheres by coreduction method to prepare Al₂O₃-Sn₅₇Bi₄₃ hybrids as thermal conductive and electrical insulating fillers for epoxy resin. During the heat curing of epoxy resin, Sn₅₇Bi₄₃ nanoparticles on the Al₂O₃ surface melt and bridge the separate fillers together to form effective thermal conductive pathway, and thus enhance the thermal conductivity of the composites. When filler volume fraction is 60vol%, the thermal conductivity of Al₂O₃-Sn₅₇Bi₄₃/epoxy composites is 2.95 W·(m·K)⁻¹, 62.1% higher than that of Al₂O₃/epoxy composites (1.82 W·(m·K)⁻¹). The results of Fogyel and Agari simulation demonstrate that the deposition of Sn₅₇Bi₄₃ on Al₂O₃ surface reduces the thermal contact resistance between fillers and forms thermally conductive networks more easily. The Al₂O₃-Sn₅₇Bi₄₃/epoxy composites exhibit higher dielectric loss, lower dielectric strength and volume resistivity than Al₂O₃/epoxy composites, still with electrical insulating properties. What is more, the tensile strength of the Al₂O₃-Sn₅₇Bi₄₃/epoxy composites is improved, because the improved interfacial properties of filler-matrix and the formed networks could transfer stress and prevent crack expansion.