Preparation of Large-Sized Flaky Al2O3 for Thermally Conductive Fillers and Its Formation Mechanisms

Combining large-sized flaky alumina and spherical alumina as thermally conductive fillers in thermal management materials can effectively establish heat-conducting pathways and significantly increase the system’s heat conduction value. Conventional preparation processes typically produce flaky alumina with a small size and a low diameter-to-thickness ratio, often failing to meet the requirements for applications as thermally conductive fillers. By combining the conventional molten salt method with gas-phase fluoride ions, this study produced large-sized, flaky α-Al2O3 with a diameter ranging from 10 to 50 μm, a thickness of 200–500 nm, and a diameter-to-thickness ratio between 80 and 150. This study revealed that as the size of the flaky alumina increases, so does the thermal conductivity value, but the viscosity also rises, and the limit filling rate decreases. When 3% of the large-sized flaky alumina was added to the compounded thermal conductive filler system, the thermal conductivity of the gel increased by 25%.