Enhancing thermal conductivity of epoxy-based composites at low temperatures by Si3N4 binary fillers

The packaging structure with efficient heat conduction and dissipation is the key to ensuring rapid cooling and heat dissipation for superconducting magnets. However, as the most common encapsulated adhesive, epoxy resin has an extremely low thermal conductivity at low temperatures (< 0.1 W/(m·K) at 77 K), which can no longer meet the demands of future superconducting technology. In this work, a high-thermal-conductivity dielectric epoxy composite was obtained by using binary fillers consisting of α- and β-silicon nitride (Si 3 N 4 ) as a reinforcement. Compared to the unitary filler system, the binary filler system can generate a more efficient thermal conduction pathway inside the composites. The results demonstrated that at a binary filler content of 60 wt%, the Si 3 N 4 -2/EP composite (α-Si 3 N 4 : β-Si 3 N 4  = 2: 8) exhibited a 687.8% increase in thermal conductivity at room temperature (RT) and a 3266% increase at low temperature (77 K) compared to neat epoxy. Over the temperature range of 77–293 K, the Si 3 N 4 -2/EP composite exhibited an average coefficient of thermal expansion (CTE) as low as 14.1 × 10 –6 ·K −1 , which was reduced by 63%. This work provides a promising strategy for obtaining high thermal conductivity encapsulation materials for superconducting magnets.