Study on Enhancing the 4-K Thermal Conductivity of Epoxy Composite

The thermal conductivity of epoxy resin decreases sharply to approximately 0.01 W·m−1·K−1 at 4 K, significantly limiting its application in nuclear fusion engineering. To address this limitation, this study prepared epoxy composite reinforced with silver, diamond, or wollastonite at 50 vol % and 70 vol %, and systematically investigated their 4-K thermal conductivity. The results demonstrated that at 70 vol %, the silver epoxy composite achieved a thermal conductivity of 5 W·m−1·K−1, which is more than two orders of magnitude higher than that of the diamond-epoxy composite (0.05 W·m−1·K−1). At 50 vol %, the silver epoxy composite (0.12 W·m−1 ·K−1) exhibited similar thermal conductivity to the wollastonite epoxy composite (0.1 W·m−1·K−1). Increasing the silver filler from 50 to 70 vol % enhanced the thermal conductivity from 0.12 to 5 W·m−1·K−1, representing a 42-fold improvement.Through combined theoretical analysis, microstructural characterization, and finite element analysis, the following conclusions were drawn. The electron conduction–dominated fillers were the preferred choice for the cryogenic thermal conductivity epoxy composite. In the discrete composite, even the electron conduction–dominated filler could not significantly improve the cryogenic thermal conductivity of the epoxy composite; even 50 vol % silver only reached approximately 0.12 W·m−1 ·K−1. The synergistic effect between the filler type and the distribution (electron conduction–dominated filler combined with continuous filler distribution) can substantially enhance the cryogenic thermal conductivity of the epoxy composite. This work provides technical support for the design of high-performance thermal management materials for superconducting magnet cooling systems in fusion reactors.