Increased Thermal Conductivity of Liquid-Phase Sintering Silicon Carbide with Ytterbium Oxide and Magnesium Oxide

Using α-SiC powder as a raw material, with ytterbium oxide and magnesium oxide as liquid-phase sintering aids, silicon carbide ceramics were prepared via spark plasma sintering (SPS) at 1900, 2000, and 2050 °C with a 10 min dwell. As the sintering temperature increased, the grain size grew from 0.54 μm to 17.59 μm, while the thermal conductivity correspondingly increased from 122.4 W/(m·K) to 231.8 W/(m·K). Microstructural analyses revealed that elevated sintering temperatures significantly accelerated the dissolution-precipitation process, thereby inducing abnormal grain growth. Grain size is identified as the dominant factor governing the thermal conductivity of SiC ceramics. Larger grains reduce grain boundary density and interfacial thermal resistance, thereby facilitating phonon transport.