Thermal conductivity of silicon carbide composites with highly oriented graphene nanoplatelets

Dense silicon carbide (SiC)-based composites containing up to 20 vol.% of graphene nanoplatelets (GNPs) were manufactured via a liquid-phase Spark Plasma Sintering (SPS) process, employing Y2O3 and Al2O3 as sintering aids. The applied uniaxial pressure during SPS produced a preferential orientation of the GNPs, with the ab-plane perpendicular to the pressing axis, thus bringing about high thermal anisotropy. Thermal diffusivity/conductivity were measured as a function of the GNPs content, being enhanced by ∼30% in the perpendicular direction to the SPS pressing axis, whereas a moderate decrease was observed in the parallel direction owing to the much lower intrinsic conductivity of the aligned GNPs in the c-axis, with no significant contribution of the thermal resistance of the GNP-SiC interfaces. A non-monotonical temperature dependence for the thermal conductivity was detected in composites containing <10 vol.% GNPs, explained by the strong p-doping of these SiC ceramics.