Thermal behavior, electrical conductivity and microstructure of hot pressed Al2O3/SiC nanocomposites

Functional properties (e.g. thermal and electrical conductivity) of polycrystalline alumina ceramics can be modified by the addition of second phases, such as silicon carbide nanoparticles, carbon nanotubes or nanofibers, or graphene sheets. In this work we studied the influence of SiC particles addition on the DC electrical and thermal conductivity of the Al2O3/SiC micro/nanocomposites both at room and elevated temperatures. The composites with high relative density and with various volume fractions of SiC ranging from 3 vol% to 20 vol% were prepared by hot pressing at 1740 °C and at 30 MPa pressure in the atmosphere of argon. The influence of the volume fraction and the size of SiC particles (two different powders with the mean size of SiC particles 40 and 200 nm were used), and final microstructure of the composites on thermal and electrical conductivity were evaluated. The properties of the composites were compared to the monolithic Al2O3 reference. The microstructure of the composites was significantly affected by the volume fraction of SiC, with the mean size of alumina matrix grains decreasing with increasing content of SiC particles. The maximum of room temperature thermal conductivity was measured in the composites with 20 vol% of SiC (38 W/m K), irrespective of the granulometry of the used SiC powder. The DC electrical conductivity increased with increasing volume fraction of SiC. The highest electrical conductivity 4.05×10−2 S/m was measured in the composites containing 20 vol% of SiC, in comparison to the electrical conductivity of the monolithic alumina reference, which was by four orders of magnitude lower. No statistically significant difference in thermal or electrical conductivity was found between the composited with different granulometry, but identical content of SiC.