The Effect of Graphite Addition on Thermal Conductivity, Microstructure, and Electrochemical Impedance Spectroscopy of AlN Ceramics

Graphite/ aluminum nitride (AlN) multiphase ceramics are pressureless sintered under 1850°C using Dy 2 O 3 and CaF 2 as sintering additives. The effects of added graphite on microstructure, thermal conductivity, and electrochemical impedance spectroscopy of AlN ceramics were investigated. It was found that with 1wt% graphite addition the thermal conductivity of AlN in the through-plane to can achieve 210W/(m·K), which 25% higher than that of AlN without graphite. The graphite addition eliminates the oxygen impurity in AlN by a carbon reduction reaction in form of nanosized Dy 2 O 3 particles. From electrochemical impedance spectroscopy manifested that the activation energy ( E a,g ) of samples in grains is increased from 0.784 eV to 1.112 eV, suggesting that the concentrations of defects and impurities of Graphite/AlN multiphase ceramics are lower than those of monophase AlN ceramics.