The effects of annealing on thermal and electrical properties of reaction-bonded AlN ceramic

An AlN ceramic sample was prepared using a reaction-bonding technique with Al and AlN powders, together with a very small amount of CaO (a sintering aid), as the starting materials. The effects of annealing at 1800 °C for 10 h in one atmosphere of Ar on the thermal and electrical properties of the ceramic were investigated. After annealing the thermal conductivity of the ceramic increased from 55 to 122 W/mK, while the AC electrical conductivity, measured as a function of frequency, decreased. The difference in AC electrical conductivity before and after annealing gradually increased as the frequency decreased, reaching about one order of magnitude at 0.01 Hz. The composition and microstructure were examined by means of XRD and SEM/EDS. The causes for the improvement in thermal and electrical properties due to the annealing are discussed.