Sintering of ultrafine aluminum nitride powder added with calcium cyanamide

The effect of calcium cyanamide (CaCN2) addition on the sintering of AIN ceramics was investigated. Pressureless sintering was carried out with 0 to 3.0 mass% CaCN2 addition, and densified sintered specimens (relative density > 97.0%) were obtained using 1.0 to 2.0 mass% CaCN2 addition depending on sintering temperature and time. All of the sintered samples exclusively belong to the same AIN phase, and no other phases were found in the X-ray diffraction (XRD) patterns. A large fraction of intergranular fracture was found in the AIN samples sintered without and with CaCN2 additive in the scanning electron microscope (SEM) observations. The characterization of the ultrafine AIN powders sintered with CaCN2 additive was preformed with a microstructural analysis using a transmission electron microscope (TEM) attached with an energy-dispersive X-ray analyzer (EDX) and electron diffraction (ED). Both microstructural results and sintering behavior in the AlN-CaCN2 system arise from the interaction between the Al2O3 surface covering the ultra-fine AIN particles and the CaCN2 additive. Most oxygen impurity are removed from AIN as CO or CO2 gas and the residual oxygen impurity reacts to form the 3CaO . Al2O3 phase, which is found at the grain boundaries.