The effect of calcium cyanamide (CaCN2) addition on the sintering of AlN ceramics was investigated. Pres sureless sintering was carried out with 0 to 3.0mass% CaCN2 addition, and densified sintered specimens (relative density>97.0%) were obtained using 1.0 to 2.0mass% CaCN2 addition depending on sintering tem perature and time. All of the sintered samples exclusively belong to the same AlN phase, and no other phases were found in the X-ray diffraction (XRD) patterns. A large fraction of intergranular fracture was found in the AlN samples sintered without and with CaCN2 additive in the scanning electron microscope (SEM) ob servations. The characterization of the ultrafine AlN 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 AlN particles and the CaCN2 additive. Most oxygen impurity are removed from AlN as CO or CO2 gas and the residual oxygen impurity reacts to form the 3CaO•EAl2O3 phase, which is found at the grain boundaries.

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Calcium cyanamide (CaCN2) has been used as a sintering aid as well as a dopant for AlN. The effect of CaCN2 addition on the densification behavior and electric properties of liquid-phase sintered AlN ceramics was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), dielectric and electric resistance measurements. Dense sintered specimens (relative density > 97.0%) were obtained using 1.0 to 2.0 wt% CaCN2 additives. With 0.5 to 3.0 wt% added CaCN2 and sintering at 1600 to 1700°C, only the AlN phase was observed in the XRD patterns. In the TEM and electron diffraction (ED) patterns, the minor phase, 3CaO·Al2O3, appeared around the AlN grain boundaries. Based on the SEM observation, the well-faceted grain morphology was considered to be due to a predominant intergranular fracture. The dielectric constant of the AlN specimens were about 8.6 and 8.2 for 150 kHz to 10 MHz, respectively, when the samples were sintered at 1650°C for 1, 3 and 6 h. The electric resistance of the AlN specimens approached 3.87×1012 Ω. The trend of the electric resistance variation in the specimens was the same as that of the linear shrinkage and relative density of the specimens.