Reaction sintering and microstructural development in the system Al2O3–AlN

The reaction sintering and microstructural development of alumina with additions of 1–25 mol% AlN have been investigated by heating under 1-atm nitrogen gas at 1600–1800°C. Sintering Al2O3 with 1 mol% AlN addition at 1750°C, resulted in a ceramic with close to theoretical density of α-Al2O3 (3.98 g/cm3). For the different compositions, the sintered densities decreased with increasing AlN content. This trend was attributed to the presence of secondary phases such as AlON(9Al2O3·5AlN) and φ(5Al2O3·AlN) formed by reacting Al2O3 with AlN. For a given AlN addition, densification increased with sintering temperature, due to Al2O3 and/or AlON grain growth control. The stability of the individual crystalline phases depends on both sintering temperature and batch composition.