In situ reaction mechanism of MgAlON in Al-Al2O3-MgO composites at 1700A°C under flowing N2

The Al-Al2O3-MgO composites with added aluminum contents of approximately 0wt%, 5wt%, and 10wt%, named as M-1, M-2, and M-3, respectively, were prepared at 1700A degrees C for 5 h under a flowing N-2 atmosphere using the reaction sintering method. After sintering, the Al-Al2O3-MgO composites were characterized and analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results show that specimen M-1 was composed of MgO and MgAl2O4. Compared with specimen M-1, specimens M-2 and M-3 possessed MgAlON, and its production increased with increasing aluminum addition. Under an N-2 atmosphere, MgO, Al2O3, and Al in the matrix of specimens M-2 and M-3 reacted to form MgAlON and AlN-polytypoids, which combined the particles and the matrix together and imparted the Al-Al2O3-MgO composites with a dense structure. The mechanism of MgAlON synthesis is described as follows. Under an N-2 atmosphere, the partial pressure of oxygen is quite low; thus, when the Al-Al2O3-MgO composites were soaked at 580A degrees C for an extended period, aluminum metal was transformed into AlN. With increasing temperature, Al2O3 diffused into AlN crystal lattices and formed AlN-polytypoids; however, MgO reacted with Al2O3 to form MgAl2O4. When the temperature was greater than (1640 +/- 10)A degrees C, AlN diffused into Al2O3 and formed spinel-structured AlON. In situ MgAlON was acquired through a solid-solution reaction between AlON and MgAl2O4 at high temperatures because of their similar spinel structures.