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

Abstract

Abstract:The Al-Al 2 O 3 -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 1700°C for 5 h under a flowing N 2 atmosphere using the reaction sintering method. After sintering, the Al-Al 2 O 3 -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 MgAl 2 O 4 . 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, Al 2 O 3 , 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-Al 2 O 3 -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-Al 2 O 3 -MgO composites were soaked at 580°C for an extended period, aluminum metal was transformed into AlN. With increasing temperature, Al 2 O 3 diffused into AlN crystal lattices and formed AlN-polytypoids; however, MgO reacted with Al 2 O 3 to form MgAl 2 O 4 . When the temperature was greater than (1640 ± 10)°C, AlN diffused into Al 2 O 3 and formed spinel-structured AlON. In situ MgAlON was acquired through a solid-solution reaction between AlON and MgAl 2 O 4 at high temperatures because of their similar spinel structures.

Magnesium Doped Hercynite: Preparation and Formation Mechanism

“…As Tong et al [22] recently reported, because for the above reaction: ΔG = − 23604 − 5.91T, and under increasing temperature: ΔG < 0, thus MgO reacts with Al2O3, forming MgAl2O4, and hence the MgAl2O4 spinel content also increases. Given that Mg-containing spinel has similar elemental compositions and that their crystal boundaries can be partly fused together, they are impossible to distinguish in SEM images, as confirmed by the XRF results in Table. 1.…”

Combustion Synthesis of Magnesium-Aluminum Oxynitride MgAlON with Tunable Composition

“…Of particular interest in recent years is the relatively new material magnesium-aluminum oxynitride (MgAlON) [ 8 , 9 , 10 , 11 ], which lies within the AlN-Al 2 O 3 -MgO ternary phase diagram and is an infinite solid solution of spinel and AlON. The synthesis of MgAlON is typically accomplished using the same methods employed for AlON powder synthesis.…”

“…The synthesis of MgAlON is typically accomplished using the same methods employed for AlON powder synthesis. The main methods for obtaining MgAlON include solid-state reaction [ 8 , 9 , 11 , 12 , 13 , 14 , 15 , 16 ] and the carbothermal reduction of Al 2 O 3 in a nitrogen atmosphere [ 17 , 18 , 19 , 20 ]. In the solid-state reaction method, mixtures of AlN, Al 2 O 3 , and MgO powders are placed in a high-temperature furnace, and synthesis is carried out at temperatures above 1700 °C for several hours.…”