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Four porous corundum‐spinel aggregates were prepared from magnesia and α‐Al2O3 micropowder via the Kirkendall effect. Effects of the particle size of magnesia (PSM, 0–74 μm, 0–15 μm, and 0–44 μm) and firing temperature (1100–1600°C) on the phase compositions, microstructures, pore characteristics of the prepared porous aggregates were investigated. As the firing temperature increased, the PSM influenced the reaction rate of magnesia and alumina, and the sintering process, leading to remarkable changes in the phase compositions, porosity, and microstructure with a negligible impact on the pore size distribution. As the PSM decreased from 0–74 μm to 0–15 μm, the apparent porosity initially increased and then decreased. Relatively compact cyclic spinels formed around the Kirkendall pores in aggregates with 0–74 μm and 0–44 μm magnesia added after fired at 1600°C, as the expansion of spinel formation was inhibited by the high strength of the alumina matrix. Finally, the optimized product is an aggregate with 0–44 μm magnesia added, which exhibits a high total porosity of 32.4%, a low bulk density of 2.69 g/cm3, and a thermal conductivity of 2.178 W/(m·K) at 1000°C, as well as a high compressive strength of 302.5 MPa and a small median pore size of.46 μm. This work provides a promising technique for preparing porous‐corundum‐based aggregates. [ABSTRACT FROM AUTHOR]

Aluminum oxynitride (AlON) ceramics doped with different sintering aids were synthesized by spark plasma sintering process. The microstructures, mechanical, and optical properties of the ceramics were investigated. The results indicate that the optimal amount of sintering aids is 0.06 wt% La2O3 + 0.16 wt% Y2O3 + 0.30 wt% MgO. The addition of La3+ and Mg2+ decreases the rate of grain boundary migration in ceramics, promotes pore elimination, and inhibits grain growth. The addition of Y3+ facilitates liquid‐phase sintering of AlON ceramics. Moreover, the addition of Mg2+ effectively promotes twin formation in the ceramics, which hinders crack propagation and dislocation motion when the ceramics are loaded. Hence, the AlON ceramic doped with 0.06 wt% La2O3 + 0.16 wt% Y2O3 + 0.30 wt% MgO exhibits a relative density of 99.95%, an average grain size of 9.42 μm, and a twin boundary content of 10.3%, which contributes to its excellent mechanical and optical properties. [ABSTRACT FROM AUTHOR]