Porous Al ₂ O ₃ –MgAl ₂ O ₄ foam ceramics with ultra‐high porosity and secondary pores via particle‐stabilized foaming method

Abstract In this work, porous Al 2 O 3 –MgAl 2 O 4 foam ceramics with ultra‐high porosities (92.8%–95.7%), high strength, and excellent thermal shock resistance were fabricated by particle‐stabilized foaming method. The effects of theoretical content of in situ formed spinel (0, 25, 50, and 75 wt.%) on the microstructure, pore characteristics, and mechanical properties of the foam ceramics were investigated. The introduction of nano‐Mg(OH) 2 powder remarkably promoted the development and growth of spinel grains in the foam ceramics, owing to the porous MgO pseudomorph from the decomposition of Mg(OH) 2 . A large number of nanopores (i.e., secondary pore structures) can be constructed on the cell wall surfaces of the foam ceramics, due to the generation of the spinel phase accompanied by the volume expansion and Kirkendall effect. The appropriate addition of nano‐Mg(OH) 2 powder led to the formation of spinel neck connections between Al 2 O 3 grains, which significantly enhanced the strength and thermal shock resistance of the foam ceramics. Overall, when the theoretical content of in situ formed spinel was 25 wt.%, the porous Al 2 O 3 –MgAl 2 O 4 foam ceramics exhibited an ultra‐high porosity of 93.50%, a high cold compressive strength of 0.67 MPa and an excellent thermal shock resistance. The cell walls were characterized by single‐layer grains (thickness of about 1 µm) with nanoscale secondary pore structures on their surfaces.