Microstructures and strengths of microporous MgO–Al ₂ O ₃ ceramics from Al(OH) ₃ and calcined magnesite

Abstract

Abstract Seven microporous MgO–Al 2 O 3 ceramics with an Al 2 O 3 content of 15–90 wt% were prepared using Al(OH) 3 and calcined magnesite as raw materials. A wet mixing process was employed during sample preparation to transform the calcined magnesite with a larger particle size to smaller Mg(OH) 2 particles. The in situ decomposition synthesis method and the Kirkendall effect were utilized to produce and control the pore structure of the microporous MgO–Al 2 O 3 ceramics. There were two kinds of pores in the microporous MgO–Al 2 O 3 ceramics. The first one resulted from the in situ decomposition of Al(OH) 3 and Mg(OH) 2 particles, which were small and equally distributed. Another one originated from the position of the Mg(OH) 2 particles due to the Kirkendall effect caused by MgO diffusion. They were similar in size to the Mg(OH) 2 pseudomorph particles. Simultaneously, the Al 2 O 3 content affected the packing behavior and the spinel formation, which changed the characteristics of the pores and necks among the particles. These mechanisms also affected the strengths of the microporous MgO–Al 2 O 3 ceramics. Thus, when the Al 2 O 3 content was 45–90 wt%, the microporous MgO–Al 2 O 3 ceramics had a high compressive strength (10.0–18.3 MPa) and apparent porosity (52.2%–58.4%).