Microstructures and strengths of microporous MgO–Al2O3 ceramics from Al(OH)3 and calcined magnesite

Abstract

AbstractSeven microporous MgO–Al2O3 ceramics with an Al2O3 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–Al2O3 ceramics. There were two kinds of pores in the microporous MgO–Al2O3 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 Al2O3 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–Al2O3 ceramics. Thus, when the Al2O3 content was 45–90 wt%, the microporous MgO–Al2O3 ceramics had a high compressive strength (10.0–18.3 MPa) and apparent porosity (52.2%–58.4%).