Enhancement mechanism of mechanical performance of highly porous mullite ceramics with bimodal pore structures prepared by selective laser sintering

Highly porous mullite ceramics with bimodal pore structures were fabricated by selective laser sintering (SLS), in which the closed pores were provided by core-shell structure of fly ash hollow spheres (FAHSs) and the open pore channels were created by spherical polyamides (PA12). With increasing sintering temperature, the total porosity of mullite ceramics decreased, in which the average closed pore size reduced and the average open pore size distribution kept constant, however, the compressive strength of ceramic foams increased. This strength enhancement was mainly attributed to the reinforced sintering necks between FAHSs when sintered below 1350 degrees C, which resulted from the liquid phase diffusion of K, Ca and Ti, while the densification and thickening of sphere shell walls played a key role when above 1350 degrees C. Our findings illustrate that understanding pore structure characteristics and strength enhancement mechanism changes will be helpful for designing highly porous mullite ceramics with high mechanical performance. (C) 2018 Elsevier B.V. All rights reserved.