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Abstract The mechanical strength of highly porous ceramic foams shows significant attenuation with the increase of porosity, especially for ceramic foams with very high porosity level above 95%. Ultra-light bulk composite ceramic foams were fabricated via introducing 20 wt% zirconia in alumina-based cell wall, aiming at improving mechanical strength of alumina based ceramic foams. The preparation and stability of alumina and zirconia particles synergistically stabilized foams were investigated. The obtained bulk ceramic foams manifested an exciting combination of both high porosity above 96% and excellent specific compressive strength, due to their closed pore structure, defect-free cell wall with uniform thickness, and uniformly distributed zirconia grains in alumina matrix. The alumina/zirconia composite ceramic foams with porosity of 96.7% exhibited compressive strength of 1.11 ± 0.07 MPa, which was much higher than that of alumina ceramic foams in the case of same porosity. [ABSTRACT FROM AUTHOR]

Compressive strength is one of the most important mechanical properties for ceramic foams but the dependence of compressive strength of highly porous ceramic foams on porosity remains unclear up to now, especially for the ceramic foams with porosity above 94%. In this paper, the relationship between compressive strength and porosity of ceramic foams with high porosity in the range of 79–98% was studied for the first time. The alumina ceramic foams and zirconia foams were prepared by particle-stabilized foaming method using sodium dodecyl sulfonate (SDS) as foaming agent. It was found that the function relation between compressive strength and porosity depended on porosity level. Specifically, compressive strength of ceramic foams fitted well with Rice Model when the porosity ranged from 79% to 94%. When the porosity increased above 95%, compressive strength of ceramic foams showed linear relation to porosity, which was probably due to the characteristic of highly porous ceramic foams with thin and lamellate cell wall. [ABSTRACT FROM AUTHOR]

A novel approach to fabricate mullite ceramic foams with high porosity and mechanical strength using fly ash hollow spheres (FAHSs) as the only raw material was reported for the first time, in which FAHSs served as both matrix and pore-forming agent. It was demonstrated that uniform FAHS ceramic foams without cracks could be fabricated by both direct stack sintering method and gel-casting route. The effect of sintering temperature on linear shrinkage, porosity, phase composition and mechanical properties was investigated. With the increase of sintering temperature from 1200 °C to 1350 °C, the fracture mechanism changed from fracturing along FAHSs to fracturing across FAHSs, and the compressive strength of the FAHS ceramic foams increased from 4.4 MPa to 33.4 MPa. The FAHS ceramic foams exhibited high porosity in the range of 73–81% and high mechanical strength, which benefited from the dense assembling of small FAHSs with natural diameter distribution and excellent wall-thickness uniformity. [ABSTRACT FROM AUTHOR]