A novel sintering additive system for porous mullite-bonded SiC ceramics: High mechanical performance with controllable pore structure

High strength and thermal shock resistant mullite-bonded porous SiC ceramics are essential for applications in catalyst, hot gas/solid filtration/separation fields. However, these properties were limited by the contradictory issue: higher temperature is necessary for the formation and densification of mullite bond phase, while lower temperature is preferred to avoid sever oxidation of SiC accompanied with detrimental cristobalite phase. Herein, a novel composite additive system, Al(OH)(3)+Y2O3+CaF2, was proposed to solve this problem for one shot. Flexural strength as high as 113 MPa (40.3 vol% porosity) was achieved for samples sintered in air, even higher than that fabricated by expensive SPS technique (103 MPa, 35.7 vol%). Critical quenching temperature reached 547 degrees C, around 227 degrees C improved. Meanwhile, additives acted as pore formers and small variation of them could effectively modify the size and shape of pores. The evolution of pore structure with additives was thoroughly evaluated and models were established for the first time. Correlations of phase composition, microstructure, porosity, pore size and shape to the performance of porous SiC were investigated. This work provides a flexible strategy to simultaneously control the mechanical performance and pore structure for low cost porous SiC ceramics.

Automated summary

A novel composite additive system, Al(OH)(3)+Y2O3+CaF2, has been proposed to address the contradictory issue in the preparation of high strength and thermal shock resistant mullite-bonded porous SiC ceramics. Experimental results showed that the flexural strength of samples sintered in air can reach as high as 113 MPa, and the additives can effectively modify the size and shape of pores. This work provides a flexible strategy to control the mechanical performance and pore structure of low-cost porous SiC ceramics simultaneously.