Mullite-corundum gas-permeable refractories reinforced by in-situ formed SiC whiskers

In this study, five mullite-corundum gas-permeable refractories reinforced by SiC whiskers were prepared with spherical porous mullite-corundum aggregates. The influence of the silicon powder content on the microstructure, phase composition, mechanical and gas-permeability properties were investigated through XRD, SEM and EDS. It was found that the silicon powder content strongly affected the mechanical and gas-permeability properties by changing the formation and distribution of mullite and SiC whiskers. SiC whiskers were formed both in the matrix and inside the pores of the aggregates. As the silicon powder content increased, the amount of SiC whiskers in the pores of the aggregates as well as at the aggregate/matrix interface increased, meanwhile more mullite was also formed at the interface. However, when the silicon powder content was larger than 9 wt%, much less mullite was observed at the interface, reducing the bonding between particles in the matrices. The formation of SiC whiskers and mullite at the interface improved the mechanical properties at a small expense of air permeability. The optimized refractory contained 6 wt% silicon powder which combined the highest cold and hot flexural strength (17.0 MPa and 10.2 MPa, respectively), as well as the best strain at fracture and a homogeneous gas permeability.