In-situ Synthesis of Column-like Mullite and SiC Whiskers and its Effect on Al2O3-SiC-C Refractory Properties

The Al2O3–SiC–C refractories were prepared with calcined bauxite, brown fused alumina, tabular alumina, flake graphite and silicon carbide as raw materials, Si powder as an additive and phenolic resin as a binder. The effect of calcination temperature on the microstructural evolution and properties of refractories was investigated. The thermodynamic calculation of Al–Si–O–C systems shows that mullite and SiC phases are stable after coking at an elevated temperature. The results indicate that the column-like mullite is formed in a coke bed after fired at 1 000 °C. When the temperature is 1 400 °C, the aspect ratio of the column-like mullite increases. Also, some SiC whiskers are generated in the refractories. It is indicated that the apparent porosity and cold crushing strength both are not changed obviously when the heat treatment temperature increases from 1 000 to 1 400 °C. However, the cold modulus of rupture is increased by 54.73% (i.e., 8.17 MPa) and the load displacement is improved by nearly 20%. It is also found that after three thermal shock cycles, the residual strength ratio of samples after cured at 200 °C is 54.36%, and the value increases to 89.10% after fired at 1 400 °C. The improvement in the flexural strength, fracture toughness and thermal shock resistance of the refractories could be attributed to the in stiu formation of well-developed column-like mullite and SiC whiskers.