Effect of ceramic bonding phases on the thermo-mechanical properties of Al2O3–C refractories

Ceramic bonding phases of non-oxide whiskers can enhance the hot strength and the thermal shock resistance of Al2O3–C refractories. In this paper, the effect of different metals on the microstructure and thermo-mechanical properties of Al2O3–C refractories has been investigated. Thermodynamic calculation of Al–Si–O–C–N systems shows that Al4C3, AlN, SiC and β-Sialon are stable at elevated temperature. AlN with the shape of short column can be generated in Al2O3–C refractories with metallic Al, which leads to high hot modulus of rupture (HMOR) and poor resistance to thermal shock. SiC whiskers formed in Al2O3–C refractories with metallic Si give rise to low HMOR and good resistance to thermal shock. When metallic Si and Al are added together in the refractories, β-Sialon (z=2) with plane structure can be generated under the action of catalyst (nano-sized Ni). The existence of the catalyst promotes the diffusion of Al and O in Si3N4 crystals and contributes to the generation of plane-shaped β-Sialon. The corresponding HMOR and residual cold modulus of rupture respectively increase to about 20 MPa and 10.3 MPa. The plane-shaped β-Sialon can significantly enhance both hot strength and thermal shock resistance of Al2O3–C refractories.