Effect of in situ synthesized SiC whiskers and mullite phases on the thermo-mechanical properties of Al2O3–SiC–C refractories

Abstract

The Al2O3–SiC–C refractory samples were prepared from raw materials of calcined bauxite, brown fused alumina, tabular alumina, flake graphite, silicon carbide and metallic Si powders. The Fe2O3 powders were used as additive and the phenolic resin was applied as binder. The effects of calcination temperature on microstructural evolution and thermo-mechanical properties of the samples had been studied. Thermodynamic calculation of Al–Si–O–C systems shows that both mullite and SiC were as equilibrium phases after coking at elevated temperatures. The experimental results indicate that the mullite whiskers with large aspect ratio were formed after fired at 1000°C in a coke bed. When the temperature was raised to 1400°C, a new phase of SiC whiskers was formed in addition to the mullite whiskers. Morever, a large number of the mullite platelets with diamond shape were generated. The property tests show that as the firing temperature rose from 1000°C to 1400°C, the value of cold modulus of rupture (CMOR) was increased by 57.1% to 8.2MPa, and the cold crushing strength (CCS) was raised from 47.5MPa to 54.8MPa; also, the flexural modulus (FM) and load displacement were almost 30% and 20% increased respectively. It is also found that the hot modulus of rupture (HMOR) measured at 1400°C reached the maximum value of 8.1MPa after firing at 1000°C. Furthermore, after three thermal shock cycles, the residual strength ratio of samples after cured at 200°C was only 47.5% while the value rose to 96.4% after fired at 1400°C. It is believed that the substantial enhancement in the thermo-mechanical properties of Al2O3–SiC–C refractory samples under room and elevated temperatures could be attributed to the synergistic effect of in-situ formed SiC whiskers, mullite whiskers and diamond-shaped mullite with plane structure.