Abstract
A study of non-oxide bonding phases formed in situ by adding La2O3 to Al2O3-C refractories, and their influence on the thermo-mechanical properties, is presented. Calculations of the thermodynamics of the Al-Si-O-C-N system were thoroughly explored. Phase assemblage and microstructure were analyzed by means of X-ray diffraction and scanning electron microscopy. The results were that β-Sialon (Si3Al3O3N5) and 15R-Sialon (SiAl4O2N4) formed during sintering at 1400 °C. In addition, the presence of the rare earth oxide, La2O3, promotes columnar β-Sialon formation in a plate-like grain morphology, and this can improve the in situ synthesis of 15R-Sialon. The non-oxide bonding phases give rise to specimens with excellent strength and toughness. Increasing the La2O3 content from 0 wt% to 0.6 wt% enhanced the cold modulus of rupture and the cold crushing strength of the specimens fired from 31.1 MPa to 34.6 MPa, and from 101.3 MPa to 113.8 MPa, respectively. Meanwhile, the displacement was increased by 68% to 0.32 mm. The generation of plate-like β-Sialon and 15R-Sialon also had a positive effect on the hot strength and thermal-shock resistance. The hot modulus of rupture of the specimens fired improved by 21% compared to specimens without La2O3. After three thermal-shock cycles, the residual strength ratios of the specimens fired were above 88%.
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