Morphology And Structure Regulation And Control Of ?-Sialon And Their Effect On Al₂O₃-C Refractory Mechanical Properties

Low-carbon Al₂O₃-C refractory samples were prepared from raw materials of tabular alumina,reactive alumina powder and flake graphite.Silicon and metallic Al powder were used as additives and phenol resin was used as binder.The phase composition and microstructure were analyzed by X-ray diffractometer,scanning electron microscope,energy dispersive spectrometer and transmission electron microscope.The properties of cold modulus of rupture?CMOR?,cold crushing strength?CCS?,force-displacement curves,flexural modulus?FM?,hot modulus of rupture?HMOR?,thermal shock resistance for low-carbon Al₂O₃-C refractories were tested.The effects of temperature and atmosphere on ceramic bonding phases and the thermo-mechanical properties of low-carbon Al₂O₃-C materials were investigated.The specific research results were given as follows:Low-carbon Al₂O₃-C refractories have Si₃N₄ whiskers,SiC whiskers and short columnar AlN were formed under the reducing atmosphere at 1200?.The?-Sialon of whiskers and two-dimensional flake could be generated at 1400?.The formation of SiC whiskers and?-Sialon phases promotes the comprehensive performance of Al₂O₃-C refractories at 1400?.The CCS is increased by 30.38%to 87.75MPa and the CMOR and HMOR are increased to 20.01MPa and 15.69MPa,respectively.The FM and the load displacement are increased by>12%.After three thermal shock cycles,the CCS is decreased by only 8.23MPa and the strength retention ratio is 89%.The in-situ formation of SiC and?-Sialon ceramic bonding phases significantly improves the thermo-shock stability of refractories at 1400?.The effects of buried carbon process on microstructure and properties of low-carbon Al₂O₃-C refractories were investigated.The experimental results showed that SiC whiskers were formed under different buried carbon process at 1400?.A few?-Sialon was formed in coked bed and a large amount of SiC whiskers and?-Sialon could be formed in mixed carbon at 1400?.Due to the formation of Si C whiskers and?-Sialon,CMOR and CCS were improved from 21.90MPa and 74.72MPa,respectively.The load displacement could be increased by 59.6%to 0.688mm.The maximum values of FM reached 5.36GPa.After three thermal shock cycles,the CCS of low-carbon Al₂O₃-C refractories with SiC whiskers and?-Sialon only decreased by 8.78 MPa at1400?and the strength retention ratio is 88%.The effects of nitrogen partial pressure and firing temperature on microstructural evolution and properties of low-carbon Al₂O₃-C refractories were investigated.The thermodynamic calculations for Al-Si-O-C-N systems suggested that SiC,AlN could be stable when the nitrogen partial pressure is more than 1.21×10^-10MPa at 1200?.The experimental results showed that short columnar AlN and SiC whiskers were formed under different nitrogen partial pressure at 1200?.The aspect ratio of AlN was higher and SiC production become larger with nitrogen partial pressure increasing 0.065MPa to 0.155MPa at 1200?.Two-dimensional flaky?-Sialon could be generated as the nitrogen partial pressure increased to higher than 0.11MPa at 1400?and the AlN phase disappears and transforms into two-dimensional flaky?-Sialon.SiC whiskers and two-dimensional flaky?-Sialon are interlinked to a network structure.By increasing the nitrogen partial pressure to 0.155 MPa at 1400?,low-carbon Al₂O₃-C refractories exhibited excellent mechanical properties due to the in situ formation of SiC whiskers and two-dimensional flaky?-Sialon.The maximum values of CMOR and CCS reached to 74.7MPa and 19.3MPa,respectively.The FM and HMOR increased to 4.2GPa and13.2MPa,respectively.The load displacement could be increased by 62% to 0.59mm.The CCS was decreased by only 6.2MPa after three thermal shock cycles and the strength retention ratio is 91.8%.The formation of flaky?-Sialon significantly enhanced the thermal shock resistance of low-carbon Al₂O₃-C refractories.