In-Situ Formation Of β-sialon Ceramic Bonding Phases And Their Effect On Al₂O₃-C Refractory Properties

Introducing the ceramic bonding phase to Al₂O₃-C refractories could significantly improve the comprehensive refractory properties,which could increase the service life and safety of refractories using in continous system of steel melting.The aim of this paper is to form β-Sialon ceramic bonding phase in Al₂O₃-C refractories and study its detail effects on the comprehensive properties of the refractories.Specific research contents and results were as follows:1.Using the quasi-parabolic rule,the relationship between standard gibbs free energy of β-Sialon and its z value at 1400 o C was worked out:Δ_fG_β-Sialon^θ=5.247z²-404.421z-359.039（kJ/mol）Under the thermodynamic calcuation,the predominance-area diagram of the Si-Al-O-N-C system was figured out.It could be seen that Si₃N₄ and Al N would be stable in this system under nitrogen atmosphere at 1400 o C.When Al₂O₃ was added to the system,the β-Sialon phases could be formed.2.The effect of the sintering temperature on the microstructural evolution and properties of Al₂O₃-C refractory samples were studied.The Al₂O₃-C refractory samples were prepared using corundum,flake graphite,reactive alumina,Al powder,Si powders and nano Ni powder.The results indicated that Al N particles,generated in Al₂O₃ refractories at 1000°C,could transform into whiskers at 1200°C.By increasing the sintering temperature to 1400°C,a large number of plate-shaped β-Sialon could be generated.Si C phases take on one-dimensional shape at 1200°C and 1400°C.When plate-shaped β-Sialon formed,the cold crushing strength（CCS）and cold modulus of rupture（CMOR）of the refractoies increased from 90.57 MPa to 148.67 MPa and from22.83 MPa to 33.02 MPa,respectively.After two thermal shock cycles,the CCS of the refractories containing the plate-shaped β-Sialon had only decreased by 4.5 MPa.Thus,the in-situ formation of plate-shaped β-Sialon could significantly improve the thermalshock resistance of Al₂O₃-C refractories.3.The effect of nano Ni powder content on the microstructural evolution and properties of Al₂O₃-C refractory samples were studied.The results indicated that there were only Al N and Si C whisker formed in all samples after sintered at 1200 o C under the nitrogen atmosphere.By increasing the sintering temperature to 1400°C,the new-born phase of β-Sialon was formed in the samples with different contant of nano Ni powder.With the increase of the nano Ni powder content,the z value of the β-Sialon phase increased.At the same time,the morphology of β-Sialon phase shifted from whisker to long-column,eventually to plate in the sample with 1.5wt% nano Ni powder.Theβ-Sialon phases grew preferentially toward the crystalline facets（111）,（210）and（101）.With the formation of β-Sialon bonding phase and the transformation of morphology,the CCS and CMOR increased from 114.94 MPa to 147.96 MPa and from 21.83 MPa to34.02 MPa,respectively.The sample with the long-column β-Sialon bonding phase had the optimum hot modulus of rupture（HMOR）with the value of 28.14 MPa.The formation of β-Sialon bonding phase was also benefit to the the thermal shock resistance of Al₂O₃-C refractories.After two thermal shock cycles,the residual cold crushing strength and keeping rate of cold crushing strength all increased with the increase of z values.