Structure Optimization And Strengthening Mechanism Of ?-Sialon Bonded Al₂O₃-C Refractory

The development of Al₂O₃-C refractories towards low-carbon and ultra-low carbonization due to the requirement of the clean steel smelting and high-temperature industrial energy saving and consumption reduction.However,low-carbon Al₂O₃-C refractories face the common problems of poor thermal shock resistance and corrosion resistance.To cope with the above problems,this paper introduced the?-Sialon with high strength and low thermal expansion coefficient into the Al₂O₃-C refractories.Thermodynamic evaluation of?-Sialon generated in the Al₂O₃-C refractory was studied.The effect of rare earth oxides on the formation of?-Sialon and its mechanical properties were explored.Based on first principles,the morphology control and simulation of?-Sialon under the action of different catalytic atoms were investigated.And the growth mechanism of?-Sialon was revealed.At the same time,the oxidation resistance and thermal shock resistance of?-Sialon bonded Al₂O₃-C refractories were studied.Through systematic research,the following conclusions were drawn:?1?Simplify the quaternary system of synthetic?-Sialon?SiO₂-Al₂O₃-AlN-Si₃N₄?into a binary system?Al₃O₃N-Si₃N₄?,and based on the quasi-parabolic rule,the quasi-parabolic equation between the standard Gibbs free energy and the Z value generated by?-Sialon were obtained.At the same time,through the Al-Si-O-N-C system reaction equation and the thermodynamic advantage zone phase diagram,the thermodynamic conditions for the formation of?-Sialon were further determined.?2?A series of synthesized factors,including sintered temperature,nitrogen partial pressure,holding time,and Si/Al ratio,of?-Sialon in Al₂O₃-C refractory and their effects on mechanical properties of Al₂O₃-C refractory were explored.The study found that when the calcination temperature was lower than 1250?,only AlN and SiC phases existed in samples;when the calcination temperature was increased to 1400?,the?-Sialon phase began to form.Too high or too low nitrogen partial pressure would inhibit the formation of?-Sialon:nitrogen partial pressure was lower than 0.118MPa,which would not provide enough nitrogen source for the formation of?-Sialon,and then effected the formation of?-Sialon.When the nitrogen partial pressure was higher than0.137MPa,the CO gas would be blocked inside the sample and hinder the nitriding inside the sample.The prolongation of the holding time and the increasement of the Si/Al ratio could promote the formation and development of?-Sialon,and the crystal structure of?-Sialon would transform from whisker-like to columnar.It is proposed that one-dimensional?-Sialon obeyed the vapor-liquid-solid?VLS?and vapor-solid?VS?growth mechanism.?3?The introduction of rare earth La₂O₃ into Al₂O₃-C refractory materials could promote the formation of AlN and SiC whiskers at 1200?and also promote the formation of flake?-Sialon and 15R-Sialon at 1400?.These ceramic phases could enhance the interaction between particles,thereby enhancing the high-temperature mechanical strength of the material.Compared with the specimens without catalyst,the hot modulus strength of the sample containing 0.6wt%La₂O₃ increased by 21%;the residual strength retention rate of the sample after three thermal shocks reached 93.4%.At the same time,the two-dimensional flake?-Sialon hinders the crack propagation under transcrystalline fracture and crack deflection.?4?In the non-catalyzed samples,the?-Sialon crystals were cylindrical,the sample crystals with Fe₂O₃ introduced had a two-dimensional sheet structure,and the metallic Ni as a catalyst showed a hexagonal prism structure.Based on density functional theory,a gas adsorption model for different catalysts was constructed.It was found that the addition of catalyst increased the adsorption of Al₂O on the crystal surface,which in turn increased the solid solution of Al-O in Si₃N₄,thereby promoting the formation of?-Sialon.?5?Using Fe₂O₃ as a catalyst,the effects of the addition amount?0wt%,0.4wt%,0.8wt%,and 1.2wt%?on the formation of two-dimensional?-Sialon in Al₂O₃-C refractories,and its mechanical properties and oxidation resistance were studied.The research results showed that,when the Fe₂O₃ addition amount was 1.2wt%,the residual strength rate of the sample after 5 times thermal cycles was as high as 96%.At the same time,during the high-temperature nitriding process,a dense protective layer was formed on the surface of the material,thereby improving the high-temperature oxidation resistance of the material.