Effects Of Particle Gradation And Inorganic Fibers On The Microstructure And Properties Of Silicon Nitride Bonded Silicon Carbide Refractories

With the rapid development of metallurgical industry,aviation industry and other industries,the performance of silicon nitride bonded silicon carbide refractory is proposed higher requirements.Aiming at the problem of short service life due to high temperature and cyclic heating during the service life of combustion nozzles in power plants,this paper proposes to improve performance by studying the gradation of raw material particles and adding inorganic fibers.Based on the research of the gradation of the raw material particles and the nitriding process,the effects of the type and content of the fibers on the microstructure and properties of silicon nitride and silicon carbide refractories were studied in detail,and the thermal shock resistance and oxidation resistance of the materials.The results of this experiment have important theoretical significance and application value for improving the service life of silicon nitride and silicon carbide refractories for combustion nozzles and expanding the application range.First,the gradation of the raw material particles was studied,and the results showed that when using 1-3 mm,0-1 mm,180 mesh silicon carbide particles and 200 mesh silicon powder for coarse particle gradation,the best gradation was 1-3 mm:0-1 mm:180 mesh:200 mesh=30:35:15:20.The flexural strength,compressive strength,and density of samples prepared with this particle gradation reached to 38 MPa,140 MPa,and 2.58 g/cm3,respectively.Secondly,the effects of fiber types and contents on the microstructure and mechanical properties of silicon nitride-bonded silicon carbide refractories were studied.The results show that the addition of fibers can increase the nitridation rate of silicon nitride combined with silicon carbide refractories and act as a silicon nitride skeleton to enhance the strength of the bonding phase of the material to improve the mechanical properties;Added mullite and alumina fibers can form a sialon phase by solid solution with silicon nitride to improve the bonding phase performance.For the coarse-grained graded silicon nitride and silicon carbide refractories,when the mullite mass fraction is 9%,the flexural strength and compressive strength of the material reach 54 MPa and 180 MPa,respectively.Up by 43%and 29%respectively.For fine particle grading of 14-36 mesh:36-70 mesh:200 mesh=70:10:20,when the mass fraction of mullite fiber is 9%,the flexural strength of the material can reach up to 43 MPa,which is 36%higher than the material without added fiber.When the mass fraction of alumina fiber is 3%,the compressive strength of the material is up to 195 MPa,which is 22%higher than that without the fiber.Finally,the effects of fiber type and content on the thermal shock resistance and oxidation resistance of silicon nitride-bonded silicon carbide refractories were studied.The results show that:the bridging effect of the fiber and the strengthening effect on the in situ generation of silicon nitride improve the thermal shock performance of the material;For materials prepared with coarse-grained gradation,the thermal shock stability is best when the mullite fiber mass fraction is 6 wt%,and the thermal shock residual flexural strength is 27 MPa,which is 35%higher than the material without added fibers;For fine-grainedmaterials,when the mullite fiber mass fraction is 9%,the thermal shock residual strength of the material is 29 MPa,which is 23%higher than that without the addition of fiber materials;Adding oxidizing fibers such as mullite can improve the oxidation resistance of the material.