Study On Gel-casting Process Of Si₃N₄/SiC Products

For solving the forming process problems of large size Si3N4/Si C products,avoiding defects in the traditional forming process,difficult subsequent processing,and the insecurity of the gel system in the traditional gel-casting process.This paper safely prepare the large size special-shaped Si3N4/Si C products by the gel-casting process.In this study,a green agarose gel system was used to prepare silicon nitride and silicon carbide products by gel-casting technology.The Si C/Si slurry with high solid content and low viscosity was prepared.Then make mold forming operation,and sintered in the N2 to prepare Si3N4/Si C productsThe main research contents are as follows.Based on the test indexes of the compressive strength and volume density of the green body,the effect of the solid content,dispersant content,PH and agarose content on the forming effect of the blank body was studied.The results of the orthogonal test show that the influence order of each factor on the compressive strength and volume density of the blank body is: the solid content > dispersant content > agarose content > PH.The analysis of variance results showed that the effect of solid content,dispersant content and agarose content on the compressive strength and volume density of the blank body reached a significant level.Due to the viscosity of the slurry is too large(generally more than 10000 m Pa·s),according to the thixotropy principle,using slurry-mold vibration assisted ge-casting process.The results show that the viscosity of the slurry decreases rapidly and the slurry is injected into the mold evenly and quickly.on the basis of previous research,the effects of dispersant,solid content and monomer content on the properties of the slurry were studied on the basis of the viscosity and stability of the slurry,and the Si C/Si slurry with high solid content and low viscosity was prepared.The results showed that with the increase of solid content and agarose content,the viscosity of the slurry increased and the stability became worse.The dispersing effect of ?-naphthalene sulfonate condensation polymerization was greater than the dispersing effect of sodium tripolyphosphate.When the content of the dispersant of?-naphthalene sulfonate condensation polymerization is 2 wt%,the dispersing effect of Si C/Si slurry is best.Since the strength of agarose gel system products is generally not high,the molded body should achieve a high bulk density as much as possible,reduce the porosity,and ensure the use performance of the body.The slurry was degassed by a combination of silicone chemical defoaming and vacuum stirring physical defoaming to obtain a smooth and smooth Si C/Si green surface.The effect of solid content,agarose content,and dispersant content on the properties of the green body was investigated.The test results show that the solids content is 67%,the content of ?-naphthalene sulfonate condensation polymerization is 2wt%,the agarose content is 2wt%,the green body has the best performance,the green bulk density reaches 2.39g·cm-3 Compressive strength is 3.75 MPa,to meet the production and transportation requirementsThrough the above-mentioned optimal data,a silicon nitride bonded silicon carbide product is prepared by sintering and the product phase is analyzed.The effect of solid content on compressive strength and microstructure of the sintered body was studied.The results show that with the increase of solid content,the compressive strength of the sintered body increases first and then decreases.Under the optimal parameters,the compressive strength of the sintered body reaches 49.45 MPa.The bulk density reaches 2.43g/cm-3 and reaches the basic production requirements.