Study On Surface Modification Of Superfine Silicon Carbide Powder And Its Slurry Properties

As an inorganic non-metallic material,recrystallized silicon carbide is widely concerned because of its excellent strength,oxidation resistance,high-temperature mechanical properties and erosion resistance.The key to affecting these properties is the density of recrystallized ceramics.However,there is still a certain gap between the density of domestically produced recrystallized silicon carbide products and foreign products,and the preparation process needs to be further improved.Among them,silicon carbide does not shrink during the sintering process,so the density of recrystallized silicon carbide products is determined by the density of its green body.The key to the preparation of high-density silicon carbide blanks is to obtain a modified silicon carbide slurry with high solid phase content and low viscosity.This article starts with the study of the interaction between traditional modifiers and silicon carbide powders,selects the appropriate modifier to modify the silicon carbide powder system to obtain high-quality modified silicon carbide slurry,and then produces high-density silicon carbide blanks and heavy Crystalline silicon carbide ceramic products.Experimental results show:1.Use traditional ionic modifier and silane coupling agent to mix and stir the modified silicon carbide powder in the aqueous solution,and combine with the experimental phenomenon to analyze the reason,it is found that the ionic modifier is prone to extrusion phenomenon,that is,it is attached to the conformation of the ionic modifier on the surface of silicon carbide changes in an alkaline environment,resulting in desorption of the modifier.The ionic modifier is enriched on the upper layer of the slurry due to the lower density and takes away part of the moisture in the slurry,resulting in delamination of the slurry.On the other hand,the silane coupling agent self-polymerizes during the modification process,causing the slurry to gel.Neither can be applied to actual production.2.Based on the analysis of the reasons for the modification failure of two commonly used modifiers,a combination of ionic modifier polymaleic acid and silane coupling agent KH550 modified silicon carbide powder.The viscosity of the modified silicon carbide slurry reaches 0.099 Pa.s when the solid phase content is 50%.The maximum absolute value of the Zeta potential of the powder increased from 50 mV to 65 mV at pH=9.Thermogravimetry,infrared spectroscopy and scanning electron microscopy verified the successful grafting and adsorption of the modifier.Not only that,the resulting slurry is free of extrusion and self-polymerization.However,in the subsequent injection molding and stirring process,the slurry appeared extrusion and self-polymerization,and the viscosity of the slurry rose to more than 1 Pa.s,which failed to obtain an ideal green body.3.To sum up the above phenomenon,use small molecule organic dye disperse black to stir the modified silicon carbide powder in the aqueous solution.The modified silicon carbide powder prepares a slurry with a solid content of 50%and a viscosity of 0.430 Pa.s.There is no slurry extrusion and self-polymerization during the grouting process.The density of the green body reached 2.43 g/cm3.The adsorption mode of dispersed black on the surface of silicon carbide is analyzed by UV spectrophotometer,which belongs to single layer physical adsorption.Subsequent experiments used disperse black and sodium alginate to modify the silicon carbide powder and heat and stir to achieve chemical connection to further improve the slurry fluidity.The final viscosity of the prepared silicon carbide powder with a solid phase content of 50%is 0.170 Pa.s.And there is no extrusion and self-polymerization of the slurry.The density of the green body reached 2.62 g/cm3.