Study On Surface Modification Of Ultrafine Silicon Carbide Powder And Dispersion Mechanism

Silicon carbide ceramics are widely used in the fields of electronics,automobiles,aerospace and so on.Slip casting is one of common methods for preparing SiC ceramic.The key step of slip casting is to fabricate SiC slurry with high solid content and low viscosity.However,SiC powder is very prone to agglomeration and shows poor dispersibility in water on account of its high surface energy,causing poor dispersion in water medium.Generally,to breakdown the agglomeration of particles and improve the dispersibility of particles in water,the technology of surface modification,as an effective method,is commonly used.There are three main dispersion mechanisms:electrostatic repulsion,space resistance and the synergy of electrostatic repulsion and steric hindrance.1.By using polyvinylpyrrolidone(PVP)and tetramethylammonium hydroxide(TMAH)as modifier,SiC powder is modified via two-step modification.It indicates that polyvinylpyrrolidone can prevent agglomeration among particles via steric hindrance,and TMAH can increase the electrostatic repulsion among particles.The dispersibility of modified SiC is increased significantly via using polyvinylpyrrolidone and tetramethylammonium hydroxide as modifier.2.SiC powder is modified via the synergy of y-mercaptopropyl trimethoxysilane(KH590)and tetramethylammonium hydroxide(TMAH).It shows that TMAH can be promoted to adsorb on the surface of SiC powder modified with KH590,and the electrostatic repulse among the SiC particles is also increased significantly.The influences of KH590 amount,TMAH additional amount,modified time and baadditional ll mill speed on the viscosity and solid content decrease successively.3.The modification effect of modified SiC powder is investigated by using sodium humate as modifier.Meanwhile,the kinetics and isothermal equation of adsorption of sodium humate on SiC sueface are investigated to further understand the adsorption process.It shows that adsorption kinetics,t/qt=0.62533t+11.0472,and isothermal equation,Lnqe=0.361LnCe-0.334,are in accordance with the pseudo-second-order kinetics model and Freundlich model respectively.0.828 KJ/mol adsorption energy indicates that the adsorption style of sodium humate on SiC surface is belonging to physical adsorption.