Study On Preparation And Properties Of Ultrafine Modified SiC Powder

As a kind of non-oxide ceramic material with excellent performance,SIC has wide value of application,but the SiC ceramic slurry with high solid content and low viscosity is the precondition for the preparation of excellent SiC ceramics.Based on the comparison of the properties of SiC powders at home and abroad and the mechanism of stable dispersion of SiC slurry,the modified SiC powder with great difference to the original SiC powder was prepared by grafting polymerization method.The main research work is as follows:1.There is a lot of differences between the domestic SiC powder and the imported SiC powder both on the surface properties and slurry properties.The particle size distribution of the two kinds of powders is roughly the same,and the distribution is between 0.1 and 10?m.The particle morphology of the domestic SiC powder is mostly flaky polyhedron,and the imported SiC powders are more regular,besides,its sphericity is better.The bulk density of imported SiC powder is 0.97 g/cm3,which is larger than that of domestic SiC powder with 0.64 g/cm3,and the wettability of imported SiC powder is better than that of domestic SiC powder.On slurry solid content,dispersion and rheological properties,the maximum solid content of imported SiC slurry is 65%,which is far higher than that of domestic SiC slurry which is only 40%.At the same time,the imported SiC slurry can keep up to 24h withno completely settlement,the dispersion stability and fluidity of imported SiC slurry are better than that of domestic SiC slurry.2.By adding three different additives to SiC slurry,the modification mechanism of SiC slurry dispersion stability was explored.KH560 and TMAH can influence the dispersion stability of the particles by changing the isoelectric point of SiC.It can influence the diffusion double electron layer formed in the SiC slurry by controlling the difference between the pH value and the isoelectric point to increase the Zeta potential of the slurry.3.With a method of graft polymerization and coating modification,a modified SiC powder which could increase solid content and reduce viscosity was prepared.The best process parameters of the modified process are studied:the first step handing way of the silane coupling agent is ball milling,the reaction time is 2h,the amount of addition is 1%,the second step grafting polymerization temperature is 90 ?,the polymerization time is 4h,the monomer dosage is 3%,the dosage of initiator is 0.5%.The surface structure and properties of the surface modified SiC powder tested by electron microscopy and infrared spectroscopy were more than that of the original SiC powder.The grafting degree of the graft product was 2.6%by TG test.After modification,the particle morphology of SiC powder is more smooth,the median diameter slightly increases,and the bulk density increases from initial 0.64g/cm3 to 0.91 g/cm3,and the wettability increases.The maximum solid content of modified SiC slurry increased from 40%to 55%,which could maintain 24h's incomplete settlement with an effect of enhancing dispersion stability and fluidity.After modification,the surface structure and properties of SiC powder changed,and the phase structure of SiC remained.