Suface Modification Of Fine SiC Powders By Polyelectrolyte And Study Of The Interaction Mechanisms

Silicon carbide(SiC)owns many properties worthy of attention,for example,good resistance to oxidation and wear,outstanding chemical stability,high strength and hardness,high thermal conductivity.These advantages allow SiC to obtain a widespread application,for example,high temperature semiconductors,electronic,armor,aerospace.Slip casting is a widely used method to prepare advanced SiC with various shapes.The key step of slip casting is to prepare a well-dispersed suspension with high solid loading.It is very difficult to disperse fine SiC particles in aqueous media,which tend to self-agglomeration easily due to its high surface energy.Therefore,it is necessary to modify the SiC surface to disperse SiC powders in aqueous media evenly.In this study,polyelectrolytes were used as dispersants for SiC powders to improve the dispersion stability of SiC powders in aqueous media.The interaction mechanism between polyelectrolytes and the SiC surface was also studied.(1)Poly(aspartic acid)was adsorbed on the SiC surface through hydrogen bonding.Due to the ionization of carboxylic acid groups on the poly(aspartic acid)chain and the extended adsorption conformation,PASP modified SiC could disperse in water evenly through electro-steric mechanism.The optimal pH,dispersant concentration,and temperature for producing SiC powders modified by PASP were 8,0.6 wt%and 85℃,respectively.The concentrated SiC slurry(48 vol%)with good fluidity(0.078 Pa.s)was prepared.(2)Poly(diallyldimethylammonium chloride)(PDADMAC)was adsorbed on the SiC surface through electrostatic interaction.With the increase of pH,the adsorption capacity of PADADMAC increased due to the increase of negatively charged sites on the SiC surface.After being modified by PDADMAC,the isoelectric point of SiC powders shifted toward alkaline pH and the charge reversal phenomenon appeared.The modified SiC powders were dispersed in water evenly at pH 3 through electro-steric mechanism.The concentrated SiC slurry(54 vol%)with low viscosity(0.539 Pa.s)was fabricated.(3)Epichlorohydrin-dimethylamine(EPI-DMA)was used as dispersant for SiC powders in aqueous media.The adsorption measurements indicated that the driving force for adsorption was mainly governed by electrostatic interaction instead of hydrogen bonding which could be neglected.Langmuir model and pseudo-first-order model were the best to fit the equilibrium and kinetics data,respectively.With the increase of adsorption capacity of EPI-DMA,the wetting properties and dispersion stability of SiC powders were improved.The superior dispersion behavior of SiC powders modified by 3.378 mg/g EPI-DMA in water was attributed to electrosteric stabilization mechanism and small effective particle size,leading to low viscosity(0.424 Pa.s)of 54 vol%SiC suspension.