| Silicon carbide(Si C)has the advantages of good thermal conductivity,high strength,high hardness,oxidation resistance,corrosion resistance and good chemical stability.It is a common ceramic material,which is widely used in semiconductor,automobile manufacturing,aerospace,nuclear energy,electronics,equipment,powder engineering and other fields.However,these excellent properties all depend on the density of Si C ceramics.In many applications,Si C ceramics with excellent properties and complex shapes are required.Therefore,it is very necessary to prepare Si C slurry with high solid content and low viscosity.It is well known that the method of changing the surface state of materials by adding polymers or small molecules is commonly used to improve the stability of ceramic colloids in aqueous media.It is very important to choose the dispersant suitable for Si C powder.(1)Polydiene dimethyl ammonium chloride(PDADMAC)is adsorbed to the surface of Si C particles through electrostatic gravitational interaction.Due to the high affinity adsorption between them,the adsorption configuration of PDADMAC on Si C surface is flat,and the adsorption capacity,adsorption configuration and modification effect do not change with the change of molecular weight.The modified p H value was 11,the addition amount was 0.24 wt%,the temperature was 90 ℃,and the modification time was 6 h.The adsorption of PDADMAC caused the charge inversion on the surface of Si C.The modified Si C powder was dissolved in water medium to adjust the p H value to 3.The modified Si C powder was dispersed uniformly in the water medium by electrostatic steric stabilization mechanism,and Si C slurry with viscosity of 0.138 Pa.s at 50 vol.% solid content was prepared.(2)Sodium polystyrene sulfonate(PSS)is adsorbed to the surface of Si C particles by hydrogen bond and van der Waals force.Due to the electrostatic repulsion interaction between the two,the adsorption configuration of PSS on Si C surface is annular and tail configuration,and with the increase of PSS molecular weight,the annular configuration on Si C particle surface expands,the adsorption capacity increases and the modification effect becomes better.PSS with molecular weight of Mw =1000000 was used.The p H value was not adjusted in the modification process.The addition amount was 0.3 wt%,the temperature was 90 ℃,and the modification time was 6 h.The modified Si C powder was dissolved in water medium,and the p H value was adjusted to 11.The modified Si C powder was dispersed uniformly in the water medium through electrostatic steric hindrance stabilization mechanism.Si C slurry with high solid content(45 vol.%)was obtained,and the corresponding slurry viscosity was 0.098 Pa.s.(3)Non-ionic surfactant octadecylamine polyoxyethylene ether(AC1830)and anionic polyelectrolyte PSS were used as dispersant to modify Si C powder.The adsorption of AC1830 is not affected by the surface charge and can shield part of the charge,which can be used as the adsorption site of PSS to promote the adsorption of PSS on Si C surface.The 50 vol.% Si C slurry with viscosity of 0.039 Pa·s was produced,which was suitable for slip casting.Zeta potential method showed that the isoelectric point(IEP)of Si C powder modified by this method shifts to the left obviously.The sedimentation experiment shows that the dispersion stability was significantly improved.Contact angle measurements showed that the modifier was successfully adsorbed on the surface of the powder and provided hydrophilic groups,which improved the wettability of the powder.The results of adsorption measurement showed that the isothermal adsorption model and kinetic adsorption model of PSS for Si C powder and Si C powder modified by AC1830 conform to Langmuir model and pseudo-second-order(PSO)model.The adsorption of AC1830 on Si C surface improves the adsorption capacity of PSS. |
