Study On The Relationship Between Surface Treatment Of SiC Powder And Rheology Of Its Slurry

SiC is an inorganic non-metallic material with a wide range of applications and good development prospects,having heat and wear resistances,high hardness and strength.Direct solidification injection molding is a simple and practical method for preparing high-performance silicon carbide devices.The key point and difficulty of this process lies in the preparation of high-solid content low-viscosity ceramic slurry.At present,the slurry prepared using domestic SiC powders is still difficult to meet the above process requirements.Therefore,the surface of SiC powder needs to be preprocessed and modified to improve the rheology of it's slurry.Based on the microscopic differences of SiC powders,the main factors affecting the rheology of the slurry were systematically analyzed.On this basis,the process conditions for removing impurity ions on the surface of SiC powders and the rheological properties of the slurry were discussed.Try to modify the surface of SiC powder with small molecular organic matter,sodium humate or tetramethylammonium hydroxide(TMAH),it is in order to improve the rheology and stability of the slurry.The main research contents are as follows:1.Study on the effect of microscopic difference of SiC powder to the rheological properties of its slurry: Selecting SiC powders produced by different manufacturers,the powders and its slurry are tested by zeta potential,particle size and viscosity.The presence of impurity ions on the surface of SiC powder,compressing the electric double layer and reducing the repulsion energy is the main factor which causing the deterioration of the slurry rheology and stability.2.Removal of impurity ions on the surface of SiC powder: The SiC powder was treated with different concentrations of hydrochloric acid solution to remove metal impurity ions.The relationship between the microscopic state of the powder and the rheology of its slurry was investigated by zeta potentiometer,material microscope,and rotational viscometer.The results show that the zeta potential of the SiC powder is significantly improved after pickling with 0.5%-1.0% hydrochloric acid solution.The solid content of the slurry is increased,the viscosity is lowered,and the stability is improved.3.Surface modification of SiC powder by small molecular organic matter: The surface modification of SiC powder under hydrothermal conditions was investigated by using acetic acid as surface modifier.The possibility of the carboxyl group of acetic acid reacted with the silanol group on the surface of SiC powder was investigated.By adjusting the silicon hydroxyl content on the surface of the powder,the solid content and stability of the slurry are improved.The research shows that when the temperature between 100 °C and 120 °C,the surface of the SiC powder being modified with acetic acid in the hydrothermal kettle,the zeta potential of the powder is improved.The combination of the surface silanol and acetic acid weakens the bound water formed by the hydrogen bond,the flowing water increasing,and the viscosity of the slurry decreasing.4.The effect of SiC surface oxide on the rheological properties of the slurry: the surface of the powder was etched by using sodium hydroxide or hydrofluoric acid to investigate the effect of etching on the surface of SiC powder.The results show that the mild etching is beneficial to the dispersion of the powder in the aqueous phase.After a short time of sodium hydroxide treatment,the dispersion of the powder in the aqueous phase is obviously improved.It is advantageous for the preparation of high solids low viscosity slurrys.5.Possibility of surface modification of SiC powder by sodium humate: The surface of SiC powder is treated under different conditions by using sodium humate.By TOC testing,it is found that a small amount of sodium humate can significantly change the microscopic state of the powder surface.The SiC powder treated under alkaline conditions is optimal,the stability of its slurry is greatly improved,and the stability is good.The viscosity is also significantly decreased at high solid content.6.Study on rheological properties of SiC slurry by TMAH adsorption: Using hydrothermal treatment to enhance the effective adsorption of TMAH on the surface of SiC powder,it is minimized free electrolyte ions in the slurry.The experimental results show that this method can effectively improve the stability of slurry,and the absolute value of Zeta potential of SiC powder is significantly improved.Using very little TMAH can form an effective adsorption layer on the surface of SiC powder,which is a very good method to industrial application prospects.