Study On The Surface Polarity Regulation Of Silicon Carbide Powder And Properties Of Its Slurry

Silicon carbide?SiC?is a new type of inorganic ceramic material,which has excellent comprehensive properties such as high strength,wear resistance,thermal shock resistance,corrosion resistance,oxidation resistance and low cost.Therefore,SiC has been widely used in mechanical and chemical fields.The preparation of green body with high density and uniform size distribution is a crucial step in the ceramic production process.Researchers have carried out a lot of laboratory studies and technological explorations.Among them,the colloidal process is one of the representative preparation methods for obtaining uniform,dense,and complex-shaped ceramic devices.The major difficulty of this process is to prepare SiC ceramic slurry with high dispersibility,low viscosity and high solid content.The surface energy of SiC powder is high,and it is easy to agglomerate in the water phase,which lead to poor dispersion and affect subsequent sintering and properties of green body.In this paper,small molecular organics,such as acetic acid and ethanol,were used to modify the surface of SiC powder to suppress the interparticle agglomeration through the change of surface polarity and steric hindrances.The effects of impurity ions and the SiO₂ oxide layer on the dispersion,stability and rheological properties of SiC slurry were systematically investigated from the microscopic state and chemical properties of powder surface.The relationship between regulation of SiO₂ oxide layer and the rheological properties of SiC slurry was studied.The main contents are as follows:1.Effect of ethanol and acetic acid solvothermal treatment on the properties of SiC slurry:In order to avoid the self-polymerization of macromolecular substances,small molecular organics,such as ethanol and acetic acid,were used to modify SiC powder under 120?solvothermal condition,exploring the effect of small organics modification on the properties of SiC slurry.The results showed that the dispersion,stability and rheological properties of SiC particles in aqueous phase can be effectively improved by modifying SiC powder with acetic acid under 120?solvothermal condition.Acetic acid was firmly adsorbed on the surface of SiC powder.With the double effects of steric hindrance and electrostatic stability,the surface Zeta potential of SiC powder was increased,so the repulsion force of double electric layers was also increased.The dispersion and stability of SiC slurry were improved.After the acetic acid modification,the content of silanol groups on the SiC surface decreased,so the content of binding water bound by hydrogen bonds can be reduced,and the rheological properties of the SiC slurry were improved.2.Influence of SiO₂ oxide layer on the properties of SiC slurry:Removing the impurity ions by HCl pickling,etching the surface SiO₂ oxide layer of SiC powder by HF,and producing a new oxide layer on the surface of SiC by calcination.The influence of surface oxide layer and metal impurity ions on the rheological properties of SiC slurry was systematically studied by ICP-AES,EDS,Zeta potential,viscosity measurement and other characterization means.The experimental results showed that the main reason for the poor dispersion,stability and rheological properties of SiC slurry is not the surface SiO₂ oxide layer,but the impurity ions existing on the surface of SiC or in the water phase.Proper amount of surface oxide layer can regulate the surface property and micro state of SiC powder after activation?calcination?,so the dispersion and rheological properties of slurry were improved.The presence of an appropriate amount of oxide layer is beneficial to improve the properties of SiC slurry.This provides a theoretical basis for seeking a new activation method for oxide layer.3.Regulation of SiC surface oxide layer by alkali treatment:Based on the reaction between alkali and acidic SiO₂ oxide,a new method of activating SiO₂ oxide layer on SiC surface was studied.The effect of the micro change of SiO₂ oxide layer on the properties of SiC slurry was studied by treating SiC powder with KOH,NaOH and Na₂CO₃ solution.The results showed that the proper amount of SiO₂ oxide layer?silanol group?on the surface of SiC powder is conducive to dispersion of the powder.The basic solution can adjust the content of the oxide layer on SiC surface,and improve the dispersion,stability and rheological properties of the SiC slurry.Among them,Na₂CO₃ aqueous solution has the best modification effect.The weakly alkaline salt Na₂CO₃ can slightly etch the oxide layer on the surface of SiC and tune the content of SiO₂ oxide layer,which activated the surface properties of SiC powder.And then,the electrostatic stability mechanism of SiC aqueous suspension is controlled to improve the dispersion,stability and rheological properties of the SiC slurry to the greatest extent.This study has great significance for the preparation of high-quality,dense and uniform SiC ceramics products.4.Influence of the experimental conditions of Na₂CO₃ modification on the properties of SiC slurry:Based on the conditions such as temperature,time and the concentration of modifier,the optimal experimental conditions of Na₂CO₃ modified SiC powder were investigated by using the control variable method.The experimental results showed that,when the SiC powder was modified by 0.1 mol/L Na₂CO₃ solution at room temperature for 30 min,the best modification effect can be achieved.The dispersion,stability and rheological properties of SiC slurry can be greatly improved.Therefore,by using the low concentration of Na₂CO₃ solution,the SiO₂ oxide layer on the surface of SiC powder can be regulated.So the amount of modifier will be saved,and the energy consumption can also be reduced.It is of great significance for the industrial preparation of high-performance SiC slurry.