Study On Dispersibility Of Ultrafine Silicon Nitride Powder In Aqueous Media

Silicon nitride?Si₃N₄?is an important structural ceramic material and is widely used in many fields because of its high strength,high hardness,high temperature resistance,good wear resistance,thermal shock resistance,oxidation resistance,and other excellent properties.High-performance Si₃N₄ powder has high purity,fine particle size,and good dispersivity.In particular,dispersion of ultra-fine powder is a key factor in restricting performance of products and downstream applications.However,Si₃N₄ powder has a strong tendency to agglomerate because of its high surface energy.Improving the dispersion stability of Si₃N₄ powder has become a hot issue in Si₃N₄ research.In this paper,silicon nitride powders were modified by hydroxyl groups,amino groups and surface coating technology,respectively.After surface modifications of Si₃N₄ powders,the surface elements change and surface morphology were determined for purpose of characterize the dispersibility of modified Si₃N₄ powders in aqueous.Furthermore,its dispersion mechanism were preliminary discussed.1)Effects of hydroxyl groups on dispersibility of silicon nitride powder in aqueous mediaIn present study,the surface of silicon nitride?Si₃N₄?powder was efficiently hydroxylated via application of nitric acid to improve dispersibility in aqueous media.Hydroxylated powder results in more stable colloidal dispersion in aqueous media compared to native powder.Results of Fourier transform infrared spectroscopy and Xray photoelectron spectroscopy show that hydroxyl group content of Si₃N₄ powder significantly increased with hydroxyl modification.This is helpful in preventing Si₃N₄ powder from aggregating in aqueous media.In addition,thermogravimetric analysis indicates that hydroxyl group content of hydroxylated Si₃N₄ powder was 68.8% higher than that of native powder.Furthermore,surface hydrophilicity of Si₃N₄ powder was enhanced with hydroxyl modification,and powder dispersibility was improved with an increase in hydroxyl content.2)Effects of amino groups on dispersibility of silicon nitride powder in aqueous mediaSilicon nitride?Si₃N₄?powder was subjected to amination modification by grafting ?-aminopropyltriethoxysilane?APTES?via a direct blending method in solution.Fourier transform infrared?FTIR?and X-ray photoelectron spectroscopy?XPS?indicated that the hydroxyl groups present on the surface of Si₃N₄ powder particles interacted with the silanols groups of APTES to combine through covalent bonding.Thermogravimetric analysis?TGA?suggested that the grafting of APTES on Si₃N₄ powder surface was successful with grafting content reaching up to 7%.Compared to native Si₃N₄,the surface hydrophilicity of amino Si₃N₄ powder enhanced and dispersibility improved.3)Preparation and dispersibility of Si₃N₄@g-C₃N₄ core-shell composites powdersA new method to improve dispersibility of silicon nitride in aqueous media were used.Specifically,novel Si₃N₄@g-C₃N₄ core-shell composites materials were synthesized using heating method anneal the mixture of silicon nitride and melamine in nitrogen atmosphere.The effects of various initial mass radios of Si₃N₄ and melamine on the composites structure and dispersibility have been systematically investigated.The results of XPS and TEM were demonstrated that as-obtained powders possess the core-shell structure.The experimental analyzes of zeta potential and sedimentation shows Si₃N₄@g-C₃N₄ composites powders exhibited good dispersion in aqueous media.Furthermore,Si@C2 has a most stable colloidal dispersion.More important,the coated g-C₃N₄ can completely remove at lowly temperature.This method is expected to provide a new way for other organic powder dispersion research.4)Preparation of highly dispersed Si₃N₄@g-C₃N₄ core-shell composites powders by spray drying methodSi₃N₄@g-C₃N₄ core-shell composites powders were synthesized by spray drying method with melamine as shell material precursor.The effect of mass radios of Si₃N₄ powders and melamine and anneal temperature on the composites dispersibility have been investigated.Research shows the raw materials radios in slurry has little effect on performance of the composites powders.However,the anneal temperature have a great impact on it,and the optimum anneal temperature is 550 ?.In this paper,a series of surface modification methods are proposed for the problem of agglomeration of ultra-fine Si₃N₄ powder,which has a significant role in improving the dispersion of Si₃N₄ powder in aqueous media.It is expected to replace the organic dispersant with water for the dispersion of Si₃N₄ powder,which is of importance to reducing the promoting the environmental protection and production cost during the Si₃N₄ powder application process.