The Preparation Technique And Research Of Si₃N₄ Nanometer Powder

Si3N4 nanometer powders were synthesized by sol-gel method and carbothermal reduction method.The organic carbon (hexamethylene tetramine, urea, formaldehyde, etc.) was chosen as carbon source, silica-gel was chosen as silicon source, organic nitrogen and nitrogen gas were chosen as nitrogen source respectively. The constitution, granularity and appearance of Si3N4 powder were analyzed by means of XRD (X-ray diffraction), FTIR (Fourier transform infrared spectrophotometer), TEM (Transmission electron microscope) and Laser Particle-size Analyser.It was discussed emphatically that the effects of urea/formaldehyde molar ratio,the PH of reaction medium, reaction temperature, reaction time, the concentration of reactant, surfactant, catalyst on organic polymer precursor and the effects of carbon/silicon molar ratio, reaction temperature,nitrogen flow,heat preservation time,carbon removal time, carbon removal temperature on Si3N4 ultra-fine powder.The optimal technical parameters of precursor preparation are as follows: urea/ formaldehyde molar ratio: 5/3; addition reaction temperature: 50℃; condensation polymerization temperature: 80℃; addition reaction PH=7; condensation polymerization PH=3~4; catalyst : CPC-1; surfactant: CPS-1.The optimal technical parameters of Si3N4 nanometer powder preparation are as follows: carbon/ silicon molar ratio: 3.5/1; nitrogen flow: 3L/min; reaction temperature: 1500℃; carbon removal temperature: 600℃.100% Si3N4 ultra-fine powder can be obtained in the optimal technical parameters, the average size of obtained Si3N4 powders is 43.82nm,90% of them isα-Si3N4,10% of them isβ-Si3N4.Condensation polymerization mechanism and carbothermal reduction mechanism are also discussed.