Of Si <sub> 3 </ Sub> N <sub> 4 </ Sub>-sio <sub> 2 </ Sub> Preparation And Study Of The Wave-transparent Materials Of The Composite Ceramics

With fast development of aviation technology and increasing demand of modern wars, speed measuring by Mach increases dramatically, radome placed on the top of crafts has to be endured against with high temperature and heat impact, for this reason waving-penetrating materials would be play an important role during the future researches.To develop a process of silicon nitride based ceramics for radome application is the fundamental goal of the present study. Besides its superior high-temperature mechanical performance, the dielectric properties and coefficient of thermal expansion are also excellent . Phase composition, microstructure, mechanical property and dielectric performance were explored.The densification ofα- Si₃N₄ is sintered by PLS.It is found that MgO can effectively help to the densification of a-Si₃N₄ at 1500℃,with 4wt% of MgO, the relative density reaches 94%, the starting sintering temperature is as high as 1350℃. when using MgO&Al₂O₃ as the sintering aid, the starting sintering temperature is reduced, at 1450℃, the relative density could be above 96% and the starting sintering temperature is around 1200℃.the densification process finishes between 1400-1450℃.The mechanical property relies on the relative density . The mixed sintering aid MgO&Al₂O₃ can enhance the strength of sintered samples with low density. Although the relative density is as low as 62.1%, the bending strength stays above 82Mpa.The dielectric constant ranges 3.5-9.5. As long as the density is high to certain extent, the dielectric constant tends to certain value and the species of sintering aid and its content difference influnences little on the dielectric constant. The dielectricloss varies from 0.001-0.03, which is sensitive to the relative density, sintering aid and its content.Porousα- Si₃N₄ is formed by dynamic gel-casing process.It was shown that volume content, particle size distribution and the PH value are major factors influnencing the properties of the slurries. Components of starting materials, amount of sintering, volume content of the slurries and sintering profiles are major factors influnencing the properties of the products.