低介电常数BNw/Si3N4复合透波材料研究

BN whisker precursors will be synthesized with melamine (C3N6H6) and boric acid (H3BO3) as raw materials at low temperature and pressure by the sol-gel method. BN whiskers (BNw) with excellent properties of regular morphology, smooth surface, large aspect ratio, low dielectric constant and dielectric loss tangent will be prepared by nitridation and decarbonization process. BNw/Si3N4 wave-transparent composites with high bending strength, high fracture toughness and high dielectric property will be prepared using isostatic pressing and gas pressure sintering process by adding toughening agent BNw to Si3N4. Well dispersed and dense ceramic bodies will be acquired by surface treatment，dispersion of BNw and isostatic pressing process. BNw/Si3N4 wave-transparent composites with complex shape, excellent mechanical and dielectric properties can be prepared by gas pressure sintering process with sintering aids. The optimal BNw preparation process will be determined, the BNw content and dispersion process, the influence of sintering temperature system and pressure of gas pressure sintering on mechanical and dielectric properties of BNw/Si3N wave-transparent composites will be investigated. The microstructure and phase transition during sintering will be analysized.Meanwhile,the sintering mechanism, toughening mechanism and wave-transparent mechanism of experimental system will be discussed.

以三聚氰胺(C3N6H6)和硼酸(H3BO3)为主要原料，采用溶胶-凝胶法低温常压合成氮化硼晶须前驱体，利用氮化工艺和除碳工艺制备出形貌规则、表面光洁度高、长径比大、介电常数和介电损耗角正切值低等优良物理化学性能的氮化硼晶须(BNw)。通过在氮化硅（Si3N4）基体中添加BNw，采用等静压成型和气压烧结工艺，制备出高强度、高断裂韧性、高介电性能的BNw/Si3N4复合透波材料。利用分散剂对BNw进行表面处理和分散，并采用等静压成型工艺获得分散均匀、致密的陶瓷坯体。采用气压烧结工艺并添加烧结助剂，可以制备出形状复杂、力学性能和介电性能优异的透波复合材料。本项目通过实验确定最佳的BNw制备工艺，研究BNw含量及分散工艺、气压烧结温度制度和压力对复合透波材料力学和介电性能的影响。分析复合透波材料的微观结构以及烧结过程中物相的演变，并对实验体系的烧结机理、强韧化机理和透波机理进行探讨。

氮化硅材料具有优异的机械性能、良好的热稳定性和耐腐蚀性能，是良好的透波材料，但其介电性能需要进一步提高。氮化硼具有比氮化硅更佳的介电性能，因此利用Si3N4和BN各自的优点制备的BN/Si3N4复合材料已成为透波材料中综合性能最优材料之一。本项目以三聚氰胺和硼酸为主要原料，采用溶胶-凝胶法低温常压合成氮化硼晶须前驱体，利用氮化工艺和除碳工艺制备出具有优良物理化学性能的氮化硼晶须。通过在氮化硅基体中添加BNw，采用等静压成型和气压烧结工艺，制备出高强度、高断裂韧性、高介电性能的BNw/Si3N4复合透波材料。本项目通过实验确定最佳的BNw制备工艺，研究BNw含量及分散工艺、气压烧结温度制度和压力对复合透波材料力学和介电性能的影响。分析复合透波材料的微观结构以及烧结过程中物相的演变，并对实验体系的烧结机理、强韧化机理和透波机理进行探讨。当BNw含量10vol%、烧成温度1800℃、保温时间1h、氮气压力7MPa时，制备出力学性能和介电性能优异的BNw/Si3N4复合透波材料，其弯曲强度为238MPa、断裂韧性为3.37MPa•m1/2、介电常数为3.71、介质损耗角正切为4.72×10-3。因此该透波材料有望应用于高超音速地空导弹、反辐射导弹和巡航导弹等先进武器装备。