BN/Si₂N₂O复合陶瓷微波介电性能研究

Research on Microwave Dielectric Loss of BN/Si₂N₂O Composite Ceramics

摘要: 透波天线罩材料是保障火箭、飞船、导弹等飞行武器装备在极端环境下实现通讯、测距与制导功能的关键部件，随着飞行速度不断提升，对其高温性能的要求日益苛刻。氮氧化硅(Si₂N₂O)陶瓷凭借独特的晶体结构与化学性能在高温透波材料领域脱颖而出，而氮化硼(BN)具有极高的分解温度和优异的介电性能，作为添加剂引入复相材料可显著提升透波性能。然而，极端高温条件下材料性能演变规律的实验测试成本高、实现困难，因此采用理论模拟方法进行预测具有重要意义。本文通过谐振腔法测试了单体Si₂N₂O和BN陶瓷的微波介电常数与损耗，并采用GEM对数定律建立了Si₂N₂O/BN复相陶瓷介电常数与介电损耗的预测模型。研究发现，复相陶瓷的介电常数与Si₂N₂O含量正相关、与BN添加量负相关，这是由于低介电常数BN含量上升导致高介电常数Si₂N₂O含量降低，同时体系气孔率随BN加入呈升高趋势，二者综合作用使介电常数不断降低，从而提升透波性能。复相陶瓷的介电损耗随温度升高呈现先缓慢变化、后急剧上升的趋势；相同温度下，BN基复合陶瓷(Si₂N₂O含量为10%)的介电损耗整体略高于Si₂N₂O基复合陶瓷(BN含量为10%)，表明BN的引入对介电损耗有一定影响。因此，工程应用中应适度控制BN相含量以优化Si₂N₂O/BN复相透波陶瓷的透波性能。研究结果为航天天线罩透波材料及高温功能复合陶瓷的制备与应用提供了新的热电分析方法的理论依据和参考基础。

Abstract: Radome-Transparent materials are key components to ensure the communication, ranging and guidance functions of aircraft such as rockets, spacecraft and missiles under extreme environments. With the continuous increase of flight speed, the requirements for their high-temperature performance are becoming increasingly stringent. Silicon oxynitride (Si₂N₂O) ceramics stand out in the field of high-temperature wave-transparent materials owing to its unique crystal structure and chemical properties. Boron nitride (BN) possesses an ultra-high decomposition temperature and excellent dielectric properties. Adding BN as additive into multiphase materials can significantly improve wave-transparent performance. Nevertheless, experimental measurement for material-property evolution under extremely high temperature is costly and difficult to implement. Hence, theoretical simulation prediction bears great practical significance. In this work, microwave dielectric constant and dielectric loss of monolithic Si₂N₂O and BN ceramics were measured by resonant-cavity method. A prediction model for dielectric constant and dielectric loss of Si₂N₂O/BN composite ceramics was established based on the GEM logarithmic law. The results show that the dielectric constant of composite ceramics is positively correlated with Si₂N₂O content and negatively correlated with BN content. Increasing BN fraction reduces the volume fraction of high-permittivity Si₂N₂O, meanwhile the porosity of composite system increases with BN addition. The combined effect reduces the effective dielectric constant and improves wave-transparent performance. The dielectric loss of composite ceramics changes slightly at first and then rises sharply with increasing temperature. At identical temperature, BN-based composite ceramic (10 vol% Si₂N₂O) exhibits slightly higher dielectric loss than Si₂N₂O-based composite ceramic (10 vol% BN), which indicates that BN addition imposes obvious influence on dielectric loss. Therefore, BN content should be properly controlled in engineering practice to optimize the wave-transparent property of Si₂N₂O/BN composite ceramics. This work provides theoretical basis and reference for preparation and application of aerospace radome materials and high-temperature functional composite ceramics.