中文摘要：

在多孔氮化硅陶瓷（Si_3N_4）表面制备氮化硼（BN）涂层,可以提高天线罩的多方面性能,其研究具有重要的工程应用价值。以硼酸（H_3BO_3）及碳黑为原料,利用两种方法制备BN涂层,一种方法是在氮化硅基体表面涂覆H_3BO_3与炭黑,然后在氮气气氛下烧结制备BN涂层（简称一步法）;另一种方法采用H_3BO_3分解在多孔Si_3N_4基体表面制备B_2O_3涂层,然后利用碳热还原反应将B2O3涂层转变为BN涂层（简称两步法）,通过X射线衍射分析（XRD）观察了涂层的物相组成,扫描电镜（SEM）观察涂层的形貌及涂层与基体的结合情况。研究结果表明：两种方法制备的涂层由BN组成,无残余B_2O_3,其中一步法制备的涂层表面粗糙,存在大量裂纹和气孔,涂层厚度较厚,大约17μm;两步法制备的涂层结构致密,表面光滑,涂层厚度约为2μm,且与基体结合良好。

英文摘要：

The preparation of boron nitride coating on the surface of porous silicon nitride ceramics can improve the performance of the radome, and this research has an important application value in engineering. In the present work, H_3BO_3 and carbon black were used as the original materials to fabricate BN coating on the surface of porous Si_3N_4 substrate. One method was that BN coating was prepared by coating H_3BO_3 and carbon black on the surface of the silicon nitride substrate and then sintered under nitrogen atmosphere（referred to as one-step method）, another method was that B_2O_3 coating was prepared by using H_3BO_3 decomposition coating on the surface of the porous Si_3N_4 substrate, and then sintering under nitrogen atmosphere by thermal reduction reaction（referred to as two-step method）. The phase composition and structure of the coating were studied by X-ray diffraction（XRD） and scanning electron microscope（SEM）. The results revealed that the coating structure prepared from two different methods consisted of BN, and no residual boron oxide（B_2O_3） was existed. The surface of the coating prepared by the one-step method was rough, and there were a lot of cracks and pores, the coating thickness was about 17 μm; the coating prepared by the two-step method had a compact structure and a smooth surface with a coating thickness of about 2 μm and good bonding with the substrate.