Preparation and properties of SiC(N)/Si₃N₄ radar wave-absorbing nanocomposites

We have engaged in a long-term project of obtaining high-quality RAM (radar wave-absorbing materials). Pressureless sintering process is promising for preparing SiC (N)/Si₃N₄, a type of RAM. But such preparation may bring with it disagreeable features. Our aim is to investigate the causes of these possible disagreeable features in preparation for discovering how to prepare satisfactory SiC(N)/Si₃N₄. SiC(N) powder was synhesized by laser induced HMDS (((CH₃)₃Si)₂NH) and ammonia. X-ray diffraction, scanning electron microscopy and strength analyses were performed on the samples. The results show that the sintering density, the content and size of β-Si₃N₄ and the strength of SiC(N)/Si₃N₄ decrease with the increase of SiC(N) powder in sample. The addition of SiC(N) powder to Si₃N₄ enhances the glutinosity of glass formed during sintering process by sintering additives and SiO₂ film on the surface of Si₃N₄ and thus lowers the sintering density of the sample. We believe that the higher glutinosity retards the dissolution of α-Si₃N₄ into it, reduces the concentration of Si₃N₄ in the glass, diminishes the formation of nuclei of β-Si₃N₄ in the glass, and counteracts the growth of β-Si₃N₄.