In situ growth of single crystal Si₃N₄ nanowire foam with good wave-transparency and heat insulation performance

The radome of high Mach number aircraft requires a bearing material that is light weight, capable of wave transmissivity, and has excellent high temperature stability. In this regard, silicon nitride (Si₃N₄) nanomaterials, especially porous macroscopic structures formed by them (such as Si₃N₄ nanowire foam), are promising candidates. However, there have been no studies on the various Si₃N₄ nanofoams. In this study, a carbon template was used with a simple and reliable in situ synthesis method to prepare Si₃N₄ single crystal nanowire foam with a cross-linking structure between nanowires. High purity Si₃N₄ nanowires have the characteristics of low density (8.9 mg/cm³) and high foam volume fraction (17.35%). The nanowires can be distributed spontaneously and uniformly in three-dimensional space. The elasticity of this foam is mainly a result of the high aspect ratio of the nanowires and the large amount of large size pores in the structure. In addition, the foam has an ultralow dielectric constant, good wave transmissivity, and excellent thermal insulation and high-temperature stability. All of these characteristics are related to the special pore structure and intrinsic single crystal structure of the nanowire foam. Thus, Si₃N₄ nanowire foam is a transparent material with heat insulation, wave-transparency, and high temperature resistance, and has special application prospects.