Mechanical and dielectric properties of two types of Si₃N₄ fibers annealed at elevated temperatures

The mechanical and dielectric properties of two types of amorphous silicon nitride (Si₃N₄) fibers prior to and following annealing at 800 °C were studied. The tensile strengths of the Si₃N₄ fiber bundles were measured using unidirectional tensile experimentation at room temperature, whereas the permittivity values were measured at 8.2-12.4 GHz using the waveguide method. The results demonstrated that the tensile strength and dielectric properties of Si₃N₄ fibers were correlated to the corresponding composition, microstructure, and intrinsic performance of electrical resistance. The Si₃N₄ fibers with a lower content of amorphous SiN_xO_y presented an improved thermal stability, a higher tensile strength, a higher conductivity, and a significantly stable wave-transparent property. These were mainly attributed to the highly pure composition and decomposition of less amorphous SiN_xO_y.