Microstructure control of porous Si₃N₄ whisker scaffolds by in-situ carbothermal reduction and nitridation reaction

Si₃N₄ whisker scaffolds have great potentials owing to the superior properties of Si₃N₄ and their unique porous structures. Obviously, the properties of the scaffolds are closely related to the morphology and distribution of phases, and the bonding between whiskers. This study proves that the above-mentioned microstructural features can be tailored to a great extent by the in-situ growth of secondary Si₃N₄ products via carbothermal reduction and nitridation (CRN) of SiO₂ inside a β-Si₃N₄ whisker network. Specifically, the yield and morphology (grain size, aspect ratio, etc.) of the CRN product are found to be strongly dependent on the composition and amount of the reactants (SiO₂ and C/SiO₂ molar ratio) and reaction temperature. When reacted at 1300 ℃, a distinctive microstructure is formed in which nano sized and CRN-derived Si₃N₄ whiskers are uniformly distributed in the original micron sized whisker network. The whisker scaffolds reveal improved flexural strength if compared with that without CRN-derived Si₃N₄. This finding indicates the formation of a strong bonding between the β-Si₃N₄ whiskers by the growth of the CRN product. The measured low dielectric constant (2.6 ∼ 3.1) and low dielectric loss (<1.1 ×10⁻²) of the scaffolds makes them suitable for wave transmission application.