In situ synthesis of Si₃N₄ from Na₂SiF₆ as a silicon solid precursor

The aim of this investigation was to synthesize Si₃N₄ through the reaction of nitrogen with SiF_4(g) produced during the thermal decomposition of sodium hexafluorosilicate (Na₂SiF₆) and based on an experiment design, optimize the processing conditions. The quantitative effect and the contribution of the processing parameters on the amount of Si₃N₄ formed was determined using analysis of variance (ANOVA). Results show that particles, whiskers/fibers and coatings of α and β-Si₃N₄ can be produced in the same reaction chamber where the silicon precursor (SiF₄) is generated. The optimum conditions for maximum amount of Si₃N₄ formed are: 60 min, 1300 °C, N₂-NH₃, 17 mbar, a preform of 85 SiC:15 Si (wt.%) with 50% porosity, and a compact of Na₂SiF₆ of 25 g. The versatility for synthesizing Si₃N₄ with a variety of morphologies through an in situ process suggests the potential of the proposed route for the economic production of Si₃N₄.