A new synthesis method for producing Si₃N₄ whiskers by heat treating porous Si objects

Silicon nitride whiskers were successfully synthesized in a porous silicon nitride body in an atmosphere of nitrogen and hydrogen gas flow by reaction bonding. Porous silicon nitride bodies, which contained 0.8 mm diameter spherical macropores and had a porosity of over 90%, were prepared by adding pore-forming agent grains. The phase of silicon nitride whiskers was mainly α-Si₃N₄, including a few β-Si₃N ₄ and Si₂N₂O phases. The diameter of the whiskers was about 0.1∼1 μm and the length was higher than 10 μm. More and longer whiskers were formed on the surface of the macropores. The silicon nitride whiskers were grown using the mechanism of chemical vapor deposition.