Synthesis of alpha-Si3N4 whiskers or equiaxed particles from amorphous Si3N4 powders

Silicon nitride (Si3N4) particles with different morphologies have been used in many fields. In this work, alpha-Si3N4 whiskers and granular particles with high-phase purity were successfully tailored by the controllable crystallisation process of amorphous Si3N4 powders under different N-2 pressure. Impressively, alpha-Si3N4 whiskers were prepared by simply heat treating amorphous Si3N4 powders at 1550 degrees C for 2 h under the low N-2 pressure of 0.2 MPa, whereas equiaxed alpha-Si3N4 particles with uniform size of similar to 280 nm were obtained under an elevated N-2 pressure of 2.0 MPa. With the evaluated N-2 pressures and temperatures, large scale alpha-Si3N4 whiskers or equiaxed alpha-Si3N4 particles could be produced. The growth mechanisms of the alpha-Si3N4 particles with distinct morphologies were rationally proposed, and these consist of two main growth processes. First, amorphous Si3N4 powders decomposed into Si(g) and N-2(g) under high-temperature treatment. Subsequently, N-2(g) dominated the recombination of the evaporated chemical with the Si3N4 molecule. The initial N-2 concentration, which plays a key role in tailoring the shape and size of products, was controlled by the N-2 pressure.