Preparation of high-purity α-Si3N4 nano-powder by precursor-carbothermal reduction and nitridation.

Abstract The high-purity α-Si 3 N 4 nano-powder without any β-Si 3 N 4 impurities was prepared by using a precursor-carbothermal reduction and nitridation method, and the detailed technical parameters were optimized. Using HNO 3 and CO(NH 2) 2 as reaction raw materials, C 6 H 12 O 6 ·H 2 O as carbon source and SiO 2 as silicon source, a porous precursor was prepared at 350 °C, in which the SiO 2 particles were uniformly distributed and in full contact with C. This precursor can be transformed into high-purity α-Si 3 N 4 nano-powder under such optimal technical conditions as the nitriding temperature of 1500 °C, the nitriding duration of 1 h and the nitrogen flow rate of 1800 ml/min. As intermediate products, SiO and Si 2 N 2 O were considered to be involved in the carbothermal process, and the presence of SiO accelerated the carbothermal reaction. Furthermore, the higher nitrogen flow rate took more heat away from the reaction area, suppressing the transformation from α-Si 3 N 4 to β-Si 3 N 4 , which might explain why the final products are mainly composed of high-purity α-Si 3 N 4 powder. [ABSTRACT FROM AUTHOR]