Synthesis and characterization of silicon nitride powders produced in a d.c. thermal plasma reactor

Abstract

Ultra-fine silicon nitride powder was synthesized from the SiCI4-NHa-H2-Ar system using a d.c. plasma torch reactor (production rate 150-400 g h-l). The powder produced is pure white, fluffy and amorphous. The particles are spheroidal in shape with a mean diameter between 30-60 nm forming aggregates of 0.1-0.4 I.tm depending on the operationalconditions. Chemical analysis on the crude powder handled at ambient atmosphere revealed: N(-NH4CI) :37-39%, 0:3-5% and C1:2-3%. The amorphous powder can be crystallized around 1500 ~ under nitrogen to give an m-phase content in excess of 90%. Infrared spectra can be used to semi-quantitatively determine the NH4CI content of the crude powder. That proportion is between 2.5 and 4%. The influence of some process parameters e.g. (N/Si and H2/N molar ratios, internal pressure) on powder properties was also investigated. The N/Si molar ratio was found to be the most important parameter for the powder composition whereas the internal pressure plays a major role on the powder morphology.

Thermal Plasma Synthesis of Ceramic Nanomaterials

“…Most metal nitride nanoparticles were synthesized with high crystallinity in the thermal plasma processes; however, synthesis of crystalline silicon nitride (α-Si 3 N 4 ) nanoparticles has been very challenging. Most reaction products were either heavily contaminated by silicon nanoparticle by-products (2.45 GHz microwave plasma, 1 kW, Ar/N 2 /H 2 plasma, silicon tetrachloride (SiCl 4 ) precursor) or were less crystallized (DC, 10 11 kW, Ar plasma, SiCl 4 /NH 3 /H 2 precursors, 15 75 kPa) [37,38]. This was caused by exposure to temperatures above 1,850 when the silicon nitride was decomposed into silicon and nitrogen.…”