Effects of NH3 Flow Rate on the Thermal Plasma Synthesis of AlN Nanoparticles

Aluminium nitride (AlN) nanoparticles were synthesized by using a non-transferred arc plasma. A pellet of micro-sized aluminium (Al) powders was evaporated by using an argon-nitrogen thermal plasma flame, and ammonia (NH3) was introduced into the reactor as a reactive gas. The flow rate of NH3 was controlled from 5 to 25 L/min at a fixed input power of 10.2 kW. In experiments, unreacted Al powder was found at low NH3 flow rates at 5 and 10 L/min. The size and the crystallinity of the synthesized AlN particles increased with increasing flow rate of NH3 until 20 L/min. The maximum particle size of AlN nanoparticle was about 100 nm at a 20 L/min NH3 flow rate. At an excessive flow rate of NH3 of 25 L/min, however, the size and the crystallinity of AlN were decreased. In order to analyze the experimental results for the thermal plasma synthesis of AlN nanoparticles, we carried out numerical simulations on the thermal plasma. The vortex flow of the thermal plasma near the Al pellet was gradually enhanced with increasing NH3 flow rate from 10 to 20 L/min. The strength of the vortex flow, however, was decreased at the highest NH3 flow rate of 25 L/min.