Synthesis of Aluminum Oxynitride Nanopowders in a Plasma Reactor with a Confined Jet Flow

Abstract

Experimental studies on the synthesis of aluminum oxynitride nanopowders in a reactor with a confined plasma jet by the interaction of disperse aluminum with ammonia and oxygen in a flow of nitrogen plasma generated in an electric arc plasma torch are performed. Preliminary calculations of the equilibrium compositions and thermodynamic characteristics of the multicomponent Al–O–N system are carried out. An optimal design of the reaction prechamber of the reactor is performed. Powders having a cubic structure and consisting of aluminum oxynitride phases with an average particle size in the range from 20 to 200 nm are obtained. It is established that the specific surface area of the obtained powders increases from 20 to 71 m²/g, and the nitrogen content in the nanopowders increases from 3.6 to 14.7 wt % with an increase in the flow rate of quenching gas from 1.8 to 6.0 m³/h. At the same time, the oxygen content decreases from 35.5 to 25.5 wt %. At a minimal flow rate of the quenching gas, the metallic aluminum and its oxide phases are present in the obtained powders. With an increase in the amount of quenching gas, the conditions for the mixing of aluminum vapors with oxygen and atomic nitrogen from decomposing ammonia are improved, which leads to the formation of aluminum oxynitride and aluminum nitride. The variation of the synthesis parameters allows us to obtain aluminum oxynitride nanopowders having a specific surface area ranging from 28 to 50 m²/g containing from 1 to 11 wt % of nitrogen and from 25 to 40 wt % of oxygen.