Analysis and experiments on thermal plasma processing for ultrafine powder synthesis of aluminum nitride

Summary form only given, as follows. Plasma synthesis experiments for producing ultrafine powders of aluminum nitride (AlN) are carried out using a non-transferred dc plasma torch of which the jet flame can vaporize the aluminum powders injected into it to make a chemical reaction with nitrogen gas. For predicting the optimum processing parameters (the size, injected location and velocity of Al powders, and the ratio of nitrogen to argon are gases), the trajectory and the evaporation state of an Al particle are found by solving momentum and heat transfer equations. In addition, equilibrium chemical compositions are analyzed by the Gibbs free-energy minimization method. The synthesis system consisting of a plasma torch, a reactor and a quenching chamber has been built for synthesis and quenching of ultrafine powders of AlN. A fully saturated fractional factorial test is employed to determine optimum process conditions for input power to the torch and flow rates of arc, carrier and reaction gases. Material evaluations of synthesized AlN are carried out by TEM, ESCA and XRD, and it is shown that some of the produced powders have a hexagonal crystal structure of AlN with the size of 10-100 nm, and that the purity of AlN reaches up to 72%.