Preparation of Spherical Alumina Particles by Means of Plasma Flame and Their Characters

Abstract

In order to prepare small spherical alumina particles by means of a plasma flame, a feeder of fluidized bed type was devised, and effects of operating conditions of the plasma on preparation of alumina spheres were investigated. Characters of the alumina spheres obtained were also examined. Results obtained were summarized as follows:1) The higher was the temperature of plasma flame, the more amounts of spherical particles were prepared. Almost all of particles smaller than 8μ and 80-90% of particles smaller than 15μ became spheres, when the plasma torch was operated with following condition: 2-3g/min of raw alumina powder with 3-5l/min of the amount of gas flow and 400A of arc electric current and 20l/min of the amount of arc gas flow.2) State of surface and internal texture of the spheres obtained varied with particle size of the samples and with operating conditions of the plasma torch.3) The small alumina spheres contained appreciable amounts of γ-alumina with α-one. Amounts of the γ-alumina increased with decrease of particle size of the spheres. Lattice constant of the γ-alumina increased with increase of temperature of the plasma flame, but did not change with particle size of the spheres. Inversion of the γ-alumina to α-one began at 950°C and finished nearly completely at 1300°C for 1h except of remaining small amount of θ-alumina.