Restructuring of alumina particles using a plasma torch

Abstract

A method to modify ceramics using a low power microwave plasma torch is described. The size, shape, surface area, and phase of alumina particles were dramatically modified by passage through an atmospheric pressure argon plasma, operated at 1 kW or less power. Specifically, irregularly shaped particles of γ-alumina with an average diameter of 11 μm were converted to smaller (ca. 4 μm) spherical particles primarily consisting of δ- and α- (corundum) phases. Also notable was the finding that modifications of the particles, such as changes in surface area, correlate to applied plasma energy. The plasma torch was operated with an argon flow rate of 5 slpm, power of between 400 and 1000 W, and average particle residence time in the plasma of 0.1 s.