Restructuring of alumina particles using a plasma torch

A method to modify ceramics using a low power microwave plasma torch is des cribed, The size, shape, surface area, and phase of alumina particles were dramatically modified by passage through an atmospheric pressure argon plas ma, operated at 1 kW or less power. Specifically, irregularly shaped partic les of gamma-alumina with an average diameter of 11 mu m were converted to smaller (ca. 4 mu m) spherical particles primarily consisting of delta- and alpha- (corundum) phases. Also notable was the finding that modifications of the particles, such as changes in surface area, correlate to applied pla sma 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 t he plasma of 0.1 s.