High-speed preparation of metal oxide fine powders by microwave cold plasma heating

Abstract

A microwave cold plasma heating technique has been developed by which metal oxide powders can be prepared in a short period of time. A microwave (2.45 GHz)-induced cold plasma was used as the heat source and it was possible to adjust the plasma heating conditions by controlling the internal pressure of the reactor and the microwave output projected into the reactor. Plasma heating is highly effective because the samples are heated directly by the plasma. Therefore, plasma heating for a few minutes could produce metal oxides having similar or better properties than those prepared by conventional heating in an electric furnace under vacuum for as long as a few hours. Almost all types of metal oxides could be prepared by this method from starting raw materials including hydroxides, carbonates, hydrates and sol materials. Silica and alumina fine powders obtained by this method had surfaces free of hydroxy groups.