Characterization of Nanocrystalline Oxide Powders Prepared by CO₂ Laser Evaporation

Abstract

Today, a world-wide interest exists in producing nanosized ceramic powders. One of the suitable techniques is based on the evaporation of solid primary materials by lasers. Although this technique has been known for nearly two decades, the literature has hitherto only rarely reported effective powder yields (a few grams per hour). We produced nanocrystalline zirconia and alumina powders by evaporation of oxides in the focus of a CO₂ laser (transversal flow of the CO₂ gas; P_L = 0.75 ... 4 kW) and by recondensation of the oxides in a carrier gas stream (air, oxygen, argon). Most experiments were carried out in the continuous wave (cw) mode, but earlier ones were also done by means of a pulsed laser (pw). The powder yield depends strongly on the laser power, on the focusing and on the velocity of the moving oxide target. Maximum yields of more than 100 g h^-1 were attained.
The zirconia and alumina powders so prepared consisted of nearly spherical particles with diameters in the range of 10 to 100 nm. The particle distribution can be controlled by the parameters of the formation process. Features of the crystal phases and of the chemical composition of the produced powders are reported.