A novel aerosol combustion process for the high rate formation of nanoscale oxide particles

We report a new method for the high rate formation of nanophase ZrO2 and Al 2O3 powders, In the experimental arrangement, a solution of metal alkoxides in their parent alcohols is converted into an aerosol of approximately 30 mu diameter droplets by means of an ultrasonic spray nozzle, The aerosol is mixed with oxygen immediately after formation and combusted in a specially designed burner at high temperature. The resulting oxide particles are the rmophoretically collected and examined using TEM and X-ray diffractometry, A novel, patented, burner design permits a significant reduction in tempera ture gradients normal to the flame, As a consequence, it is possible to obt ain significantly better control over particle size and morphology and, in addition, hard agglomerates are absent. This is a significant departure fro m the process found in a typical flame reactor. With this technique, spheri cal, unnecked particles in the range from 5 to 140 nm (peaking sharply at 4 0 nm) are produced. There is no correlation between the initial liquid drop let size and the final particle size. The method was successfully applied t o the formation of zirconium and aluminum oxide at synthesis rates in exces s of 3 g/min, Experiments to measure the flame temperature using an optical technique yielded temperatures between 2300 K and 3000 K, depending on the position in the dame and the type of precursor solution used. We note that this technique can be readily extended to more complex oxides such as YAG and BaSrTiO3.