Apparatus for producing nanoscale ceramic powders
Assignee:
Inventors:
Joseph J. Helble, Gary A. Moniz, Theodore F. Morse
Patent:
Ultrasonic spray of nanoscale ceramics
An apparatus provides high temperature and short residence time conditions for the production of nanoscale ceramic powders. The apparatus includes a confinement structure having a multiple inclined surfaces for confining flame located between the surfaces so as to define a flame zone. A burner system employs one or more burners to provide flame to the flame zone. Each burner is located in the flame zone in close proximity to at least one of the inclined surfaces. A ultrasonic spray delivery system disposed adjacent the flame zone delivers an aerosol, comprising an organic or carbonaceous carrier material and a ceramic precursor, to the flame zone to expose the aerosol to a temperature sufficient to induce combustion of the carrier material and vaporization and nucleation, or diffusion and oxidation, of the ceramic precursor to form pure, crystalline, narrow size distribution, nanophase ceramic particles.
The mixture is introduced as an aerosol or fine spray by the delivery system, such as by forcing it through a ultrasonic spray nozzle, by atomization or any other device. The temperature environment of the flame zone should be sufficiently high to cause the organic carrier to ignite and react exothermically (i.e., combustion). The high temperature environment preferably comprises a temperature at least 1000 K. and an atmosphere of at least 20% (by volume) oxygen. The temperature range for applications of the present process can be from about 1200 K. to about 3200 K. However, higher or lower temperatures may be preferred for certain specific embodiments. The overall residence time in the high temperature environment typically is less than 5 seconds, more than 20 milliseconds, and preferably about 100 milliseconds. The residence time of the formed ceramic particles in the actual combustion zone (i.e., the burning carrier droplets) is believed to be less than about 50 μs. Residence time in the cooler flame zone typically is about 100 milliseconds.