Method for making amorphous particles using a uniform melt-state in a microwave generated plasma torch
Feed material comprising uniform solution precursor droplets is processed in a uniform melt state using microwave generated plasma. The plasma torch employed is capable of generating laminar gas flows and providing a uniform temperature profile within the plasma. Plasma exhaust products are quenched at high rates to yield amorphous products. Products of this process include spherical, highly porous and amorphous oxide ceramic particles such as magnesia-yttria (MgO—Y 2 O 3 ). The present invention can also be used to produce amorphous non oxide ceramic particles comprised of Boron, Carbon, and Nitrogen which can be subsequently consolidated into super hard materials.
1. A method of producing amorphous powder particles using a uniform melt state process comprising:
a) introducing a feed material in the form of axially uniform precursor droplets from a feed injection device into a microwave plasma torch;
b) entraining said feed material using laminar flow towards a microwave generated plasma;
c) processing said feed material by exposing it to a uniform high temperature profile within said microwave generated plasma to form plasma exhaust gas;
d) quenching at a high rate the plasma exhaust gas of said microwave generated plasma;
e) filtering the quenched plasma exhaust gas; and
f) extracting amorphous powder particle products from said filtered plasma exhaust gas.
2. The method of claim 1 wherein the feed material is comprised of homogenous precursor solutions of nitrates, acetates, alkoxides, or organometallics.
3. The method of claim 1 wherein the axially introduced uniform precursor droplets have a diameter between 1 and 300 micrometers and a size distribution not exceeding 5%.
4. The method of claim 1 wherein the plasma torch is axisymmetric.
5. The method of claim 1 wherein the quenching step is done in air, or under inert gas conditions or under oxidizing conditions, and the quenching rates are less than or equal to 10 6 degrees Kelvin per second (K/s).
6. The method of claim 1 wherein the amorphous powder products are collected using ceramic or stainless steel filters with pore diameters not exceeding the diameter of the product particles.
7. The method of claim 1 wherein the product particles are spherical, dense or porous, and uniform in diameter.
8. The method of claim 1 wherein the powder particles are metal oxides or metal oxide composites.
9. The method of claim 1 wherein the powder product particles are non-oxide compounds with the chemical formula C 3 N 4 , BN, B 4 C, or BC 2 N.
10. The method of claim 8 wherein the metal oxides or metal oxide composites are selected from the group consisting of: MgO, Y 2 O 3 , Al 2 O 3 , MgO—Y 2 O 3 , Y 3 Al 5 O 12 , and MgAl 2 O 4 .