Method for the densification and spheroidization of solid and solution precursor droplets of materials using microwave generated plasma processing
A method for processing feed material to produce dense and spheroidal products is described. The feed material is comprised of powder particles from the spray-drying technique or solution precursor droplets from ceramic or metallic materials. The feed material is processed using plasma generated from a microwave. The microwave plasma torch employed is capable of generating laminar flow during processing which allows for the production of spheroidal particles with a homogenous materials distribution. This results in products having improved thermal properties, improved corrosion and wear resistance and a higher tolerance to interface stresses.
1. A method of producing spheroidal and dense powder products which comprises:
introducing feed material through a materials feeder into a microwave plasma torch;
entraining said feed material using an axis-symmetric laminar entrainment flow towards a microwave generated plasma;
guiding said feed material towards the microwave generated plasma using an axis-symmetric laminar cooling flow;
processing said feed material by exposing it to a uniform temperature profile within the microwave generated plasma;
quenching plasma exhaust of said microwave generated plasma;
filtering the exhaust gas of said microwave generated plasma; and
extracting powder products from said filtered exhaust gas.
2. The method of claim 1 wherein said feed material is a powder with a substantially non-spherical shape.
3. The method of claim 1 wherein said feed material is a homogenous solution or a suspension of solution precursors injected as droplets.
4. The method of claim 1 wherein the microwave plasma torch is an axis-symmetric microwave plasma torch and said feed material is introduced along the central axis of said axis-symmetric microwave plasma torch.
5. The method of claim 1 wherein said materials feeder uses a fluidized bed.
6. The method of claim 1 wherein the materials feeder is a nebulizing atomizer which produces a mist of droplets having a diameter size ranging between 0.5 micrometers and 200 micrometers.
7. The method of claim 1 wherein the materials feeder is a droplet maker which uses a piezo electric transducer that injects uniform droplets to obtain uniformly dense and spherical products.
8. The method of claim 1 wherein the quenching step includes cooling the microwave plasma exhaust at quenching rates not less than 10 3 ° C./sec.
9. The method of claim 1 wherein the filtering step includes filtering the exhaust from the microwave plasma through bag filters and collecting spherical powder.
10. The method of claim 1 wherein the filtering step includes quenching into water.
11. The method of claim 1 wherein the powder product is densified to a range of 95% to 100%.