The present invention is generally directed to a microwave plasma torch used in materials processing. More particularly, the present invention is directed to a microwave plasma torch which generates laminar flow during materials processing. The laminar flow produced allows for the production of uniform particles and a homogenous materials distribution, which leads to improved characteristics in the final product. Even more particularly, the present invention is directed to a microwave plasma torch which can be used for nanomaterial powder production and for spray coating materials onto various substrates.
When processing materials using a microwave plasma torch, a gas swirl flowing at high velocity prevents the plasma from attaching to the walls of the dielectric tube. This swirl gas subjects the materials to turbulent flow causing the materials to travel from the center of the tube, in line with the materials injection point, towards the surface of the tube wall, where the temperature is significantly lower than in the center of the tube. This subjects the materials to significantly asymmetrical temperature profiles and results in non-uniform particles and non-homogenous materials, which adversely affects the properties of the final product. Thus there is a need for a uniform processing environment for materials processed using microwave plasma. However, no such method has yet been reported.
From the above, it is therefore seen that there exists a need in the art to overcome the deficiencies and limitations described herein and above.
The shortcomings of the prior art are overcome and additional advantages are provided through the use of a plasma torch apparatus that is capable of producing laminar flow patterns.
In accordance with one embodiment of the present invention there is provided a method for producing laminar flow inside a plasma forming chamber while maximizing the entrainment velocity of injected particles used in materials processing. The present invention accomplishes this through the use of a plasma torch possessing several features.
The plasma torch of the present invention comprises a set of at least three staggered tubes fused together at one end. The lengths of the tubes are selected to provide laminar flow patterns for both particle entrainment and for protection from the plasma plume. The inner tube is the shortest and the outer tube is the longest. The length differential between the inner tube and the middle tube is chosen to provide a flow path for the gases so as to prevent turbulent flow effects from forming. A second laminar flow is also formed between the outer and middle tubes, which serves to protect the walls of the outer tube from contact with the plasma plume.
Another feature which promotes laminar flow is provided by gas injection ports which are angled relative to the central axis of the torch. This serves to ensure the uniformity in the laminar flow of gases inside the plasma torch.
Thirdly, the inner tube is tapered at the open end. This serves to reduce turbulent effects when the entrainment gas meets the injected particles at the open end of the inner tube.
A further feature of the current invention is that the spacing between the inner and middle tubes is selected so as to increase the entrainment velocity of the injected particles.
A source of microwave energy propagated by a waveguide is used to create a plasma plume at the open end of the middle tube. The maximum outside diameter of the outer tube is generally selected to be inversely proportional to the frequency of the microwave radiation.
Therefore, an object of the present invention is to provide a laminar flow environment, free of turbulent flow effects, for the material that goes through the plasma resulting in nanoparticles with uniform sizes and shapes and a homogenous materials distribution.
It is another object of the present invention to enhance plasma processing of materials so as to provide a product with improved thermal properties, improved corrosion and wear resistance and a higher tolerance to interface stresses.
It is still another object of the present invention to keep the tube walls cleaner.
It is also another object of the present invention to keep the tube walls cooler.
The microwave plasma torch described in this application can be used to produce nanomaterial powder and for the spray coating of materials onto various substrates.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention.
The recitation herein of desirable objects which are met by various embodiments of the present invention is not meant to imply or suggest that any or all of these objects are present as essential features, either individually or collectively, in the most general embodiment of the present invention or in any of its more specific embodiments.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with the further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:
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While the invention has been described in detail herein in accordance with certain preferred embodiments thereof, many modifications and changes therein may be effected by those skilled in the art. Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the spirit and scope of the invention.
This invention was made with government support under Personal Service Agreement No. 6497 awarded by the Department of Defense/Navy/Office of Naval Research. The government has certain rights in the invention.
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