Powder treatment for enhanced flowability

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Ser. No. 61/284,329, filed Dec. 15, 2009 and entitled “MATERIALS PROCESSING,” which is hereby incorporated herein by reference in its entirety as if set forth herein.

FIELD OF THE INVENTION

The present invention relates generally to the field of powder material production. More specifically, the present invention relates to a process for enhancing the flowability of powder materials.

BACKGROUND OF THE INVENTION

This disclosure refers to both particles and powders. These two terms are equivalent, except for the caveat that a singular “powder” refers to a collection of particles. The present invention may apply to a wide variety of powders and particles. Powders that fall within the scope of the present invention may include, but are not limited to, any of the following: (a) nano-structured powders(nano-powders), having an average grain size less than 250 nanometers and an aspect ratio between one and one million; (b) submicron powders, having an average grain size less than 1 micron and an aspect ratio between one and one million; (c) ultra-fine powders, having an average grain size less than 100 microns and an aspect ratio between one and one million; and (d) fine powders, having an average grain size less than 500 microns and an aspect ratio between one and one million.

Powders may be used in a wide variety of applications. In preparation for their respective applications, powders can be operated on by a plasma arc chamber. In one embodiment, the plasma arc chamber comprises two spaced apart electrodes. Working gas flows through the chamber. When current is passed across the gap between the two electrodes, the current energizes the working gas and forms a plasma arc.

FIGS. 1-2 illustrate one embodiment of a general work flow 100 and a simplified system 200 for operating on a powder using a plasma arc chamber. System 200 is presented for illustrative purposes only and is not intended to limit the present invention with respect to size and shape beyond the scope of the claims. Powder is provided by a powder supply 204. For example, the powder can be provided by a cannister of powder. At step 104, the powder is fluidized, such as by means of an introduction gas. At step 106, the fluidized powder then flows through a conduit 206, such as a hose, and into the plasma arc chamber 208. At step 108, the powder is operated on by the plasma arc chamber. Such operation preferably includes a plasma arc being generated by the plasma arc chamber and vaporizing the powder. This vaporization can be used for a variety of different applications, including, but not limited to, nano-sizing the powder, coating the powder, and applying the powder as a coating.

However, problems can arise in flowing the powder through the conduit into the plasma arc chamber. Inter-particle forces between the particles can cause attraction and agglomeration of the particles, making the powder difficult to flow and leading to an inconsistent feed. As a result, the powder is not provided with sufficient control and uniformity.

What is needed in the art is a process for modulating the inter-particle forces between the powder particles in order to enhance the powder's flowability.

SUMMARY OF THE INVENTION

The present invention provides a process for enhancing the flowability of powder material prior to introduction into the plasma arc chamber. This enhancement is achieved by substantially decreasing the inter-particle forces between each particle, thereby reducing the risk of agglomeration.

In one embodiment, a method of enhancing the flowability of a powder is disclosed where the powder is defined by a plurality of particles having an initial level of inter-particle forces between each particle. The powder is treated such that the level of inter-particle forces between each particle is substantially decreased from the initial level. The treated powder is then fluidized and flowed into a plasma arc chamber. The plasma arc chamber generates a plasma arc, and the plasma arc chamber operates on the treated powder using the generated plasma arc.

Preferably, the inter-particle forces are decreased by coating the particles with an organic surfactant. The selection of the coating material depends on the makeup of the powder particles. In a preferred embodiment, non-oxide powder can be coated with sorbitan monooleate, whereas oxide powder can be coated with a material selected from the group consisting of trialkoxysilane, alkyltrialkoxysilane, trialkylalkoxysilane, trialkyldimethylaminosilane, trialkylchlorosilane, and octyltriethoxysilane.

The particles may be coated in a variety of ways. However, in a preferred embodiment, the powder is disposed in a solvent that contains the coating material. The combination of the powder and the solvent can be agitated in order to facilitate the attachment of the coating material to each particle. The remaining solvent is then separated from the coated powder, such as by means of decanting. At this point, the powder can be dried by applying heat to the particles. Additionally, a vacuum pressure may be applied to the particles in order to help remove any of the excess solvent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a general work flow for operating on a powder using a plasma arc chamber.

FIG. 2 is a simplified block diagram illustrating a system for operating on a powder using a plasma arc chamber.

FIG. 3 is a flowchart illustrating one embodiment of a general work flow for operating on a treated powder using a plasma arc chamber in accordance with the principles of the present invention.

FIG. 4 is a flowchart illustrating one embodiment of a general work flow for enhancing the flowability of a powder in accordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the described embodiments will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.

FIG. 3 is a flowchart illustrating one embodiment of a general work flow 300 for operating on a treated powder using a plasma arc chamber in accordance with the principles of the present invention. The powder is defined by a plurality of particles having an initial level of inter-particle forces between each particle. These inter-particle forces create an attraction between the particles which can lead to agglomeration.

At step 302, the powder is treated such that the level of inter-particle forces between each particle is substantially decreased from the initial level. In a preferred embodiment, the level of inter-particle forces is decreased to a negligible level. However, it is contemplated that a minimal amount of inter-particle forces can still exist even after the treatment. While a variety of procedures may be employed to decrease the level of inter-particle forces, a preferred embodiment will be discussed below with respect to FIG. 4.

At step 304, the treated powder is fluidized. This fluidization can be achieved in a variety of ways. In a preferred embodiment, a gas is introduced in order to suspend the particles in air. For example, an introduction gas can be injected into a cannister holding the treated powder.

At step 306, the treated powder is then flowed into a plasma arc chamber, preferably through a conduit. In this fashion, the process 300 can use the same basic system illustrated in FIG. 2. In this case, the powder supply 204 would contain the treated powder, which would then flow through the conduit 206 and into the plasma arc chamber 208.

At step 308, the plasma arc chamber generates a plasma arc and operates on the treated powder using the generated plasma arc. This operation on the treated powder preferably includes the plasma arc vaporizing the powder. Such vaporization can be used for nano-sizing the powder, coating the powder, applying the powder as a coating, and a variety of other applications as well.

As mentioned above, the flowability of the powder can be enhanced in a variety of ways. In a preferred embodiment, each particle is coated with a coating material in order to substantially decrease the inter-particle forces attracting the particles to one another. FIG. 4 is a flowchart illustrating one embodiment of a general work flow 400 for enhancing the flowability of a powder by coating the particles with a coating material.

At step 402, the powder is provided as a plurality of particles having an initial level of inter-particle forces between each particle. The process of the present invention can apply to various types of particles, including oxides and non-oxides.

At step 404, the powder is disposed in a solvent, preferably within a container. The solvent comprises a coating material. In a preferred embodiment, the coating material is organic and is a surfactant. The specific chemical makeup of the coating material depends on the chemical makeup of the powder particles. For non-oxide particles, such as borides, carbides, nitrides, and bare metals, sorbitan monooleate is preferably used as the coating material. For oxide particles, such as silica, the coating material is preferably selected from the group consisting of trialkoxysilane, alkyltrialkoxysilane, trialkylalkoxysilane, trialkyldimethylaminosilane, and trialkylchlorosilane. Octyltriethoxysilane can also be used to coat oxide particles and works particularly well with Y₂O₃. However, it is contemplated that a variety of other coating materials may be used for either oxide or non-oxide particles. While different concentrations of the coating material can be employed, the coating material preferably accounts for a small percentage of the solvent, while the rest of the solvent is formed from solvent materials known in the art, such as water, alcohols (ethanol, methanol, etc.) and hydrocarbons (toluene, cyclohexane, etc.). In a preferred embodiment, the solvent comprises approximately 1% coating material. The coating material can be used to determine the rest of the solvent. For instance, hydrocarbons work particularly well with sorbitan monooleate in coating non-oxide particles.

At step 406, the powder and the solvent are agitated in order to facilitate the attachment of the coating material to each particle. In one embodiment, this agitation includes stirring the powder and the solvent for approximately 1 to 60 minutes at a temperature between approximately room temperature and 80 degrees Celsius. Since the powder has a lot of surface area and the coating material is preferably a surface active agent, a portion of the coating material migrates to the particle surface in a spontaneous process in order to decrease the energy of that interface. While the coating material preferably surrounds the entire particle, it is contemplated that the coating could only cover a portion or portions of the particle and still achieve the objective of the present invention.

At step 408, substantially all of the remaining solvent is separated from the coated powder. The remaining solvent is any portion of the solvent that has not attached to the particles to form a coating. While preferably all of this remaining solvent is removed, a minimal amount may still be left over. In one embodiment, separating the solvent involves decanting the solvent from the container, thereby leaving behind a wet coated powder.

The powder can be washed in the solvent multiple times in order to ensure sufficient coating. For example, the process may repeat at step 404, where the powder is once again disposed in the solvent containing the coating material.

After sufficient washing with the solvent, the powder can be dried at step 410. Heat can be applied to the particles. In one embodiment, the powder is dried at approximately 150 degrees Fahrenheit for about an hour. Mechanical agitation, such as stirring, may be incorporated into the drying process. Additionally, a slight vacuum pressure may be applied to the particles in order to help in removing any of the excess solvent and drying out the coating.

Optionally, the coated powder can be placed with ball bearings in a tumbling dryer with a heating element. The application of this mechanical agitation along with the heating element helps avoid clumping of the particles.

Finally, at step 412, the coated powder is provided having substantially decreased inter-particle forces between each particle. The coating material serves to decrease the inter-particle forces, thereby improving the flow characteristics of the powder.

When the coated particles are vaporized by the plasma arc, the coating material preferably transfers to a gas, thereby separating from the powder particle. In a preferred embodiment, organic materials are used for the coating material because they stand the best chance of being transferred into gases that can be carried away by the flow of gas through the system. On the other hand, heavy alloys, such as silica, are preferably avoided.

The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of principles of construction and operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto. It will be readily apparent to one skilled in the art that other various modifications may be made in the embodiment chosen for illustration without departing from the spirit and scope of the invention as defined by the claims.