Patent Application
20130192517
1. Field of the Invention
This invention relates in general to nano technology and, more specifically, to technology for synthesizing alumina Al2O3 nanofibers from molten aluminum.
2. Description of the Related Art
Nanotechnology deals with developing materials, devices, or other structures having at least one dimension sized between 1 and 100 nanometers. Nanoparticles are the particles having at least one dimension sized between 1 and 100 nanometers. On the other hand, nanofibers are defined as fibers with diameters less than 1000 nanometers.
At the present time, several kinds of nanoparticles are known in the art, including, without limitation, carbon nano tubes (CNT), nano powders produced from silicon carbide, alumina and other materials. Also known in the art are various methods for nanoparticle or nanofiber fabrication, including, without limitation: hydrothermal process, sol gel process, mercury mediated process, flame-spray method, vapor-liquid-solid process as well as electrospinning method.
However, the conventional methods for nanoparticle fabrication suffer from low production output and, consequently, are expensive and time consuming. For example, a system for enabling a typical electrospinning nanofiber fabrication process consists of three major components: a high-voltage power supply, a spinneret, and an electrically conductive collector. A liquid used in the aforesaid electrospinning technique is fed at a predetermined rate using a syringe or other suitable pump. In many cases, a well-controlled environment (e.g., humidity, temperature, and atmosphere) is critical to the operation of electrospinning, especially for the fabrication of ceramic nanofibers. As would be appreciated by those of skill in the art, these features make the electrospinning process rather expensive as well as resource and time-consuming. The other conventional nanofiber fabrication methods suffer from similar drawbacks and production bottlenecks, which reduce their throughput. In addition, the conventional nanofiber fabrication techniques such as the aforesaid electrospinning process are not suitable for manufacturing metal oxide nanofibers.
Thus, new techniques for manufacturing of nanofibers, including, without limitation, metal oxide nanofibers, are needed to address the growing industrial demands for these materials.
The inventive methodology is directed to methods and systems that substantially obviate one or more of the above and other problems associated with conventional techniques for producing nanoparticles and nanofibers.
In accordance with one aspect of the present invention there is provided a method for synthesizing monocrystalline alumina Al2O3 nanofibers directly from a melt comprising molten metallic aluminum, the method involving a controlled liquid phase oxidation of the melt. In the inventive method, the nanofibers have a diameter between 3 and 45 nm and length of more than 100 nm.
In one or more embodiments, the synthesis of the monocrystalline alumina Al2O3 nanofibers is performed at a temperature of the melt within a range of 660° C. to 1000° C.
In one or more embodiments, the melt further includes at least one of:
In one or more embodiments, the synthesis of the monocrystalline alumina Al2O3 nanofibers is performed at oxygen content between 0.001 and 5 wt. %.
In one or more embodiments, the growth of the monocrystalline alumina Al2O3 nanofibers takes place on the surface of melt or on the boundary of the melt and another medium.
In one or more embodiments, the inventive method further involves harvesting the grown monocrystalline alumina Al2O3 nanofibers from the surface of the melt or from the boundary of the melt and another medium.
In accordance with another aspect of the present invention there is provided a method for synthesizing monocrystalline alumina Al2O3 nanofibers. The inventive method involves: obtaining a melt by heating metallic aluminum in a reactor; controlling oxygen content inside the reactor; adding at least one additive to the melt; and performing controlled liquid phase oxidation of the melt by providing additional oxygen into the reactor. In the inventive method, the synthesized monocrystalline alumina Al2O3 nanofibers have a diameter between 3 and 45 nm and length of more than 100 nm.
In one or more embodiments, the synthesis of the monocrystalline alumina Al2O3 nanofibers is performed at a temperature of the melt within a range of 660° C. to 1000° C.
In one or more embodiments, the at least one additive includes at least one of:
In one or more embodiments, the synthesis of the monocrystalline alumina Al2O3 nanofibers is performed at oxygen content between 0.001 and 5 wt. %.
In one or more embodiments, the growth of the monocrystalline alumina Al2O3 nanofibers takes place on the surface of melt or on the boundary of the melt and another medium.
In one or more embodiments, the inventive method further involves harvesting the grown monocrystalline alumina Al2O3 nanofibers from the surface of the melt or from the boundary of the melt and another medium.
In accordance with yet another aspect of the present invention there is provided a reactor for synthesizing monocrystalline alumina Al2O3 nanofibers. The inventive reactor incorporates: a reaction chamber and a heating mechanism for heating metallic aluminum to obtain a melt, the metallic aluminum being heated in the reaction chamber; a valve assembly for controlling oxygen content inside the reactor; and an inlet for adding at least one additive to the melt and providing additional oxygen into the reaction chamber. A controlled liquid phase oxidation of the melt takes place inside the reaction chamber to synthesize monocrystalline alumina Al2O3 nanofibers when additional oxygen is provided into the reaction chamber. The synthesized monocrystalline alumina Al2O3 nanofibers have a diameter between 3 and 45 nm and length of more than 100 nm.
In one or more embodiments, the reactor further incorporates a sensor assembly for monitoring at least one parameter inside the reaction chamber.
In one or more embodiments, the heating mechanism is an induction based heating mechanism.
In one or more embodiments, the reactor further incorporates a cover closing the reaction chamber adopted for removal of the synthesized monocrystalline alumina Al2O3 nanofibers.
In one or more embodiments, the reactor further incorporates a control logic configured to maintain at oxygen content inside the reactor between 0.001 and 5 wt. %.
In one or more embodiments, the reactor further incorporates a stirring mechanism for achieving homogeneity of the melt.
Additional aspects related to the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Aspects of the invention may be realized and attained by means of the elements and combinations of various elements and aspects particularly pointed out in the following detailed description and the appended claims.
It is to be understood that both the foregoing and the following descriptions are exemplary and explanatory only and are not intended to limit the claimed invention or application thereof in any manner whatsoever.
The accompanying drawings, which are incorporated in and constitute a part of this specification exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the inventive technique. Specifically:
In the following detailed description, reference will be made to the accompanying drawing(s), in which identical functional elements are designated with like numerals. The aforementioned accompanying drawings show by way of illustration, and not by way of limitation, specific embodiments and implementations consistent with principles of the present invention. These implementations are described in sufficient detail to enable those skilled in the art to practice the invention and it is to be understood that other implementations may be utilized and that structural changes and/or substitutions of various elements may be made without departing from the scope and spirit of present invention. The following detailed description is, therefore, not to be construed in a limited sense.
The most important characteristics of the nanoparticles fabrication process is the consistency of the produced nanoparticle size, as well as diameter to length ratio, and the throughput of the fabrication process. When compared with other methods, nanoparticle synthesis technology called controlled liquid phase oxidation of aluminum (also know as Kutuzov process) achieves the highest degree of size consistency of produced nanoparticles. Using this method, nanoparticles (nanofibers) with diameters between 3 and 45 nanometers and lengths of more than 100 nanometers may be produced. It should be noted that the length of the produced nanoparticles (nanofibers) is not limited in the aforesaid process and that fibers of any length may be achieved. Moreover, the aforesaid nanofiber synthesis process provides high throughput reaching several kilograms of high quality nanofibers per hour from one equipment unit.
The below description of various embodiments of the invention, primarily deals with nanofibers possessing two linear dimensions of less than 45 nm. Because the nanofibers described herein have circular cross section, the size of the nanofiber will be specified below by reference to its diameter.
In accordance with one or more embodiments of the invention, there is provided a method for synthesizing monocrystalline alumina nanofibers by controlled liquid phase oxidation of aluminum. In one or more embodiments, the method comprises two stages. During the first stage, various additives are introduced into molten metallic aluminum. During the second stage, the alumina nanofibers are synthesized from the resulting melt in the presence of oxygen. In one or more embodiments, the inventive method is performed in a reactor.
In accordance with one or more embodiments of the invention, the reactor is designed to provide the heating and enable melting of the aluminum. An exemplary embodiment of the reactor 100 is illustrated in
In one or more embodiments, the reactor is designed to maintain a sustained temperature of between 660° C. and 1,000° C. When the additives described below are introduced into the molten aluminum, it is desirable to provide steady and uniform the stirring of the melt. To this end, the aforesaid reactor may be provided with a stirring mechanism (not shown in
In accordance with one or more embodiments of the invention, the heating of the melt is performed using induction heating or electrical resistance heating (ERH, also known as electrical resistive heating) methods, which are well known to persons of ordinary skill in the art. To this end, the reactor may incorporate an appropriate heater. However, the present invention is not limited only to the aforesaid induction heating or electrical resistance heating methods and any other suitable heating method could be utilized for heating, melting and maintaining the required temperature of the material. It should be noted that the heater should preferably provide even heating of the entire volume of the material in the reactor. In addition, in one or more embodiment, the reactor incorporates means for controlling the content of the atmosphere inside the reactor. Construction and methods of application of such means are well known to persons of ordinary skill in the art.
In accordance with one or more embodiments of the invention, in order to synthesize alumina nanofibers, metallic aluminum having purity of 99.7% is first loaded into the reactor 100 in step 201 and melted in the reactor n step 202, see
In accordance with one or more embodiments of the invention, the following additives are introduced into the heated melt in step 203 to achieve an additive concentration in the range indicated next to the respective additive:
In one or more embodiments, a. through z. above summed up represent less than 49 wt. % of the molten metallic aluminum, all other elements (except for aluminum) represent less than 0.03 wt. % each, and all other elements (except for aluminum) together comprise less than 1 wt. % of the molten metallic aluminum.
In accordance with one or more embodiments of the invention, the aforesaid additives are introduced into the melt not in their pure form, but as part of compositions and/or alloys. This may facilitate the dissolution of the respective additives in the melt and result in a higher degree of homogeneity of the melt.
In one embodiment of the inventive technique, one or more of the aforesaid additives are introduced into the melt in a solid powder form. In an alternative embodiment, the additives may be introduced in a pre-melted form. To facilitate attaining the proper homogeneity of the resulting melt, in one or more embodiments, the stirring mechanism may be used in the reactor 100 to perform mixing in of the additives in step 204, see
In accordance with one or more embodiments of the invention, once suitably homogeneous melt is obtained, oxygen is introduced into the melt, see step 205. In one or more embodiments, oxygen is introduced through melt's surface by means of diffusion. In another embodiment, oxygen is injected into the melt using an injector. Finally, in an alternative embodiment, oxygen is introduced into the melt through introducing a composition or compositions of oxygen with one or more of the following chemical elements: Vanadium (V), Chrome (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Cuprum (Cu) , Zink (Zn), Selenium (Se), Silicon (Si), Sulfur (S), Tellurium (Te), Cerium (Ce), Praseodimium (Pr), Neodimium (Nd), Promethium (Pm), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutecium (Lu).
In accordance with one or more embodiments of the invention, oxygen is introduced up to a concentration of 0.001 to 5 wt. %. Once oxygen is introduced and reaches the indicated concentration, the synthesis of nanofibers takes place either on the surface of the melt or on a boundary between the molten aluminum and another medium. In one or more embodiments, the grown monocrystalline alumina Al2O3 nanofibers are harvested from the surface of the molten metallic aluminum or from the boundary of the molten metallic aluminum and another medium. In accordance with one or more embodiments of the invention, the synthesis of the monocrystalline alumina Al2O3 nanofibers is performed within temperature range of the molten metallic aluminum from 660° C. to 1000° C. Finally, the aluminum nanofibers are collected at step 206. In one or more embodiments, the aluminum nanofibers are synthesized in gamma phase. In various alternative embodiments, the aluminum nanofibers may be synthesized in Xi phase or other phases, depending on the specific parameters of the synthesis process.
In accordance with one or more embodiments of the invention, it order to insure continuous nanofiber synthesis process, it is desirable to provide a steady supply of oxygen to the reactor to maintain oxygen concentration within desired limits. In addition, the chemical composition of the melt and the temperature should also be appropriately maintained within proper limits during the synthesis process.
As the alumina nanofibers are formed on the surface of the melt during the synthesis process, they can be harvested from the melt's surface. The diameter of the produced nanofibers can be controlled through the parameters of the synthesis process, such as temperature and chemical composition of the melt. On the other hand, the length of the produced nanofibers is determined by synthesis time. In one or more embodiments, the nanofiber synthesis speed may vary from 0.01 mm/hour to 100 mm/hour.
It should be noted that the described method may also be utilized to synthesize polycrystalline alumina nanofibers by changing the synthesis conditions during the synthesis process and/or by applying an external action on the surface of the molten aluminum.
Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. Various aspects and/or components of the described embodiments may be used singly or in any combination in the process for nanofiber synthesis. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
This regular U.S. patent application relies on and claims the benefit of priority to U.S. provisional patent application No. 61/593,204 filed on Jan. 31, 2012, the entire disclosure of which is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61593204 | Jan 2012 | US |
