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Our Technologies: Low-Cost Nano Materials

 (A) Mass Production of Nano Powder (Results of National Science Foundation SBIR Support)

1.                  J. H. Liu and B. Z. Jang, “Process and Apparatus for the Production of Nano-Scaled Powders,” U.S. Patent No. 6,398,125 (June 4, 2002). 

2.                  J. H. Liu and B. Z. Jang, “Method for Producing Environmentally Stable Reactive Alloy Powders,” U.S. Patent No. 6,444,009, 09/03/2002.

3.                  J. H. Liu, “A Dynamic Filtration Method for Separating Nano Powders,” U.S. Patent No. 6,616,734, Sept.9, 2003.

4.                  S. Z. Chen, J. S. Yang and B. Z. Jang, “High-Energy Ball Milling Apparatus and Method for the Preparation of Nanometer-Sized Powders,” U.S. Patent No. 6,126,097 (10/03/00).

5.                  L. W. Wu, “Method for Production of Nano-Porous Coatings” U.S. Patent No. 6,465,052 10/15/2002.

6.                  W. C. Huang, “Method for the Production of Semiconductor Quantum Particles,” U.S. Patent No. 6,623,559, 9/23/2003.

            Nano-scaled Particles (Nano Powder): Nano-phased or nano-structured metals, semiconductors, compounds, and ceramics derived from nano-scaled particles are known to exhibit unique physical and mechanical properties and are finding increasing use in a wide range of industrial sectors, such as biomedical, micro-electronic, pharmaceutical, energy conversion and storage, and structural reinforcement.  Conventional techniques for producing nanometer-sized particles share the severe drawback of extremely low production rates.  These low production rates, resulting in high product costs, have severely hampered the widespread acceptance of nano-phased materials. There is a clear need for a method of preparing nanometer-sized powder materials at much higher rates and lower costs.

With NSF SBIR Phase-II support, researchers at Nanotek Instruments, Inc., have developed innovative nano materials processes, twin-wire arc vapor deposition (AVD), which are capable of mass-producing a wide range of nano-scaled particles including metals, metal compounds, semiconductors, oxides, non-oxide ceramics, and composites.  AVD processes also allow for concurrent surface treatment or individual particle encapsulation of nano materials during their formation procedures. These AVD-based technologies are protected by 14 patents (5 issued and 9 pending).    

The  AVD method is capable of synthesizing a nano-structured material, which can be a nano powder, nano-porous coating, or solid film of nanometer thickness or nano-scaled phases. The method includes four primary steps (Fig.1):

(A) operating a twin-wire arc nozzle (comprising two wires and a working gas being controllably fed into a reaction chamber) to form an arc between two converging leading tips of the two wires to heat and melt (preferably vaporize) the starting material at the leading tips for providing a stream of liquid droplets (preferably vapor species);

(B) optionally operating a second high energy source for producing a vaporizing zone adjacent to the arc wherein the unvaporized droplets are vaporized to form vapor species;

(C) cooling the vapor species for forming the nano-structured material. The second high energy source can be a laser beam, electron beam, ion beam, flame, or arc plasma. The method may further include an additional step:

(D) introducing a stream of reactive gas into the reaction chamber to impinge upon and exothermically react with the vapor species to produce the nano-scaled clusters.  Features of the AVD method may be summarized as follows:

1.         A wide variety of nano-structured metals, alloys, metal compounds, semiconductors, and ceramic materials (including simple oxides and mixed oxides) can be readily produced using the present method. Any metal element may be vaporized to react with hydrogen, oxygen, carbon, nitrogen, chlorine, fluorine, boron, and sulfur to form, respectively, metal hydrides, oxides, carbides, nitrides, chlorides, fluorides, borides, and sulfides.

2.         The wire material may contain an alloy of two or more elements to form uniformly mixed compound or ceramic powder particles (e.g., composites or complex mixed oxides).

3.         The method allows a spontaneous reaction to proceed between a metallic element and a reactive gas such as oxygen. The reaction heat released is spontaneously used to maintain the reacting medium at a sufficiently high temperature so that the reaction can be self-sustaining until completion for the purpose of producing a compound or ceramic material. 

4.         The method permits an uninterrupted feed of wires or rods, which can be of great or continuous length. This feature makes the process fast and continuous and now enables the mass production of nano-structured materials cost-effectively.

5.         The method is simple and easy to operate. It does not require the utilization of heavy and expensive equipment. The overall product costs are very low.

6.         This method enables simultaneous nano particle formation and surface coating (or encapsulation) of individual particles for improved compatibility with an intended matrix material or improved dispersibility in an intended liquid medium. This coating or encapsulating technology has been developed by us [4,13,14].

These features distinguish AVD technology from other state-of-the-art technologies in many ways, as summarized in Table 1.

Table 1. The features, advantages, and benefits of AVD technology.

            A pilot-scale AVD system (Fig.2) with a production capacity of 10 kg/hour has been constructed and is now fully functional. This system has a reaction chamber that is capable of synthesizing a broad array of nano materials.  These patent-protected, AVD-based nano materials technologies are innovative, technically superior, and commercially viable.