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Process and apparatus for producing metal nanoparticlesRelated Patent Categories: Specialized Metallurgical Processes, Compositions For Use Therein, Consolidated Metal Powder Compositions, And Loose Metal Particulate Mixtures, Processes, Producing Or Purifying Free Metal Powder Or Producing Or Purifying Alloys In Powder Form (i.e., Named Or Of Size Up To 1,000 Microns In Its Largest Dimension), Utilizing Electrothermic, Magnetic, Or Wave EnergyProcess and apparatus for producing metal nanoparticles description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070101823, Process and apparatus for producing metal nanoparticles. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to a novel process for producing metal nanoparticles by electro-explosion of wires. More particularly, the present invention provides a process for the production of nanoparticles comprising exploding wires into small fragments by application of suitable voltages, at low voltages in order to supply energy to the wires such that the nanoparticle size depends upon various controlling parameters such as applied voltages and current densities. The present invention provides a simple, repeatable process to achieve large production volumes for nanoparticles. BACKGROUND OF THE INVENTION [0002] Nanoparticles have been a source of great interest due to their novel electrical, optical, physical, chemical, magnetic etc. properties. They have significant potential for a wide range of applications including catalysis, magnetic recording media, optoelectronic materials, magnetic fluids, composite materials, fuel cells, pigments and sensors. Their uniqueness arises from their high ratio of surface area to volume (aspect ratio), as these materials have diameters of 100 nm or less. [0003] There are several reports of physical/chemical processes for the production of nanoparticles in technical literature. Nanoparticles prepared by physical methods such as vapour deposition and sputtering have high quality, i.e. clean surfaces and uniform particle size distribution. However, industrial applications for such particles are limited due to the low production rates and high cost. Alternative chemical production methods, such as thermal decomposition and precipitation are currently being studied for the preparation of a wide range of nanoparticles. Chemical methods can provide large quantities of ceramic particles for industrial applications. However, except for precious metals, chemical methods are generally not applied to the production of metallic nanoparticles. [0004] Reference is made to U.S. Pat. No. 6,203,768 for "Process for the production of ultrafine particles" by McCormick, Paul Gerard, Ding, Jun, Miao, Wie-Pang, Street, Robert; wherein a mixture of a metal compound and a suitable reagent is subjected to mechanical activation (using ball mills) to increase the reaction kinetics such that a chemical reaction can occur; which produces a solid nano phase substance. Here the particle size depends on ball size and milling time. The main drawback of this process is that it is time consuming. In one example, for steel balls of size 4.8 mm; 10 nm size particles are produced by 8 hours milling. [0005] Reference is made to U.S. Pat. No. 5,772,754 "Ultra-fine particles and their production method thereof" by Tanaka, Shun-ichiro, Xu,Bing She; wherein electron beam is used to facilitate the reaction. By irradiating with an electron beam in vacuum of metastable particles of a metal oxide, dispersed on an amorphous carbon film, an ultrafine powder comprising ultrafine stable particles of metal oxide and nanoparticles of a metal are produced. The metal particles so produced is a component of the metal oxide. The main drawbacks of this process are that it has to be operated in a vacuum environment and the product is a mixture of the metal and its oxide. [0006] Reference is made to U.S. Pat. No. 4,503,013 "Ultra-high power exploding wire systems" by Lowther, Frank E., where explosion of wires is used to enhance chemical and physical reactions. The material to be exploded is mounted in the housing of a reactor and firing is provided in the housing which will explode the members when the element is moved into contact there with. Here firing is meant in the sense of providing the electrical power for exploding the material. Hot, fast metallic atoms from the exploding element activate given physical or chemical reactions. Here explosion is used to enhance the reaction rate and not to produce nanoparticles. The drawback of this process is that it is used to enhance reactivity and does not result in the formation of nanoparticles. [0007] Reference is made here to U.S. patent application 0020037320 of 2002, wherein it is claimed that nanomaterials are produced with the help of two electrodes by achieving sputtering from one of the electrodes (the target material) in the presence of a dense medium. The basic process, namely sputtering, is well-established in the literature. Use is made here of the process of sputtering in a dense medium to achieve large sputtering yields from a target material. The particles produced are claimed to be nanometer in size. The drawback of this process is that only an ionisable medium can be employed for this purpose together with the use of DC voltages high enough to achieve ionization of the medium. Further, only one of the electrodes is consumed in the process to produce the nanoparticles. [0008] It is therefore important to devise a process for the production of nanoparticles which is simple to apply, results in large production volumes and is therefore industrially feasible, economical and energy efficient. OBJECTS OF THE INVENTION [0009] The main object of the present invention is to provide a novel process for producing metal nanoparticles by electro-explosion of wires, which obviates the above drawbacks. [0010] Another object of the present invention is to produce nanoparticles from conducting parent materials shaped in the form of a wire/plate and are used as electrodes, whereby both electrodes produce the particles. [0011] Yet another object of the present invention is to generate nanoparticles through the dominant mechanism of spark explosion, which is an adaptation of the phenomena called electro-explosion of wires. [0012] Still another object of the present invention is to use low voltages between 12V-50V DC, while also having the possibility of employing AC voltages for the purpose, thereby reducing the energy costs involved in production of nanoparticles. [0013] Still another object of the present invention is to provide for the use of various dense liquids as medium of explosion, irrespective of their dielectric property. [0014] Still another object of the present invention is to provide a method by which capping is achieved of the nanomaterials with a suitable layer of an inert material produced around the nanomaterial due to a reactive step in the environment of the medium present. SUMMARY OF THE INVENTION [0015] The present invention provides a novel process for the production of metallic nanoparticles based on the electro-explosion of wires in a suitable medium. Particularly, the present invention relates to a novel process for the production of metallic nanoparticles by way of controlled explosion of the metal in a suitable medium applying voltages of about 12V and above, to two electrodes, one in the form of a wire and another in the form of a plate, so as to achieve a spark between the electrodes, thereby simulating a situation where the wire cross-section is pinched or reduced and whereby high current densities are achieved along the length of the wire, instantaneously exploding the electrodes by sending shock waves through the bulk of the material, melting them and dispersing them to form small fragments which are then collected by a suitable medium in which the process is initiated, not only for efficient recovery of the material but also to form a protective layer around the now highly reactive nanomaterial so to prevent the nanomaterials from coalescing into large particles by forming a cap, wherein the capping efficiency is determined by the combination of the metal and the medium in which the metal electrodes are exploded and the particle size can be modified by way of altering parameters such as applied voltage, explosion current density and wire diameters. [0016] Accordingly, the present invention provides a process for the production of metallic nanoparticles by the controlled electro-explosion of a metallic wire in a suitable medium comprising: [0017] i. applying a voltage of greater than 12V to a first electrode and a second electrode, both said first and said second electrodes being formed of the metal whose nanoparticles are desired, said first electrode being in the form of a plate, and said second electrode being in the form of a wire, so as to achieve a spark between the said first and second electrodes, thereby simulating a situation where the second electrode cross-section is pinched or reduced and whereby high current densities are achieved along the length of the second electrode, [0018] ii. instantaneously exploding both said first and second electrodes by sending shock waves through the bulk of the material, thereby melting the electrodes and dispersing them to form nanoparticles of the metal, collecting the fragments in a suitable medium such as herein described and recovering the nanoparticles therefrom. [0019] The present also provides an apparatus for the production of metallic nanoparticles by the controlled electro-explosion of a metallic wire in a suitable medium which comprises a reaction vessel containing said medium, a first and second electrodes mounted inside said vessel, submerged in said medium, said first and second electrodes being formed of a metal whose nanoparticles are desired, said first electrode being in the form of a plate, and said second electrode being in the form of a wire, so as to achieve a spark between the said first and second electrodes, thereby simulating a situation where the second electrode cross-section is pinched or reduced and whereby high current densities are achieved along the length of the second electrode, said electrodes being connected to a power source so that current is passed through said electrodes, instantaneously exploding both said first and second electrodes by sending shock waves through the bulk of the material, thereby melting the electrodes and dispersing them to form said nanoparticles of said metal. [0020] Preferably, said first electrode is mounted wherein said first electrode is mounted perpendicular to the base of said reactor. [0021] In another preferred feature, said first electrode is mounted in said reaction vessel through stainless steel slides on an insulating block [0022] In another preferred feature, said insulating block is a plastic block. Continue reading about Process and apparatus for producing metal nanoparticles... Full patent description for Process and apparatus for producing metal nanoparticles Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Process and apparatus for producing metal nanoparticles patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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