Invented by Gary A. Pozarnsky, Michael J. Fee, Cima Nanotech Inc
The Cima Nanotech Inc invention works as followsA method and apparatus for preparing and collecting metal nanoparticles is formed by vaporizing a metal at room temperature. The vaporized metal is then carried in an inert, gaseous medium. A minimum amount of metal solidifies within the gaseous flow. Gaseous material and gaseous flow are moved through or into a dry mechanical pumping device in a gaseous environment. The vaporized metal and nanoparticles, while in the dry mechanical pumping systems or after they have passed through the system are then contacted with a liquid collection medium.
Background for Process for manufacturing metal nanoparticles
Metal particles are used in a variety of applications, including as fillers, active materials, explosives and magnetically sensitive materials. They can also be used for decorative materials, taggants or reflective materials. The present invention is in the field of metal nanoparticle manufacturing and the apparatus used to manufacture nanoparticles.
2. “Background of the Art
There are many processes available to manufacture small metal particles. These processes are available in a variety of technologies, and they exhibit a range of efficiency. Some processes produce solid particles while others produce liquid dispersion particles.
There have been many references describing the use of gas evaporation to produce ultrafine powders. This is especially true for magnetic metal/metal dioxide powders. They appear to be referring to a dry method and not involving liquids. Yatsuya et al., Jpn. J. Appl. The Phys. 13, 749 (1974) involves the evaporation metals on a thin layer of hydrocarbon oil. This is similar to Kimura’s (supra). Nakatani et al., J. Magn. Magn. Magn. Metal atom techniques require high vacuums (pressures lower than 10?3 Torr), so that discrete metals can impinge on the surface of the dispersing medium, before they have the chance to interact with a second species. The metal atom technique involves nucleation in the dispersing media, and not the gas phase. The particle size depends on the dispersing media and cannot be controlled. Additionally, U.S. Pat. No. No.
Kimura and Bandow Bull. Chem. Soc. Japan, 56.3578 (1983), discloses the nonmechanical dispersing fine metal particles. Gas evaporation is also used in this method to prepare colloidal metal particles dispersions. C. Hayashi’s general references on ultrafine metallic particles and gas evaporation can be found in Physics Today December 1987, p.44 and J. Vac. Sci. “Sci.
EPA 209403″ (Toyatoma), describes a method for preparing ultrafine dry particles of organic compounds by using a gas evaporation process. These ultrafine particles are dispersible in water because they have increased hydrophilicity. The particle sizes range from 500 Angstroms up to 4 micrometers. This practice is well-known in the industry. These particles are dispersed using ultrasound, which provides mechanical energy to break up aggregates. The dispersions produced have increased stability toward flocculation.
Other references for dispersing material that is delivered to a medium through a gas stream are U.S. No. No. The particle growth is not described in the gas phase but in the dispersing media. The examples are also all elements in their elemental state and have a significant vapor pressure at room temperature.
U.S. Pat. No. No.
U.S. Pat. No. No. The average particle size for silica gel particles that are to be dispersed into a solution of alkali-silicate and acid must range from 0.05 micrometers to 3.0. If the average particle size is less than 0.05 micrometers then the mechanical strength of spherical particles will be lower and it’s likely that irregular particles will form. This would be unsuitable. In a similar way, if the average particle size is greater than 3.0 micrometers then the mechanical strength of spherical particles will be lower and irregular particles may form. This would be unsuitable. The preferred range for the average particle sizes of silica gel is between 0.1 and 1.0 micrometers.
The use of magnetic fluidized beds, such as those shown in U.S. Pat. No. 5,962,082 (Hendrickson et al.). A magnetic field fluidizes the bed of particles that are magnetically responsive. The fluidized bed is coated with the material (e.g. a liquid). It is possible to transfer the coating composition from magnetic particles onto non-magnetic ones. This process allows for excellent control of the coating thickness and can produce large quantities of coated particles. It also provides other advantages.
U.S. Pat. No. No. 5,958,329 is a method and an apparatus for producing high-speed nanoparticles. (There, nanoparticles are defined as particles with a diameter of 1 to 50 nanometers). A narrow duct separates two chambers. The source material comes from a lower room where it is heated to vaporization. It is then fed continuously into the upper chamber. The upper chamber is where nanoparticles form when the vapor from the lower chamber collides against a gas inert or reactive. The particles are collected in a cooled deposit (e.g. finger 107) and then scraped off. “The particles move in a connective flow to the collection site.
U.S. Pat. No. No. The nanoparticles collected on a surface that is cold (20). After oxidation, the vacuum chamber in which the particles formed is evacuated, and the oxide particle are collected and condensed under different atmospheric conditions such as vacuum, oxygen, and/or air.
The collection process is inefficient, expensive, time-consuming, and harmful to the particles. The chamber must be opened to scrape particles from the deposition surfaces. The system must be shut down for a period of time. The scraping of particles off the deposition surface can fracture some particles, while leaving others agglomerated. Scraping the surface can also cause damage. Layering particles on the finger-sized deposition surface reduces deposition efficiency. The coating of the particles is possible, but it must be done as a re-dispersion or re-distribution of the dried and aggregated particles.
Filtration is an alternative method for particle collection. The filtration is done by placing a particle source, a filtering medium and a vacuum in order. The filter is made up of two surfaces: one facing the source of particles and the other facing the source. The lower pressure on the rear surface allows for the higher pressure to be applied at the front surface, which will push the gas and particles into the filter. A filtration system can have a variety of issues, especially when used with nanoparticles. To collect nanoparticles with an average particle diameter between 1 and 100 nanometers the largest pore in the filter should be smaller than 1 nanometer. Even before the particles begin to collect, it is difficult for a filter surface to be maintained at a pressure that will work. As nanoparticles accumulate on the filter surface gas flow (and pressure-driven movement) becomes more restricted. Fewer particles can be collected, and process efficiency decreases. The particles clog the pores quickly and do not collect efficiently.
U.S. Pat. No. No.
a main tube having a first pipe connecting the closed container to the collector, and a second pipe connecting the centrifugal collection and the vacuum pump
a bifurcated tube which is connected to the vacuum pumps by branching off from the main pipe;
a metal mesh filter disposed on the bifurcated tube; and
pipe switching means” for changing between the main pipe, and a bifurcated tube. The dust collector may be provided between the dust source and the vacuum pump which can include a dry-pump.
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