Process for the manufacture of metal nanoparticle

Details Process for the manufacture of metal nanoparticle Process for the manufacture of metal nanoparticle

2001-12-20

2004-02-10

Wyszomierski, George (Department: 1742)

Dispensing

Gas or vapor dispensing

With nongaseous material dispensing

C222S603000, C422S213000, C422S244000

Reexamination Certificate

active

06688494

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
Metal particles find a wide range of use as fillers, active media, explosives, magnetically sensitive materials, decorative materials, taggants, and reflective material. The present invention relates to the field of metal nanoparticle manufacture and apparatus for the manufacture of nanoparticles.
2. Background of the Art
Many processes are available for the manufacture of small metal particles. These processes cover a wide range of technologies and exhibit a wide range of efficiencies. Some processes produce dry particles, while other processes produce particles in liquid dispersions.
Numerous references have appeared describing use of the gas evaporation technique to produce ultrafine metal powders, especially magnetic metal/metal oxide powders (often referred to as magnetic pigments). These appear to exclusively refer to a dry process and do not involve contact with liquids. Yatsuya et al., Jpn. J. Appl. Phys., 13, 749 (1974), involves evaporation of metals onto a thin film of a hydrocarbon oil (VEROS technique) and is similar to Kimura (supra). Nakatani et al., J. Magn. Magn. Mater., 65, 261 (1987), describe a process in which surface active agents stabilize a dispersion of a ferromagnetic metal (Fe, Co, or Ni) vaporized directly into a hydrocarbon oil to give a ferrofluid using a metal atom technique. The metal atom technique requires high vacuum (pressures less than 10
−3
torr) such that discrete metal atoms impinge onto the surface of a dispersing medium before the metal atoms have a chance to contact a second species in the gas phase. In this metal atom process, nucleation and particle growth occur in the dispersing medium, not in the gas phase. Thus, particle size is dependent on the dispersing medium and is not easily controlled. Additionally, U.S. Pat. No. 4,576,725 describes a process for making magnetic fluids which involves vaporization of a ferromagnetic metal, adiabatic expansion of the metal vapor and an inert gas through a cooling nozzle to condense the metal and form small metal particles, and impingement of the particles at high velocity onto the surface of a base liquid.
Kimura and Bandow, Bull. Chem. Soc. Japan, 56, 3578 (1983) disclose the nonmechanical dispersing of fine metal particles. This method for prepares colloidal metal dispersions in nonaqueous media also uses a gas evaporation technique. General references by C. Hayashi on ultrafine metal particles and the gas evaporation technique can be found in
Physics Today
, December 1987, p. 44 and J. Vac. Sci. and Tech., AS, p. 1375 (1987).
EPA 209403 (Toyatoma) describes a process for preparing dry ultrafine particles of organic compounds using a gas evaporation method. The ultrafine particles, having increased hydrophilicity, are taught to be dispersible in aqueous media. Particle sizes obtained are from 500 Angstroms to 4 micrometers. These particles are dispersed by ultrasound to provide mechanical energy that breaks up aggregates, a practice that in itself is known in the art. The resulting dispersions have improved stability towards flocculation.
Other references for dispersing materials that are delivered to a dispersing medium by means of a gas stream include U.S. Pat. No. 1,509,824, which describes introduction of a molecularly dispersed material, generated either by vaporization or atomization, from a pressurized gas stream into a liquid medium such that condensation of the dispersed material occurs in the liquid. Therefore, particle growth occurs in the dispersing medium, not in the gas phase, as described above. Furthermore, the examples given are all materials in their elemental form and all of which have appreciable vapor pressures at room temperature.
U.S. Pat. No. 5,030,669 describes a method consisting essentially of the steps: (a) vaporizing a nonelemental pigment or precursor to a nonelemental pigment in the presence of a nonreactive gas stream to provide ultrafine nonelemental pigment particles or precursor to nonelemental pigment particles; (b) when precursor particles to a nonelemental pigment are present, providing a second gas capable of reacting with the ultrafine precursor particles to a nonelemental pigment and reacting the second gas with the ultrafine precursor particles to a nonelemental pigment to provide ultrafine nonelemental pigment particles; (c) transporting the ultrafine nonelemental pigment particles in said gas stream to a dispersing medium, to provide a dispersion of nonelemental pigment particles in the medium, the particles having an average diameter size of less than 0.1 micrometer; wherein the method takes place in a reactor under subatmospheric pressure in the range of 0.001 to 300 torr.
U.S. Pat. No. 5,106,533 provides a nonaqueous dispersion comprising pigment particles having an average size (diameter) of less than 0.1 micrometer dispersed in an organic medium. That invention provides an aqueous dispersion comprising certain classes of inorganic pigment particles having an average size (diameter) of less than 0.1 micrometer dispersed in a water or water-containing medium. The dispersions require less time for preparation, are more stable, have a more uniform size distribution, a smaller number average particle diameter, fewer surface asperities, and avoid contamination of dispersed material due to the presence of milling media and the wear of mechanical parts, these problems having been noted above for dispersions prepared by conventional methods employing mechanical grinding of particulates. Additionally, no chemical pretreatment of the pigment is required in order to achieve the fine particle sizes obtained in the final dispersion. The pigments of the dispersions are found to have narrower size distributions (standard deviations generally being in the range of ±0.5 x, where x is the mean number average particle diameter), are more resistant to flocculation (i.e., the dispersions are stable, that is they are substantially free of settled particles, that is, no more than 10% of the particles settle out for at least 12 hours at 25° C.), and demonstrate superior overall stability and color as demonstrated by lack of turbidity, by increased transparency, and by greater tinctorial strength, compared to mechanically dispersed pigment dispersions. Furthermore, the method requires no mechanical energy, such as ultrasound, to break up aggregates. Aggregates do not form since there is no isolation of dry ultrafine pigment particles prior to contacting the dispersing medium. The dispersions of any organic or inorganic pigment or dispersion that can be generated from a pigment precursor, are prepared by a gas evaporation technique which generates ultrafine pigment particles. Bulk pigment is heated under reduced pressure until vaporization occurs. The pigment vaporizes in the presence of a gas stream wherein the gas preferably is inert (nonreactive), although any gas that does not react with the pigment may be used. The ultrafine pigment particles are transported to a liquid dispersing medium by the gas stream and deposited therein by bubbling the gas stream into or impinging the gas stream onto the dispersing medium.
U.S. Pat. No. 6,267,942 describes a process for manufacture of spherical silica particles. Silica gel particles to be dispersed in a mixed solution of an alkali silicate and an acid are required to have an average particle size of from 0.05 to 3.0 micrometers. In a ease where the average particle size of the silica gel particles is smaller than 0.05 micrometers, mechanical strength of the spherical silica particles to be obtained will be low, and irregular particles are likely to form, such being unsuitable. Similarly, in a case where the average particle size of the silica gel particles is larger than 3.0 micrometers, mechanical strength of the spherical silica particles to be obtained will be low, and irregular particles are likely to form, such being unsuitable. The more preferred range of the average particle size of the silica gel particles is from 0.1 to 1.0 micrometers.
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