Efficient production of particles by chemical reaction

Details Efficient production of particles by chemical reaction Efficient production of particles by chemical reaction

1999-06-21

2001-06-19

Wong, Edna (Department: 1741)

Chemistry: electrical and wave energy

Processes and products

Processes of treating materials by wave energy

C204S157410, C423S210000, C075S336000, C075S338000

Reexamination Certificate

active

06248216

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to producing particles by chemically reacting gaseous reactants.
BACKGROUND OF THE INVENTION
There has been growing demand for solid state materials with dimensions in the range from 1 to100nanometers (nm). These nanoscale particles have been found to exhibit unusual chemical, mechanical, electrical, magnetic and optical properties that are different from the corresponding properties of the bulk material and conventional powders. These unusual properties can be exploited in a number of applications.
One advantage of nanoparticles relative to larger particles is the increased surface area for a given weight of material. The surface area per weight of nanoscale particles can be one or two orders of magnitude greater than the surface area per weight of conventional powders. This increase in surface area is desirable for a variety of applications such as those involving catalysis, hydrogen storage and electrical capacitors.
A variety of nanoparticles have been produced using a pyrolytic reaction of chemicals in the gas phase. For example, laser pyrolysis has been used to produce nanoparticles of carbon black, &agr;-Fe, Fe
3
C and Fe
7
C
3
. These were described in the following two references: Bi, et al., J. Mater. Res.
8:1666-1674(1993)
and Bi, et al., J. Mater. Res.10:2875-2884 (1995).
SUMMARY OF THE INVENTION
In one aspect, the invention features an apparatus having a reaction chamber and an elongated reactant inlet generally characterized by a major axis and a minor axis for introducing a stream of reactant gas into the reactant chamber. The reaction chamber is configured to conform generally to the shape of the elongated reaction inlet, and to have a beam of radiation projected through it along a radiation path corresponding to the major axis of the elongated reactant inlet and intersecting the reactant stream. Preferably, the apparatus further includes one or more inert gas inlets configured to form a confining stream of inert gas surrounding at least a portion of the reactant stream, and the reaction chamber is configured such that the reactant stream and the confining inert gas stream occupy a significant fraction of the volume of the reaction chamber. The apparatus can further include a laser for producing the beam of radiation.
The apparatus preferably includes a conduit or a pair of conduits for introducing shielding gas into the reaction chamber. If a pair of conduits for introducing shielding gas into the reaction chamber are used, each can be positioned at an angle relative to the elongated reactant inlet such that they define a path intersecting the reactant stream. The conduit for introducing shielding gas preferably, terminates along a surface of the reaction chamber.
Preferably, the reaction chamber includes a window for introducing the beam of radiation. The reactant chamber preferably includes a tube, with an inner diameter no more than twice the diameter of the radiation beam, oriented along the radiation path, and a window for introducing the radiation beam into the reaction chamber. This window is located near the end of the tube away from the reactant stream. The reaction chamber can include a pair of windows along the radiation path. Alternatively, the reaction chamber may include a mirror along the radiation path.
In another aspect, the invention features a method for producing particles. The method includes the step of introducing a reactant gas into a reaction chamber in the form of an elongated reactant stream characterized by a major axis and a minor axis. The reaction chamber is configured to conform generally to the shape of the reactant stream. A radiation beam is projected through the reaction chamber along a path along the major axis of the reactant stream, inducing a reaction in the reactant gas to form particles. In a preferred embodiment, the radiation beam includes electromagnetic radiation, which can be generated by a laser. The reactant stream preferably has a generally rectangular cross section.
The invention provides an apparatus for producing particles, where the apparatus makes efficient use of resources at high production capacity without sacrificing quality of the resulting particles. Thus, the apparatus is appropriate for the commercial production of particles, especially nanoparticles with average diameters of 100 nm or less. The commercial production requirements are met for particles that can be produced by the chemical reaction of gaseous reactants.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.


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