Nanomaterials fabricated using spark erosion and other particle fabrication processes

Patent metadata

Field	Value
Publication number	US-9789554-B2
Application number	US-201214351700-A
Country	US
Kind code	B2
Filing date	Oct 12, 2012
Priority date	Oct 12, 2011
Publication date	Oct 17, 2017
Grant date	Oct 17, 2017

Abstract

Methods, systems, and devices are disclosed for fabricating clean, oxidation-free nanoparticles of electrically conducting metals and alloys using spark erosion techniques. In one aspect, a method includes dispersing bulk pieces of an electrically conducting material in a dielectric fluid with mechanical vibrations within a container; generating an electric field using electrodes in the dielectric fluid using by an electric pulse, in which the electric field creates a plasma in a volume existing between the bulk pieces that locally heats the bulk pieces to form structures within the volume, the dielectric fluid quenching the structures to form nanoparticles, and filtering the nanoparticles through a screen including holes of a size allowing nanoparticles of the size or smaller to pass through the screen to a region in the container, in which the dielectric fluid inhibits oxidation of the surface of the nanoparticles.

First claim

What is claimed is:

1. A method of producing nanoparticles by spark erosion, comprising:
dispersing bulk pieces of an electrically conducting material in a dielectric fluid within a container by providing mechanical vibrations within the dielectric fluid, wherein the dispersing includes continuously or semi-continuously depositing the bulk pieces into the dielectric fluid within the container, wherein the bulk pieces include an alloy material and the dielectric fluid within the container excludes oxygen, wherein the alloy material includes a first material with a first vapor pressure property and a second material with a second vapor pressure property higher than the first vapor pressure property, and wherein the first material includes at least one of Si, Ge, Ni, Ti, Co, Fe, Cr, V, Mn, Cu, Al, Mo, Nb, W, Hf, Ta, W, Re, or Os, and wherein the second material includes at least one of Zn, Mg, Ca, Sb, Bi, In, Ga, or Ag;
using electrodes in contact with the dielectric fluid that are separate from one another to apply electric pulses to the bulk pieces near the electrodes to generate an electric field which creates a plasma in a volume existing between the bulk pieces that locally heats the bulk pieces to form structures within the volume, wherein the dielectric fluid quenches the formed structures to form nanoparticles, and wherein generating the electric field in the dielectric fluid creates the plasma in the volume existing between the bulk pieces that locally heats the second material to vaporize such that the vaporization of the second material induces the first material to vaporize and form structures within the volume, wherein the dielectric fluid quenches the formed structures to form the nanoparticles;
and
filtering the nanoparticles in the dielectric fluid through a screen including holes of a size allowing nanoparticles of the size or smaller to pass through the screen to a region in the container, wherein the dielectric fluid is selected to inhibit oxidation of a surface of the nanoparticles.

2. The method of claim 1 , wherein the dielectric fluid includes at least one of liquid nitrogen or liquid argon.

3. The method of claim 1 , wherein the size is in a range of 10 nm to 300 nm.

4. The method of claim 1 , further comprising annealing the filtered nanoparticles.

5. The method of claim 4 , wherein the annealing is implemented at a temperature in a range of 200 to 300° C. over a time duration in a range of 2 to 24 hours.

6. The method of claim 1 , further comprising:
coating the surface of the nanoparticles with smaller nanoparticles; and
sintering the coated nanoparticles to form a nanocomposite material including nanoscale grains of the material of the nanoparticles and the smaller nanoparticles along the boundaries of the grains,
wherein the smaller nanoparticles inhibit growth of the grains in the nanocomposite material.

7. A method of producing nanoparticles by spark erosion, comprising:
dispersing bulk pieces of an electrically conducting material in a dielectric fluid within a container by providing mechanical vibrations within the dielectric fluid, wherein the dispersing includes continuously or semi-continuously depositing the bulk pieces into the dielectric fluid within the container;
using electrodes in contact with the dielectric fluid that are separate from one another to apply electric pulses to the bulk pieces near the electrodes to generate an electric field which creates a plasma in a volume existing between the bulk pieces that locally heats the bulk pieces to form structures within the volume, wherein the dielectric fluid quenches the formed structures to form nanoparticles;
filtering the nanoparticles in the dielectric fluid through a screen including holes of a size allowing nanoparticles of the size or smaller to pass through the screen to a region in the container, wherein the dielectric fluid is selected to inhibit oxidation of a surface of the nanoparticles;
forming an oxidized coating on the surface of the nanoparticles to produce core-shell surface oxidized nanoparticles;
compacting the core-shell surface oxidized nanoparticles; and
sintering the compacted core-shell surface oxidized nanoparticles to form a nanocomposite material including nanoscale grains of the material of the nanoparticles and nanoscale oxide regions.

8. The method of claim 7 , wherein the forming includes at least one of using an oxygen-containing dielectric liquid as the dielectric fluid, dispersing the bulk pieces in the dielectric fluid with liquid oxygen, doping the material of the bulk pieces or the electrodes with an oxidizable element, or exposing the nanoparticles to an oxygen-containing atmosphere including at least one of air or oxygen-containing Ar gas.

9. The method of claim 1 , wherein at least one of the electrodes or the bulk pieces comprise a composite material including a metal or alloy and at least one other phase material, and wherein the formed nanoparticles include a multi-phase nanostructure.

10. The method of claim 1 , wherein the container includes a first aperture at a top of the container and a second aperture at a bottom of the container, and further comprises:
an upper container to store the bulk pieces and deposit the bulk pieces into the container, the upper container having a hollowed interior with an opening at the bottom and a valve to expose or seal the opening, wherein the opening of the upper container is connected to the first aperture of the container via the valve to control deposition of the bulk pieces into the container; and
a lower container to receive the nanoparticles, the lower container having a hollowed interior with an opening at the top and a valve to expose or seal the opening, wherein the opening of the lower container is connected to the second aperture of the container via the valve to control collection of the nanoparticles from the container.

11. The method of claim 1 , wherein the formed nanoparticles are nanocomposite particles of the first and second materials, and wherein the nanocomposite particles include at least one of an amorphous metastable solid solution structure, a mixed phase crystalline structure, or a core-shell structure, or
wherein the nanoparticles include separate nanoparticles of the first material and nanoparticles of the second material, or
wherein the separate nanoparticles include a hollow sphere structure of one of the first material or second material.

12. The method of claim 1 , further comprising:
storing the bulk pieces in an upper container above the container;
operating a valve between the upper container and a lower container to control continuous or semi-continuous deposition of the bulk pieces into the container.

13. The method of claim 1 , wherein the mechanical vibrations cause an increased number of local discharge contact points for spark erosion between the bulk pieces in the reaction chamber.

14. The method of claim 1 , further comprising rotating two adjacent electrodes of the electrodes in opposite rotations to facilitate formation of the nanoparticles from the bulk pieces.

15. The method of claim 1 , wherein the applied electric pulses include a voltage of at least 100 V and at a frequency of at least 60 Hz, and wherein the generated electric field is capable to produce a capacitance discharge between the bulk pieces of at least 20 μF in the formation of the structures.

16. A method of producing nanoparticles by spark erosion, comprising:
dispersing bulk pieces of an electrically conducting material in a dielectric fluid within a container by providing mechanical vibrations within t

Assignees

• Univ California

Inventors

• Jin Sungho
• Berkowitz Ami

Classifications

• B23H1/04 Primary

  Electrodes specially adapted therefor or their manufacture (B23H9/00 takes precedence) · CPC title

• B23H7/12

  Rotating-disc electrodes · CPC title

• B23H1/08 Primary

  Working media · CPC title

• B23H9/001

  Disintegrating · CPC title