Method and apparatus for high mass concentration nano particle generation

Abstract

A method and apparatus for generating nano particles, including but not limited to nano particles of Ceo, at high concentration. The invention uses a solid aerosol disperser in communication with a furnace tube having a vaporization chamber and a dilution chamber. A heating element surrounds the furnace tube. Heat from the heating element heats bulk materials contained within a gas flow in the vaporization chamber to a temperature sufficient to convert the bulk materials to a vapor phase. Vaporized bulk materials are then moved to a dilution chamber, where an inert gas is introduced through a dilution gas port. The flow of the inert gas into the dilution chamber through the dilution gas port is sufficient to eject the bulk material from the exit of the dilution chamber, thereby condensing the bulk material into nano sized particles in a gas flow of sufficient volume to prevent agglomeration of the nano sized particles.

Claims

1. An apparatus for generating nano particles at high concentration comprising: a. a solid aerosol disperser, b. the solid aerosol disperser in communication with a furnace tube having a vaporization chamber, the vaporization chamber having an input end and an output end, c. a heating element in proximity to said furnace tube, the heating element capable of heating bulk materials contained within a gas flow in the vaporization chamber to a temperature sufficient to convert the bulk materials to a vapor phase, d. a dilution chamber having a cup receiver and an output end, the output end of the vaporization chamber in communication with the input end of the dilution chamber, e. wherein the cup receiver has a cup receiver outlet at the outlet end and wherein the dilution chamber further comprises a dilution gas port disposed at the outlet end of the dilution chamber that is separate from the outlet of the cup receiver.

2. The apparatus of claim 1 further comprising an extraction port positioned between the solid aerosol disperser and the vaporization chamber where a portion of the gas flow may be extracted prior to introduction into the vaporization chamber.

3. The apparatus of claim 2 wherein the extraction port includes a separator where a portion of the bulk material having relatively larger particle sizes is separated and extracted prior to introduction into the vaporization chamber.

4. The apparatus of claim 3 wherein the separator is a cyclone, an impact device, or combinations thereof.

5. A method for generating nano particles at high concentration comprising the steps of: a. generating flow of bulk particles in a first inert gas in a solid aerosol disperser, b. introducing flow of bulk particles in the inert gas from the solid aerosol disperser into a vaporization chamber, c. maintaining the vaporization chamber at a temperature sufficient to vaporize the bulk particles, d. introducing the vaporized particles to a dilution chamber having a cup receiver and an exit, the exit maintained at a temperature sufficient to condense the bulk materials, e. introducing a flow of a second inert gas into the dilution chamber through a dilution port, the second inert gas cooling the vaporized materials in the cup receiver, and the flow of the inert gas sufficient to eject the bulk material from the exit, thereby condensing the bulk material into nano sized particles in a gas flow of sufficient volume to prevent agglomeration of the nano sized particles.

6. The method of claim 5 wherein the bulk material is processed by milling the bulk material prior to introducing it to the solid aerosol disperser.

7. The method of claim 5 wherein the bulk material is selected from the group cerium oxide, carbon nano tubes, titanium dioxide, C.sub.70, C.sub.76, and C.sub.84.

8. The method of claim 5 wherein the bulk material is C.sub.60.

9. The method of claim 8 wherein the C.sub.60 has a particle size of between about 1 μm and about 1.5 μm mass median aerodynamic diameter (MMAD) when it is introduced into the vaporization chamber.

10. The method of claim 8 wherein the C.sub.60 has a particle size of between about 1 μm and about 5 μm mass median aerodynamic diameter (MMAD) when it is introduced into the solid aerosol disperser.

11. The method of claim 8 wherein the C.sub.60 has a particle size of less than 100 nm count median diameter (CMD) when it is condensed as nano sized particles.

12. The method of claim 5 wherein the temperature sufficient to vaporize the bulk particles is between about 500° C. and 600° C.

13. The method of claim 5 wherein the gas flow rate into the vaporization chamber and the gas flow rate into the dilution chamber are adjusted to insure that the residence time that the vaporized bulk material is in the dilution chamber is no more than 30 seconds.

14. The method of claim 5 wherein the first and the second inert gas are selected from the group He, N.sub.2, Ar, Kr, Ne, and combinations thereof.

15. The method of claim 5 wherein a portion of the gas flow from the solid aerosol disperser is extracted prior to introduction into the vaporization chamber.

16. The method of claim 5 wherein the gas flow from the solid aerosol disperser is directed into a separator where a portion of the gas flow is extracted prior to introduction into the vaporization chamber.

17. The method of claim 16 wherein the separator is a cyclone, an impact regime, or combinations thereof.

18. The method of claim 5 wherein dilution materials are moved through the cup receiver essentially along a linear pathway.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following detailed description of the embodiments of the invention will be more readily understood when taken in conjunction with the following drawings, wherein:

(2) FIG. 1a is a graph showing the phase identification of C.sub.60 Buckminster fullerene bulk powder using X-Ray Diffraction Analysis.

(3) FIG. 1b is a graph showing an exploded view of the XRD spectrum to confirm purity of C.sub.60 sample.

(4) FIG. 1c is a graph showing the Rietveld refinement of C.sub.60 sample.

(5) FIG. 1d is a graph showing the phase identification of nanoparticulate C.sub.60 on the filter using XRD.

(6) FIG. 1e is a graph showing the phase identification of microparticulate C.sub.60 on the filter using XRD.

(7) FIG. 2 shows the fully assembled rotary dust generator showing drum driver, body and cap.

(8) FIG. 3a is a perspective view of PAC.

(9) FIG. 3b is a schematic diagram of PAC.

(10) FIG. 4 is two SEM images of C.sub.60 aerosols without using the furnace.

(11) FIG. 5 is a graph showing the concentration (y-axis) versus diameter (x-axis) at the inlet of SMPS.

(12) FIG. 6 is two TEM images of the filter samples with furnace inline.

(13) FIG. 7 is a histogram obtained using a Scion imaging software applied on TEM images.

(14) FIG. 8 is a graph showing the MOUDI mass distribution.

(15) FIG. 9 is a graph showing the Raman spectrum at two different temperatures of the furnace tube.

(16) FIG. 10 is a graph showing the XPS Photoelectron Spectrum.

(17) FIG. 11 is a graph showing the typical HPLC spectrum of a C.sub.60 standard and a sample.

(18) FIG. 12 is a schematic showing the assembly of a preferred embodiment of the present invention.

(19) FIG. 13 is a schematic showing the design of the furnace tube.

(20) FIG. 14 is a graph showing the particle size distribution of test aerosols obtained using SMPS.

(21) FIG. 15 is a graph showing the particle size distribution of test aerosols obtained using MOUDI impactor.

(22) FIG. 16 is a graph showing the chemical characterization using Raman spectroscopy.

(23) FIG. 17 is a schematic showing the design of a preferred embodiment of the furnace tube.

(24) FIG. 18 is a three dimensional model of a preferred embodiment of the furnace tube created by The FLUENT® Computational Fluid Dynamics Package, Release 6.2.16 (3-dimensional, double precision, segregated solver, laminar flow model with conjugate heat transfer), Fluent Inc., Lebanon, N.H. U.S.A.

(25) FIG. 19 is a three dimensional view of the temperature profile inside a preferred embodiment of the furnace tube created by The FLUENT® Computational Fluid Dynamics Package, Release 6.2.16 (3-dimensional, double precision, segregated solver, laminar flow model with conjugate heat transfer), Fluent Inc., Lebanon, N.H. U.S.A.

(26) FIG. 20 is a three dimensional view of the gas velocity profile inside a preferred embodiment of the furnace tube created by The FLUENT® Computational Fluid Dynamics Package, Release 6.2.16 (3-dimensional, double precision, segregated solver, laminar flow model with conjugate heat transfer), Fluent Inc., Lebanon, N.H. U.S.A.

(27) FIG. 21 is a three dimensional view of the particle trajectories inside a preferred embodiment of the furnace tube created by The FLUENT® Computational Fluid Dynamics Package, Release 6.2.16 (3-dimensional, double precision, segregated solver, laminar flow model with conjugate heat transfer), Fluent Inc., Lebanon, N.H. U.S.A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(28) The final schematic of the system used to generate the aerosols of C.sub.60 nano particles is depicted in FIG. 12.

(29) To demonstrate one embodiment of the present invention, a series of experiments were conducted using C.sub.60 particles supplied by SES Research, Houston, Tex. The bulk material consisted of dark colored, fine particles and had been stored at room temperature. The bulk material was milled in a Wig-L-Bug (Crystal Laboratories, Garfield, N.J.) for about 2 minutes before feeding to the generator.

(30) The solid air disperser used to initially generate C.sub.60 aerosols for these studies is available from the assignee herein, Battelle Memorial Institute, Columbus Ohio. Briefly, as shown in FIGS. 2, 3a and 3b, it consisted of a rotary dust feed device 10 coupled to a single jet Particle Attrition Chamber (PAC) 14.

(31) As shown in FIG. 2, the rotary dust feed device 10 consists of a drum (not visible), a body 11, a cap 12 and a drum rotation driver 13. The drum, which rotated during the generation, serves as the reservoir for the bulk material. The drum rotation is accomplished by a compressed air driven Valco valve driver (VICI Valco Instruments Co., Houston, Tex.) which in turn is controlled by the generator control unit. As the drum rotates, metering ports in a disk on the bottom of the drum are filled with a small amount of the powdered C.sub.60 bulk material. A stainless steel screen at the bottom of each metering port prevents the material from falling through the port, while allowing the carrier gas (nitrogen) to pass through from below. Each metering port is sequentially aligned with the carrier gas inlet in the body each time the driver was actuated by the generator control circuit.

(32) A carrier gas solenoid valve is then pulsed open by the generator control unit, creating a carrier gas puff which blows the bulk material from the port and disperses it into a flow of nitrogen. The output of the generator is regulated by adjusting the rotation cadence and duration of the nitrogen puff using the generator control unit.

(33) A Particle Attrition Chamber (PAC) 14 shown in FIGS. 3 and 3b serves to reduce the particle size of the suspended powder of the bulk material. The PAC 14 is similar to a cyclone separator with the addition of an air jet 15 operated at 30 psi at 90° to the aerosol inlet flow 17. The air jet 15 breaks up the particle clumps until the particles are small enough to exit the center aerosol outlet port 18. A portion of the flow exiting the PAC 14 was siphoned such that ˜0.400 lpm was passed through to the furnace tube 1 (shown on FIGS. 13 and 17). Referring to FIG. 12, siphoning using a generator siphon 20, occurred at a t-joint 19, which may have had the additional effect of separating larger particles and passing smaller particles to the furnace tube 1. The t-joint 19 has the effect of acting as a separator by acting as an impact regime where the larger particles impact the t-joint 19 and are thus siphoned off, whereas smaller particles remain in the gas flow, and are directed toward the furnace tube 1. By way of example and not of limitation, other devices, such as a cyclone, could also be used as a separator.

(34) The aerosols exiting the t-joint 19 were passed to the furnace tube 1 shown in FIGS. 13 and 17. As shown in FIG. 17, the furnace tube 1 consists of an inlet 2 and a vaporization chamber 3 in communication with a dilution chamber 4. The dilution chamber 4 has an exit 5 and a gas port 6. Surrounding the furnace tube 1 is a heating element 7. In these experiments, the vaporization chamber 3 was a 12 inch long glass tube with a 2 inch diameter. The dilution chamber 4 was a 2 inch long glass tube with a 2 inch diameter. The inlet 2 to the vaporization chamber 3 and the exit 5 were all ⅜ inch glass tubing. The opening between the vaporization chamber 3 and the dilution chamber 4 was also ⅜ inch. The gas port 6 in the dilution chamber 4 was ¼ inch tubing.

(35) Surrounding the furnace tube 1 is a heating element 7. The heating element 7 for these experiments was a commercial furnace Model F21135 supplied by Bamstead International Dubuque, Iowa. The furnace was maintained at a temperature (550° C.) and the flow rate through inlet 2 was ˜0.400 lpm, which was sufficient to ensure flash vaporization of the C.sub.60 aerosol. Rapid cooling caused by the introduction of compressed nitrogen at ˜0.500 lpm at gas port 6 resulted in the creation of nano-sized aerosols.

(36) The general arrangement of a preferred embodiment is shown in FIG. 13. As shown in the figure, the furnace tube 1 consists of an inlet 2, a vaporization chamber 3 in communication with a dilution chamber 4. The dilution chamber 4 has a cup receiver 8, with an output or exit 5 and a gas port 6. Surrounding the furnace tube 1 is a heating element 7. At either end of the furnace tube 1, buffer zones 9 isolate the interior of the furnace tube 1 from the surrounding atmosphere.

(37) FIGS. 18, 19, 20 and 21 are models of the gas flow in the preferred embodiment of the furnace tube 1. The models were created by The FLUENT® Computational Fluid Dynamics Package, Release 6.2.16 (3-dimensional, double precision, segregated solver, laminar flow model with conjugate heat transfer), Fluent Inc., Lebanon, N.H. U.S.A. FIG. 18 is a three dimensional model of a preferred embodiment of the furnace tube 1, FIG. 19 is a three dimensional view of the temperature profile inside the furnace tube 1, FIG. 20 is a three dimensional view of the gas velocity profile inside the furnace tube 1, and FIG. 21 is a three dimensional view of the particle trajectories inside the furnace tube 1. As shown in the figures, the dilution materials are moved through the cup receiver 8 essentially along a linear pathway, thus maximizing the temperature drop thereby cooling the vaporized materials as quickly as possible.

(38) The size distribution of the aerosols produced by the methods and apparatuses of the present invention was determined using a cascade impactor (In-Tox Products, Model No. 02-130/SMK, Albuquerque, N. Mex.), Scanning Mobility Particle Sizer (TSI Model 3034, Shoreview, Minn.) (SMPS) (see FIGS. 5 and 14), TEM imaging (JEOL 2010F, Jeol, Peabody, Mass.) (see FIGS. 6 and 7) and MOUDI impactor (MSP Corp, 125B NanoMOUDI, Shoreview, Minn.) (see FIGS. 8 and 15). The chemical characterization of C.sub.60 was performed using Laser Raman Infrared spectroscopy (Spex Model 1877, Spex, Edison, N.J.) (see FIGS. 9 and 16) and high performance liquid chromatography (HPLC, Agilent 1100) (see FIG. 11).

(39) Samples of aerosols produced by the present invention were collected at sampling port 22 (see FIG. 12). The collected samples were analyzed for particle size distribution using four different instruments. In the initial stages of the experiments, an 8 stage mercer cascade impactor was used to establish the proof of principle. The cut-point of the last stage of the impactor was ˜230 nm. The flow rate through the impactor was approximately 1.645 lpm. The cascade impactor stages were pre-coated with silicone grease. The individual stage filters were analyzed using High Performance Liquid Chromatography.

(40) At the later stages, the aerosols were sampled through a Scanning Mobility Particle Sizer (TSI Model 303s Shoreview, Minn.) (see FIGS. 5 and 14). The SMPS size separates the particles on the basis of electrical mobility of the particles. The Model 3034 has the size range from 10 to 487 nm electrical mobility diameter. The aerosol stream passes through a single-stage cyclone which removes large particles (>0.8 μm) outside the instrument measurement range. The aerosol then passes through a bipolar ion neutralizer that imparts a high level of positive and negative ions. Charged and neutral particles enter the differential mobility analyzer (DMA) column where particles are separated according to their electrical mobility. Electrical mobility is inversely proportional to the particle size so a determination of this property reveals the latter. The particles exiting the DMA are first passed through a saturator picking up butyl alcohol vapor in the sample stream. A second cooling stage causes the vapor to condense on the particles, growing them to readily detectable size. These particles are then directed to a condensation particle counter where a determination of particle concentration is made by passing the particles through a focused laser light.

(41) The samples were also analyzed using a Scanning Electron Microscope (LEO 982 FE-SEM, Zeiss Thomwood, N.Y.) (see FIG. 4) and a Transmission Electron Microscope (JEOL 2010F, Jeol, Peabody, Mass.) (see FIG. 6). The SEM images of the bulk material and during the initial stages of the experiments were taken to establish the size distribution of bulk test material. For SEM, the aerosols were collected on a gold plated 25 mm membrane filters (Pal Gelman, N.Y.). During the later stages of the experiments, TEM images of the samples were taken. For TEM, the samples were collected on a carbon coated lacy copper grid. The samples were collected for enough duration to have uniform coating of test material on the grid. The microscope was operated at 200 KeV with a field emission gun. The compositional analysis software used was INCA x-ray energy spectroscopy system from Oxford Instruments.

(42) The particle size distribution was also determined using a Micro Orifice Uniform Deposit Impactor (MOUDI, MSP Corp, 125B NanoMOUD, I Shoreview, Minn.) (see FIGS. 8 and 15). This impactor has thirteen rotating stages with nominal cut points varying from 10 μm to 10 nm when operated at an inlet flow rate of 10.0 lpm. The last few stages of the MOUDI impactor are under low pressure which increases the Cunningham slip correction and thus reduces the cut point of the stages.

(43) Laser Raman Infrared spectroscopy, XRD and HPLC were used to establish the chemical purity of the test material at the sampling port 22. Raman spectra were obtained in the backscatter configuration using a Spex (Edison, N.J.) Model 1877 Raman spectrometer equipped with a Princeton Instruments (Trenton, N.J.) LN/CCD detector (see FIGS. 9 and 16). The 488.0 nm line of Coherent (Santa Clara, Calif.) Innova 307 Argon Ion Laser was used for excitation. The laser power was reduced to about 5 mW for most measurements to prevent sample burning, using a combination of filters and beam chopping. Slit width was 400 microns and the exposure time was 500 sec for most measurements. Spectra were corrected for back ground by subtracting the spectrum of filter paper.

(44) The detection of C.sub.60 was also carried out using an Agilent 1100 high pressure liquid chromatograph (HPLC) equipped with an Agilent 1100 variable wavelength detector (see FIG. 11). The detector was configured at a wavelength of 330 nm and a peak width of >0.1 min. The iso critical separation method involved a 5 μl injection onto a Cosmosil BuckyPrep analytical column (25 cm×4.6 mm ID; 5 μm) with toluene as the mobile phase. The flow rate of the mobile phase was set at 1 mL/min with a run time of 20 minutes; retention time for the C.sub.60 was ˜8 minutes.

(45) The purity of C.sub.60 was also verified using XRD analysis (see FIGS. 1a-1d and 10). The XRD spectrum was obtained on 3 samples. The XRD analysis was performed on C.sub.60 bulk powder, the nano sized C.sub.60 and the micro sized C.sub.60. All samples were run in a Siemens D5000 Θ/Θ diffractometer using Cu radiation at 40 Kv/30 mA. Scans were run over the range of 5 to 80 with a step size of 0.02°. For the powder sample, the scan time was 10 hours while the filter samples had to be run for 36 hours each. FIGS. 1a-1d show the phase identification of C.sub.60 Buckminster fullerene bulk powder using X-Ray Diffraction Analysis.

(46) The Mercer cascade impactor analysis was very helpful during the early stages of the experiments while optimizing the furnace temperature and location. During the early stages of testing, the mercer cascade impactor samples were collected without a tube furnace in line to determine the size distribution of the bulk material. Two samples were collected at different pressure of the compressed nitrogen in the PAC. Table 2 shows the MMAD and GSD of the results obtained.

(47) TABLE-US-00002 TABLE 2 PAC Aerosol Aerosol Size Run Pressure Concn. Distribution No. (psig) (μg/L) (MMAD/GSD) 1 20 87 1.16/2.43 2 40 19.3 0.94/2.18

(48) FIG. 5 shows the SEM images of the filters at 2 different magnifications. Clearly, large aggregates were observed by both the TEM and the cascade impactor analysis.

(49) The furnace tube was then installed in-line into the system and the samples were collected at the sampling port at the outlet of the furnace tube. Initially, samples were collected on the mercer cascade impactor. Most of the particles were observed on the last 2 stages of the impactor with very less mass (<2% of total mass) on the first five stages (>490 nm). The cut point of the sixth stage was 0.49 μm and the last stage (eighth stage) was 0.23 μm. Nearly 92% of the total mass was collected on the last 2 stages with the cut points of 0.33 μm and 0.23 μm respectively. Some of the operating parameters were changed to further reduce the particle size and other instruments were used for further characterization.

(50) The SMPS was used to determine the particle size distribution for smaller particle sizes. The vaporization condensation process was able to reliably and reproducibly generate a C.sub.60 aerosol with a count median size of 36.6 nm. Table 3 summarizes the aerosol data for a 3 minute sampling period during the stable generation of aerosol, and FIG. 6 shows the particle number based distribution during a 3 minute sample.

(51) TABLE-US-00003 TABLE 3 Num. Particle Dia. Particle Vol. Particle Size Size Size Median (nm) 59.1 67.3 85.4 Mean (nm) 62.1 70.6 94.8 Geo. Mean (nm) 58.0 66.3 86.3 Mode (nm) 62.6 67.3 89.8 GSD 1.45 1.43 1.49 Total conc. 4.66e05 (#/ 28.9 (mm/ 8.59e10 (nm.sup.3/ cm.sup.3) cm.sup.3) cm.sup.3)

(52) SMPS analysis showed that more 99.7% of the total number of particles were less than 100 nm electrical mobility diameter. The TEM images of the samples were also taken. FIG. 7 shows the TEM images of the filter samples at two different resolutions.

(53) Five images of the grid were taken at 25KX magnification to provide sufficient particles for size analysis. These images were analyzed using a Scion Image imaging and analysis program (Gaithersburg, Md.). FIG. 8 shows the Kaleidagraph histogram obtained using this information. The mean particle size was observed to be ˜24.6 nm.

(54) The samples were also run through a MOUDI impactor to determine the mass size distribution. The MOUDI impactor has 13 stages with the cut points ranging from 10 μm to 10 nm. The rotation of the stages during sampling helped in uniform deposition of the test material on the filter. The MOUDI impactor and SMPS were placed at the same distance from the sampling port and both of these instruments sampled simultaneously for same duration of time. The results obtained were compared to each other and the results were in good agreement with previous reported literature.

(55) FIG. 9 shows a MOUDI mass distribution obtained at ˜10 LPM for a sample period of 20 minutes. The cumulative percent mass was plotted against nominal cut diameter of each stage and the MMAD was observed to be ˜25 nm.

(56) Tests were also performed to ensure the chemical purity of C.sub.60 at the sampling port 22. There has been previously reported literature which suggests that C.sub.60 decomposes into amorphous carbon when heated to high temperature

(57) FIG. 10 shows the Raman spectrum obtained for nano and micro sized C.sub.60 aerosols. A spectrum for bulk C.sub.60 powder is also shown on the same plot. The sample number 010906-2 represents the nano sized C.sub.60 spectrum while sample number 010906-5 represents the spectrum for micro sized C.sub.60 particles.

(58) The high performance liquid chromatography (HPLC) analysis was carried on a regular basis to establish the chemical purity of C.sub.60. The samples were collected on a Teflon filter which was analyzed gravimetrically and then dissolved in toluene to extract C.sub.60. The HPLC analysis on this solution gave the mass of C.sub.60 present on the filter. This mass was compared to the gravimetric mass to ensure there was nothing besides C.sub.60 present in the sample. The results at furnace temperature of 600° C. and above showed the presence of something else besides C.sub.60 present in the sample whereas at the furnace temperature of 500° C., the ratio of gravimetric mass to the HPLC determined C.sub.60 mass was observed to be close to 1. FIG. 11 shows a typical HPLC spectrum obtained using C.sub.60 standard and the filter sample collected.