CA2263902A1

CA2263902A1 - Integrated thermal process and apparatus for the continuous synthesis of nanoscale powders

Info

Publication number: CA2263902A1
Application number: CA002263902A
Authority: CA
Inventors: Shahid Pirzada; Steven Just; Tapesh Yadav; Bryce Anton; Forrest Bray
Original assignee: NANOMATERIALS RESEARCH LLC
Current assignee: Individual
Priority date: 1996-09-03
Filing date: 1997-09-03
Publication date: 1998-03-12
Also published as: WO1998009753A1

Abstract

A continuous process that produces nanoscale powders from different types of precursor material by evaporating the material and quenching the vaporized phase preferably in a converging diverging expansion nozzle. The precursor material suspended in a carrier gas is continuously vaporized at very high temperatures, preferably exceeding 2000 degrees C, and most preferably exceeding 5000 degrees K, in a thermal reaction chamber under conditions that favor nucleation of the resulting vapor. Immediately after the initial nucleation stages, the vapor stream is rapidly and uniformly quenched at rates of at least 1,000 K/sec, preferably above 1,000,000 K/sec, to block the continued growth of the nucleated particles and produce a nanosize powder suspension of narrow particle size distribution. The nanopowder is then harvested by filtration from the quenched vapor stream and the carrier medium is purified, compressed and recycled for mixing with new precursor material in the feed stream.

Description

W 09~ 75~ PCTrUS97/15463 INl'EGRATED THERMA~ PROCESS AND APPARATUS
FOR THE CONTINUOUS SYNTHESIS OF NANOSCALE POWDERS

BACKGROUND OF THE INVENTION

This invention pertains in general to a process and apparatus for the synthesis of submicron particles. In particular, the invention relates to a novel approachlltili7.ing vaporization and ultra-rapid thermal quenching based on adiabatic expansion of the vapor through a boundary layer converging-diverging nozzle to produce 0 submicron particles under controlled operating conditions.
As defined in the art, submicron powders are materials havin~ average grain size below I micrometer. Of particular interest are nanoscale powders. namely, submicron powders with grain size less than 100 nanometers and with a significant fraction of interfacial atoms. Of great interest are powders with grain size of less than 15 50 nanometers. Of greater interest are powders with grain size less than 20 nanometers. Of greatest interest are powders with grain size less than 10 nanometers.
It is known that within these size ranges a variety of confinement effects occur that dramatically change the properties of the material. A property will be altered when the entity or mech~ni~m responsible for that property is confined within a space20 smaller than some critical length associated with that entity or mech~ni~m. See H.
Gleiter. Mechanical Properties and Deformation Behavior of Materials Havin~ Ultra-Fine Microstructures~ Nastasi et al. Ed., 3-35 (1993); and R. W. Siegel, Mechanical Properties and Deformation Behavior of Materials Havin~ Ultra-fine Microstructures.
Nastasi et al. Ed., 509 (1993), which are included herein by reference. Such 25 confinement effects can, therefore lead to a wide range of commercially important properties. For example, a normally ductile metal will become significantly harder if its grain size is reduced to the point where moving dislocations through its crystal lattice are no longer able to occur at norrnal levels of applied stress. Since the stress required to produce a Frank-Read dislocation is inversely proportional to the spacing 30 between its pinning points, as one skilled in the art would readily understand, a critical length in this case is that for which the stress necessary to produce adislocation becomes larger than the conventional yield stress for the given metal.

. . , ... .. . .,, .,,.. _ .~ .. ...

CA 02263902 l999-02-23 W 098/09753 PCTrUS97/15463 Thus, confinement effects can be exploited to produce extremely hard and strong materials with much higher yield stress than exhibited by the conventional form of their precursors. See Nieman et al., "Mechanical Behavior of Nanocrystalline Cu and Pd," J. Mater. Res., 6, 1012 ( I g91); and Nieman et al., "Tensile Strength and Creep Properties of Nanocrystalline Palladium," Scripta Metall. et Mater., 24,145 (1990), which are included herein by reference. The same principle has also beenused to m~nllfActure unique optical materials with grain sizes tailored for excitonic interactions with particular wavelengths, Skandon et al., "Nanostructured Y,03:
Synthesis and Relation to Microstructure and Properties," Scripta Metall. et Mater., o 25, 2389 (1991); electroceramics with unique electronic and electrical characteristics, F.~.ctm~n et al., "Processing and Properties of Nanophase Oxides," Mater. Res. Soc.
Symp. Proc., 155,255 (1989); superplastic ceramics with grain sizes engineered to allow low cost, rapid net-shape forming of ceramics as a substitute process for m~f~hining of ceramics, H. Hahn et al., "Low Temperature Sintering and Deformation of Nanocrystalline TiO~," Mater. Res. Soc. Symp. Proc., 196, 71 (1990) and M. J.Mayo, Mechanical Properties and Deformation Behavior of Materials Havin Ultra-fine Microstructures, Nastasi et al. Ed.,361 (1993); catalysts with extremely high surface areas, high selectivity and activity, Beck and Siegel, "The DissociativeAdsorption of Hydrogen Sulfide over Nanophase Titanium Dioxide," J. Mater. Res.,7, 2840 (1992); materials with unique electrochemical properties, Tamaki et al.,"Grain-Size Effects in Tungsten Oxide-Based Sensor for Nitrogen Oxides,"
J. Electrochem. Soc., 141,2207 (1994); and materials that exhibit unprecedented magnetic properties, Sugaya et al., "Soft Magnetic Properties of Nanostructure-Controlled Magnetic Materials," IEEE Trans. on Magnetics,31,2197 (1995) and C.E.Yeack-Scranton, Nanoma~netism~ Kluwer Academic, Netherland, 1-6 (1993), all of which are included herein by reference. Quantum confined and nanometer cluster m~teri~l~, therefore, are an extraordinary opportunity for design, development and commercialization of a wide range of structural, electrochemical, electrical, optical, electronic, magnetic and chemical applications. Furthermore, since they represent a whole new family of material precursors where conventional coarse-grain physiochemical mech:~ni~m~ are not applicable, these materials offer a unique CA 02263902 l999-02-23 WO ~a~s~ PCTAUS97/15463 combination of properties that can enable novel and multifunctional components of nm~tçhed performance.
Although this opportunity has been apparent for several years, large scale commercialization has remained unrealized because of the high cost and low 5 throughput of existing processes for producing nanopowders, the current lack of process control over size and size distribution of the resulting material, the unpredictable composition of its constituent phases, and the lack of control over the nature of and the interactions arnong the interfaces created between the constituent phases. Nanopowders may indeed represent the threshold of a new era in materialsI o technology, but the key to their full utilization depends on the development of new processes for producing nanopowders economically and in commercially viable quantities under controlled operating conditions.
In recent years, several methods have been used for producing nanopowders and the materials produced by this prior-art technology have confirmed the fact that 5 nanopowders possess important technical properties that show the potential forbccoming commercially significant. However, all known production methods consistof batch processes that are too expensive to yield commercially affordable materials for bulk applications (current production costs for these processes are orders of magnitude higher than the $1 0.00/lb target price considered economical for bulk20 applications of these materials). Therefore, the commercial future of nanopowders depends on the development of a process that can produce nanopowders with predetermined properties, in commercially viable quantities~ and at an affordable cost.
An additional and significant problem encountered by the performance ceramics industry is the use of environment~lly undesirable solvents and additives 25 (acids, alkalis, ammonia and aromatic dispersants to name a new examples) in large quantities. Unfortunately, the present processing techniques continue to require the use of solvents and additives and the anticipated growth in this market for ceramic devices suggests that this environmental hazard will only increase.
Ideally, the synthesis and processing technology for nanopowders should 30 allow control of the size and size distribution of the constituent structures and phases (this is critical to the mechanistic perforrnance of nanopowders); allow control of the composition of the phases in the nanomaterial (critical to define the property domain W 098~ 75~ PCTrUS97/15463 of the nanomaterial); allow control over the nature of interfaces (e.g. purity) and the interaction between interfaces (critical to the interface-based characteristics of the nanopowders); and minimi7~ the use of environmentally undesirable solvents and additives. None of the known processes for the synthesis of nanomaterials possesses 5 these characteristics; therefore, none is suitable for bulk commercialization of nanopowders.
In particular. prior-art processes are all batch, and have high energy or solvent processing requirements, which are all inherent limitations to the cost-effective and large-scale production of nanopowders. The processes currently in use can be o classified into three general groups: chemical, mechanical-attrition, and gas-condens~tion methods. The chemical methods include precipitation techniques, sol-gel processes~ and inverse-micelle methods. See Beck and Siegel, "The Dissociative Adsorption of Hydrogen Sulfide over Nanophase Titanium Dioxide," J. Mater. Res.,7, 2840 ( 1992), and Steigerwald and Brus, "Synthesis, Stabilization, and Electronic Structure of Quantum Semiconductor Nanoclusters," 1 1 Ann. Rev. Mater. Sci., 191471 (1989), which are included herein by reference. These processes have been used to successfully synthPci7e narrowly distributed nanopowders; howeven being chemical-media based, the resulting nanopowders are covered with chemical surface layers. This surface covering adversely affects the properties of the nanopowders and 20 inhibits their further processing into bulk materials. In addition, the use of solvents and chemicals has a significant economic impact on the synthesis process because of the costs of chemicals and. as ~ cn~ced above, the pollution remediation required by their use.
The mechanical attrition methods rely on the physical decomposition of 25 coarser grains through severe mechanical deformation. Such processing methods are energy intensive, have low flexibility, are susceptible to cont~min~lion by attrition tools or media, and afford little control over the quality and con.~i~te~ry of the final product.
The gas con(len~tion methods essentially involve the evaporation of a coarse 30 (at least micron size) source of precursor material, such as a metal, inorganic, etc., in an inert gas at a low plt;S:iul~. The evaporated source atoms or molecules collide with the gas atoms or molecules and lose energy, thereby causing a homogeneous W O 98/09753 PCTrUS97/15463 condensation of atom or molecule clusters in the supersaturated vicinity of the precursor source. The further accretion and/or coalescence of the nucleated particles is minimi7f d by rapid removal ofthe nanometer-sized powders so forrned from theregion of supersaturation. See R. Uyeda, "Studies of Ultrafine Particles in Japan:
5 Crystallography7 Methods of Preparation and Technological Applications," I I Prog.
Mater. Sci., 35, 1 (1991), and R. W. Siegel, Materials Science and TechnoloF~y, 15, VCH, Weinhem, 583 (1991), which are incorporated herein by reference.
Alternatively, gas condensation processes may involve gas-phase reactions. some of the known gas con(len~tion processes have produced nanomaterials of acceptable 10 size distribution, but they are all batch operations and are not readily scaleable for commercial exploitation.
Additionally, rapid solidification processing of high temperature liquids and vapors has been extensively researched. See Loren A. Jacobson and J. McKittrick,"Rapid Solidification Processing ", Materials Sciences & Eng., R-l 1, 355-408 (1994), 5 which is incorporated herein by reference. Such process techniques are used toprepare fine microstructures (micron sized), increase solid solubility of alloy elements, and prepare non-equilibrium phases, particularly in powder metallurgy.Conventional rapid solidification methods, such as oil quench, gas quench, chillcasting, and centrifugal atomization, achieve therrnal quench rates of I o2 to 105KJsec.
Higher quench rates are very desirable because they can enable the synthesis of powders that are submicron in domain size and, at rates greater than I o6 K/sec7 can enable the synthesis of powders with domain size less than 100 nanometers. As defined in the art, submicron powders are materials having average grain size below I
25 micrometer. Of particular interest are nanoscale powders; namely, submicron powders with grain size less than 100 nanometers. Finer domain sizes are desirable because the physiochemical properties of materials are remarkably different and commercially useful when the domain size is reduced below 100 nanometers.
Nanoscale powders also exhibit very high surface areas and enh~nced surface activity 30 for physical and chemical reactions.
To achieve higher cooling rates, contact qllen~hing methods such as splat cooling and glazing have been suggested. See Jones, "Splat Cooling and Metastable W 098~'0~75~ PCT~US97/1~463 Phases," Rep. Progr. Phys.,36,1425 (1973), which is incorporated herein by reference. However. these methods are not suitable for thermal 4uenching of hightemperature vapors (greater than l S00 K) because these temp~ldLu,~s lead to thermokinetic transformations from reactions at contact surfaces. These methods are 5 also not useful for high temperature vapors of materials such as carbides, nitride, refractory metals, alloys, and multiphase nonequilibrium phases because the hightemperatures can irreversibly damage the contact surfaces. Furthermore, these prior-art methods are not suited for thenn~lly quenching high telllpclalllre~ chemically-active vapors ~such as those resulting from chemical reactions between feed lo components at high temp~ldtu~es).
U. S. Patents 5,407,458,5,403,375, 5,384,306, and 5,389,585 by Konig et al.
all describe the production of nanoscale powders using a process of the reaction of chemically active vapors between feed components at high temperatures. The corresponding metal compounds and corresponding reactants are reacted in the gas15 phase in a reactor at a temperature of 2000 degrees C or lower, homogeneouslycon-lPn~ed directly from the gas phase in the absence of any wall reactions and subsequently removed from the reaction medium. It is asserted that, by separately preh~ ting the process gases to at least the reaction temperature, the nucleation site can be confined. A flow optimized hot wall reactor is used as the source because it is 20 believed by KBnig et al that other sources such as a plasma flame or laser beam result in uncontrollable reaction conditions prevailing in various parts of the reaction zone with very steep tt;~ ucldl~lre gradients and/or turbulent flow conditions, resulting in the powders having broad particle size distribution. The nozzle in the Konig et al.
process relates to feed system ofthe process and does not merh~ni~tically participate 25 with the evaporation, reactions, con-l~n~tion or growth of fine powders. Mostnotably, because the process described by Konig et al. is a reactive process, byproducts such as HCI are formed, which ultimately affect the purity of the nanomaterials. Because their temperature is limited to 2000 degrees, the process is limited to precursors that have a vaporization temperature less than 2000 degrees C.
30 In addition, Konig et al. teach a laminar flow technique that would face scale up limitations. rhis is so because the powder characteristics are related to residence time of gases in the reactor, which in turn is related to the parabolic flow associated with W O 9~ PCTrUS97/15463 laminar flow. In other words, in the Konig et al. process~ there is a radially varying profile in residence time (the gas at the center is moving faster than the gas near the wall). As the reactor is scaled up, the powder size will get more broad in distribution.
.

Therefore, there continues to be a need for a low-cost process (less than $1 0/lb) that is suitable for large-scale production of nanopowders under controlled operating conditions. The present invention discloses a pioneering and unique therrnal cond~n~tion process. This process can be a strictly physical process which starts with a material, vaporizes it at very high temperatures (above 2000 degrees C), 0 then very rapidly recondenses it to produce nanoscale powders, thus elimin~ting the forrnation of undesirable byproducts. This process satisfies these requirements for the continuous production of nanopowders in bulk quantities, and additionally discloses a Joule-Thompson nozzle that is particularly suited for ultra-rapid quenching and conrl~n~tion of vaporized material described above.
1s SUMMARY OF THE INVENTION

One of the objectives of this invention is a low capital-cost process for the production of quantum confined and nanometer cluster materials of various inorganic 20 compositions including but not limited to carbides, nitrides, oxides, chalcogenides, halogenides, alloys, metals, complex compositions, and composites in bulk quantities.

Another objective of this invention is to develop techniques to control the size, shape, 2s surface area, morphology, surface characteristics, surface composition, distribution, and degree of agglomeration.

Another objective ofthe invention is a device that enables very high quench rates of high te~ c~d~ule vapors that can produce nanoscale powders.

W0981'~7~ PCT~US97/15463 Yet another objective of this invention is to develop a method of preventing thedeposition of the quantum confined and nanometer cluster materials on the walls of the process equipment.

5 Another objective is to develop a process which allows vaporization of ingredients at very high temperatures (> 2000 degrees C) yet permits quenching at very high rates.

Yet another objective is to develop a process which produces product but generates no byproduct.

A further objective of this invention is to develop a method of ensuring high yie}d and high selectivity, including but not limited to harvesting 95% + of the quantum confined and nanometer cluster material produced.

15 Yet another objective of this invention is to prevent the damage of the quantum confined and nanometer cluster materials during and after their synthesis.

Another objective is a device that is simple, easy to operate, and flexible with respect to operating parameters, so as to allow the production of multiple products.
Another objective is a device that prevents cont~min:ltion of the quenched product from the materials of construction used for the quench equipment.

Yet another objective is a device that allows flexibility in the composition of the 25 vapor q~ n(~.h~l, in quench rates and quench volume.

Another objective of the invention is a process and device that can be carried out with low utility costs (that is, low energy input, energy output, and m~inten~nce expenses).

30 Another objective is a process and device with low operating costs (i.e., labor, recycling, raw materials, plant space, etc.); accordingly, the invention aims at a process and device with high yield per pass and high product selectivity.

CA 02263902 l999-02-23 W 098/09753 PCT~US97/15463 Another objective is a process that is continuous and suitable for scaling up toproduction rates in the order of tons per day.

~ Yet another objective is a process that is simple, easy to operate. and flexible~ so as to 5 allow the production of multiple products with relatively simple operating changes.

Still another objective is a process and device that are safe and environrnentally benign.

10 Finally, another objective is an operationally stable process that requires a minim~l external-control structure for steady-state operation.

A process that satisfies most of these features would be very desirable because it would enable the economical manufacture of nanopowders in bulk quantities.
I s Therefore, according to the foregoing objectives, one aspect of the this invention involves the continuous vaporization at very high temperatures of commercially-available, coarse precursor material suspended in a carrier gas in a therrnal reaction chamber under conditions that minimi7~ superhe~ting and favor nucleation of the resulting vapor. Optionally, a kinetic gas feed may be mixed with the vapor in the 20 reactor to reach a thermokinetic state of the vapor that may be required to produce controlled nucleation of solid powders from the vapor stream. Immediately after the initial nucleation stages, the vapor stream is rapidly and uniformly quenched at rates of at least 1,000 K per second, preferably greater than 1,000,000 K per second, to block the continued growth of the nucleated particles and produce a nanosize powder 25 suspension of narrow particle-size distribution. The nanopowder is then harvested by filtration from the quenched vapor stream and the carrier medium is purified, compressed and recycled for mixing with new precursor material in the feed stream.
According to another aspect of the invention, the thermal quen~hing is carried out in a converging-diverging expansion nozzle that exploits the Joule-Thompson 30 principle of adiabatic expansion of high-temperature vapors. Since the physical characteristics of the nozzle determine the extent of cooling, pressure drop anddensity drop, the con~ien~;ltion process can be advantageously controlled by ntili7.ing W 0981'~3753 PCTrUS97/lS463 a nozle of predetermined key dimensions to fit the requirements of the material being condensed.
Various other purposes and advantages of the invention will become clear from its description in the specification that follows and from the novel features 5 particularly pointed out in the appended claims. Therefore, to the accomplishment of the objectives described above, this invention consists ofthe features hereinafter illustrated in the drawings, fully described in the detailed description of the preferred embodiments and particularly pointed out in the claims. However, such drawings and description disclose only some of the various ways in which the invention may beo practiced.

W 098/09753 PCT~US97/15463 BRIEF DESCRIPTION OF THE DRAWINGS

Figure I is a schematic representation of the adiabatic-expansion, thermal quenching process of the present invention.

Figure 2a is a sketch of a converging-diverging nozle illustrating the relationship between critical parameters of the process and of the nozzle used to carry out the nventlon.

0 Figure 2b is a sketch of a converging-diverging nozzle illustrating the key design pararneters of the device.

Fig~lre 3a, 3b and 3c are cross-sectional elevational, top, and cross-sectional elevational drawings, respectively of a converging-diverging, adiabatic expansion s nozzle according to the preferred embodiment of the invention.

Figure 4 is a sçhem~tic illustration of a pilot-plant process according to the preferred embodiment of the invention.

20 Figures 5a, 5b, 5c, and 5d are drawings ofthe preferred embodiment ofthe present invention for a scaled up process.

Figure 6 is the tr~n.cmiccion electron micrograph of the zinc nanosize powder produced by the invention.
2s Figure 7 is an X-ray diffraction patters of the product of Example I, indicating that the only phase present was zinc.

Figure ~ is a SEM micrograph of the feed powders iron and titanium used, showing30 that they were greater than 1 micrometer when fed.

W O 98~1S~ PCT/US97/15463 .

Figure 9 is a tr~n.cmi~cion electron microscope image of the iron-titanium alloynanopowders produced in Example 2, showing them to be in the 10-45 manometer range.

5 Figure 10 is an X-ray diffraction pattern of the product of Example 2, indicating that the phases formed were titanium, iron and iron-titanium intermetallic.

Figure 11 is a tr~ncmiccion electron microscope image of the nickel aluminide nanopowder produced in Example 3.

Figure 12 is an X-ray diffraction pattern of the product of Example 3, indicating that the phase formed was NiAl.

Figure 13 is a tr~n~miccion electron microscope image of the tungsten oxide s nanopowder produced in Example 4.

Figure 14 is an X-ray diffraction pattern of the product of Example 4, indicating that the phase formed was W O3.

20 Figure 15 is a tr~n.cmiccion electron microscope image of the cerium oxide nanopowder produced in Exarnple 5.

Figure 16 is an X-ray dif~action pattern of the product of Example 5, indicating that the phase formed was CeO~.
Figure 17 is a tr~n.cmi.ccion electron microscope image of the silicon carbide nanopowder produced in Example 6.

Figure 18 is an X-ray diffraction pattern of the product of Example 6, indicating that 30 the phase formed was SiC.

. . .

W O ~3~ 7~ PCTrUS97/15463 Figure 19 is a tr~ncmi~ion electron microscope image of the molybdenum nitride nanopowder produced in Example 7.

Figure 20 is an X-ray diffraction pattern of the product of Example 7, indicating that 5 the phase formed was Mo2N.

Figure 21 is a sc~nning electron microscope image of the nickel boride ceramic used in Example 8, showing that the feed powder was greater than I micrometer.

o Figure 22 is a tr~n~mi~ion electron microscope image of the Ni and Ni3B
nanopowders produced in Example 8, showing them to be in the 10-30 manometer range.

Figure 23 is an X-ray diffraction pattern of the product of Example 8, indicating that 15 the phases forrned were Ni and Ni3B.

Figure 24 is a tr~n~mi~.~ion electron microscope image of the calcium-oxide nanopowders produced in Example 9, showing them to be in the 5-20 manometer range.
Figure 25 is an X-ray diffraction pattern of the product of Example 9, indicating that the phase formed was CaO.

Figures 26a and 26b are trRn~mi~ion electron microscope micrographs of bariurn 25 titanate produced in Example 10.

Figure 27 is an X-ray diffraction pattern of bariurn titanate produced in Example 10.

Figures 28a and 28b are tr~n~mission electron microscope micrographs of ~ Liu 30 titanate produced in Example 10.

W O 98/09753 PCT~US97/15463 Figure 29 is an X-ray diffraction pattern of strontium titanate produced in Example 10.

Figures 30a and 30b are tran~mi~.~ion electron microscope micrographs of barium 5 titante produced in Example 10.

Figure 31 is an X-ray diffraction pattern of barium titanate produced in Example 10.

Figure 32 is a tr~n.~mi~sion electron microscope micrograph of nickel zinc ferrite lo produced in Exarnple 11.

Figure 33 is an X-ray diffraction pattern of nickel zinc ferrite produced in Example I 1 .

15 Figures 34a and 34b are tr~ncmi.s~ion electron micrographs of Ni/Cr/Co/Mo alloy produced in Example 12.

Figure 35 is an X-ray diffraction pattern of Ni/Cr/Co/Mo alloy produced in Exarnple 12.
Figure 36 is a tr In.~mi~cion electron micrograph of bismuth telluride produced in Example 13.

Figure 37 is an X-ray diffraction pattern of bismuth telluride produced in Example 13 .

W O 9~0~7~ PCTrUS97/15463 DETAILED DESCRIPTION OF THE INVENTION

A primary aspect of this invention lies in the discovery that the size and size ~ distribution of nanopowders produced by vapor condensation can be controlled by 5 interrupting the growth process through ultra-rapid thermal quenching of the condensing vapor. Another critical aspect of the invention is the realization that Joule-Thompson adiabatic expansion provides a controllable process for quenchingsuch con~1~n~ing vapor at predetermined rates as high as I o6 ~C/sec, or greater, as required for producing nanopowders of desired properties. A third, important aspect o of the invention is the development of a converging-diverging nozle to implement the adiabatic expansion process of the invention under predictable conditions for a variety of precursor materials and operating conditions.
Referring to the drawings, wherein like parts are designated throughout with like numerals and symbols, Fig. l shows the process flow diagram and a srhem~tics representation ofthe apparatus ofthe invention as applied to solid precursors, such as metals, alloys, ceramics, composites, and combinations thereof. It is understood that the process applies equivalently to other forms of precursors such as liquid, gaseous, slurry, and combinations thereof. A feed stream 10 of such a ple~ o~ material inpowder form is premixed with a feed gas stream 12 (such as argon, heliurn, nitrogen, 20 oxygen, hydrogen, water vapor, methane, air, or a combination thereof, depending on the particular precursor being processed and the corresponding atmosphere - inert, oxidizing, or reducing - required for the process) in mixing apl)~dlus 14 appl~,pl;ate to create a suspension. It is preferred that the feed be a low-cost, coarser form of composition desired. However, if the coarse forrn is expensive, it is equally feasible 25 to use a mix of low-cost precursors that when combined reflect the composition desired. While stoichiometry is preferred, non-stoichiometric feed ratios can be used if the non-stoichiometric feed is less expensive or if the final product streams have the properties as desired. The feed can be a pure composition, a mix of solids and reactant gases, a mix of solids and reactant liquids, a mix of solids, a mix of liquids 30 and gases, a mix of liquids, a mix of gases, a mix of solids, liquids and gases, or combinations thereof. In one preferred embodiment, essPnti~lly the only conctitllent atoms present in the feed other than inert components are the constituent atoms WO 98~57~3 PCT~US97115463 present in the desired solid product. There may be very minor impurity atoms in the feedt but undesired atoms are not present to any significant extent. As an example, if the desired oxide product is nanoscale zinc oxide (ZnO), the feed would be micron scale zinc oxide. If the desired product is indium tin oxide (ITO) the feed would be 5 indium oxide and tin oxide. If the desired product is nonstoichiometric titanium dioxide. the feed would be titanium dioxide and the process would be run to produce a non-stoichiometric product. An example of a system which would not ~ es~ this embodiment would be the reaction of titanium tetrachloride with water to producetitanium dioxide and hydrogen chloride as follows:

TiCI4 + 2H2O --------> TiO~ +4HCI (l) In this case there are constituent atoms present in the feed. namely hydrogen and chlorine, which are not present in the desired solid product.
The preferred method is premixing the feed to as homogeneous levels as possible. ~owever, heterogeneous, series. or parallel feeds are suitable for certain applications. The feed precursors are preferably carried in a gas or a mix of gases that does not possess or can contribute an element that is not desired in the final composition. A preferred carrier stream are inert gases such as argon, heliurn, neon 20 and xenon. The powder 10 is then suspended in the gas l 2, preferably in a continuous operation, using fluidized beds, spouting beds. hoppers. or combinations thereof, as best suited to the nature of the precursor. The test runs perforrned to reduce the invention to practice were conducted with precursor feeds having particle size greater than 1 micrometer, but the process could be used with any size suitable 25 for its continuous vaporization in a gas stream. The resulting gas-stream suspension 16 is advantageously plclleated in a heat exchanger 18 and then is fed into a therrnal reactor 20 where the suspended powder particles preferably completely evaporated in a therrnal evaporation zone 22 by the input of thermal energy. The dimensions of the hot zone are established based on energy balance equations derived from basic 30 principles of transport phenomena. The telllpe,~Lu,~ histories of the feed material depend upon the enthalpy of the plasma discharge and the thermodynamic properties of the feed m~teri~l The times required for heating the particulate material to the W O ~ 5/~ PCT~US97/15463 melting point, melting, heating to the vaporization point and vaporization are calculated using heat transfer equations. Additionally, the steps of heating up to the melting temperature and boiling point. and melting and vaporization can be described ~ using a~ ".ate heat transfer equations. These equations can be found in the U.S.
Provisional patent application Express Mail number EI813191 155US dated August 26, 1997, and in Transport Phenomena in Mettalurgy, G.H. Geiger and D. R. Pourier, Addison-Wesley Publishing Co., Reading, MA, USA (1973) both of which are included herein by reference. The source 24 of such therrnal energy can be accomplished by external heat transfer or by internal heat or both. Examples of lo external heat include but are not limited to induction, d.c. arc, plasma and radiation.
Examples of internal heat include, but are not limited to reaction heat such as combustion and latent heats of phase transformation. Any of these may be used solong as they are sufficient to cause the rapid vaporization of the powder suspension being processed. It is desirable that the te."pe,dlure in the thermal evaporation zone be in excess of 2000 degrees C. It is p,~f~ ,d that the t~l.p~dl lre in the thermal evaporation zone be in excess of 3000 degrees K. It is more preferred that the temperature in the thermal evaporation zone be in excess of 4000 degrees K. It is most preferred that the T in the thermal evaporation zone be in excess of 5000 degrees K. It is necessary that the t~-"~G,dlure in the thermal evaporation zone be above the vaporization t~mpclalul~ of all constituent species. Optionally, in order to prevent cont~rnin:~tion of the vapor stream caused by partial sublimation or vaporization of the thermal reactor's interior walls, they may be pre-coated with the same material being processed. Additionally, this problem can be prevented most preferably by actively cooling the reactor walls and by using a confinement gas stream, i.e. ablanket of the inert gases along the walls of the reactor.
The vaporized gas-stream suspension next enters an e~t~nt1ed reaction zone 26 of the thermal reactor that provides additional residence time, as needed to complete the evaporation of the feed material and to provide additional reaction time (ifnecessary). It is desirable that the telllp~,lalule in the extended reaction zone be in excess of 2000 degrees C. It is preferred that the temperature in the extended reaction zone be in excess of 2500 degrees K. It is more preferred that the t~ p~,dl~lre in the extended reaction zone be in excess of 30no degrees K. It is necessary that the .. ~ .. . . . .. ..

W 098/09753 PCTrUS97/15~63 temperature in the extended reaction zone be above the vaporization temperature of all constituent species. In some cases, this may m~ncl Ite a temperature in excess of 3000 degrees K. As the stream leaves the reactor, it passes through a zone 56 where the thermokinetic conditions favor the nucleation of solid powders from the vaporized 5 precursor. These conditions are deterrnined by calculating the supersaturation ratio and critical cluster size required to initiate nucleation. Rapid quenching leads to hig~h supersaturation which gives rise to homogeneous nucleation. The unstable vapor phase system self-nucleates on atomic clusters of critical size. Below the critical size, the clusters are unstable for a given supersaturation, while above the cluster size the 10 free energy of the cluster is negative. For an ideal vapor phase, the radius of the critical cluster size is given by the relation rn = 2yV/kTln(P,/P~) (2) 15 where ~y is the surface free energy, V is the molecular volume of the condensed phase, k is Boltzman's constant, P, is the pressure of the vapor in the system, and P~ is the vapor pressure of the condensed phase. See G. S. Springer, Advances in Heat Transfer,14, 281-341, Academic Press (1978) which is included herein by reference.
Using titanium powder as an example, based on the physical properties of the 20 feed material and operating conditions in the reactor (size = 1 O~L, melting point =
l ,660 ~C, boiling point 3,287 ~C, heat of vaporization of titanium = 10.985 Btu/g, hot gas temperature = 4,000 ~C), it is possible to calculate the residence time required for vaporization (2.32 msec for heating to melting point, 0.265 msec for melting,5.24 msec for vaporization; total time required = 8-10 msec). Based on the velocity of the 25 suspension injected into the reactor and the travel distance through the reactor, one can ~letennine that a velocity of about 46 ft/sec produces a reci~ence time of 10.7 msec, sufficient for ~oli~lion. If the process requires a predetermin~-d thermokinetic state of the powder being processed which can be enh~ncecl by the presence of a particular gas, a kinetic gas feed 28 (such as argon, helium, nitrogen, 30 oxygen, hydrogen, water vapor, methane, air, or combinations thereof) can also be mixed with the precursor vapor to reach the desired thermokinetic state. As soon as the vapor has begun nucleation, the process stream is quen~hPd in a converging-WO ~ 57a~ PCT/US97/15463 diverging nozzle-driven adiabatic expansion chamber 30 at rates at least exceeding 103 K/sec, preferably greater than I o6 K/sec, or as high as possible. As further detailed below, a cooling medium 32 is utilized for the converging-diverging nozzle to prevent cont~min~tion of the product and damage to the expansion chamber 30.
s Additionally, the use of a confinement blanket gas stream all along the periphery of the product stream also prevents the deposition of nanometer clusters to the walls of the reactor from thermophoresis. Rapid qllen~hing ensures that the powder produced is homogeneous, its size is uniform and the mean powder size remains in submicron scale. The quenrhing of the product gas, however, can be accomplished in numerous o ways and combinations thereof. Some additional examples include, but are not limited to, addition of coolant gases or liquids. addition of materials which absorb heat, radiative cooling, conductive cooling, convective cooling, application of a cooled surface, impinging into liquid such as but not limited to water. The preferred method however, is gas expansion as is described in detail below.
I s The theoretical behavior of the Joule-Thompson adiabatic expansion process is described by the well-known equation:

T,/T, (P2/P,) , (3) 20 where T, and T2 are the temperatures before and after expansion, respectively; P, and P2 are the pressures before and after expansion, respectively; and k is the ratio of specific heats at constant pressure and constant volume (C,JCV).

Applying Equation 2 to a t~ p~ldlUlC change occurring during adiabatic expansion, 25 AT, AT/T~ = (T2 - T,)/T~ = (P2/p~) (k-lyk_ 1; (4) or, for a steady state process, dT/dt = T, d[(P,/P,) (k-'Yk]/dt, (5) W O 981'~ 3 PCTrUS97/lS463 which suggests that Joule-Thompson expansion can quench high-t~ p~,dlure vapors at a steady-state quench rate that depends on the rate at which the pressure is reduced across a given adiabatic expansion-device. Thus, in a continuous, steady-state process, the quench rate can be changed by ch~nging the rate of expansion, which5 provides a much-sought form of control over the nucleation process of nanopowders produced by vapor condensation. Since it is known that the size, size distribution and other properties of vapor con-~en.c~t-on products depend on the speed at which the nucleating material is quenched, the adiabatic expansion approach of the presentinvention provides an invaluable tool, missing in all prior-art processes, for o controlling the quality of the resulting nanopowders. In addition, because the process can be carried out stably in continuous fashion~ it provides a suitable vehicle for large scale applications and commercial production of bulk nanomaterials.
Figure 2a is a sketch of a converging-diverging nozzle 50 to illustrate the relationship between critical parameters of the process and of the nozzle used to carry 15 out the invention. It consists of an optimally-shaped combination of a convergent section 52, a throat section 54, and a divergent section 56. At steady state, the condensing fluid is restricted through a uniformly decreasing cross-section A, from an initial cross-section Al at pressure P, and temperature T,, it is passed through the cross-section A* ofthe throat 54, and then it is expanded through a final cross-section 20 A2 at pressure P2 and t~nlp~ld~u~e T2. The process is carried out through a cross-section A that is first uniformly decreasing and then uniformly increasing through the device. In the converging section 52, the Mach number M for the nozzle is less than 1, while it is equal to I in the throat 54, and greater than I in the diverging section 56.
(Mach number is defined as the ratio of the hydrodynamic flow velocity to the local 25 speed of sound.) Therefore, the initial subsonic flow is accelerated in the converging section of the nozzle, and the flow expands supersonically in the divergent section of the nozzle. At any cross-section A, the Mach number is given by the local value of A/A*, with m=l at the throat. Provided the flow is accelerated to a uniforrn design Mach number, the extent of cooling, ~les~ult;, and density drop can be predicted by 30 the following one-dimensional relationships:

T2/T, = [1 + (k-l)M2/2]-' (6) W O 9~ 3/5~ PCTrUS97/15463 P2/P, = [ I + (k-l )M2/2]~(k-l) (7) P2/P~ = [I + (k-l)M2/2]1'(k-l) (8) where Tz, P2 and p~ are the flow temperature, pressure and density of the condensing fluid after the divergent section, T" Pl and Pl, are at the inlet section of the nozzle, M
is the Mach number, and K is the ratio of heat capacities at constant pressure and constant volume (C~Cv). See J.D. Anderson, Modern Compressible Flow, McGraw-Hill, N.Y., N.Y., (1990) which is included herein by reference.
0 Based on these equations, it is clear that the dimensions of the nozzle are key to its performance as a quenching device. In particular, by the selection of diarneter and length of the three critical sections (52, 54 and 56) and the convergent and divergent angles of the corresponding sections, it is possible to design a nozzle that will produce the necessary Mach number to yield the desired quenching rate. A simple drawing of such a converging-diverging nozzle is also shown in Fig. 2b to illustrate the key design parameters of the device. They are the diameter Dc, the length Lc and theconverging angle ~c, for the converging section; the diameter Dd, the length Ld and the diverging angle ~3d for the diverging section; and the diameter Dt, and length L"
for the throat. In the preferred embodiment of the invention, the dimensions used on the basis ofthe previously stated equations were as follows: Dc = 3.0 in, Lc = 4.125 in, 13C = 17.965~, Dd = 0.75 in, Ld = 1.261 in, ~d= 9.648~, Dt = 0.325 in~ and Ll =
0. 1 14 in.
For example, using argon as the medium, with a pressure drop of 0.72 atmospheres across the nozle, a te~ )eldlllre drop of T~/T, = 0.54 can be expected across the nozzle. It should be noted that in the preferred nozzle, as further detailed below, besides the cooling effect due to expansion, the tt;l,ll,cldl~lre drop across the nozzle is also enh~nced by heat transfer with a boundary-layer gas blanket in the nozzle and by water cooling of the nozle itself.
Referring back to Figs. 3a, 3b and 3c, the particulars of the nozle S0 of the invention, as adapted to a process for rapidly quenching conden~ing vapors to produce nanopowders, are illustrated in sectional-elevational and top views. Fordurability and continuous operation, it is n~ce~s~ry to keep the nozle wall cool to W 0~ 3/~ PCTAUS97/15463 avoid cont~min~tion of the quenched product with the material of construction of the nozle or, in worst cases~ even to avoid melt down and structural failure of the nozzle.
Keeping the nozzle wall cool enhances the quenching effect of the nozzle, leading to yet higher quench rates (exceeding lo6 K/sec). Accordingly, as shown in Figure 3a, 5 the ten,~ dl~lre of the nozle is maintained low with a coolant stream 32, such as cooling water, circulating in a cooling jacket 29 surrounding the nozzle's interior wall 58 between inlet and outlet ports 60 and 62. The cooling medium is preferably circulated in countercurrent flow to optimize uniform cooling of the wall.
In addition, although lower nozzle-wall temp~lalules improve the lo cont~min~tion and failure problems, such lower temperatures can also lead to vapor condensation on the nozzle walls because of mech~nicm~ such as thermophoresis.
Vapor condensation can, in turn, lead to increasing restriction in the no771e throat diameter, with subsequent closure of the throat and failure of the no~le. We solved this additional problem by providing a gaseous boundary-layer stream 33 to form a 15 blanket over the internal surface of the nozzle. As shown in Figure 3c, the blanket gases can be introduced into the nozle' s interior wall axially, radially or tangentially, through an inlet port 31, and can be inert, such as argon or helium when metals and alloys are being processed; or reactive, such as nitrogen, when nitrides are being synthe~i7l~-1; or oxygen or air, when oxides are being processed; methane and 20 hydrocarbons, when carbides are being processed; halogens when halides are being synthe~i7~i; or combinations thereof, depending on the uleimate material being synthesized. Thus, reactive gases can participate in heat transfer with the nucleation process, or reactively on powder surface to selectively modify the composition of the surface (coated powders), or reactively to transform the bulk composition of the2s powder, or in combinations to achieve multiple functions. This secondary gas feed 33 can help eneineer the product nucleation process and the resultant characteristics of the powder. Such nanosize powders will be passivated by precision controlled exposure to N2, O" CH4 or NH3.
Referring back to Figure 1, the quenched gas stream 34 is then filtered in 30 a~ropliate separation equipment 36 to remove the submicron powder product 38 from the gas stream. The separation can be accomplished using various methods including, but not limited to, bag houses cont~ining polymeric or inorganic filters, W 0~ 7~3 PCT~US97115463 electrostatic filtration. surface deposition on cold surfaces followed by scraping with a blade, centrifugal separation~ in situ deposition in porous media, adsorption in liquids or soJids. The preferred method for use in the present invention, however, is the use of bag houses. As well understood in the art, the filtration can be accomplished by 5 single stage or multistage impingement filters, electrostatic filters, screen filters, fabric filters, cyclones, scrubbers, magnetic filters, or combinations thereof. The filtered nanopowder product 38 is then harvested from the filter 36 either in batch mode or continuously using screw conveyors or phase solid transport and the product stream is conveyed to powder processing or pack~ing unit operations (not shown in lo the drawings). The filtered gas stream 40 is compressed in a vacuum-pump/compressor unit 42 and cooled by prehP~ting the gas-stream suspension 16 inheat exchanger 18. Thus, the enthalpy of compression can be utilized by the process as process heat through heat integration. Stream 40 is then treated in a gas cleaning unit 44 to remove impurities and any undesirable process product gases (such as CO, 15 CO" H~O, HC I, NH3, etc). The gas treatment can be accomplished by single stage or multistage gas-gas separation unit operations such as absorption, adsorption, extraction, con-len.~tion, membrane separation, fractional diffusion, reactive separation, fractional separation, and combinations thereof. Finally, the treated gases 46 are recycled back to be reused with the feed gas stream 12. A small split stream 48 20 of the compressed treated gas 46 is purged to ensure steady state operation of the continuous thermal process.
Additionally, the invention was reduced to practice in a pilot plant illustratedschPn~tically in Fig. 4. This thermal reactor, system consists of an upper, cylindrical, thermal evaporation chamber 22 made of quartz and cooled by circulating water (not 2s shown). The gas-stream suspension 16 is formed by mixing the solid feed material 10 fed by a powder feeder I I with an inert gas stream 12, such as argon. The suspension 16 is injected continuously from the top of the thermal evaporation chamber 22 through a water-cooled injection probe 23 and it is heated inductively by means of a DC plasma torch. Note that for the smaller scale process an ICP torch was used as the 30 heat torch. However, one problem associated with the ICP torch is its low thermal efficiency. For scaled up processes, the use of a DC plasma torch is more advantageous because it enables better thermal efficiency, higher feed rates, no RF

W O~ 7-,', PCTrUS97/15463 radiation shielding is required~ and it is easily positionable as compared to the ICP
torch. In a DC plasma torch, plasma is produced by electrical discharge between two electrodes in the presence of a gas-. The classifications of plasma torches are based on the position of electrodes, for example, non-transferred or transferred arc modes. In the non-transferred arc mode~ both the anode and the cathode are located in the torch and the arc is established between these electrodes. ~n the transferred arc mode, one electrode is located outside the torch, which may be the workpiece or material to be heated. In the scaled-up nanosize metal powders production unit, a non-transferred arc DC thermal plasma torch will be used as the heat source. The reactor also I o comprises another, cylindrical, extended reaction zone 26 made of stainless steel, water cooled, positioned downstream of the thermal evaporation zone 22, and sufficiently large to give the feed strearn the residence time required to complete the vaporization and reaction. The reaction zone 26 is lined with a zirconia refractory felt and a layer of silicon-carbide refractory material to reduce heat losses from the hot reaction zone. If necessary to prevent cont~min~tion of the reacting fluid by the reactor or refractory material, the reactor's interior walls (and refractory lining) may be further lined with the same m~t~ri~l constituting the solid feed.
The afli~batic expansion chamber 30 consists of a converging-diverging nozzle, as illustrated in Fig. 3a, operated with a pressure drop (created by the vacuum pump 42 operated at 50 to 650 Torr) sufficient for quenching the high-temperature vapors produced by plasma induction upstrearn in the reactor. The theoretical behavior or the Joule Thompson adi~hatic expansion process has already been described above.After rapid qu~?nrhing leading to homogeneous nucleation and nanosized powders, the powders are passivated by precision controlled exposure to N" ~2~ CH4 or NH3. The separation system of the invention is realized by means of a collection chamber 35, rhed to the outlet of the expansion chamber 30, where the very fine particles entrained in the gaseous stream are collected on a water-cooled metallic coil 37(copper was used successfully for the test runs detailed below) and periodicallyextracted. It is anticipated that commercial-scale equipment would incorporate ascrew or similar conveyor for the continuous removal of the nanopowder product from the collection chamber 35. The gas stream 40 out of the collection chamber is further passed through a filter 39 and trap 41 to thoroughly clean it prior to passage W 098/09753 PCTAUS97/1~463 through the vacuum pump 42. A monitor and fluid-control panel 43 is utilized to monitor process variables (temperatures, pressures, water and gas flow rates), record them, and control all water and gas streams to maintain steady-state operation. It is noted that for simplicity the gas stream 48 exh~l-cted from the vacuum pump 42 was 5 not recycled in the demonstration plant of Fig. 4, but a commercial application would ~ preferably do so for energy and material conservation. Additionally, Figures 5a, 5b, 5c, and 5d show the preferred embodiment of the present invention for a scaled up process.
Additionally, towards one of the goals of the present invention to produce a cost I o effective process, a detailed engineering cost analysis of the thermal process was performed for nanosize passivated alllnninllm powder. The results of the analysis suggested that the future total product cost for nanosize aluminum powder will be about 47.00/lb, therefore the first estimate for future nanosize aluminum powdermarket price was ~ccccce~l at about 82.00/lb.
The effectiveness ofthe invention was demonstrated by lltili7ing the system of Fig. 2 to produce nanosize powders of several different materials. In each case, the powders harvested were characterized for phases, size, morphology, and size distribution. X-ray diffraction (XRD) was used to deterrnine the phases present in the samples using a Siemens D5000 diffractometer with Ni-filtered Cu Ka radiation. The 20 peak widths for average grain size analysis were deterrnined by a least-square fit of a Cauchy function. The average size of the powder produced was estim~tecl by Scherrer's method. Tr~ncmi.c.cion electron microscopy (Hitachi TEM H-8100 equipped with a Kevex6~) EDX) was used for size, morphology, and size distribution.
The particle size of the powders produced was in the manometer range. Scanning 25 electron microscopy (SEM) was used for the coarser size feed powders.

Example 1 Zinc: Commercially available zinc powder (-325 mesh) was used as the precursor to 30 produce n~noci7e zinc powder. Feed zinc powder was fed into the thermal reactor suspended in an argon stream (argon was used as the plasma gas; the total argon flow rate was 2.5 ft3/min). The reactor was inductively heated with 16 kW of RF plasma to WO 98/09753 PCTrUS97/15463 over 5,000 K in the plasma zone and about 3,000 K in the extended reactor zone adjacent the converging portion of the nozzle. The vaporized stream was quenchedthrough the converging-diverging nozzle. The preferred pressure drop across the nozle was 250-Torr, but useful results were obtained at different pressure drops, s ranging from 100 to 550 Torr. After undergoing a pressure drop of 100 to 550 Torr through the converging-diverging nozle, the powder produced was separated from the gas by means of a cooled copper-coil-based impact filter followed by a screen filter. Fig. 6 is the TEM micrograph (or nanograph) of the nanosize powder produced by the invention, showing it to be in the 5-25 manometer range. The size distribution o was narrow, with a mean size of approximately 15 nm and a standard deviation of about 7.5 nm. Variations in the operating variables (such as power input, gas pressure, gas flow rates, and nozzle throat size) affected the size of the powder produced. An XRD pattern of the product is shown in Fig. 7, which indicates that the only phase present was zinc. To avoid conden~tion at the wall, argon was introduced I s tangentially (radial or axial injections have also been proven to be effective) at the nozzle walls. The inert gas provided cooling as well as a boundary layer to act as a barrier for any cond~ n~tion on the nozzle walls.

Example 2 Iron-Titanium Interrnetallic: 2-5 micron powders of iron and 1025 micron powders of titanium were mixed in 1:1 molar ratio and fed into the thermal reactor suspended in an argon stream (total gas flow rate, including plasma gas, was 2.75 ft3/min). The reactor was inductively heated with 18 kW of RF plasma to over 5,000 K in the 2s plasma zone and above 3,000 K in the extended reactor zone adjacent the converging portion of the nozzle. The vaporized strearn was ~uenched through the converging-diverging nozzle. The preferred plc:S:iule drop across the nozzle was 250 Torr, but useful results were obtained at different ~ u,e drops, ranging from 100 to 550 Torr.
After undergoing a p,~ssu~e drop of 100 to 550 Torr through the converging-diverging nozzle, the powder produced was separated from the gas by means of a cooled copper-coil-based impact filter followed by a screen filter. Fig. 8 is the SEM
micrograph of the feed powders used, showing that they were greater than I

WO ~ a~ PCT/US97/lS463 micrometer when fed. Fig. 9 is a TEM image of nanopowders produced by the invention, showing them to be in the 10-45 nanometer range. The size distribution was narrow, with a mean size of approximately 32 nm and a standard deviation of about 13.3 nm. Variations in the operating variables affected the size of the powder 5 produced. The XRD pattern of the product is shown in Fig. 10, which indicates that the phases formed were titanium, iron and iron-titanium intermetallic (FeTi). The phases present illustrate that the invention can produce nanoscale powders of metals and intermetallics. To avoid condensation at the wall, argon was introduced tangentially (radial or axial injections have also been proven to be effective) at the I o nozle walls. The inert gas provided cooling as well as a boundary layer to act as a barrier for any con~ n~tion on the nozzle walls.

Example 3 Nickel-Ah-minllm Interrnetallic: 1-4 micron powders of nickel and ] 0-30 micron powders of aluminum were mixed in 1:1 molar ratio and fed into the thermal reactor suspended in an argon stream (total feed, including plasma gas, at 2.75 ft3/min). The reactor was inductively heated with 18 kW of RF plasma to over 5,000 K in the plasma zone and above 3,000 K in the extended reactor zone adjacent the converging 20 portion of the nozzle. The vaporized stream was quenched through the converging-diverging nozzle. The preferred pressure drop across the nozzle was 250 Torr, but useful results were obtained at different pressure drops, ranging from 100 to 550 Torr.
The powder produced was separated from the gas by means of a cooled copper-coil-based impact filter followed by a screen filter. Fig. 11 is a TEM image of the 25 nanopowder produced by the invention, showing it to be in the 10-30 nanometerrange. The size distribution was narrow, with a mean size of approximately 16.4 nm and a standard deviation of about nm. Variations in the operating variables affected the size of the powder produced. The XRD pattern of the product is shown in Fig. 12, which indicates that the phase formed was NiAI. The phases present illustrate that the 30 invention can produce nanoscale powders of metals and intermetallics. To avoid con~len.~tion at the wall, argon was introduced tangentially at the nozzle walls. The W 098/09753 PCTrUS97/15463 inert gas provided cooling as well as a boundary layer to act as a barrier for any conl1ens~tion on the nozle walls.

Example 4 Tun~sten Oxide: Commercially available tungsten oxide powder (-325 mesh size) was used as the p~ ;UISOl' to produce nanosize WO3. The tungsten oxide powder was suspended in a mixture of argon and oxygen as the feed stream (flow rates were 2.25 ft3/min for argon and 0.25 ft31min for oxygen). The reactor was inductively heated o with 18 kW of RF plasma to over 5,000 K in the plasma zone and about 3,000 K in the extended reactor zone adjacent the converging portion of the nozzle. The vaporized stream was ~uenched through the converging-diverging nozzle. The preferred pressure drop across the nozle was 250 Torr, but useful results were obtained at different pressure drops, ranging from 100 to 550 Torr. After undergoing a pressure drop of 100 to 550 Torr through the converging-diverging nozzle, the powder produced was separated from the gas by means of a cooled copper-coil-based impact filter followed by a screen filter. Fig. 13 is the TEM nanograph of the W03 powder produced by the invention, showing it to be in the 10-25 manometer range.The size distribution was narrow, with a mean size of about 16.1 nm and a standard deviation of about 6.3 nm. Variations in the operating variables (such as power input, gas pressure, gas flow rates, and nozzle throat size) affected the size of the powder produced. An XRO pattern of the product is shown in Fig. 14, which indicates that the phase present was WO3. To avoid condensation at the wall, argon was introduced tangentially at the nozzle walls. The inert gas provided cooling as well as a boundary layer to act as a barrier for any condensation on the nozzle walls.

F.Ya~rle 5 Cerium Oxide: Commercially available cerium oxide powder (5-10 micron size) was used as the precursor to produce nanosize CeO2. The cerium oxide powder was suspended in a mixture of argon and oxygen as the feed stream (at total rates of 2.25 ft3/Min for argon and 0.25 ft3/min for oxygen). The reactor was inductively heated W O ~'U57~ PCTrUS97/15463 with 18 kW of RF plasma to over 5,000 K in the plasma zone and about 3.000 K in the extended reactor zone adjacent the converging portion of the nozle. The vaporized stream was quenched through the converging-diverging nozzle. The preferred pressure drop across the nozle was 250 Torr, but useful results were obtained at different pressure drops, ranging from 100 to 650 Torr. The powder produced was separated from the gas by means of a cooled copper-coil-based impact filter followed by a screen filter. Fig.15 is the TEM nanograph of the CeO2, powder produced by the invention, showing it to be in the 5-25 manometer range. The size distribution was narrow, with a mean size of about 18.6 nm and a standard deviation I o of about 5.8 nm. Variations in the operating variables affected the size of the powder produced. An XRD pattern of the product is shown in Fig. 16, which indicates that the phase present was CeO7. To avoid condensation at the wall, argon was introduced tangentially at the nozzle walls. The inert gas provided cooling as well as a boundary layer to act as a barrier for any condenc~tion on the nozzle walls.
Example 6 Silicon Carbide: Commercially available silicon carbide powder (-325 mesh size) was used as the precursor to produce nanosize SiC. The powder was suspended in argonas the feed stream (total argon flow rate of 2.5 ft3/min). The reactor was inductively heated with 18 kW of RF plasma to over 5,000 K in the plasma zone and about 3,000 K in the extended reactor zone ~ ç~nt the converging portion of the nozzle. The vaporized stream was quenched through the converging diverging nozzle. The preferred pressure drop across the nozzle was 250 l orr, but useful results wereobtained at different pressure drops, ranging from 100 to 550 Torr. The powder produced was separated from the gas by means of a cooled copper coil based impact filter followed by a screen filter. Fig.17 is the TEM nanograph of the SiC powder produced by the invention, showing it to be in the 10-40 manometer range. The size distribution was narrow, with a mean size of approximately 28 nm and a standard deviation of about 8.4 nm. Variations in the operating variables affected the size of the powder produced. An XRD pattern of the product is shown in Fig. 18, which indicates that the phase present was SiC. To avoid con~lenc~tion at the wall, argon W 038~'~3/~ PCTrUS97/15463 was introduced tangentially at the nozzle walls. The inert gas provided cooling as well as a boundary layer to act as a barrier for any condensation on the nozle walls.

Example 7 Molvbdenum Nitride: Commercially available molybdenum oxide (MoO3) powder ( 325 mesh size) was used as the precursor to produce nanosize Mo.N. Argon was used as the plasma gas at a feed rate of 2.5 ft3/min. A mixture of ammonia and hydrogen was used as the reactant gases (NH3 at 0.1 ft3/min; H~ at 0.1 ft3/min). The reactor was 0 inductively heated with 18 kW of RF plasma to over 5,000 K in the plasma zone and about 3,000 K in the extended reactor zone adjacent the converging portion of the nozzle. The vaporized stream was quenched through the converging diverging nozzle. The preferred pressure drop across the nozzle was 250 Torr, but useful results were obtained at dirr~ pressure drops, ranging from 100 to 550 Torr. The powder produced was separated from the gas by means of a cooled copper coil based impact filter followed by a screen filter. Fig. 19 is the TEM nanograph of the Mo,N powder produced by the invention, showing it to be in the 5-30 manometer range. The size distribution was narrow, with a mean size of about 14 nm and a standard deviation of about 4.6 nm. Variations in the operating variables affected the size of the powder produced. An XRD pattern of the product is shown in Fig. 20, which indicates that the phase present was Mo~N. To avoid cond.?nc~tion at the wall, argon was introduced tangentially at the nozle walls. The inert gas provided cooling as well as a boundary layer to act as a barrier for any con~lenc~tion on the nozle walls.

2s Example 8 Nickel Boride Ceramic: 10 50 micron powder of nickel boride were fed into the thermal reactor with argon (fed at a total rate, including plasma gas, of 2.75 ft3/min).
once again, the reactor was inductively heated with 18 kW of RF plasma to over 5,000 K in the plasma zone and about 3,000 K in the extended reactor zone ~ nt the converging portion of the nozzle. The vaporized stream was quenched through the converging diverging nozzle. The preferred ples~ e drop across the nozzle was W 0981'U37~ PCTrUS97/15463 250 Torr, but useful results were obtained at different pressure drops, ranging from 100 to 550 Torr. The powder produced was separated from the gas by means of a cooled copper coil based impact filter followed by a screen filter. Fig.21 shows the SEM micrograph of the feed powders used, demonstrating that they were greater than 5 l micrometer when fed. Fig 22 is the TEM nanograph of the Ni3B powder produced~ by the invention, showing it to be in the 10 to 30 manometer range. The size distribution was narrow, with a mean size of about 12.8 nm and a standard deviation of about 4.2 nm. Variations in the operating variab}es affected the size of the powder produced. An XRD pattern of the product is shown in Fig. 23, which indicates that o the phase present were Ni and Ni3B. To avoid conclen~;~tion at the wall, argon was introduced tangentially at the nozzle walls. The inert gas provided cooling as well as a boundary layer to act as a barrier for any condensation on the nozzle walls.

Example 9 Oxide Ceramics: 5-10 micron powders of calcium carbonate were fed into the thermal reactor with argon (at 2.5 ft3/min). The reactor was inductively heated with 16 kW of RF plasma to over 5,000 K in the plasma zone and about 2,500 K in the extended reactor zone adjacent the converging portion of the nozzle. The vaporized stream was 20 quenched by thermal expansion to about 100 Torr. The pressure drop across thenozzle was 250 Torr, but useful results were obtained at different pressure drops, ranging from 50 to 550 Torr. The powder produced was se~)a,dt~d from the gas by means of a cooled copper coil based impact filter followed by a screen filter. Fig.24 is the TEM image of powder produced by the invention, showing it to be in the S to 25 20 manometer range. As expected from the calcination reaction occ~-rnng in the reactor, the XRD data (shown in Fig. 25) established that the main phase of the nanopowder was CaO. Some other phases, such as Ca(OH)2, were also present due toexposure to atmospheric moisture. The size distribution of the CaO was narrow, with a mean size of about 14.8 nm and standard deviation of about 3.8 nm.
An alternate run was made with MgCO3 powders with mean size of about 7 microns processed with argon. Once again, nanoscale powders of MgO were .. .... ....... .

W O 9~37~ PCT~US97/15463 produced as evidenced by TEM and XRD data. The final product powder size was observed to vary with changes in the pressure, temperature, flow rate~ and compositions.

s Example 10 Barium titanate (BaTiO3): Commerically available barium titanate, micron size (5-10 micron) was used as the precursor to produce nanosize barium titanate powder. The feeding was calibrated to this required feed rate by adjusting the power feeder and the flow rate of the carrier gas. The reactor was inductively heated with 18 kW of lo RFplasma to a themnal steady state. Thermal steady state was established by monitoring the temperature in the reactor. Feed barium titanate powder was feed into the thermal reactor suspended in an argon stream at a gas flow rate of 1.0 ft.3/min.
The power was tumed offand the system allowed to cool down under inert conditions by keeping some flow of argon in the reactor. The product was collected from thequench section and filter, weighed and saved for analysis and perfomnance testing.
TEM images of the powder produced are shown in Figures 26a and 26b. The X-ray diffraction pattem of the powder produced is shown in Figure 27.

An alternate run was made with strontium titanate (SrTiO3) powder to produce nanosize SrTiO3 powder. The feed precursor for strontium titanate was micron size (5-10 microns) SrTiO3 powder. TEM images of the produced powder are shown in Figures 28a and 28b. X-ray diffraction pattem of the powder produced is shown inFigure 29, which reveals that the main phase present is SrTiO3. The surface area of the powder produced was 22.3 m~/g. Most of the produced powder ranged from 10-2s 40 nm.

Additionally, another run was performed to produce nanosize barium titanate (BaTiO3) powder by the following reaction BaCO3 + TiOg = BaTiO3 + CO

W O 98/09753 PCTrUS97/15463 using commercially available barium carbonate (BaCO3) and titanium oxide (TiO~
powders. Both precursors had a size of-325 mesh and were obtained from a commercial supplier. As a result of this test using the abovementioned thermal reactor, nanosize powder of barium titanate was produced. TEM images of the powder produced are shown in Figures 30a and 30b. Figure 31 shows the X-ray diffraction pattern of the powder produced, which shows that the main phase present is BaTiO3. The surface area of the produced powder was 11.9 m~/g. The powder produced was in the nanosize range (10-75 nm).

o Example 11 Nickel Zinc Ferrite: Commercially available nickel zinc ferrite powder (-325 mesh) was used as a precursor to produce nanosize NiZnFe,04 powder. Feed NiZnFe,04 powder was fed into the thermal reactor suspended in an argon stream (argon and helium were used as the plasma gases; the total argon flow rate was I .6ft3/min and the helium flow rate was 0.57 ft3/min). The reactor was heated with a 25 kW DC plasma to over S,OOO K in the plasma zone and about 3,000 K in the extended reactor zone adjacent the converging portion of the nozzle. The vaporized stream was quenchedthrough the converging-diverging nozzle. The preferred pressure drop across the nozzle was 250 Torr, but useful results were obtained at different pressure drops, ranging from 100 to 650 Torr. The powder produced was separated from the gas by means of a cooled copper coil-based impact filter followed by a screen filter. Figure 32 is the TEM nanograph of the NiZnFe204 powder produced by the invention, showing it to be in the 5-50 nanometer range. Variations in the operating variables affected the size of the powder produced. An XRD pattern of the product is shown in Figure 33, which indicates that the main phase present was NiZnFe204. To avoid con(i~n.~z~tion at the wall, argon was introduced tangentially at the nozzle walls. The inert gas provided cooling as well as a boundary layer for any condensation on the nozzle walls.

Example 12 Nickel-Chromium-Cobalt-Molybdenum Allov: Commercially available nickel-chromium-cobalt-molybdenum alloy powder (-325 mesh) was used as a precursor to W O 98/Og753 PCTrUS97/15463 produce nanosize Ni-Cr-Co-Mo powder. Feed Ni-Cr-Co-Mo powder was fed into the thermal reactor suspended in an argon strearn (argon was used as the plasma gas; the total argon flow rate was 2.5 ft3/min3. The reactor was inductively heated with 18 kW
of RF plasma to over 5,000 K in the plasma zone and about 3,000 K in the extended 5 reactor zone adjacent the converging portion of the nozzle. The vaporized stream was quenched through the converging-diverging nozzle. The preferred pressure drop across the nozzle was 250 Torr, but useful results were obtained at different pressure drops, ranging from 100 to 650 Torr. The powder produced was separated from the gas by means of a cooled copper-coil-based impact filter followed by a screen filter.
lo Figure 34 is the TEM nanograph of the Ni-Cr-Co-Mo powder produced by the invention, showing it to be in the 5-100 nanometer range. Variations in the operating variables affected the size of the powder produced. An XRD pattem of the product is shown in Figure 3 5, which indicates that the main phase present was Ni-Cr-Co-Mowith minor amounts of NiCr~04 and Ni3TiOs. To avoid condensation at the wall.
15 argon was introduced tangentially at the nozzle walls. The inert gas provided cooling as well as a boundary layer for any con~enc~tion on the nozzle walls.

Example 13 Bismuth Telluride: Commercially available bismuth telluride powder (-325 mesh) 20 was used as a precursor to produce nanosize Bi,Te3 powder. Feed Bi7Te3 powder was fed into the thermal reactor suspended in an argon stream (argon was used as theplasma gas; the total argon flow rate was 2.5 ft3/min). The reactor was inductively heated with 18 kW of RF plasma to over 5,000 K in the plasma zone and about 3,000 K in the extended reactor zone ~ acent the converging portion of the nozzle. The2s vaporized stream was quenched through the converging portion of the nozzle. The vaporized stream was q~l~nch~c~ through the converging-diverging nozzle. The preferred pressure drop across the nozzle was 250 Torr, but useful results were obtained at different pressure drops, ranging from lO0 to 650 Torr. The powder produced was separated from the gas by means of a cooled copper-coil-based impact 30 filter followed by a screen filter. Figure 36 is the TEM nanograph of the Bi,Te3 powder produced by the invention, showing it to be in the 20-100 nanometer range.
Variations in the operating variables affected the size of the powder produced. An W 0981W 753 PCT~US97/1~463 XRD pattern of the product is shown in Figure 37~ which indicates that the phasepresent was Bi,Te3. To avoid condensation at the wall, argon was introduced tangentially at the nozzle walls. The inert gas provided cooling as well as a boundary layer for any condensation on the nozzle walls.
s These examples demonstrate the feasibility and effectiveness of the principles of this invention in producing nanosize powders from micron sized precursors. The process and apparatus of the invention, lltili7ing ultra rapid qllenrhing as the process step for the formation of nanopowders, provide a practical method for controlling the I o size of the product by manipulating process parameters. In particular, by controlling the quenching rate by ch~nging the pressure drop over the expansion nozzle of the invention, we found that predeterrnined particle sizes and size distributions can be produced reliably in a continuous. steady state process, which is easily scaleable for commercial bulk production. The process was proven viable for metals, alloys, 15 intermetallics, ceramics, composites, and combinations thereof. ln addition, we demonstrated that the process can utilize feeds of reactive components and produce submicron powders of corresponding thermodynamically stable or metastable product species at high temperatures; that it is suitable for recycling and reusing product gases as feed gases; and for recycling and reusing any unseparated product powders as feed 20 material. The method and apparatus of the invention solve many problems unresolved by existing processes to produce submicron powders in general and nanostructured materials in particular. Especially, the process is scaleable; it is solvent free and therefore inherently non polluting and of low cost; it is flexible in relation to processing different feed materials; it allows simple control of product 2s powder size and size distribution; and it does not utilize cont~min~ting components in the feed or for processing, therefore yielding product powders that are as pure as the powders fed to the process.
Inasmuch as one of the primary inventive concepts of the invention is the effective thermal quenching and the attendant advantages produced by ultra rapid30 expansion of a vaporized suspension of the feed material, it is clear that the concept could be applied as well to a system where the precursor material is in the form of a mass evaporated by any method in a low pressure gas. Similarly, the process is . . , ~ . . ~

W O 98/09753 PCTrUS97/15463 applicable to liquid or gaseous precursors that are combined with one or more reactive gases in a reactor and then quenched ultra rapidly according to the invention to produce nanosize particles with a narrow size distribution. For example, silieon tetrachloride (normally liquid at room temperature) can be reacted with methane to 5 produce a silicon carbide vapor which, rapidly quenched according to the invention, can produce a nanosize SiC powder. Similarly, silane (SiH4, normally gaseous at room t~ peldl~lre) can be reacted with methane to produce a silicon carbide vapor which can also be rapidly quenched to produce a nanosize SiC powder with a narrow size distribution. Finally, it is understood that specific changes in materials and o procedures may be made by one skilled in the art to produce equivalent results.
Therefore, while the present invention has been shown and described herein in what is believed to be the most practical and preferred embodiments. it is recognized that departures can be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein but is to be accorded the full 15 scope of the claims so as to embrace any and all equivalent apparatus and methods.

Claims

What we claim is:

1. A process for producing a nanoscale powder from a precursor material comprising the following steps:
evaporating the precursor material in a gaseous atmosphere in a thermal reactor,thereby creating a vapor/gas mixture; and quenching said vapor/gas mixture by effecting its expansion through a predetermined pressure drop, thereby causing the formation of nanoscale particles of product material in a product gas.

2. The process of claim 1, wherein said pressure drop in the quenching step is sufficient to cause a temperature of the vapor/gas mixture to change at a rate of at least 1,000 °C per second.

3. The process of claim 1, wherein said pressure drop in the quenching step is sufficient to cause a temperature of the vapor/gas mixture to change at a rate of at least 1,000,000 °C per second.

4. The process of claim 1, wherein the temperature of said thermal reactor is inexcess of 2000 degrees C.

5. The process of claim 1, wherein the temperature of said thermal reactor is inexcess of 5000 degrees K.

6. The process of claim 1, wherein the constituent atoms of said precursor material consist essentially of the constituent atoms of said product material.

7. The process of claim 1, wherein said expansion through a predetermined pressure drop is carried out by passing the vapor/gas mixture through a converging diverging expansion nozzle.

8. The process of claim 7, wherein the temperature of said thermal reactor is inexcess of 2000 degrees C.

9. The process of claim 7, wherein the temperature of said thermal reactor is inexcess of 5000 degrees K.

10. The process of claim 7, wherein the constituent atoms of said precursor material consist essentially of the constituent atoms of said product material.

11. The process of claim 7, wherein said pressure drop through the converging diverging expansion nozzle is sufficient to cause a temperature of the vapor/gasmixture to change at a rate of at least 1,000 °C per second.

12. The process of claim 7, wherein said pressure drop through the converging diverging expansion nozzle is sufficient to cause a temperature of the vapor/gasmixture to change at a rate of at least 1,000,000 °C per second.

13. The process of claim 7, wherein said pressure drop is between 50 and 650 Torr.

14. The process of claim 1, wherein said evaporation and quenching steps are carried out on a continuous basis.

15. The process of claim 14, wherein said evaporation step is carried out by feeding said precursor material to the thermal reactor as a suspension in said gaseous atmosphere and by subjecting the suspension to an input of thermal energy.

16. The process of claim 15, wherein said thermal energy is at least partially produced by an inductive source.

17. The process of claim 15, wherein said thermal energy is at least partially produced by a microwave source.

18. The process of claim 15, wherein said thermal energy is at least partially produced by an electric are.

19. The process of claim 15, wherein said thermal energy is at least partially produced by heat of reaction.

20. The process of claim 7, further comprising the step of providing a gaseous boundary layer stream to form a blanket over an internal surface of the nozzle.

21. The process of claim 1, further comprising the step of coating an internal surface of said thermal reactor with a layer of said precursor material.

22. The process of claim 21, wherein said expansion through a predetermined pressure drop is carried out by passing the vapor/gas mixture through a converging diverging expansion nozzle.

23. The process of claim 22, wherein said pressure drop through the converging diverging expansion nozzle is sufficient to cause a temperature of the vapor/gasmixture to change at a rate of at least 1,000 °C per second.

24. The process of claim 21, further comprising the step of providing a gaseous boundary layer stream to form a blanket over an internal surface of the nozzle.

25. The process of claim 1, further comprising the step of separating said nanoscale particles of product material from said product gas.

26. The process of claim 25, further comprising the step of recycling said product gas by feeding the product gas to the thermal reactor with said precursor material.

27. The process of claim 7, wherein said nanoscale powder is free of any byproducts.

28. The process of claim 7, wherein said process is a physical process.

29. A nanoscale powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 1.

30. A nanoscale powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 13.

31. A nanoscale powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 14.

32. A nanoscale powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 20.

33. A nanoscale powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 21.

34. A nanoscale metal alloy powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 1.

35. A nanoscale metal oxide powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 1.

36. A nanoscale carbide powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 1.

37. A nanoscale nitride powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 1.

38. A nanoscale ceramic powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 1.

39. A complex nanoscale powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 1.

40. A complex nanoscale powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 7.

41. A complex nanoscale powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 13.

42. A complex nanoscale powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 14.

43. A complex nanoscale powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 20.

44. A complex nanoscale powder having a mean size less than 100 nm and a size distribution with a standard deviation less than 25 nm produced by the process of claim 21.

45. Apparatus for producing a nanoscale powder from a precursor material comprising, in combination: means for evaporating said precursor material in a gaseous atmosphere at a predetermined minimum evaporation temperature, thereby creating a vapor/gas mixture; and means for quenching said vapor/gas mixture by effecting its expansion through a predetermined pressure drop, thereby causing the formation of nanoscale particles of a product material.

46. The apparatus of claim 45, wherein the minimum evaporation temperature is greater than 2000 degrees C.

47. The apparatus of claim 45, further comprising means for providing a gaseous boundary layer stream to form a blanket over an internal surface of said means for quenching the vapor/gas mixture by allowing its expansion through a predetermined pressure drop.

48. The apparatus of claim 47, further comprising means for coating with a layerof said precursor material an internal surface of said means for evaporating theprecursor material in a gaseous atmosphere.

49. A device for quenching a vapor stream of a precursor material to produce itscondensation into a nanoscale powder, comprising:
convergent means for channeling said vapor stream into a flow restriction of a predetermined cross-section from an inlet zone of predetermined inlet pressure;
divergent means for channeling said vapor stream out of said flow restriction to an outlet zone of predetermined outlet pressure; and means for maintaining said inlet and outlet pressures, thereby creating a pressure differential therebetween;

wherein said pressure differential and said cross-section of the flow restriction are selected to produce a quenching of said vapor stream at a rate of at least 1,000 K
per second.

50. The device of claim 49, further comprising means for cooling an internal surface thereof.

51. The device of claim 49, further comprising means for providing a gaseous boundary-layer stream to form a gas blanket over an internal surface of the device.

52. The device of claim 49, further comprising means for cooling an internal surface thereof, and means for providing a gaseous boundary-layer stream to form a gas blanket over an internal surface of the device.

53. The device of claim 49, wherein said convergent means, flow restriction and divergent means consist of a convergent-divergent nozzle having uniformly converging and diverging sections.

54. The device of claim 53, further comprising means for cooling an internal surface of the device.

55. The device of claim 53, further comprising means for introducing a reactive gas into the device.

56. The device of claim 53, further comprising means for providing a gaseous boundary-layer stream to form a gas blanket over an internal surface of the device.

57. The device of claim 53, further comprising means for cooling an internal surface of the device, and means for providing a gaseous boundary-layer stream to form a gas blanket over an internal surface of the device.

58. The apparatus of claim 45, in which said product material consists essentially of nanoscale particles of said precursor material.

59. The apparatus of claim 58, wherein the minimum evaporation temperature is greater than 2000 degrees C.

60. The apparatus of claim 58, further comprising means for cooling an internal surface of said quenching means.

61. The apparatus of claim 58, further comprising means for providing a gaseous boundary-layer stream to form a gas blanket over an internal surface of said quenching means.

62. The apparatus of claim 58, further comprising means for cooling an internal surface of said quenching means, and means for providing a gaseous boundary-layer stream to form a gas blanket over an internal surface of said quenching means.

63 . The apparatus-of claim 58, further comprising means for coating with a layer of said precursor material an internal surface of said means for evaporating theprecursor material in a gaseous atmosphere.

64. The apparatus of claim 58, further comprising means for cooling an internal surface of said quenching means; means for providing a gaseous boundary-layer stream to form a gas blanket over an internal surface of said quenching means; and means for coating with a layer of said precursor material an internal surface of said means for evaporating the precursor material in a gaseous atmosphere.

65. The apparatus claim 58, wherein said quenching means consists of a convergent-divergent nozzle having uniformly converging and diverging sections.

66. The apparatus of claim 64, further comprising means for cooling an internal surface of said convergent-divergent nozzle.

67. The apparatus of claim 64, further comprising means for providing a gaseous boundary-layer stream to form a gas blanket over an internal surface of said quenching means.

68. The apparatus of claim 64, further comprising means for cooling an internal surface of said convergent-divergent nozzle, and means for providing a gaseous boundary-layer stream to form a gas blanket over an internal surface of said nozzle.

69. The apparatus of claim 64, further comprising means for coating with a layerof said precursor material an internal surface of said means for evaporating theprecursor material in a gaseous atmosphere at a predetermined reactor pressure.

70. The apparatus of claim 64, further comprising means for cooling an internal surface of said convergent-divergent nozzle; means for providing a gaseous boundary-layer stream to form a gas blanket over an internal surface of said nozzle;
and means for coating with a layer of said precursor material an internal surface of said means for evaporating the precursor material in a gaseous atmosphere.

71. A method of quenching a high-temperature vapor of a precursor material to produce a nanoscale powder thereof, comprising the following steps:
(a) producing a vapor stream of said high-temperature vapor from an inlet zone of predetermined inlet pressure and passing said vapor stream through a convergent means to channel the vapor stream into a flow restriction of a predetermined cross-section;
(b) channeling the vapor stream out of said flow restriction through divergent means to an outlet zone of predetermined outlet pressure smaller than said inlet pressure; and (c) maintaining said inlet and outlet pressures, thereby creating a pressure differential therebetween;
wherein said pressure differential and said cross-section of the flow restriction are adapted to produce a supersonic flow of said vapor stream.

72. The method of claim 71, wherein said pressure drop in the quenching step is sufficient to cause a temperature of the vapor/gas mixture to change at a rate of at least 1,000 °C per second.

73. The method of claim 71, further comprising the step of providing a gaseous boundary-layer stream to form a blanket over an internal surface of the convergent means.