Method of producing metal nano-sized powders

FIELD: process engineering.

SUBSTANCE: invention relates to power metallurgy, particularly, to production of metallic nano-sized powders.Initial powder of metal oxide compounds with particle size not exceeding 50 mcm is fed by carrier gas into reactor of gas discharge plasma. Initial material is heated to temperature exceeding that of oxides sublimation to evaporate metal and to reduce metal oxides in hydrogen flow or its mix with nitrogen or by argon. Metallic powder is isolated on cooling metal vapors by pulsating inert gas flow at gas flow rate of 1·10-6-1·10-3 m3/s.

EFFECT: ruled out or minimised agglomeration of condensed nano-sized pareticles.

7 cl, 3 ex

 

The invention relates to the technology of production of metal nano-powders, and can be used for production of powders of pure metals and metal alloys in the chemical industry, powder metallurgy, machine building and other industries.

There are two main ways of obtaining nanosized metal powders: chemical and physical. The chemical method involves the precipitation in aqueous solutions and the recovery of the powder of the oxides and hydroxides of metals. Physical is a high - temperature vaporization of the metal and its subsequent condensation, or the method of production of powders by mechanical grinding (mechanical activation). The latter method due to the low performance is only used in special industries powders.

A method of obtaining powder of Nickel /1/ by restoration of basic Nickel carbonate in water at 80-90°C, in accordance with which the restoration carried out in an aqueous solution of hydrazine hydrate is added with the concentration of hydrazine is not less than 4 mol/l at a molar ratio of hydrazine to Nickel is not less than 1.3.

A method of obtaining nanosized copper powder /2/ recovery, which includes a mixture of a salt of copper with glucose solution, dissolution of salt when heated, the introduction is s sodium hydroxide, aging in isothermal mode and the subsequent allocation of metallic copper in the form of nanosized powder. As a salt of copper using copper sulfate. The inventors believe that this method simplifies and reduces the cost of technology for nanoscale powders of copper by reducing the number of technological operations of synthesis.

The method of obtaining nano-sized metal powder described in patent /3/ is in the grinding of hard-to-deform material with an amorphous structure in high-speed disintegrator due to the relative motion of the percussion elements with regulated speed bumps. Pre-selected material with initial particle size of not more than 80 μm, is subjected to the heat treatment, in which form the nanocrystalline inclusions in the amorphous matrix. Crushed at the speed of relative movement of the percussion elements 410-450 m/s and the frequency of strikes 5000-8000 beats./S. Technical result is to obtain a finer powder.

The known method of producing nanoscale powders of iron, copper, Nickel, cobalt, tungsten, molybdenum and metal alloys, which includes chemical precipitation, at least one metal hydroxide solution of alkali with the formation of the suspension, diafiltration the resulting suspension with CTD the population of a solution of at least one metal hydroxide, his dehydration, pre-heating at least one metal hydroxide and restoration production of metal powder and subsequent passivation of the specified powder, at the same time with diafiltrate perform sorption purification of the suspension and restoration of the hydroxide of the metal and passivation of the metal powder is carried out at the active mixing of the material /4/. This method allows to obtain nanosized metallic powder with the structure of the particles, with low distortion and lack of extended defects, as well as high-purity metal powder consisting of particles of monodisperse state while maintaining a narrow fractional composition and a given morphology, and provides the ability to control dispersion at all stages of the process.

Methods of evaporation (condensation), or gas-phase synthesis of nano-powders of metals, based on the evaporation of metals, alloys or oxides and their subsequent condensation in the reactor with a controlled temperature and atmosphere. Phase transitions vapor - liquid - solid or vapor - solid occur in the reactor volume or on the surface of the cooled substrate or walls. The essence of the method is that the original substance is evaporated by the intense heat, with what omashu carrier gas is supplied into the reaction space, where is abruptly cooled. Heating of the evaporated substance is carried out by using plasma, laser, electric arc, resistance furnaces, induction method, passing electric current through a wire.

Depending on the type of starting materials and the resulting product, evaporation and condensation is carried out in vacuum, in inert gas, the flow of gas or plasma. The size and shape of the particles depend on the process temperature, atmospheric composition and pressure in the reaction space. In the atmosphere of helium particles will be smaller than in the atmosphere of argon is more dense gas. This method get the powders of Ni, Mo, Fe, Ti, and Al. The particle size is tens of nanometers. In his time appeared, and further established way of nanomaterials by electrical explosion of wires (conductors). In this case, the reactor between electrodes placed wire metal from which the planned receiving nanopowder with a diameter of 0.1 to 1.0 mm To the electrodes serves a large current pulse power (104-106 A/mm2). When this happens instant heat-up and evaporation of wires. A pair of metal fly, cooled and condensed. The process goes in the atmosphere of helium or argon. The nanoparticles are deposited in the reactor. In this way we obtain a metal (Ti, Co, W, Fe, Mo) and aluminum oxide (TiO2, Al2About3, ZrO2) nanopowders with what rupesciu particles up to 100 nm.

A method of obtaining metallic nano-powders /5/, which includes the heating source of the metal in a stream of inert gas to a temperature of the evaporation source of the metal with the formation of the metal vapor in a stream of inert gas and the selection of the named stream of inert gas metal powder at a temperature below the melting temperature of the original metal. The heat source of the metal is performed by the electron beam with energies of 0.4-3 MeV and a power not exceeding 200 kW, at a pressure close to atmospheric, and the flow rate of the inert gas of 0.5-25000 l/min Inert gas is argon, or helium, or neon, or krypton, or carbon dioxide, or a mixture. The original metal can be virtually any known metal or two metals that are heated together.

In the invention /6/ metal nanopowders produced by decomposition of the metal carbonyl using induction plasma torch at a temperature of 3000-11000 K. CARBONYLS of metals are low decomposition temperature and sublimation of the metals, resulting in the cooling of the formed fine spherical particles of metals. The carbonyl of the metal is at least one carbonyl selected from the group consisting of carbonyl Nickel carbonyl iron, carbonyl copper, cobalt carbonyl, carbonifera, of molybdenum carbonyl, tungsten carbonyl and carbonyl ruthenium. Nanosized particles are rapidly cooled in the reactor, located on the discharge side of a plasma torch. The carrier gas is at least one gas selected from the group consisting of helium, argon, nitrogen, hydrogen and carbon monoxide. For plasma formation using at least one gas selected from the group consisting of helium, argon, nitrogen and hydrogen. The shielding gas may be one of the gases: helium, argon, nitrogen or hydrogen. Gas for rapid cooling can be one of the gases: argon, nitrogen, oxygen, ammonia or methane. The residence time of the carbonyl in the plasma torch is 0.001-10 seconds. The particles of the metal powders have a typical average size of from 1 to 100 nm.

The method of obtaining nanopowders are described in U.S. patents /7/. Plasma installation is arranged so that the direction of flow of plasma gas, the reaction gas and the gas retarding the velocity of the particles of the metal varies depending on the desired residence time of the material in the reaction zone and cooling time of the metal particles. In the plasma reactor can be entered alloying components.

Method of producing nanoscale tungsten powder described in patent /8/. As a result of sublimation of tungsten containing compounds that produce tungsten in almost the re inert gas at a pressure below atmospheric. As the source material used ethylate tungsten, tungsten chloride and hexacarbonyl tungsten. In a similar way it is possible to obtain powders of tungsten carbide, as follows from the patent /9/.

A method of obtaining powders based on tungsten carbide, as proposed in patent /10/. In a plasma reactor restore oxygenated compounds hydrocarbons using a plasma electric discharge receiving a mixture of powders consisting of WC, WC2, tungsten and free carbon content total carbon 5.5 to 7.0 wt.% and a specific surface area of 15-60 m2/year After averaging the resulting mixture of powders is subjected to heat treatment in the presence of hydrogen at a temperature of 850-1300°C To produce powder based on WC. The resulting powder has a hexagonal structure and a wide range of average particle size of from 0.03 to 1 μm. In the reactor additionally serves compounds of metals selected from groups V, Cr, Nb, TA, in an amount of 0.1 to 3.0 wt.%, with the receipt of the carbides, which are inhibitors of the growth of grains during compaction of hard alloys based on tungsten carbide.

The authors of the proposed patent apparatus for producing powders of metal oxides /11/. The device is distinguished by the possibility of varying the directions of gas flows, that is Enate characteristics of the obtained nanopowder metal oxides.

The closest to the technical nature of the claimed invention is a patent (prototype), which describes production of nano-sized powders in the plasma installation, the design of which allows you to remove the deposited nanopowder metals with different surfaces of the reactor /12/. The reactor has a certain aspect ratio, connects the output diameter of the nozzle of the plasma torch, the diameter and the length of the reactor. Surface of the reactor, on which is deposited the obtained nanopowder, have special cleaners to remove nanopowder. The reactor allows to raise the temperature of the plasma for the execution of processes, while avoiding sintering the obtained nanopowders get nanopowder without pollution coarse inclusions class.

The disadvantages of the prototype, as well as other cited inventions, is the inability to prevent the formation of cakes and agglomerates condensed powders and the complexity of removal of sediments nanopowder with different surfaces of the reactor.

The technical result of the invention is the production of metal nano-sized powders with a minimum content of cakes and agglomerates.

The technical result is achieved in that in the method of producing nanoscale powders of metals, comprising a supply source of the second oxide powder metal compounds with a particle size of not more than 50 μm in the reactor discharge plasma transporting gas, the heat source of an oxide material above the temperature of sublimation of the source of metal oxides, evaporation of the metal oxide and the recovery of oxide compounds of metals in the stream of hydrogen or its mixture with nitrogen or argon, the selection of metal powder upon cooling metal vapor with an inert gas to a temperature below the melting temperature of the metal, while the inert gas for cooling serves nozzle with a pulsed input gas.

The pulsating input inert gas provides the use of nozzles with the impeller. The use of larger initial powders of oxide compounds of metals is undesirable, as this would be complete processing of the feedstock into the plasma flow.

A common characteristic of all small metal particles is their aglomerirovannosti. Metal nanopowders have high reactivity, in particular, they are sintered at relatively low temperatures. The high reactivity of nano-powders is related to their metastability and energy saturation, since their formation occurs in strongly nonequilibrium conditions. The average cooling rate of the particles is 109K/sec. Sintering of nanopowders of metals leads to the formation of the nanopowder bulk of agglomerates of strongly bound particles with fractal clusters. Nano is astitsy together, forming agglomerates or chain structures. As a rule, the chain structures of small particles are grouped around the large particles. According to theory of mutual charging /13/ large particles oppositely charged particles. This phenomenon adversely affects the formation of products from nanosized powders. Therefore, the solution of the metal powders with a minimum content of the agglomerates is very important.

Among the numerous methods of struggle with the formation of agglomerates and cakes from nanopowders are used such methods as reducing contact between particles by coating (encapsulation), then, prior to compaction, is removed. This method leads to additional technological operations and, therefore, ineffective.

Mechanical methods of vibration surface of inlet chambers, where condensation occurs nanosized powders, ineffective as it does not affect the behavior of particles in the volume of the chamber. Also inefficient use of ultrasonic energy to prevent agglomeration of the nanoparticles, since this method is effective for continuous media.

The proposed method is as follows. The original powder of oxide compounds of metals with particle size not exceeding 50 μm is served in the reactor discharge plasma transport is atom - nitrogen or argon. Plasma-forming gas is hydrogen or a mixture of nitrogen or argon. At a temperature above the sublimation temperature of the source of metal oxide, the evaporation of the metal oxide and the recovery of oxide compounds of metals in the stream of hydrogen or its mixture with nitrogen or argon gas, with the formation of gas-phase metal vapor, which at the outlet of the plasma reactor picked up by the flow of the cooled inert gas and are deposited in water cooled receiver at a temperature below the melting temperature of the metal and partially taken out of the gas flow in the filter. To prevent or minimize agglomeration condensed nanosized particles of metal powder stream is cooled inert gas is fed by a nozzle, a pulsed gas inlet. Thus, instead of a uniform laminar flow creates turbulence. Laminar flow of the refrigerant gas upon contact with water-cooled walls of the receiver forms a so-called "boundary layer", which promotes agglomeration of nanosized metallic powder. Pulsating turbulent flow allows to avoid the formation of "boundary layer". In addition, the vibration of the dense gas flow creates additional fluctuations in metal nanoparticles, which reduces the likelihood of clicks the education of agglomerates condensed metal powder. The pulsating input a cooled inert gas nozzle with a circuit breaker of the gas supply, made in the form of impeller. By changing the flow rate of cooled inert gas (flow rate of inert gas) change the speed of rotation of the impeller, i.e. the pulse frequency of the gas stream. The flow rate of the inert gas is varied in the range of 1·10-6-1·10-3m2/s. Such a flow of inert gas provided the speed of rotation of the impeller, in which a pulsed gas flow allowed to get metal powders with typical dimensions of 0.5-100 nm and a specific surface area of 10-55 m2/year

The method is implemented in the following way.

Example 1.

In thermal plasma flow produced when heated in a plasma generator of a mixture of hydrogen (70%) and nitrogen (about 30%), transporting gas nitrogen is injected powder of copper oxide with a particle size of <50 μm. In the sublimation source of copper oxide and reduction with hydrogen in the gas phase is formed of metallic copper, which at the outlet of the plasma reactor picked up a pulsing stream of inert argon gas when the flow rate of 5·10-4m3/s. Condensed in water-cooled inlet chamber, the copper powder had an average particle size of 30 nm and a specific surface area of 35 m2/year

Example 2.

In thermal plasma flow obtained when n is Greve in plasma hydrogen generator (100%), transporting argon gas is injected powder of tungsten trioxide with a particle size of <50 μm. In the sublimation source of tungsten trioxide and reduction with hydrogen in the gas phase form metallic tungsten, which at the outlet of the plasma reactor picked up a pulsing stream of inert gas krypton in its consumption of 2·10-5m3/s. Condensed in water-cooled inlet chamber of the tungsten powder had an average particle size of 20 nm and a specific surface area of 45 m2/year

Example 3.

In thermal plasma flow produced when heated in a plasma generator of a mixture of hydrogen (50%) and argon (50%), transporting gas nitrogen is introduced alumina powder with a particle size of <50 μm. In the sublimation source of aluminum oxide and reduction with hydrogen in the gas phase formed aluminum metal, which at the outlet of the plasma reactor picked up a pulsing stream of inert gas helium in its consumption of 1·10-3m2/s. Condensed in water-cooled inlet chamber, the aluminum powder had an average particle size of 40 nm and a specific surface area of 30 m2/year

Granulometric analysis of nanosized metal powders obtained in the above examples showed that the metal powders have uniform structure is round without agglomerates. The proposed method of producing nano-sized powders of metals with high efficiency and reliability of its implementation and can be used for production of powders of pure metals and metal alloys in the chemical industry, powder metallurgy, machine building and other industries.

The list of cited sources:

1. Capanina R.A., Safin BYR, Starodumov VP, krutovsky L.A. the Method of producing the Nickel powder. RF patent 2102191, 20.01.1998

2. Simenyuk GU, Obraztsova I.I., Eremenko NICHOLAS Way proceduralizing of copper powder. RF patent 2426805, 21.12.2009.

3. Korkina M.A., Semanisin EJ, Farmakovsky BV, Samodelkin E.A., Vasiliev A.F., Tarakanova T.A., Barannikov N.V. a Method of obtaining nano-sized metal powder. RF patent 2397024. 20.08.2010.

4. Novikov A.V., Novikov S.A., Mr. A.K. Way to obtain ultrafine metal powder. RF patent 2170647, 20.07.2001.

5. Bardachanov S. p. Method for producing metallic nano-powders. RF patent 2432231, 27.01.2011.

6. Paserin V., Adams, R. S., Boulos M.I., J. Jurewicz, J. Guo Method of producing metal powders decomposition of the metal carbonyl using induction plasma torch. US Patent 7,967,891, 28.06.2011.

7. Boulos M.I., Jurewicz J.W., Nessim C.A., Obtaining powders of metal oxides and the device to receive them. US Patent 6,994,83. 07.02.2006. Boulos M.I., Jurewicz J.W., Nessim C.A., a Device for the synthesis of plasma powders of metal oxides. US Patent 7,501,599, 10.03.2009.

8. Kim VK, Kim J.C. Method of obtaining nanopowders W from the vapor phase low pressure. US Patent 7,208,028 24.04.2007.

9. Kim VK, Kim J.C. On Gook H., Choi C.J. Method of nano-powders of WC vapor phase low pressure. US Patent 7,118,724. 10.10.2006.

10. Annunciation J.V., Alekseev, NV, Samokhin A.V., Miller SCI, Flowers, J.V., Kornev S.A. is a Method of obtaining powders on the basis of tungsten carbide. RF patent 2349424. 20.03.2007.

11. Plischke J.K., De La Veaux, S.C., took place S.R., Witt J.L., Normand C. apparatus for producing powders of metal oxides. US Patent 7,465,430. 16.12.2008.

12. Alekseev, NV, Samokhin A.V., Flowers, J.V. Plasma device for producing nanosized powders. Patent of the Russian Federation 2 331 225. 27.11.2007.

13. Grigorieva L.K., Lidorenko NS, Nagaev NSI other Pis'ma ZH. - 1986. - V.91. - S - 1062.

1. Method of producing nanoscale powders of metals, including the filing of the original powder of oxide compounds of metals with particle sizes of not more than 50 μm in the reactor discharge plasma transporting gas, heat source oxide material above the temperature of sublimation of the source of metal oxides, evaporation of metal oxide, the recovery of oxide compounds of metals in the stream of hydrogen or its mixture with nitrogen or argon, the selection of metal powder upon cooling steam is metal inert gas to a temperature below the melting temperature of the metal, characterized in that the cooling of the metal vapor carry out a pulsing stream of inert gas at the flow rate of 1·10-6-1·10-3m3/s

2. The method according to claim 1, characterized in that the starting oxide material may be one of the oxides of the following metals: Ti, Zr, Hf, Cr, Cu, Mo, W, V, TA, Nb, Al, Si, Pb, Sn, Na, K, Mg, Ca, Zn, Fe, Co, Ni.

3. The method according to claim 1, characterized in that as the carrier gas used argon or nitrogen.

4. The method according to claim 1, characterized in that as the plasma gas using hydrogen or a mixture of nitrogen or argon.

5. The method according to claim 1, characterized in that as the inert gas for cooling use one of the following gases: helium, neon, argon, krypton, xenon.

6. The method according to claim 1, characterized in that the pulsating input inert gas for cooling is performed using the nozzles with the impeller.



 

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