WO2008082031A1

WO2008082031A1 - Plasma reactor system for the mass production of metal nanoparticle powder and the method thereof

Info

Publication number: WO2008082031A1
Application number: PCT/KR2007/001691
Authority: WO
Inventors: Myoung Chul Kyum
Original assignee: Abc Nanotech Ltd.
Priority date: 2006-12-29
Filing date: 2007-04-06
Publication date: 2008-07-10
Also published as: KR100833574B1

Abstract

The present invention relates to a plasma reactor system for the mass production of metal nanoparticle powder and a method thereof, More particularly, this invention relates to a plasma reactor system in which a metal precursor droplet inlet part and an RF inductively coupled plasma reaction unit are integrated into a body for the maximization of a volatilizing rate of the metal droplet and the continuous step thereof by generating a precursor wire metal in a droplet state using DC arc and injecting it into high temperature and high density plasma, and which is capable of controlling a function to regulate the particle size in a vacuum vessel part for adiabatic expansion, and a method thereof.

Description

PLASMA REACTOR SYSTEM FOR THE MASS PRODUCTION OF METAL NANOPARTICLE POWDER AND THE METHOD

THEREOF

Technical Field

[1] The present invention relates to a plasma reactor system for the mass production of metal nanoparticle powder and a method thereof. More particularly, this invention relates to a plasma reactor system in which a metal precursor droplet inlet part and an RF inductively coupled plasma reaction unit are integrated into a body for the maximization of a volatilizing rate of the metal droplet and the continuous step thereof by generating a precursor wire metal in a droplet state using DC arc and injecting it into high temperature and high density plasma, and which is capable of controlling a function to regulate the particle size in a vacuum vessel part for adiabatic expansion, and a method thereof. Background Art

[2] With the rapid development of the modern industrial technology, the study on synthesis and application of nanopowder of from several tens to several hundreds of nanometers having remarkable excellence as compared to conventional materials of micrometer size has been paid attention to in the field of advanced material science because of the necessity of new materials corresponding to the demand of extremely fine parts and equipments using these parts. Nanoparticles in this range exhibit peculiar physical properties which are not found in general particles of micro unit by either surface or volume effects caused by making fine particles. So, such nanoparticles have been expected to be applied as functional materials of magnetic recording media, catalysts, electrically conductive pastes, ferrofluids, abrasives or the like.

[3] As a method for producing nanoparticles, there are currently used a vapor phase deposition method, a liquid phase deposition method, a pulsed wire evaporation method and the like. In the liquid phase deposition method, the productivity of powder is high, whereas there is a problem of purity in nanopowder caused by the adsorption of foreign substances. In case of the pulsed wire evaporation method, energy efficiency is good, thus enabling the mass production, whereas there is a problem in that the shape of powder cannot be controlled. As the vapor phase deposition method for producing metal-based nanopowder, there are an inert gas condensation method (IGC), a metal salt spray-drying method, an evaporation-condensation method and the like. But, the inert gas condensation method and the metal salt spray-drying method have many unfavorable aspects such as energy efficiency, economic problems in the precursor and the like. The evaporation-condensation method is capable of minimizing aggregation of nanopowder and producing ultrafine nanopowder having high purity so that the study thereof has been very actively carried out by using plasma. Disclosure of Invention

Technical Problem

[4] In the past, there has been used a method comprising preparing a reactor by using an

RF plasma torch with the yield for the collection of nanoparticle of less than 100 nm at a laboratory level being from 5% to 10%, and injecting the first reacted powder into the second reactive precursor in order to enhance the yield. But there is a problem in that the cost involved in the process becomes higher due to the increased energy in use.

[5] In recent years, in order to enhance the atomization yield, a new method comprising laminating two or more RF antennas has been attempted. However, there are problems such that the nano yield does not exceed 10% as compared to the applied electric power because solid metal precursors have been used in both cases, metal vapor inside a reaction tube is deposition-coated as the positron range of a precursor becomes longer for abruptly deteriorating the efficiency in which the RF electric power is applied to plasma, and a repair period of a quartz tube or a reaction tube with a low dielectric constant is shortened.

[6] Also, by improving a method for injecting solid precursors, methods in which the amount of the injected reacting gas and precursor can be independently adjusted have been attempted. In this case, in order to secure the stability of plasma, the amount of the precursor must be injected in an amount of about not more than 10 g/sec. So, there is a problem in that the amount of production cannot but be restricted, while when the applied electric power of plasma is enhanced, the efficiency of the productivity to the electric powder has been evaluated to be low. Technical Solution

[7] To solve the aforementioned problems, the present invention is to provide a plasma rector system for the mass production of nano-sized powder having a target particle diameter by comprising continuous steps of making a metal precursor into droplets of micron size using DC arc and injecting the droplets to high- temperature/high-density /argon plasma for complete vaporization, and cooling via low-temperature plasma to be induced in a multilayer RF antenna element disposed on a vacuum vessel for adiabatic expansion for the intended purpose, and a method thereof.

[8] In order to achieve the aforementioned objects, the present invention provides a plasma reactor system for the mass production of metal-nanoparticle powder, comprising a metal precursor droplet inlet part which is capable of supplying a metal precursor to be a raw material for the plasma reaction and changing the precursor into a droplet state before vaporizing the droplet, an RF inductively coupled plasma reaction unit for vaporizing the metal precursor droplet, and a vacuum vessel part for adiabatic expansion for expanding and condensing the vaporized metal vapor.

[9] Furthermore, the metal precursor droplet inlet part has a pair of precursor wire rolls with precursor wires wound therearound, a precursor wire transfer part capable of transferring the precursor wires and a DC arc real-time control part for causing DC arc discharge in a pair of the above precursor wires due to the applied DC current.

[10] Further, the precursor wire transfer part has a pair of current applying rollers and transfers the precursor wires, the current applying roller is electrically connected with a current applying terminal block and supplies the current to the precursor wires, the transfer part is insulated by an insulator, and the current applying roller can adjust its distances by a roller fine gap adjusting screw.

[11] Further, the metal precursor droplet inlet part and the RF inductively coupled plasma reaction unit are integrated into a body for enabling to continuously vaporize the metal in a droplet state, the RF inductively coupled plasma reaction unit has a ceramic plate on its top and the ceramic plate is coated with the same substance as the metal precursor substance, the RF inductively coupled plasma reaction unit has a metal plate on its top and the metal plate has a coating preventive gas inlet tube, and the frequency of the RF inductively coupled plasma reaction unit in use is preferably from 4MHz to 13.56 MHz.

[12] Further, the vacuum vessel part for adiabatic expansion has an induced RF antenna array for regulating the particle size, thus enabling to generate low-temperature plasma, and the induced RF antenna array for regulating the particle size is mounted on an antenna support structure and an extended part of the antenna support structure is coupled to a position adjusting slider for enabling to move vertically.

[13] On the other hand, the present invention relates to a method for the mass production of metal-nanoparticle powder comprising a step of generating DC arc discharge on metal precursor wires which exist in a pair in a metal precursor droplet inlet part and making the precursor wires into a droplet state, a step of vaporizing the metal precursor in a droplet state in an RF inductively coupled plasma reaction unit or a step of adjusting the position of generating low-temperature plasma for making the vaporized metal precursor into nanoparticle powder in a vacuum vessel part for adiabatic expansion.

Advantageous Effects

[14] According to the present invention, there is no problem in injecting non-uniform precursor even though solid precursor substance is used, and the volatizing rate is maximized by making the precursor into a droplet state in the plasma reaction unit prior to supply and vaporizing the droplet. Further, the steps of vaporizing the droplet are continuously carried out for enabling the mass production of nanoparticle powder. In the course of expanding and condensing the vaporized metal, the particle size can be regulated by adjustment of the position of low-temperature plasma. Brief Description of the Drawings

[15] Fig. 1 is a schematic view of a plasma rector for the mass production of nanopowder according to the present invention.

[16] Fig. 2 is a detailed configuration view of a metal precursor droplet inlet part using

DC arc.

[17] Fig. 3 is a detailed view of the precursor wire transfer part (a) in Fig. 2.

[18] Fig. 4 is a whole configuration conceptual view of the plasma reactor for the mass production of nanopowder according to the present invention.

[19] Fig. 5 illustrates a particle size regulating part upon reaction using an induced RF antenna of a vacuum vessel part for adiabatic expansion. Best Mode for Carrying Out the Invention

[20] One preferred embodiment of the present invention will be specifically explained hereinafter with reference to the drawings attached to the present invention. Firstly, of the drawings, the same components and parts are assigned the same reference numbers as far as possible. To describe the present invention, related known functions or constructions will not be explained lest the gist of the present invention be ambiguous.

[21] Fig. 1 is a schematic view of a plasma rector for the mass production of nanopowder according to the present invention which largely comprises a metal precursor droplet inlet part (A), an RF inductively coupled plasma reaction unit (B) and a vacuum vessel part for adiabatic expansion (C). The metal precursor droplet inlet part (A) a part to generate arc discharge on a precursor metal before vaporizing it in the plasma reaction unit and making the metal into a droplet state, and then supplying it to the reaction unit.

[22] In the past, there have been problems such that both liquefaction and vaporization are arranged to occur in the plasma reaction unit so that the efficiency of vaporization is low or a distribution/diffusion phenomenon of the generated particles happens and the positron range becomes longer so that the metal vapor is deposited in a reaction tube. Thus, in order to maximize the volatilizing rate, the metal precursor is injected in a droplet state.

[23] The RF inductively coupled plasma reaction unit (B) is a region to generate high temperature and high density plasma, and receive the above metal precursor in a droplet state to change it to metal vapor. [24] In the present invention, the above two parts are integrated into a body such that steps of changing the metal precursor in a droplet state to metal vapor are continuously carried out, which is different in its manner from the pulsed wire evaporation method comprising continuously changing the metal into a droplet state and vaporizing the droplet. For example, in the pulsed wire evaporation method, the whole metal wire is melted in a very short time and a surface of the metal wire is cooled by a medium around it while the inside of the metal wire is formed in a droplet state and vaporized by discharge among droplets. When the metal gas reaches a pressure of not less than the critical value, it is instantaneously exploded due to the pinch effect and inertia for forming fine particles. A single continuous feeding method is used due to a shock wave at the time of explosion or a separate device is required due to an explosive sound. So, there is such a difference in system configuration. The vacuum vessel part for adiabatic expansion (C) is a place where metal vapor is condensed and nanoparticle is generated. Its entire outer wall is cooled by the cooling water or low-temperature gas vaporized by liquid nitrogen while the inside thereof has a multilayered structure of the induced RF antenna for regulating the particle size.

[25] Fig. 2 is a detailed configuration view of a metal precursor droplet inlet part using

DC arc, and shows the principle of injecting the metal precursor wire and its injection type in the present invention. This part is generally mounted inside the vacuum vessel. The current and gas are connected by a vacuum terminal. Major component parts comprise a precursor wire (155) which is a raw material, a precursor wire roll (151) equipped with the wire, a driving motor (145) for transferring the precursor wire (155), a current vacuum terminal (141) for generating DC arc, a gas vacuum terminal (131) for transmitting high purity argon gas, a gas nozzle (135) and the like.

[26] A diameter of the precursor metal in a wire type is preferably from 0.2 mm to 1 mm.

Because nanoparticle powder can be produced in a large quantity when the metal droplet of about several grams per second must be generated using DC arc prior to injection. More preferably, a ductile material such as gold, silver, copper or the like has a diameter of from 0.5 mm to 1 mm, while a hard material such as nickel, molybdenum or the like has a diameter of from about 0.2 mm to 0.6 mm. It is effective to use such materials. To adjust the size of the generated droplet or the like, the amount of injected gas and the size of the gas nozzle are optimized depending on the properties of the precursor to be used. The metal precursor wire (155) is wound around the precursor wire roll (151) and the precursor wire roll (151) is located on a wire roll insulation mount (150) that is insulated. They exist in a pair on a vertical position adjusting guide (167). The precursor wire coming out of the precursor wire roll (151) moves along a ceramic wire guide (160) coated with Teflon and is extended to near the gas nozzle (135). The current is applied to the current vacuum terminal (141) by a real-time control command of DC arc in a state that a DC power supply is turned on, the gas vacuum terminal (131) is opened for supplying high purity argon, the precursor wires (155) are in contact with each other for generating arc, and thus the metal droplet is continuously generated.

[27] On the other hand, DC arc discharge is adopted as a means to generate droplets before the precursor wire (155) is subjected to a plasma reaction. However, the skilled person in the art can adopt various variations which belong to the technical idea of the present invention. In order to protect the periphery from lots of heat generated at a place where metal droplets are generated, a cooling tube (170) is provided. It is preferable to protect the periphery of the metal droplet generated part by coating with the same metal intended to produce.

[28] Fig. 3 is a detailed view of the precursor wire transfer part (a) in Fig. 2. The generation rate of the metal precursor droplet is affected by the transfer speed as well as the thickness of the precursor wire. A current applying roller (161) functions to hold the precursor wire (155), moves it, and is operated by a driving motor (not illustrated). An interval of the current applying roller (161) is adjusted by using a roller fine gap adjusting screw (162) according to the thickness of the precursor wire (155) in use. A current applying terminal block (142) and the current applying roller (161) are electrically connected and functions to transfer the current necessary for DC arc to the wire. There is a voltage difference of about less than 50 V between the two wires and an arc current of not less than 500A flows there so that the transfer part must be electrically insulated by an insulator.

[29] Fig. 4 is a whole configuration conceptual view of the plasma reactor for the mass production of nanopowder according to the present invention. Devices for injecting the metal precursor by making it in a droplet state into the RF inductively coupled plasma reaction unit comprise a precursor inlet part (100), a power supply for DC arc (120), an argon gas inlet part (130), a DC arc real-time control part (140) and a wire roll insulation mount (150). Both of the precursor inlet part (100) and the wire roll insulation mount (150) are mounted inside the vacuum vessel of not more than 10 torr. When the current is applied by the command from the DC arc real-time control part (140) at a state that the power supply for DC arc (120) is turned on, the driving motor of the precursor inlet part (100) moves the precursor wire according to the command from the DC arc real-time control part (140) while at the same time the high purity argon is supplied to the bottom of the precursor inlet part (100) by the command of adjusting the gas amount of the argon gas inlet part (130). A pair of wires supplied from the wire roll insulation mount (150) come into contact with each other for generating arc, thus continuously generating the precursor wires in a form of metal droplet. In this case, the two precursor wires are electrified positively (+) and negatively (- or ground) so that one of the wires is an anode while the other wire is a cathode. Thus, since the two metal wires of the same kind function as an anode and a cathode for discharging, its meaning is different from the existing plasma discharge of an anode and cathode. Arc discharge might be very delicately generated for forming plasma as well. But, this does not affect the precursor wire in a droplet state.

[30] In the RF inductively coupled plasma reaction unit (B), metal droplets received from the above metal precursor inlet part are reacted with argon in a plasma state by applying an RF electric power supplied by an RF power supply (212) and a matching circuit (215) to an RF antenna in a region of the reaction tube to be metal vapor. This is in a type of an RF shielding structure (200) comprising an RF antenna (210), a quartz tube (230) for locking up plasma and an insulation support (250), which is connected to a slow conduction cooling water manufacturing device (240) that is a peripheral device, and a cooling water circulating device (245) having a heat exchanger. The RF antenna (210) is directly connected with the RF power supply (212) and the matching circuit (215). On the top, there are a metal plate (220) and a ceramic plate (225) that are required because of high temperature environment. Particularly, in the middle, a ceramic plate (225) of a ceramic material having strong heat resistance is used.

[31] When the device is operated, its temperature becomes very high so that a cooling channel is included. In particular, the surface of the ceramic plate (225) is coated with the same substance in a thickness of from 10 to 50 mm according to the type of precursor to be used. The reason of using the same substance for coating is that nanopowder produced by vaporizing a substance of a metal plate and a ceramic plate is not to be contaminated with other substance due to the impact of ion and electron of the plasma during operation for a long time. A coating preventive gas inlet tube (221) is arranged in the metal plate (220) at regular intervals around the circumference adjacently to the quartz tube for injecting gas, whereby it is possible to prevent the evaporated precursor from being coated on the quartz tube (230).

[32] The RF frequency may be preferably used in a band of from 4 to 13.56 MHz, and can be used from 10 to 200 kW in terms of electric power. In case the RF power of 4 MHz is used, an ignition device is generally needed, but a precursor droplet inlet device functions as an ignition device in the present device (a droplet inlet device and a reaction unit integrated into a body) so that such an ignition device is not needed. The meaning of frequency is as follows. When a high frequency of less than 4 MHz is used, real-time RF matching is not possible, and only less than 50% of the electric power applied is used as effective electric power for generating plasma. So, such a frequency is not economic in view of the energy efficiency. When a frequency is not less than 13.56 MHz, it is very difficult to do real-time RF matching and a special transmission system is involved for transferring RF power, resulting in an increase of the production cost and operational cost. Thus, the range of frequency is limited. Furthermore, for the mass production of nanopowder, a daily production capacity can be not less than 20 Kg when the electric power must be at least 20 KW or more. In case of 200 kW level or more, since the electric power exceeds the power band that is industrially allowed, it is preferable to restrict the electric power. That is, the frequency will be most preferably from 4 to 13.56 MHz of 20 to 100 kW level.

[33] Turning to a structure of the vacuum vessel part for adiabatic expansion, a whole cooling channel (350) is cooled by the cooling water or low-temperature gas vaporized by liquid nitrogen while the induced RF antenna array (310) for regulating the particle size having a multilayered structure is fixed by an insulation antenna support structure (320). The induced RF antenna array (310) comprising a cooling channel of a cylindrical structure is respectively connected to the vacuum connection terminals and the respective channels are connected to a variable coil and a variable capacitor that are put on the outside, thus forming an L-C circuit structure which is then connected to a ground port (325). In this vessel part, metal vapor is expanded and condensed for generating nanoparticle powder. A collection connecting part (340) for connecting to a collection vessel for collecting such powder is arranged, while particles having a particle size larger than a desired size are recovered through a nanopowder recovery part (360).

[34] Fig. 5 illustrates a particle size regulating part upon reaction using an induced RF antenna of the vacuum vessel part for adiabatic expansion. Since the reaction regime for complete vaporization is a little different depending on the kind of the precursor, the whole position of the induced RF antenna array (310) must be vertically adjusted. For this purpose, a position adjusting slider (330) for vertical movement and a fixing bolt (335) for fixing at an appropriate position are provided. A coil (312) part of the induced RF antenna array (310) is located in a sintering ceramic case (313), the extended parts of the antenna support structure (320) on both sides are arranged to move upward and downward on the position adjusting slider (330), and are mounted at a specific position by the fixing bolt (335).

[35] At an early stage, a matching signal part (315) is varied lest plasma be generated due to induction. When metal vapor comes down at a steady state from the RF inductively coupled plasma reaction unit (B), the matching signal part (315) is varied for regulating the particle size, and plasma is induced by the above RF antenna (21) in the induced RF antenna array (310). The low-temperature plasma (370) generated by induction has a very low-temperature as compared to the plasma by the above RF antenna (210). A variable capacitor and a variable coil in each antenna are regulated for adjusting the distribution of the plasma temperature in a vertical direction. In order to obtain particles having a particle diameter of not more than 100 nm, plasma is not induced in the antenna but the antenna is just cooled. To obtain particles having a particle diameter of more than 100 nm, a little plasma is induced in the antenna.

[36] A method for the mass production of nanoparticle powder according to the technical idea of the present invention comprises a step of making the metal precursor into a droplet state before supplying the metal precursor to the RF inductively coupled plasma reaction unit. Also, to make the precursor into a droplet state, a pair of the metal precursor wires are prepared and come into contact with each other when the current is applied for generating DC arc discharge. The precursor wires are transferred by a transfer means and connected to the RF inductively coupled plasma reaction unit in a droplet state. In order to regulate the particle size, the position of low-temperature plasma induced in the vacuum vessel part for adiabatic expansion is adjusted.

[37] That is, the present invention includes a step of making the precursor wire into a droplet state by generating DC arc discharge in metal precursor wires which exist in a pair in the metal precursor droplet inlet part, a step of vaporizing the metal precursor in a droplet state in the RF inductively coupled plasma reaction unit, and a step of adjusting the position of low-temperature plasma in the vacuum vessel part for adiabatic expansion, for the mass production of metal nanoparticle powder.

[38] The present invention as described above is not restricted to the aforementioned embodiment and drawings as attached herewith. The present invention can be sub stituted, modified and changed in many ways in the ranges in which the technical idea of the present invention is not deviated, which is obvious to the skilled person in the art in the technical field of the present invention.

Claims

[1] A plasma reactor system for the mass production of metal-nanoparticle powder, comprising a metal precursor droplet inlet part which is capable of supplying a metal precursor to be a raw material for the plasma reaction and changing the precursor into a droplet state before vaporizing the droplet, an RF inductively coupled plasma reaction unit for vaporizing the metal precursor droplet and a vacuum vessel part for adiabatic expansion for expanding and condensing the vaporized metal vapor.

[2] The plasma reactor system according to claim 1, wherein the metal precursor droplet inlet part has a pair of precursor wire rolls with precursor wires wound therearound, a precursor wire transfer part capable of transferring the precursor wires and a DC arc real-time control part for causing DC arc discharge in a pair of the precursor wires due to the applied DC current.

[3] The plasma reactor system according to claim 2, wherein the precursor wire transfer part has a pair of current applying rollers and transfers the precursor wires, the current applying roller is electrically connected with a current applying terminal block and supplies the current to the precursor wires, and the transfer part is insulated by an insulator.

[4] The plasma reactor system according to claim 3, wherein the current applying roller adjusts its distances by a roller fine gap adjusting screw.

[5] The plasma reactor system according to claim 1, wherein the metal precursor droplet inlet part and the RF inductively coupled plasma reaction unit are integrated into a body for enabling to continuously vaporize the metal in a droplet state.

[6] The plasma reactor system according to claim 5, wherein the RF inductively coupled plasma reaction unit has a ceramic plate on its top and the ceramic plate is coated with the same substance as the metal precursor substance.

[7] The plasma reactor system according to claim 5, wherein the RF inductively coupled plasma reaction unit has a metal plate on its top and the metal plate has a coating preventive gas inlet tube.

[8] The plasma reactor system according to claim 5, wherein the frequency of the RF inductively coupled plasma reaction unit in use is from 4 to 13.56 MHz.

[9] The plasma reactor system according to claim 1, wherein the vacuum vessel part for adiabatic expansion has an induced RF antenna array for regulating the particle size, thus enabling to generate low-temperature plasma.

[10] The plasma reactor system according to claim 9, wherein the induced RF antenna array for regulating the particle size is mounted on an antenna support structure and an extended part of the antenna support structure is coupled to a position adjusting slider for enabling to move vertically.

[11] A method for the mass production of metal-nanoparticle powder by the system as set forth in claim 1, which comprises a step of generating DC arc discharge on metal precursor wires which exist in a pair in a metal precursor droplet inlet part and making the precursor wire into a droplet state.

[12] The method for the mass production of metal-nanoparticle powder according to claim 11, which further comprises a step of vaporizing the metal precursor in a droplet state in an RF inductively coupled plasma reaction unit.

[13] The method for the mass production of metal-nanoparticle powder according to claim 12, which further comprises a step of adjusting the position of generating low-temperature plasma for making the vaporized metal precursor into nanoparticle powder in a vacuum vessel part for adiabatic expansion.