Double-frequency power-driven inductively coupled plasma torch, and apparatus for generating nanoparticle using same

Abstract

A dual frequency power-driven inductively coupled plasma torch according to an exemplary embodiment of the present invention includes: a hollow confinement tube provided with a space in which thermal plasma is formed; an induction coil that surrounds the confinement tube; and a power supply source that supplies power to the induction coil, wherein the power supply source may supply at least two powers having different frequencies to the induction coil.

Claims

1. A dual frequency power-driven inductively coupled plasma torch, comprising: a hollow confinement tube provided with a space in which thermal plasma is formed; an induction coil that surrounds the confinement tube; and a power supply source that supplies power to the induction coil, wherein the power supply source supplies at least two powers having different frequencies to the induction coil, wherein the at least two powers includes a first power having a first frequency and a second power having a second frequency higher than the first frequency, and wherein the first power and the second power are supplied to the induction coil in a simultaneous dual frequency (SDF) manner where the first frequency and the second frequency are combined in a modulated form.

2. The dual frequency power-driven inductively coupled plasma torch of claim 1, wherein the at least two powers having different frequencies are implemented by two separate power sources and two inverters.

3. The dual frequency power-driven inductively coupled plasma torch of claim 1, wherein the at least two powers having different frequencies are implemented by one power source and two inverters connected in parallel to the one power source.

4. A dual frequency power-driven inductively coupled plasma torch, comprising: a hollow confinement tube provided with a space in which thermal plasma is formed; an induction coil that surrounds the confinement tube; and a power supply source that supplies power to the induction coil, wherein the power supply source supplies at least two powers having different frequencies to the induction coil, wherein the at least two powers having different frequencies are time sharing dual frequency powers that are time-shared and alternately supplied to the induction coil.

5. The dual frequency power-driven inductively coupled plasma torch of claim 1, wherein a low-frequency power of the at least two powers having different frequencies has a frequency of 0.05-0.5 MHz, and a high-frequency power thereof has a frequency of 1-20 MHz.

6. The dual frequency power-driven inductively coupled plasma torch of claim 1, further comprising an injection probe that introduces nano-metal particle precursors into the confinement tube.

7. An apparatus for generating nanoparticles, comprising: a device that supplies nanoparticle precursors; and the dual frequency power-driven inductively coupled plasma torch of claim 1, wherein the dual frequency power-driven inductively coupled plasma torch receives and evaporates the nanoparticle precursors from the device to form nanoparticles.

8. The apparatus for generating the nanoparticles of claim 7, wherein the nanoparticle precursors are introduced into the confinement tube from the device through an injection probe.

9. The apparatus for generating the nanoparticles of claim 7, wherein the nanoparticle precursors are one or more materials selected from a metal, a metal oxide, and a ceramic.

10. The dual frequency power-driven inductively coupled plasma torch of claim 4, wherein a low-frequency power of the at least two powers having different frequencies has a frequency of 0.05-0.5 MHz, and a high-frequency power thereof has a frequency of 1-20 MHz.

11. The dual frequency power-driven inductively coupled plasma torch of claim 4, further comprising an injection probe that introduces nano-metal particle precursors into the confinement tube.

12. An apparatus for generating nanoparticles, comprising: a device that supplies nanoparticle precursors; and the dual frequency power-driven inductively coupled plasma torch of claim 4, wherein the dual frequency power-driven inductively coupled plasma torch receives and evaporates the nanoparticle precursors from the device to form nanoparticles.

13. The apparatus for generating the nanoparticles of claim 12, wherein the nanoparticle precursors are introduced into the confinement tube from the device through an injection probe.

14. The apparatus for generating the nanoparticles of claim 12, wherein the nanoparticle precursors are one or more materials selected from a metal, a metal oxide, and a ceramic.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a schematic view of a conventional inductively coupled plasma torch.

(2) FIG. 2 illustrates an operational principle of an inductively coupled plasma torch.

(3) FIG. 3 illustrates a graph of an electric field according to positions in a confinement tube.

(4) FIG. 4 illustrates a schematic view of an inductively coupled plasma torch according to a first exemplary embodiment of the present invention.

(5) FIG. 5 illustrates a schematic view of an inductively coupled plasma torch according to a second exemplary embodiment of the present invention.

(6) FIG. 6 illustrates an example of a simultaneous dual frequency (SDF) power waveform.

(7) FIG. 7 illustrates a schematic view of an inductively coupled plasma torch according to a third exemplary embodiment of the present invention.

(8) FIG. 8 illustrates an example of a time sharing dual frequency (TSDF) power waveform.

(9) FIG. 9 illustrates temperature distribution in a confinement tube when the same power is supplied to each of induction coils in a form of dual frequency power and when it is supplied to each of the induction coils in a form of single frequency power.

(10) FIG. 10 illustrates an electric field with respect to each position in a confinement tube when the same power is supplied to each of induction coils in a form of dual frequency power and when it is supplied to each of the induction coils in a form of single frequency power.

DESCRIPTION OF SYMBOLS

(11) TABLE-US-00001 101: power supply 106, 206: injection probe 105, 205: induction coil 108, 208: confinement tube 300, 400, 500: power source 301, 302, 401, 402, 501: inverter 501: switch

MODE FOR INVENTION

(12) The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

(13) The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.

(14) Throughout this specification and the claims that follow, when it is described that an element is coupled to another element, the element may be directly coupled to the other element or indirectly coupled to the other element through a third element. In addition, unless explicitly described to the contrary, the word comprise and variations such as comprises or comprising will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

(15) FIGS. 4, 5, and 7 illustrate exemplary embodiments of a dual frequency power-driven inductively coupled plasma torch according to an exemplary embodiment of the present invention, and since configurations of a confinement tube 208, an induction coil 205 surrounding the confinement tube 208, and an injection probe 206 are the same as or similar to those of the conventional inductively coupled plasma torch, a detailed description thereof will be omitted.

(16) However, unlike the conventional power supply 101, a driving power supply according to an exemplary embodiment of the present invention may supply at least two powers having different frequencies at the same time (which may be referred to as simultaneous dual frequency (SDF)), or alternately supply at least two powers having different frequencies at predetermined intervals (which may be referred to as time sharing dual frequency (TSDF)). That is, it may be operated so as to stop power of a relatively low frequency when power of a relatively high frequency is inputted, while it may be operated so as to stop power of a relatively high frequency when power of a relatively low frequency is inputted.

(17) Hereinafter, for better understanding and ease of description, power having a relatively high frequency of at least two powers having different frequencies will be referred to as high-frequency power, and power having a relatively low frequency thereof will be referred to as low-frequency power.

(18) FIG. 4 illustrates a first exemplary embodiment that supplies SDF power to an inductively coupled plasma torch through two separate power sources 300 and 300 and dual inverters 301 and 302. Each of output terminals of the inverter 301 generating low-frequency power and the inverter 302 generating high-frequency power forms a primary side of a current transformer 410, and the induction coil of the inductively coupled plasma torch is connected to a secondary side of the current transformer, such that the high-frequency power and the low-frequency power may be simultaneously supplied to the induction coil 205. The power supplied from the two power sources 300 and 300 may be adjusted in consideration of temperature distribution, volume, etc. of the thermal plasma. Simultaneous dual frequency (hereinafter referred to as SDF) corresponds to a combination of high-frequency power and low-frequency power, and as shown in FIG. 6, the high-frequency power and the low-frequency power are supplied to the induction coil of the inductively coupled plasma torch in a modulated form.

(19) FIG. 5 illustrates a second exemplary embodiment that supplies the SDF power to the inductively coupled plasma torch in a similar fashion to the first exemplary embodiment, however unlike the first exemplary embodiment, after power is supplied from one power source 400 to inverters 401 and 402, the power is inverted into high-frequency power and low-frequency power through the inverters 401 and 402, respectively, which are then modulated to be supplied to the inductively coupled plasma torch.

(20) FIG. 7 illustrates a third exemplary embodiment related to the time sharing dual frequency power, wherein a power source 500 is connected to one inverter 501 and is controlled by a switch 510 in the inverter 501 so that high-frequency power and low-frequency power may be time-shared (or time-divided) and supplied. Unlike the first or second exemplary embodiment, in the third exemplary embodiment, the high-frequency power and the low-frequency power are not supplied as SDF power but are alternately supplied in a time-sharing manner. That is, as in a power waveform shown in FIG. 8, when the high-frequency power is supplied, the low-frequency power is not supplied, and when the low-frequency power is supplied, the high-frequency power is not supplied.

(21) Although the method of supplying the power to the inductively coupled plasma torch according to the first to third exemplary embodiments has been described, since the specific SDF power supply/time sharing power supply method or topology may be selected by an ordinary technician as necessary, the present invention is not limited to the topologies of the SDF power supply method and the time sharing power supply method described above.

(22) The frequency of the low-frequency power among the dual frequency powers, when an inner diameter of the confinement tube is given, may be determined through Equation 1, and when the inner diameter thereof is 100 mm or more, the frequency may be selected between 0.1-0.5 MHz. In this case, a frequency of the high-frequency power may be selected between 1-20 MHz. That is, the frequency of the low-frequency power may be determined by the inner diameter of the confinement tube, and the frequency of the high-frequency power may be selected so that thermal plasma may be formed between an inner circumferential surface of the confinement tube and a central portion of the confinement tube. In addition, the inductively coupled plasma torch may further include a water-cooled injection probe 206, which serves to inject materials to be processed into the plasma, and in this case, a low frequency and an inner diameter of the torch may be appropriately selected within a range in which an electromagnetic field by the low-frequency power does not interact with the injection probe 206.

(23) Generally, in a case of a large-output torch with a torch input power of 100 kW or more, the inner diameter of the confinement tube thereof should be 100 mm or more to prevent damage to the confinement tube due to excessive heat. However, when a high frequency of 1 MHz or more is used in a torch requiring that the inner diameter is 100 mm or more and the torch input power is 100 kW or more, an off-axis characteristic of radial temperature distribution in the torch is more apparent as the torch input power increases, which reduces efficiency of heat utilization in a central axis region through which most of the materials to be processed pass and increases heat loss of the confinement tube. On the other hand, when a low frequency of 0.5 MHz or less is used in a large-output and high-frequency inductively coupled plasma torch of 100 kW or more, an electric field at a central axis thereof increases, thus it is difficult to insert a metallic water-cooled injection probe 206, and a taper phenomenon due to reduction of a diameter of the plasma becomes severe.

(24) When the dual frequency power driving method according to the exemplary embodiment of the present invention is applied to the large-output torch of 100 kW or more having the above-mentioned problem, the plasma near the central axis thereof may be directly heated by the low-frequency power of 0.5 MHz or less to be maintained at a high temperature, and an outside portion of the plasma may be relatively heated by the high-frequency power of 1 MHz or more. Thus, the temperature and the electromagnetic field distribution within the plasma may be controlled to be fit for a purpose, such as stabilizing the entire plasma flame while reducing the off-axis temperature distribution characteristic. Particularly, in the high frequency power technology, a high efficiency semiconductor power device technology having power conversion efficiency of 95% or more is restrictively applied to a low output power supply of about 30 kW at a high frequency of 1 MHz or more, while it is commercially applied to a large-output power supply of 100 kW or more at a frequency of 0-0.5 MHz, thus when the mentioned two types of power supplies are combined and used, they may generate high-frequency inductively coupled plasma of 100 kW or more without using a conventional low-efficiency (50-60%) vacuum tube type of high-frequency power supply.

(25) For reference, the present invention is suitable for a large plasma torch in which an inner diameter of the confinement tube is 80 mm or more and an output thereof is 50 kW or more, and more preferably, the present invention is suitable for a large plasma torch in which an inner diameter of the confinement tube is 200 mm or less and an output thereof is 400 kW or less. For example, a torch having an inner diameter of 100 mm and an output of 100 kW typically consumes about 300 slpm of gas, but when the inner diameter of the confinement tube thereof exceeds 200 mm, since at least four times as much gas must be supplied in order to obtain the same plasma speed, as the inner diameter increases, the gas consumption exponentially increases, thereby deteriorating economic efficiency. As compared with the torch having the inner diameter of 100 mm and the output of 100 kW, when a torch having a diameter of 200 mm or less is used, it is desirable to maintain plasma output to be 400 kW or less in order to maintain heat-flowing and torch efficiency in the torch.

(26) Hereinafter, an effect according to the first embodiment of the present invention will be described through computer simulation. Specifically, performance of a 100 kW class high frequency inductively coupled plasma torch (of which inner diameter is 100 mm) driven at a 4 MHz single frequency and performance of a 100 kW class dual frequency power-driven high frequency inductively coupled plasma torch (of which inner diameter is 100 mm) driven at 0.5 MHz and 30 kW and 4 MHz and 70 kW are compared.

(27) Table 1 below represents conditions of computer simulation performed for the present exemplary embodiment, except for the above-mentioned frequencies and output conditions. Results of the present exemplary embodiment were obtained by computer-numerical-analyzing electromagnetic fluid equations (a continuous equation, a momentum equation, an energy equation, and a vector potential equation), which are well known for behavioral description methods such as a temperature field and a velocity field in the high-frequency inductively coupled plasma, according to the conditions of Table 1.

(28) TABLE-US-00002 TABLE 1 Item Condition Design condition (1) Torch radius 50 mm (2) Radius of induction coil 60 mm (3) Winding number of induction coil 4 (4) Torch length 160 mm Driving condition (1) Central gas 100 slpm (2) Carrier gas 0 (3) Sheath gas 200 slpm (4) Gas type Mixture of 70% Ar and 30% H.sub.2

(29) Test conditions for computational analysis of electromagnetic fluid equations

(30) FIG. 9 illustrates graphs in which temperature field distributions expected to be formed inside a torch having an inner diameter of 100 mm are obtained and compared by computer simulation when driven at a 4 MHz single frequency and when driven at a ratio of 3:7 of 0.5 MHz and 4 MHz frequencies, respectively. In this case, total energy supplied to the plasma torch driven at the single frequency and total energy supplied to the plasma torch driven at the dual frequencies were set to be the same.

(31) As can be seen from the temperature distribution shown in FIG. 9, when the torch is driven by the dual frequency power, a high temperature region of 7000 K or more is maintained even in the vicinity of the central axis of the torch. In contrast, when the torch is driven by the single frequency power, the off-axis temperature distribution, which is a typical characteristic of the conventional high-frequency inductively coupled plasma torch, such as falling below 5000 K in the vicinity of the central axis of the torch, is formed. That is, it can be seen from FIG. 9 that in the case of the dual frequency power-driven method in which the low-frequency power and the high-frequency power are simultaneously supplied, it is possible to control a non-uniformity problem of the conventional high-frequency single-driven method.

(32) FIG. 10 illustrates electric field distribution calculated in a radial direction at 0.05 m in a longitudinal direction of two types of torches. In the case of the dual frequency power-driven method, the relative high temperature region observed near the central axis is due to the Joule heat heating by the 0.5 MHz low-frequency power-driven electric field that exists from the penetration depth of the high-frequency electric field of 4 MHz to the vicinity of the center axis. As described above, when the torch is driven with different outputs for each frequency, the dual frequency power-driven method may control the internal temperature distribution and the electromagnetic field distribution of the torch in accordance with the application purpose.

(33) According to the simulation described above, even though the same power is supplied, when it is converted into two powers having different frequencies and supplied, it can be seen that excellent effects may be obtained in both the highest temperature and the temperature distribution of the thermal plasma compared to the case of supplying the single frequency power.

(34) While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but those skilled in the art may suggest another exemplary embodiment by adding, modifying, or deleting components within the spirit and scope of the appended claims, and the other exemplary embodiment also falls in the scope of the present invention.