Normal-pressure heat-assisted microwave plasma ionization source device and discharge tube

Abstract

The invention relates to a normal-pressure heat-assisted microwave plasma ionization source device and a discharge tube, and belongs to the technical field of plasma generation devices. The discharge tube is composed of a section of reducing glass tube, a heating resistance wire is arranged in the thick tube section to heat discharge gas to a required temperature, the thin tube section is used for winding a working coil, and the thick tube section and the thin tube section form a complete gas heating and plasma induction path. When gas is introduced into the discharge tube, the gas is heated to a set temperature by the resistance wire and then passes through the metal wire winding tube section, the discharge gas absorbs magnetic field energy in the metal coil to generate high-density chemical active substances, and the substances are ignited by the igniter to form plasmas. According to the invention, the gas heat-assisted technology and the microwave-induced plasma technology are combined, the structure is simple, the operation is simple and convenient, the combination of the heat-assisted technology reduces the gas breakdown power and the plasma maintenance power in the microwave discharge process, and the energy utilization rate is improved.

Description

Technical Field

[0001] The invention relates to a normal-pressure heat-assisted microwave plasma ionization source device and a discharge tube, belonging to the technical field of plasma generating devices. Background Art

[0002] Microwave induced plasma technology is a technology based on microwave energy to excite gas molecules to generate plasma. Microwave induced plasma technology has a wide range of application value in many fields such as element detection, material deposition, waste gas treatment and surface cleaning. In the field of element detection, microwave plasma emission spectrometry has great application advantages in the detection of trace elements, trace elements and heavy metal elements due to its high sensitivity, wide linear range, multi-element analysis and high precision.

[0003] The existing microwave induced plasma technology generally provides sufficient energy to the discharge gas in the plasma discharge tube through a microwave source via a coaxial cable or a rectangular waveguide, and uses a complex resonant cavity to make the microwave inside the wall resonate, forming the maximum energy absorption, and finally causing the gas to break down and produce microwave plasma discharge. However, the overall resonant cavity structure is complex and the operation is cumbersome, which causes great inconvenience in use. Summary of the invention

[0004] The purpose of the present invention is to provide a normal pressure heat-assisted microwave plasma ionization source device and a discharge tube, so as to solve the problem that the existing microwave plasma ionization source has a complex structure and cumbersome operation.

[0005] To achieve the above object, the solution of the present invention includes: The present invention discloses a technical solution for a microwave plasma ionization source discharge tube. The discharge tube comprises two sections with different inner diameters. One end of a thick tube section with a larger inner diameter is used to be connected to a gas supply system for providing discharge gas. A heating resistance wire for preheating the discharge gas is arranged inside the thick tube section. A working coil is wound around the outside of a thin tube section with a smaller inner diameter. The working coil is used to be connected to a microwave generator for generating high-frequency microwave current and is used to transmit microwave energy to the discharge gas through an electromagnetic field.

[0006] Furthermore, the heating resistance wire is a spiral resistance wire wrapped around the inner wall of the thick pipe section.

[0007] Furthermore, a temperature probe is provided at the ceramic tip inside the heating resistance wire, and the temperature probe is externally connected to a temperature controller for monitoring and controlling the real-time temperature of the discharge gas.

[0008] Furthermore, the inner diameter of the thick tube section is 8.5 mm, and the inner diameter of the thin tube section is 1 mm.

[0009] Furthermore, the length of the working coil is the length of one wavelength of the high-frequency microwave current generated by the microwave generator.

[0010] The technical solution of a normal-pressure heat-assisted microwave plasma ionization source device of the present invention comprises a microwave generator for generating high-frequency microwave current and a gas supply system for providing discharge gas, and also comprises a discharge tube, wherein the discharge tube comprises two sections with different inner diameters, one end of a thick tube section with a larger inner diameter is connected to the gas supply system, a heating resistance wire for preheating the discharge gas is arranged in the thick tube section, and a working coil is wound around the outside of a thin tube section with a smaller inner diameter, the working coil is connected to the microwave generator, and is used to transmit microwave energy to the discharge gas through an electromagnetic field.

[0011] Furthermore, the heating resistance wire is a spiral resistance wire wrapped around the inner wall of the thick pipe section.

[0012] Furthermore, a temperature probe is provided at the ceramic tip inside the heating resistance wire, and the temperature probe is externally connected to a temperature controller for monitoring and controlling the real-time temperature of the discharge gas.

[0013] Furthermore, the discharge tube is fixed on the discharge tube bracket by a tube clamp, and the tube clamp is hinged to the top of the discharge tube bracket to adjust the inclination angle of the discharge tube.

[0014] Furthermore, the length of the working coil is the length of one wavelength of the high-frequency microwave current generated by the microwave generator.

[0015] The beneficial effects of the present invention are: The present invention provides a microwave plasma ionization source discharge tube and a normal pressure heat-assisted microwave plasma ionization source device using the discharge tube, which makes the microwave plasma ionization source device simple in structure and easy to operate. At the same time, the added heat-assisted technology can not only meet the temperature requirements of samples with different boiling points, but also reduce the breakdown power and maintenance power of plasma discharge to a certain extent, thereby improving the existing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of a normal-pressure thermally assisted microwave plasma ionization source device of the present invention; Figure 2 It is the breakdown power and maintenance power of microwave discharge at different flow rates when no thermal assist technology is used; Figure 3 It is the breakdown power and maintenance power of microwave discharge at different temperatures when the discharge gas flow rate is fixed at 1.5L / min when using thermal assisted technology.

[0017] The figure includes: a microwave generator 1; a working coil 2; a heating resistor 4; a gas heating tube 5; a plasma induction tube 6; a coaxial line 7; a gas cylinder 8; a pressure reducing valve 9; a gas flow meter 10; a gas pipe 11; a discharge tube bracket 12; and a temperature controller 13. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail in a clear and complete manner in conjunction with the accompanying drawings and embodiments.

[0019] The heat-assisted technology used in the present invention is a common gas heating technology. Its basic principle is to use the Joule-Lenz law, that is, the thermal effect of electric current. When electric current passes through the resistance wire, the resistance wire will generate heat, and the heat generated is proportional to the square of the current intensity. Therefore, by controlling the current intensity, the heat generated by the resistance wire can be controlled, thereby achieving the purpose of heating. The resistance wire heating device usually uses a thermostat to control the current intensity to keep the temperature of the device stable.

[0020] The present invention uses a microwave generator to connect a coaxial cable and a working coil to conduct high-frequency electromagnetic energy to a discharge tube to induce plasma. The microwave generator generates a high-frequency microwave current that is conducted to the working coil along the coaxial cable. When the high-frequency current passes through the conductor of the working coil, a high-frequency electromagnetic field is generated, and the direction of the magnetic field is perpendicular to the cross section of the coil. The pipe material for the discharge gas in the coil is quartz glass, and the glass does not block the propagation of electromagnetic signals. When the discharge gas is passed into the glass tube, the discharge gas absorbs the magnetic field energy to generate high-density chemically active substances, such as high-energy electrons, metastable neutral substances, ionized molecules, and free radical ions under atmospheric pressure. These substances are ignited by an igniter to form plasma.

[0021] The concept of the present invention is to use a thermal assist and microwave discharge in series, so that the discharge gas is heated by a temperature-controllable resistor and then to the microwave energy coupling section. The device is simple, easy to operate, and has low energy consumption. Under the condition of meeting the temperature requirements of sample volatilization, the combination of thermal assist reduces the breakdown power and maintenance power of microwave discharge to a certain extent, reduces energy consumption and improves energy utilization.

[0022] Device Example: like Figure 1 The atmospheric pressure heat-assisted microwave plasma ionization source device of the present invention shown in the figure mainly comprises a microwave generator 1, a discharge tube 3 and a gas supply system.

[0023] The discharge tube 3 is composed of a glass tube with different inner and outer diameters. The thick tube section is a gas heating tube 5, and the built-in heating resistor 4 constitutes a gas heating part to heat the discharge gas to the required temperature. The thin tube section is a plasma induction tube 6, and the working coil 2 is wound outside the tube to form a microwave energy coupling section. The microwave generator 1 is connected to the working coil 2 through a coaxial cable 7 to provide high-frequency microwave current to the working coil; the thick tube section and the thin tube section together form a complete gas heating and plasma induction passage. The gas heating tube 5 and the plasma induction tube 6 are an integrated gas passage. The discharge gas output from the gas supply system is first heated in the discharge tube 3, and then absorbs the microwave energy conducted by the working coil 2, and is ignited by the igniter to generate plasma.

[0024] The gas supply system is mainly composed of a gas cylinder 8, a pressure reducing valve 9, a gas flow meter 10, and a gas pipe 11. The discharge gas output by the gas cylinder 8 flows into the thick tube section of the discharge tube 3 through the gas pipe 11, and flows out after passing through the heating resistance wire 4 and the plasma induction tube 6. The heated gas absorbs microwave energy and is ignited by the igniter to generate plasma, and the plasma jet is emitted from the mouth of the thin tube section. The microwave generator 1, the coaxial cable 7, the working coil 2, and the plasma induction tube 6 together constitute a microwave discharge system. The high-frequency microwave current generated by the microwave generator 1 is transmitted to the working coil 2 through the coaxial line 7. The heated discharge gas absorbs high-frequency electromagnetic energy through the inside of the working coil 2 and is ignited by the igniter to generate plasma.

[0025] The discharge tube 3 is a key component that combines the microwave energy coupling section with the gas heating section. The thick tube section has a built-in gas heating component, and the thin tube section is wrapped with a working coil to couple microwave energy. Specifically, the discharge tube 3 is a variable diameter pipeline, in which the inner diameter of the thick tube section must be sufficient to fit the heating resistance wire; in this embodiment, the inner diameter of the thick tube section is 8.5mm and the outer diameter is 10mm. The working coil needs to be wrapped around the outside of the thin tube section. In this embodiment, the inner diameter of the thin tube section is 1mm and the outer diameter is 3mm. The diameter of the discharge tube 3 changes from thick to thin, forming a local low pressure in the thin tube, which is also conducive to the occurrence of plasma.

[0026] The material of the discharge tube 3 is quartz glass, because quartz glass is different from conductive metal materials such as iron and copper, and it will not block the propagation of electromagnetic signals. When the high-frequency microwave current generated by the microwave generator is transmitted to the working coil through the coaxial line, the microwave energy can be smoothly transmitted to the internal discharge gas through the quartz glass, and the discharge gas absorbs the microwave energy and becomes a metastable state. After being ignited by the igniter, plasma can be formed, and a plasma jet is formed at the tube mouth.

[0027] The discharge tube 3 is fixed on the discharge tube support 12 by a tube clamp. The tube clamp is hinged to the top of the discharge tube support 12 so as to adjust the inclination angle of the discharge tube 3 .

[0028] The gas heating part is composed of a heating resistor 4, insulating ceramics, a temperature probe, and a temperature controller 13. When current flows through the resistor 4, the heat energy generated by the Joule effect is absorbed by the discharge gas passing through, thereby increasing the gas temperature. The tip of the ceramic 8 inside the resistor contains a temperature probe, and is externally connected to the temperature controller 13, so as to monitor and control the real-time temperature of the discharge gas, that is, the temperature of the discharge gas is controlled and adjusted through the temperature probe and the temperature controller 13.

[0029] When the device of this embodiment is working, the gas supply system outputs the discharge gas argon Ar, which continuously flows into the gas heating tube 5 of the discharge tube 3 and the plasma induction tube 6, firstly heated to the set temperature in the area where the heating resistor wire 4 is located, and then flows into the plasma induction tube 6. The plasma induction tube 6 is wound with a working coil 2, and the discharge gas in the working coil 2 absorbs the energy input by the microwave generator 1, and is ignited by the igniter to generate plasma, thereby realizing the combination of thermal assisted technology and microwave induced plasma technology.

[0030] In this embodiment, the discharge gas flow rate in the gas discharge tube 3 is 0-3L / min; the temperature of the gas heating part is controlled to be 0-900°C; the power of the microwave generator 1 is 0-100W, and the frequency is 2.45GHz; the length of the working coil is 12.2mm, which is one wavelength of the high-frequency microwave current, the coil diameter is 3mm, and the wire diameter is 0.5mm.

[0031] As another embodiment, the gas heating part and the microwave discharge system connected by the discharge tube 3 can be operated separately, that is, when the boiling point of the detected sample is not high and the discharge gas does not need to be heated, the gas heating part can be closed to stop the operation of heating the discharge gas, and the microwave discharge system and the gas supply system can be used separately without affecting each other. Conversely, the gas heating system can also be operated separately.

[0032] Compared with the microwave induced plasma technology in the prior art, the atmospheric pressure thermally assisted microwave plasma ionization source device of the present invention does not require complicated tuning operations and complex resonant cavities, has a simple structure and is easy to operate, connects the thermal assistance technology in series with the microwave plasma induction technology, and the addition of the thermal assistance technology reduces the breakdown energy of the working gas and the maintenance energy of the plasma, reduces the energy consumption to a certain extent, and is conducive to improving the energy utilization rate.

[0033] like Figure 2As shown in the figure, when the thermal assist technology is not used, when the microwave frequency of the microwave generator is 2.45GHZ, the gas breakdown power and plasma breakdown power required for pure argon gas to generate plasma discharge are obtained. In the following steps, the gas flow rate is gradually changed to obtain the gas breakdown power and maintenance power at different flow rates. As a whole, it can be seen that as the flow rate gradually increases, the gas breakdown power and maintenance power maintain an increasing trend. Analysis shows that when the gas flow rate gradually increases, it means that more gas passes through the discharge tube in the same time. In order to achieve the purpose of discharge, more high-frequency electromagnetic energy needs to be absorbed, so the required power will increase.

[0034] like Figure 3 As shown in Figure 2, after adding the thermal auxiliary technology, the corresponding gas breakdown power and plasma maintenance power at different discharge gas preheating temperatures are obtained, which is consistent with Figure 2 The opposite trend is shown. As the temperature increases, the breakdown power of the gas and the maintenance power of the plasma show a decreasing trend. Analysis shows that when the gas temperature continues to rise, the gas gets more heat energy, and the high-frequency electromagnetic energy required to achieve the discharge purpose is less, so the corresponding gas breakdown power and plasma maintenance power will be smaller.

[0035] It is worth noting that Figure 2 At room temperature and a flow rate of 1.5 L / min, the gas breakdown power and plasma maintenance power are 33 W and 25 W respectively. Figure 3 The medium flow rate is 1.5 L / min, and the gas breakdown power and plasma maintenance power at 100°C are 28 W and 22 W respectively. It can be seen that the present invention utilizes the series connection of thermal assisted technology to reduce the gas breakdown power and plasma maintenance power, reduce energy consumption, and improve energy utilization.

[0036] Discharge tube embodiment: A microwave plasma ionization source discharge tube of the present invention has been clearly introduced as the discharge tube 3 in the device embodiment, and will not be described in detail in this embodiment.

Claims

1. A microwave plasma ionization source discharge tube, characterized in that: The discharge tube includes two sections with different inner diameters. One end of the thick tube section with a larger inner diameter is used to be connected to a gas supply system that provides discharge gas, and a heating resistance wire for preheating the discharge gas is arranged in the thick tube section; a working coil is wound around the outside of the thin tube section with a smaller inner diameter, and the working coil is used to be connected to a microwave generator that generates high-frequency microwave current, and is used to transmit microwave energy to the discharge gas through an electromagnetic field.

2. The microwave plasma ionization source discharge tube according to claim 1, characterized in that: The heating resistance wire is a spiral resistance wire wrapped around the inner wall of the thick pipe section.

3. The microwave plasma ionization source discharge tube according to claim 1, characterized in that: A temperature probe is arranged at the ceramic tip inside the heating resistance wire, and the temperature probe is externally connected to a temperature controller for monitoring and controlling the real-time temperature of the discharge gas.

4. The microwave plasma ionization source discharge tube according to claim 1, characterized in that: The inner diameter of the thick tube section is 8.5 mm, and the inner diameter of the thin tube section is 1 mm.

5. The microwave plasma ionization source discharge tube according to claim 1, characterized in that: The length of the working coil is the length of one wavelength of the high-frequency microwave current generated by the microwave generator.

6. A normal pressure heat-assisted microwave plasma ionization source device, comprising a microwave generator for generating high-frequency microwave current and a gas supply system for providing discharge gas, characterized in that: It also includes a discharge tube, which includes two sections with different inner diameters. One end of the thick tube section with a larger inner diameter is connected to the gas supply system, and a heating resistance wire for preheating the discharge gas is arranged in the thick tube section; a working coil is wound around the thin tube section with a smaller inner diameter, and the working coil is connected to a microwave generator and is used to transmit microwave energy to the discharge gas through an electromagnetic field.

7. The atmospheric pressure thermally assisted microwave plasma ionization source device according to claim 6, characterized in that: The heating resistance wire is a spiral resistance wire wrapped around the inner wall of the thick pipe section.

8. The atmospheric pressure thermally assisted microwave plasma ionization source device according to claim 6, characterized in that: A temperature probe is arranged at the ceramic tip inside the heating resistance wire, and the temperature probe is externally connected to a temperature controller for monitoring and controlling the real-time temperature of the discharge gas.

9. The atmospheric pressure thermally assisted microwave plasma ionization source device according to claim 6, characterized in that: The discharge tube is fixed on the discharge tube bracket by a tube clamp, and the tube clamp is hinged to the top of the discharge tube bracket to adjust the inclination angle of the discharge tube.

10. The atmospheric pressure thermally assisted microwave plasma ionization source device according to claim 6, characterized in that: The length of the working coil is the length of one wavelength of the high-frequency microwave current generated by the microwave generator.

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