Microwave Plasma Torch Research Articles

Microwave N2–Ar plasma torch. II. Experiment and comparison with theory

Spatially resolved emission spectroscopy techniques have been used to determine the gas temperature, the electron, and N2+ ion densities and the relative emission intensities of radiative species in a microwave (2.45 GHz) plasma torch driven by a surface wave. The experimental results have been analyzed in terms of a two-dimensional theoretical model based on a self-consistent treatment of particles kinetics, gas dynamics, and wave electrodynamics. The measured spatial variations in the various quantities agree well with the model predictions. The radially averaged gas temperature is around 3000 K and varies only slowly along the discharge zone of the source but it drops sharply down to about 400 K in the postdischarge. The experimental wave dispersion characteristics nearly follow the theoretical ones, thus confirming that this plasma source is driven by a surface wave.

Microwave N2–Ar plasma torch. I. Modeling

The spatial structure of a microwave plasma torch driven by an azimuthally symmetric surface wave operating in a N2–Ar mixture at atmospheric pressure is investigated. A two-dimensional (2D) self-consistent theoretical model is developed to investigate the entire spatial structure of the source, including the discharge zone, sustained by the field of the surface TM00 mode, and the postdischarge plasma. Maxwell’s equations, the rate balance equations for the most important excited species—vibrationally and electronically excited states, ions and nitrogen atoms N(S4)—and the Boltzmann equation for electrons are consistently solved. Model calculations of the 2D spatial distributions of species of interest such as charged particles (electrons and positive ions), N2(Χ Σ1g+,v) vibrationally excited molecules, N2(A Σ3u+) metastable molecules, and N(S4) ground state atoms are presented and discussed.

新型大气压微波等离子体炬的仿真研究

新型大气压微波等离子体炬的仿真研究

Polycrystal diamond growth in a microwave plasma torch

Diamond films of different structures were deposited on quartz, WC-Co, and molybdenum substrates in a microwave plasma torch discharge in an argon-hydrogen-methane gas mixture in a sealed chamber at pressures close to atmospheric by using the chemical vapor deposition technique. Images of diamond polycrystal films and separate crystals, as well as results of Raman spectroscopy, are presented. The spectra of optical plasma radiation recorded during film deposition demonstrate the presence of intense Hα hydrogen and C2 radical bands known as Swan bands.

Application of microwave air plasma in the destruction of trichloroethylene and carbon tetrachloride at atmospheric pressure

In this study, the destruction rate of a volatile waste destruction system based on a microwave plasma torch operating at atmospheric pressure was investigated. Atmospheric air was used to maintain the plasma and was introduced by a compressor, which resulted in lower operating costs compared to other gases such as argon and helium. To isolate the output gases and control the plasma discharge atmosphere, the plasma was coupled to a reactor. The effect of the gas flow rate, microwave power and initial concentration of compound on the destruction efficiency of the system was evaluated. In this study, trichloroethylene and carbon tetrachloride were used as representative volatile organic compounds to determine the destruction rate of the system. Based on the experimental results, at an applied microwave power less than 1000W, the proposed system can reduce input concentrations in the ppmv range to output concentrations at the ppbv level. High air flow rates and initial concentrations produced energy efficiency values greater than 1000g/kWh. The output gases and species present in the plasma were analysed by gas chromatography and optical emission spectroscopy, respectively, and negligible amounts of halogenated compounds resulting from the cleavage of C2HCl3 and CCl4 were observed. The gaseous byproducts of decomposition consisted mainly of CO2, NO and N2O, as well as trace amounts of Cl2 and solid CuCl.

Characteristics of Microwave Plasma Torch at Atmospheric Pressure

We studied the characteristics of a microwave argon plasma torch at atmospheric pressure. The electron temperature of the plasma was measured by optical-emission spectroscopy and increases nonlinearly from 3000 to 3800 K with the increase of the microwave power from 1.0 to 4.0 kW. The spatial distribution of the electron density was measured with a Mach-Zehnder interferometer to be on the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and characterized by fluctuating with the time under the same experimental conditions. Based on the plasma parameters measured, it can be concluded that the plasma is in the state of local thermodynamic equilibrium.

Microwave plasma torches driven by surface wave applied for hydrogen production

A microwave (2.45 GHz) Ar plasma torch at atmospheric pressure has been applied for hydrogen production from the decomposition of alcohols (methanol and ethanol). The hydrogen yield dependence on the gas fluxes and the microwave input power has been investigated both in Ar and Ar + water plasma environments. Mass and FTIR spectroscopy have been used to detect the molecular hydrogen produced and the H 2O, CO 2 and CO molecules in the exhaust gas stream. Nearly 100% decomposition of methanol molecules was achieved in the Ar plasma torch. It was further found that the H 2 yield increases significantly when water is added into the Ar/methanol/ethanol mixtures. Moreover, optical emission spectroscopy has been applied to determine the gas temperature, the electron density and the radiative species present in the plasma torch. The results clearly show that this device provides an efficient plasma environment for hydrogen production.

Synthesis of titanium dioxide in O 2/Ar/SO 2/TiCl 4 microwave torch plasma and its band gap narrowing

Titanium dioxide (TiO 2) nanoparticles were synthesized directly by injecting gas-phase titanium tetrachloride (TiCl 4) bubbled with a mixture of Ar and SO 2 into a 2.45 GHz microwave torch plasma operated in O 2 gas at atmospheric pressure. The absorption edge of the as-produced TiO 2 powders in the UV–Visible spectrum shifted from 457 nm to 483 nm as the SO 2 gas content in the mixture gas carrying the TiCl 4 was increased. According to X-ray photoelectron spectroscopy (XPS) and UV–Visible spectroscopy, the band gap narrowing was due to the incorporation of sulphur (S) species from the Ar and SO 2 mixture in the oxygen microwave torch plasma into the O site of TiO 2.

Quenching of the OH and nitrogen molecular emission by methane addition in an Ar capacitively coupled plasma to remove spectral interference in lead determination by atomic fluorescence spectrometry

A new method is proposed to remove the spectral interference on elements in atomic fluorescence spectrometry by quenching of the molecular emission of the OH radical (A 2Σ + → X 2Π) and N 2 second positive system (C 3Π u → B 3Σ g) in the background spectrum of medium power Ar plasmas. The experiments were carried out in a radiofrequency capacitively coupled plasma (275 W, 27.12 MHz) by CH 4 addition. The quenching is the result of the high affinity of OH radical for a hydrogen atom from the CH 4 molecule and the collisions of the second kind between nitrogen excited molecules and CH 4, respectively. The decrease of the emission of N 2 second positive system in the presence of CH 4 is also the result of the deactivation of the metastable argon atoms that could excite the nitrogen molecules. For flow rates of 0.7 l min − 1 Ar with addition of 7.5 ml min − 1 CH 4, the molecular emission of OH and N 2 was completely removed from the plasma jet spectrum at viewing heights above 60 mm. The molecular emission associated to CH and CH 2 species was not observed in the emission spectrum of Ar/CH 4 plasma in the ultraviolet range. The method was experimented for the determination of Pb at 283.31 nm by atomic fluorescence spectrometry with electrodeless discharge lamp and a multichannel microspectrometer. The detection limit was 35 ng ml − 1 , 2–3 times better than in atomic emission spectrometry using the same plasma source, and similar to that in hollow cathode lamp microwave plasma torch atomic fluorescence spectrometry.

Crosslinked Carboxymethyl Modified Starch for Treatment of Heavy Metals Water by Technique of Chelating-Ultrafiltration

Crosslinked carboxymethyl modified starch (CCMS) was prepared by chemical modification of nature cornstarch. This modified degradable polymer had turned out to be a strong ability to chelate heavy metal ions. Using the instrument of microwave plasma torch atomic emission spectrometer(MPT-AES), 20.00 mg/L of Cu, Zn, Ni, Pb, Cd were detected under the Sewage Discharge Standards requirements after adding 90, 154, 86, 70, 546mg/L of CCMS respectively. The separation of the heavy metal ions and CCMS solutions were used the technique of ultrafiltration, with a molecular weight cut-off (MWCO) of 50000. By the same treatment, the chelating sequence of the heavy metals were also measured and decreased in the order of Pb&gt;Cu&gt;Cd&gt;Zn&gt;Ni.

Multiple diagnostics in a high-pressure hydrogen microwave plasma torch

We present an experimental study of a hydrogen plasma produced by a microwave axial injection torch, launching the plasma in a helium-filled chamber. Three different diagnostic methods have been used to obtain the electron density and temperature as follows: The Stark intersection method of Balmer spectral lines (already tested in argon and helium plasmas); the modified Boltzmann-plot showing that the plasma is far from the local thermodynamic equilibrium but ruled by the excitation-saturation balance; and a study by the disturbed bilateral relations theory. All of these diagnostic techniques show a good agreement.

大气压微波等离子体炬的仿真设计与实验

大气压微波等离子体炬的仿真设计与实验

Removal of Fluorinated Compound Gases by an Enhanced Methane Microwave Plasma Burner

Removal of fluorinated compound (FC) gases was experimentally investigated for various gas mixture constituents by making use of an enhanced methane microwave plasma burner. Methane (CH4) as a fuel was injected into the microwave plasma torch for generating an enlarged high-temperature plasma flame. A mixture of nitrogen and FC gases was introduced into the burner flame. Abatement experiments of FC gases were carried out in terms of destruction and removal efficiency (DRE). The plasma burner generated at 1.4 kW microwave power and 15 liters per minute (lpm) CH4 achieved DREs>99.9% for NF3 in 400 lpm nitrogen and SF6 in 120 lpm nitrogen. Also, the plasma burner removed 94.7% of CF4 concentration in 60 lpm nitrogen. Eventually, the experimental results showed that the microwave plasma burner can significantly eliminate FCs from the semiconductor industries.

Nonself-Sustained Microwave Discharge in a System for Hydrocarbon Decomposition and Generation of Carbon Nanotubes

This paper deals with the investigation of a method for sustainment of high-power microwave discharge in the installation for natural-gas decomposition. The essence of the method is to provide a generation of auxiliary discharge plasma in the area where the main microwave plasma torch burns. The design of the electrode system of auxiliary discharge resembles that for a coaxial plasmatron that consumes an average current of about 0.1 A. Then, the nonself-sustained microwave discharge with a frequency of 2.45 GHz has been obtained at a power level from 1 to 3 kW. Such a discharge has been used in the installation for natural-gas decomposition and generation of the carbon nanotubes. With a typical gas flow of 1 m3/h, the natural-gas conversion achieves 40%-80%. Three types of nanotubes are contained in the final product: multilayer tubes, single-layer tubes, and onion-type tubes.

Measurement of the electron density in a microwave plasma torch at atmospheric pressure

The electron density in a microwave plasma torch at atmospheric pressure was measured with a Mach–Zehnder interferometer. The electron density is on the order of 1017/cm3, one order higher than that deduced from the Stark broadening of spectral lines, and increases with the increase in the microwave power. The spatial distribution of the electron density was obtained. The highest electron density locates at the symmetrical axis of the plasma torch and decreases radially. It was found that the electron density fluctuates within a range of 0.3 with the time under the same experimental conditions.

Development of Steam Plasma-Enhanced Coal Gasifier and Future Plan for Poly-Generation

A microwave plasma torch at the atmospheric pressure by making use of magnetrons operated at the 2.45 ㎓ and used in a home microwave oven has been developed. This electrodeless torch can be used to various areas, including industrial, environmental and military applications. Although the microwave plasma torch has many applications, we in the present work focused on the microwave plasma torch operated in pure steam and several applications, which may be used in future and r ight now. For example, a high-temperature steam microwave plasma torch may have a potential application of the hydrocarbon fuel reforming at one atmospheric pressure. Moreover, the radicals including hydrogen, oxygen and hydroxide molecules are abundantly available in the steam torch, dramatically enhancing the reaction speed. Also, the microwave plasma torch can be used as a high-temperature, large-volume plasma burner by injecting hydrocarbon fuels in gas, liquid, and solid into the plasma flame. Finally, we briefly report treatment of soils contaminated with oils, volatile organic compounds, heavy metals, etc., which is an underway research in our group.

Investigation of Synthesis‐Gas Production via CH4O2Ar Gas Mixture Using Microwave Plasma Torch

AbstractIn this study, a non‐thermal plasma reactor under atmospheric pressure instead of the usual catalytic processes was developed to produce synthesis‐gas (CO, H2) “syngas” from the CH4O2Ar system. Moreover, using the Gibbs free energy minimization method, the gas phase composition of plasma species was calculated as quantitative pre‐estimate for our analytical observations. In our experimental investigation, a plasma reactor consisting of a microwave plasma torch, gas tube, cooling section, and sampling part was used. The experiments have been carried out under atmospheric pressure with maximum 300 W microwave power. To analyze the produced gas, the gas chromatography (GC) and the Fourier transform infrared (FTIR) spectroscopy have been used. In order to optimize the production conditions, the effect of O2/CH4 gas flow rate and plasma power in the plasma chemistry phenomenon, CH4 conversion and CO selectivity have been investigated. Our experimental results confirm our simulations and they are in good agreement with existing literature data so far.

Development and Characterisation of a Microwave‐heated Atmospheric Plasma Torch

AbstractAmong other applications, microwave plasma sources at atmospheric pressure are used for the decomposition of halogenated volatile organic compounds (VOC). The presented microwave plasma torch is based on an axially symmetric resonator. Simulations of the electric field distribution, Eigen frequency analyses and measurements of the resonant frequency resulted in an improved design. Microwaves of 2.45 GHz are fed into this cavity resulting in a sufficiently high electric field for ignition and maintaining stable plasma. The characterisation of the plasma is made with optical emission spectroscopy. The decomposition of VOC was analysed with FTIR‐spectroscopy, a mass spectrometer and an FID.

Optical diagnostics of a low power—low gas flow rates atmospheric-pressure argon plasma created by a microwave plasma torch

We employ a suite of optical techniques, namely, visual imaging, optical emission spectroscopy and cavity ringdown spectroscopy (CRDS), to characterize a low power, low gas flow rates, atmospheric-pressure argon microwave induced plasma. The plasma is created by a microwave plasma torch, which is excited by a 2.45 GHz microwave with powers ranging from 60 to 120 W. A series of plasma images captured in a time-resolution range of as fine as 10 µs shows that the converging point is actually a time-averaged visual effect and the converging point does not exist when the plasma is visualized under high time resolution, e.g. <2 ms. Simulations of the emission spectra of OH, N2 and in the range 200–450 nm enable the plasma electronic excitation temperature (Texc) to be determined at 8000–9000 K, while the vibrational temperature (Tv), the rotational temperature (Tr) and the gas temperature (Tg) at different locations along the axis of the plasma column are all determined to be in the range 1800–2200 K. Thermal equilibrium properties of the plasma are discussed. OH radical concentrations along the plasma column axis are measured by CRDS and the concentrations are in the range 1.6 × 1013–3.0 × 1014 cm−3 with the highest density at the tail of the plasma column. The upper limit of electron density ne is estimated to be 5.0 × 1014 cm−3 from the Lorentzian component of the broadened lineshape obtained by ringdown spectral scans of the rovibrational line S21 of the OH A–X (0–0) band.

Production of nanocrystalline Y 2O 3:Eu powder by microwave plasma-torch and its characterization

Y 2O 3:Eu red-emitting nanophosphors were synthesized directly by dissolving Y 2O 3 and Eu 2O 3 in HNO 3 and by using an atmospheric microwave-plasma torch for a direct continuous preparation and for mass production of Y 2O 3:Eu powders. Atmospheric microwave plasmas produce a high-temperature plasma flame due to ohmic heating by high frequency electric fields, revealing a maximum central temperature of 6500 ± 350 K. Therefore, the synthesized Y 2O 3:Eu nanophosphors from instantaneous evaporation of dissolved Y 2O 3 and Eu 2O 3 in HNO 3 have favorable characteristics such as regular size and cubic equilibrium structure. The nanophosphors were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL).