Atmospheric Pressure Microwave Plasma Jet Research Articles

Precise surface machining of fused silica using high stability atmospheric pressure microwave plasma jet with a new internal electrode

Plasma is a promising approach for machining of fused glass substrates. Developing high-performance microwave torch is the core element to ensure the processing accuracy of this technology. In this study, a spline curve-based microwave torch internal electrode structure was proposed, which increased the internal electric field strength by 54 %. The discharge dynamics simulation based on this electrode shows that the plasma is excited at the inner electrode tip and the bottom of the resonant cavity, then it expands to form a linear discharge region and eventually fill the discharge tube. It was revealed by CCD images that with the increase of carrier gas flow rate, turbulent flow state appears in the tail of the jet. OES data shows that microwave Ar plasma can effectively dissociate CF4, and due to the oxidation effect of oxygen, CFx and C2 content decrease significantly with the addition of oxygen. The machining experiment on fused silica shows that the material removal stability of this torch reaches 3.69 %, and the removal rate increases nYarly with dwell time due to thermal effect. Finally, the machining performance of the atmospheric pressure microwave plasma jet was verified by figuring of a planar fused silica surface reducing the form error from 108.1 nm RMS to 16.5 nm RMS.

Research on ionization characteristics of atmospheric pressure pulse-modulated microwave He/air plasma jet

The atmospheric pressure pulsed microwave He plasma jet has the advantages of high electron density and abundant active particles, but its shrinking on the discharge electrode morphology limits its application range. In order to modulate a He plasma jet with a longer plume and study its ionization development characteristics, we constructed a dual-channel pulsed microwave coaxial discharge device. He and air were, respectively, injected into the inner and outer gas channels of the resonator to generate a double-layer atmospheric pressure microwave plasma jet with a longer plume. It is observed that the bifurcation of the stratified plasma jet will occur by changing the gas flow. The ionization development of plasma jet was observed by using enhanced charge-coupled device and microwave Rayleigh scattering apparatus measured the space-time evolution of plasma and observed the three times ionization enhancement process of plasma jet development. The spectral lines of the active products associated with Penning ionization were observed by using a fiber optic spectrometer. A fluid model was constructed to simulate and analyze that under the condition of sufficient He flow rate (He flow rate is above 0.6 slm), there will be sufficient and stable He mole fraction (64%) at the stratification of the plasma jet. The experimental and simulation results show that the jet profile of the microwave He plasma is related to the inlet structure of the discharger and He flow rate. Stratified intake structure can produce stratified He plasma jet, and the unique appearance of bifurcation of jet can be produced by changing the flow rate of He. In the bifurcation process of the plasma jet, the product of Penning ionization inhibits the development of the main branch of the plasma jet, and the secondary electron avalanche of the local electric field promotes the formation of the branch of the plasma jet and is accompanied by the enhancement of the second ionization. The ionization mechanism of microwave He plasma is the resonance excitation of local enhanced electric field, the advance of ionizing waves, and the interaction between the spatially distributed active particles.

A Novel Self-Excited Atmospheric Pressure Microwave Plasma Jet Using Rectangular Coaxial Line

A novel self-excited atmospheric pressure microwave plasma jet (APMPJ) based on a coaxial line is successfully proposed for the medical treatment. The finite-element method (FEM) is applied to obtain the optimal size of the APMPJ. The plasma parameters, such as electron density and electron temperature, are calculated within 0.1 ms. When the plasma reaches a stable state, the electron density is closed to 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{22}$</tex-math> </inline-formula> m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-3}$</tex-math> </inline-formula> , and the electron temperature is calculated to be 1.3 eV. According to the experimental results, the argon plasma jet can be self-excited at an incident power of 20 W, and the gas temperature of the plasma jet is closed to 318 K at an incident power of 15 W. In addition, the air plasma jet can be self-excited at an incident power of 110 W. Finally, the change in the density ratio of hydroxyl (OH) radical to other particles when water vapor is added to the APMPJ at different flow rates is analyzed. It is found that a small amount of water vapor can greatly increase the relative content of OH which is tested by spectrometer.

A Highly Efficient Microwave Plasma Jet Based on Evanescent-Mode Cavity Resonator Technology

This article introduces a novel low-power and highly efficient atmospheric pressure microwave plasma jet (APPJ). Specifically, a capillary tube passing through the critical gap area of a high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> evanescent-mode (EVA) cavity resonator provides a controlled gas flow rate to realize microwave gas breakdown and plasma jet formation even with milliwatts range input power. The theory, simulation, fabrication, and characterization of the introduced plasma jet technology are discussed. A prototype 2.45 GHz device can operate at powers as low as 400 mW with >80% power efficiency and provides up to a 6-mm-long plasma jet with electron density in the range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{15}$ </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-3}$ </tex-math></inline-formula> in a 1 to 7 slpm helium flow rate. Considering its high plasma density as well as low operating power and jet temperature, this device is a viable and safe solution for a wide range of applications, including emerging plasma medicine needs.

Atmospheric pressure plasma‐jet treatment of polyacrylonitrile‐nonwovens—Stabilization and roll‐to‐roll processing

AbstractCarbon nanofiber nonwovens represent a powerful class of materials with prospective application in filtration technology or as electrodes with high surface area in batteries, fuel cells, and supercapacitors. While new precursor‐to‐carbon conversion processes have been explored to overcome productivity restrictions for carbon fiber tows, alternatives for the two‐step thermal conversion of polyacrylonitrile precursors into carbon fiber nonwovens are absent. In this work, we develop a continuous roll‐to‐roll stabilization process using an atmospheric pressure microwave plasma jet. We explore the influence of various plasma‐jet parameters on the morphology of the nonwoven and compare the stabilized nonwoven to thermally stabilized samples using scanning electron microscopy, differential scanning calorimetry, and infrared spectroscopy. We show that stabilization with a non‐equilibrium plasma‐jet can be twice as productive as the conventional thermal stabilization in a convection furnace, while producing electrodes of comparable electrochemical performance.

Ionization behavior of hairpin argon plasma jets resonantly generated by microwave pulses at atmospheric pressure

<p indent="0mm">Atmospheric pressure microwave plasma jet has many advantages, such as high density and high activity. However, their application is limited because it is difficult to modulate the morphology of the plasma jet for specific requirements. This study constructs a pulsed microwave hairpin resonant discharge device to generate an atmospheric pressure pulsed microwave argon plasma jet. The results show that the plasma jet has three typical discharge forms on different pulse frequencies. When the pulse frequency is <sc>10 kHz,</sc> the argon plasma jet changes periodically with an arched plasma morphology at the open end of the hairpin electrode. When the pulse frequency is <sc>30 kHz,</sc> the argon plasma jet presents a nonperiodical change, and the plasma morphology exhibits a crescent-shaped pattern. When the pulse frequency is <sc>60 kHz,</sc> the argon plasma jet presents a largescale nonperiodic change with similar oval plasma morphology. In addition, the spatiotemporal electron evolution process of the argon plasma jet is measured by a microwave Rayleigh scattering device, which reveals that the peak electron density is <sc>4.06×10²¹ m⁻³,</sc> the number of electrons is on the amplitude order of 10¹³, and the number of electrons changes periodically with the pulsed power. Combining the experimental and simulation results, it can be concluded that the formation mechanism of the three discharge forms is attributed to the resonance excitation of the locally enhanced electric field, the ionization wave propulsion in the microwave plasma jet, and the temporal and spatial distribution of different particles in the pulsed microwave argon plasmas.

Gas mixing enhanced by power modulations in atmospheric pressure microwave plasma jet

Microwave plasma jet operating in atmospheric pressure argon was power modulated by audio frequency sine envelope in the 102 W power range. Its effluent was imaged using interference filters and ICCD camera for several different phases of the modulating signal. The combination of this fast imaging with spatially resolved optical emission spectroscopy provides useful insights into the plasmachemical processes involved. Phase-resolved schlieren photography was performed to visualize the gas dynamics. The results show that for higher modulation frequencies the plasma chemistry is strongly influenced by formation of transient flow perturbation resembling a vortex during each period. The perturbation formation and speed are strongly influenced by the frequency and power variations while they depend only weakly on the working gas flow rate. From application point of view, the perturbation presence significantly broadened lateral distribution of active species, effectively increasing cross-sectional area suitable for applications.

Atomic oxygen TALIF measurements in an atmospheric-pressure microwave plasma jet with in situ xenon calibration

Two-photon absorption laser-induced fluorescence (TALIF) is used to measure the absolute density of atomic oxygen (O) in a coaxial microwave jet in ambient air at atmospheric pressure, operated with a mixture of He and a few per cent of air. The TALIF signal is calibrated using a gas mixture containing Xe. A novel method to perform calibration in situ, at atmospheric pressure, is introduced. The branching ratios of several Xe mixtures are reported, to enable us to perform the Xe calibration without the need for a vacuum vessel. The O densities are measured spatially resolved, and as a function of admixed air to the He, and microwave power. The electron density and temperatures are measured using Thomson scattering, and the N2 and O2 densities are measured using Raman scattering. O densities are found to have a maximum of (4–6) × 1022 m−3, which indicate that O2 is close to fully dissociated in the plasma. This is confirmed by the Raman scattering measurements. O is found to recombine mainly into species other than O2 in the afterglow, which is suggested to consist of O3 and oxidized components of NO.

Thermalization of rotational states of NO A 2Σ+(v = 0) in an atmospheric pressure plasma

Laser induced fluorescence (LIF) measurements of nitric oxide (NO) are performed in an atmospheric pressure microwave plasma jet, operated with a mixture of He and 3% air. The fluorescence signal of NO A(2)Σ(+)(v = 0) is measured time and fluorescence wavelength resolved. Based on the evolution of the rotational spectrum at different positions in the plasma, we determined the thermalization time of the rotational distribution of NO A after pumping a single transition, at temperatures in the range 300-1500 K. Also, a LIF-RET (rotational energy transfer) model is developed to simulate the RET and to calculate the thermalization time. The RET rate coefficients are calculated using the energy corrected sudden-exponential power scaling law. It was found that it is necessary to take the fine structure of the rotational states into account. At room temperature the results of the measurement and the simulation are consistent, and the thermalization occurs during the laser pulse (11 ± 1 ns). At elevated temperatures the measurements show a large increase in thermalization time, up to 35 ± 4 ns at 1474 K. This time is much longer than the laser pulse, and of the order of the NO A lifetime. This means that for spectroscopy measurements of the rotational states of NO A, the RET has to be taken into account to derive gas temperatures from the rotational distribution of NO A.

Increase of wettability of soft- and hardwoods using microwave plasma

The experiments presented in this paper deal with plasma surface treatment of various wood species in order to enhance their hydrophilic properties. As a plasma source we used atmospheric pressure microwave plasma jet—the surfatron. The changes on wood surface were evaluated using water uptake time and contact angle measurement. We investigated the influence of treatment time, discharge power, argon flow rate and effect of nitrogen and oxygen admixtures. The results showed that microwave plasma treatment was able to achieve significant improvement of wood wettability even after treatment time in a matter of seconds.

大气微波等离子体射流处理H2S废气

The treatment of H2S gas by the atmospheric pressure microwave plasma jet (MPJ) technology was studied. The influences of the temperature, the microwave power, the carrier(Ar) flow and total gas flow rate on H2S decomposition were investigated. The results show that, the temperature must be controlled in a certain range in order to process hydrogen sulfide; as the microwave power and the carrier gas flow increases, the decomposition rate of H2S first increases, then decreases; with the increase of the total gas flow rate, the decomposition rate of H2S falls. The maximum decomposition rate of H2S reaches to 91.32%, when the mass ratio of H2S to Ar is 10:90, the total flow is 1000 mL/min, and the microwave power is 1000 W. The production of the treatment was characterized by Raman spectroscopy and XRD (X-ray diffraction), and the results show the solid state material is high purity sulfur.

Temperature fitting of partially resolved rotational spectra

In this paper we present a method to automatically fit the temperature of a rotational spectrum. It is shown that this fitting method yields similar results as the traditional Boltzmann plot, but is applicable in situations where lines of the spectrum overlap. The method is demonstrated on rotational spectra of nitric oxide from an atmospheric pressure microwave plasma jet operated with a flow of helium and air, obtained with two different methods: laser induced fluorescence and optical emission spectroscopy. Axial profiles of the rotational temperatures are presented for the ground NO X state and the excited NO A state.

Laser scattering on an atmospheric pressure plasma jet: disentangling Rayleigh, Raman and Thomson scattering

Laser scattering provides a very direct method for measuring the local densities and temperatures inside a plasma. We present new experimental results of laser scattering on an argon atmospheric pressure microwave plasma jet operating in an air environment. The plasma is very small so a high spatial resolution is required to study the effect of the penetration of air molecules into the plasma. The scattering signal has three overlapping contributions: Rayleigh scattering from heavy particles, Thomson scattering from free electrons and Raman scattering from molecules. The Rayleigh scattering signal is filtered out optically with a triple grating spectrometer. The disentanglement of the Thomson and Raman signals is done with a newly designed fitting method. With a single measurement we determine profiles of the electron temperature, electron density, gas temperature, partial air pressure and the N2/O2 ratio, with a spatial resolution of 50 µm, and including absolute calibration.

常压微波等离子体炬装置的模拟与设计

常压微波等离子体炬装置的模拟与设计

Gas-Phase, Bulk Production of Metal Oxide Nanowires and Nanoparticles Using a Microwave Plasma Jet Reactor

We report gas-phase production of metal oxide nanowires (NWs) and nanoparticles (NPs) using direct oxidation of micron-size metal particles in a high-throughput, atmospheric pressure microwave plasma jet reactor. We demonstrate the concept with production of SnO2, ZnO, TiO2, and Al2O3 NWs. The results suggest that the NW production primarily depends upon the starting metal particle size, microwave power, and the gas-phase composition. The resulting NW powders could be separated from the unreacted metal and metal oxide NPs by sonication in 1-methoxy 2-propanol followed by gravity sedimentation. The experiments conducted using higher microwave powers resulted in spherical, unagglomerated, metal oxide NPs. The results obtained using various metal oxides suggest that the mechanism of NW nucleation and growth in the gas phase is similar to that observed in experiments with metal particles supported on substrates. A simplified analysis suggests that the metal powders melt in the plasma primarily with the heat g...