Arc Plasma Jet Research Articles

Plasma Torch Test of an Ultra-High-Temperature Ceramics Nose Cone Demonstrator

An ultra-high-temperatureZrB2–SiC ceramic nose cone was tested in an arcjet plasma torch facility for 10min at temperatures above 2000 C. The nose cone model was obtained from a hot-pressed billet via electrical discharge machining.The relevant portions of themodels directly exposed to the hot streamwere analyzedby scanning electron microscopy and energy-dispersive spectroscopy. The posttest cross sectioning of the model showed a nonnegligible surface recession on the tip of the nose. Nonetheless, the material exhibited a promising potential to withstand severe reentry conditions with temperatures exceeding 2000 C in a single-use application. Spectral directional emissivity evaluationswere performed on the fly during the test bymeans of thermography coupledwith dual-color pyrometer. The numerical calculations, which simulated the chemical nonequilibrium flow around the model assuming a low catalytic surface behavior, are in good accordance with the experimental results.

Modelling of non- transferred argon-nitrogen plasma arc and plasma jet

One of the challenging problems in the plasma spray technique is reproducibility of the coating quality. This problem is mainly associated with arc fluctuations, which affect the plasma jet temperature and velocity inside the plasma torch. In this study, three- dimensional numerical models are developed to study the behaviour of Ar-N2 plasma arc inside a non-transferred torch and plasma jet. Ar-N2 plasma arc is simulated for given arc current and gas flow rate. Different arc sizes, which correspond to given torch power, are predicted. A most feasible arc size, which corresponds to an actual physical situation of the arc inside the torch, is identified using thermodynamic principle of minimum entropy production for particular torch power. Predicted torch efficiency is comparable with measured one. Cathode and anode losses are reported. Predicted temperature and velocity profiles at the nozzle exit are used to simulate the plasma jet. Since plasma gas is mixed with cold air, plasma jet is diffused in the radial direction. Three-dimensional effect on plasma jet temperature and velocity is diminishes along the axial direction.

Thermal Stress in Free-standing Diamond Films with Cr Interlayer Destroyed

Thermal stress in large area free-standing diamond films was remarkable during the post-deposition cooling of direct current (DC) arc plasma jet chemical vapor deposition (CVD) process. In this research, the stress release caused by delamination of Cr interlayer was of great importance to ensure the integrity of free-standing diamond film. The effects of Cr interlayer on Mo substrate, namely composite substrate, on thermal stress were investigated. Thermo-mechanical coupling analysis of the thermal stress was applied by finite element analysis (FEA) using ANSYS code. It was found that the interlayer could be destroyed first by the large thermal stress, and then the stress could be released and the probability of diamond film crack initiation would be reduced. The stress concentration at the bent edge of diamond film was also discussed. In addition, diamond films deposited on Mo substrates with and without Cr interlayer were prepared by DC arc plasma jet CVD system and experimental measurements were used to characterize these films. It was found that composite substrate could be an effective method of growing free-standing crack-free diamond films by DC arc plasma jet CVD system when there is no special requirement to the film strength.

H123 金属多孔質体を用いた10MW/m^2クラス高熱流束除去デバイスの開発(OS-2:沸騰・凝縮伝熱の最近の進展(II)(相変化研究会としての話題提供))

A sub-channels-inserted porous evaporator is proposed as a heat removal device of a power device with a heat load exceeding 10MW/m^2. The porous media are made by sintering metal particles with micro scale in pore and have several sub-channels to enhance discharge of generated vapor outside the porous medium. This porous cooling devise is attached onto the back surface of a high heat loading equipment such as an divertor. In order to prove the effect of the sub-channels, the heat transfer characteristics of this porous device are evaluated experimentally using a plasma arcjet as a high heat flux source. The result shows that the heat transfer performance of copper-particles-sintered porous medium with the sub-channels enables to remove much higher heat flux under lower flow rate and lower wall superheat conditions, compared with the normal porous media. The removal heat flux, 8.1MW//m^2, is 1.8 times as higher than that of the normal porous medium at a wall superheat of 50 degrees. The removal heat flux reaches almost 10MW/m^2 although the wall superheat exceeds 100 degrees (The wall temperature is around 220 degrees C. in a fully developed boiling regime).

Stress in Freestanding CVD Diamond Thick Film

The present paper describes research on stress in freestanding diamond thick film, diameter of 60mm, prepared on Mo substrate by DC arc plasma jet chemical vapor deposition (DCPCVD) method. The stress in the CVD diamond film was investigated by X-ray diffraction and Raman spectrum. The results show that the stress in the film is compressive. The stress changes little at the same homocentric round. The compressive stress along radial direction is that the stress in the centre of the film is lower than that in the edge at both the final surface and the original surface.

Effect of Input Power on the Deposition of Optical Grade Thick Diamond Film in a DCPJ CVD Jet System

High quality optical grade thick diamond film wafers with different thickness are prepared by high power DC arc plasma jet CVD (DCPJ CVD) method using a CH4/Ar/H2 gas mixture. Three different powers, 13.65, 15.40 and 17.94kW, were employed during the investigation. The aim was to investigate the effect of these powers on the deposition of thick diamond film. The controlled system was discussed together. The results show that the average diamond grain size and growth rate increase with input plasma power, but a further increase in input power, diamond thick-film defects and amorphous carbon content increased.

酸素プラズマ切断におけるハフニュウム電極損耗現象についての研究

Experimental study has been conducted on erosion of hafnium electrodes for oxygen plasma arc cutting. Hafnium (Hf) is used as a refractory cathode material for thermionic emission at high temperature region.Erosion of Hf electrode was investigated by measuring the concavity depth on Hf electrodes after operations. The measurements were done on several operating conditions. The erosion properties have been found to be separated to two portions. One of the Hf erosion happens in transient period including start-up and shut-off phases of plasma arc when arc current is increasing or decreasing. The other erosion happens in the stable arc phase when arc current is kept at operating current.Spectroscopic measurements of the arc plasma jet coming out from a nozzle have been conducted in order to study the behavior of erosion of Hf electrode. An atm line of Hf at λ=340 nm was observed by a monochromator. Characteristic intermittent radiations of Hf in addition to background continuum were observed in transient period when the arc current or gas pressure changes. It is considered that the intermittent radiation comes from droplets of Hf ejected from the melted electrode surface. And the ejection is considered to be induced by a break of balance of fluid dynamic on the melted electrode.

Research on chemical and discharge oxygen-iodine lasers

Novel methods and device configurations for singlet oxygen and atomic iodine generation were proposed and investigated for operation of the chemical or discharge oxygen-iodine lasers (COIL/DOIL). A chemical centrifugal spray generator of singlet oxygen was developed, based on the conventional chlorine-basic hydrogen peroxide chemistry. Results of theoretical and experimental investigation of the generator parameters are presented and compared with parameters of other generator types. A design of experimental device for singlet oxygen generation by means of the hybrid DC arc and RF plasma jet is presented. An alternative method of atomic iodine generation by a radiofrequency discharge decomposition of iodine compounds like CH3I or CF3I is described employing advanced experimental configuration. Some representative experimental results of this investigation are presented.

Three Stages Modeling of n-Octane Reforming Assisted by a Nonthermal Arc Discharge

This paper presents a simplified one-dimensional kinetic model (phenomenological approach) of a nonthermal arc discharge plasma reactor used for n-octane reforming. After a description of the model and its main assumptions, a parametric analysis of plasma reformer performance addressing the influence of plasma volume, H 2 O/C ratio, O/C ratio, and input electric power is presented. Results focusing on energy efficiency and conversion rate, including comparison with experimental gasoline reforming data, are analyzed and discussed. The parametric study has provided an optimum for actual plasma reformer, H 2 O/C = 0, O/C = 1.1, and input electric power between 20 and 25% LHV. The model shows that nonequilibrium chemistry is produced via fast mixing of arc plasma jet and reactants to quench radicals and other active species generated in the high-temperature region.

In situ observation of nucleation by optical emission spectra in CVD diamond

Optical emission spectroscopy (OES) was used to in situ detect the intensity variation of C 2 radical with the deposition time in the boundary layer during homo-nucleation of CVD diamond by DC Arcjet Plasma. The obvious drop and fluctuation of the optical emission intensity were found during the early growth stage. The samples grown after selected deposition time were characterized by micro-structural probes (transmission electron microscope (TEM), high resolution electronic microscope (HREM), selected area diffraction (SAD) and electron energy loss spectra (EELS)), in order to determine the occurrence of the diamond nucleation. Based on the results of the OES and the micro-structural probes, it was revealed that the variation of the optical emission intensity corresponded to the diamond nucleation. The incubation period and the lasting time of nucleation were thus deduced as 6–8 min and 20–60 s depending on the concentration of CH 4 in H 2. The incubation period decreased and the lasting time of nucleation increased with the increase of the concentration of CH 4 in H 2.

Electron Density and Temperature Measurement by Stark Broadening in a Cold Argon Arc-Plasma Jet at Atmospheric Pressure

Determination of both the electron density and temperature simultaneously in a cold argon arc-plasma jet by analyzing the Stark broadening of two different emission lines is presented. This method is based on the fact that the Stark broadening of different lines has a different dependence on the electron density and temperature. Therefore, a comparison of two or more line broadenings allows us to diagnose the electron density and temperature simultaneously. In this study we used the first two Balmer series hydrogen lines Hα and Hβ for their large broadening width. For this purpose, a small amount of hydrogen was introduced into the discharge gas. The results of the Gigosos–Cardenoso computational model, considering more relevant processes for the hydrogen Balmer lines, is used to process the experimental data. With this method, we obtained reliable electron density and temperature, 1.88 × 1015 cm−3 and 13000 K, respectively. Possible sources of error were also analyzed.

Numerical and experimental studies on DC plasma spray torch

One of the challenging problems in the plasma spray technique is reproducibility of the coating quality. This problem is mainly associated with arc fluctuations, which affect the plasma jet temperature and velocity, inside the plasma torch. In this study, 3D numerical models are developed to study the arc behavior inside the torch and effect of arc fluctuations on plasma jet temperature and velocity. Plasma arc is simulated for different operating parameters. Different arc sizes are predicted by using thermo-dynamical principle of minimum entropy production for given torch power. The influence of arc current and gas flow rate on the Ar–N 2 plasma arc characteristics, plasma jet and torch efficiency is presented. Predicted torch efficiencies and arc voltages are comparable with measurements. At the nozzle exit, velocity shows stronger three-dimensional effect than temperature. Plasma jets are simulated using different nozzle exit profiles obtained from the plasma arc model and their temperature and velocity distributions are clarified.

Free-standing diamond films deposited by DC arc plasma jet on graphite substrates with a destroyable Ti interlayer

A destroyable Ti interlayer on graphite substrate was used for fabrication of crack-free free-standing diamond films by high-power DC Arc Plasma Jet. Ti interlayer was arc ion plated on the polycrystalline graphite substrate. The thickness, morphology and composite phase of the Ti interlayer were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Titanium carbide (TiC) was detected in both sides of the interlayer, which played an important role with respect to reasonable adhesion and diamond nucleation. Semi-translucent and crack-free diamond films were obtained and characterized by SEM and Raman spectroscopy. It is shown that the diamond films so obtained have excellent Raman signature. The overall results suggest that plating Ti interlayer on graphite substrate is an effective way to obtain potentially crack-free free-standing diamond films.

Ion Acceleration in Arc Jet Plasma Along Open Field Lines

We experimentally study plasma parameters including the ion acoustic Mach number and the flow direction of expanding helium plasma jet flowing along open field lines. It is experimentally found that the ion Mach number increases. We discuss the mechanism of the ion acceleration. Since the ions do not rotate in electromagnets, the Hall and the swirl acceleration do not occur. We investigate the experimental results based on quasi-1-D flow model including the aerodynamic effect and the electric field. Our model describes the ion acceleration. Therefore, it is concluded that the helium ions are accelerated both by the electric field and by the increasing cross-sectional area of the supersonic flowing channel, which is determined by the magnetic flux conservation.

Mode Transition of an Atmospheric Pressure Arc Plasma Jet Sustained by Pulsed DC Power

An atmospheric pressure arc plasma jet sustained using pulsed DC power is studied by examining its appearance using a high-speed camera and measuring current and voltage waveforms at the powered electrode using current and high-voltage probes. Given the seemingly uniform in time visual appearance, the high-speed camera images show that the plasma jet undergoes some transition within each power cycle. Current and voltage waveform characteristics suggest that such a transition is most likely due to a glow-to-arc mode transition. The occurrence of this transition is controlled by the plasma physics rather than by the duty cycle of the pulsed power.

WITHDRAWN: Synthesis of SiC nanopowders by DC arc plasma jet chemical vapor deposition: Effects of methane gas and arc current

This article has been withdrawn at the request of the author(s) and editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy .

Effects of deposition parameters on microstructure and thermal conductivity of diamond films deposited by DC arc plasma jet chemical vapor deposition

The uniform diamond films with 60 mm in diameter were deposited by improved DC arc plasma jet chemical vapor deposition technique. The structure of the film was characterized by scanning electronic microcopy(SEM) and laser Raman spectrometry. The thermal conductivity was measured by a photo thermal deflection technique. The effects of main deposition parameters on microstructure and thermal conductivity of the films were investigated. The results show that high thermal conductivity, 10.0 W/(K·cm), can be obtained at a CH 4 concentration of 1.5% (volume fraction) and the substrate temperatures of 880–920 °C due to the high density and high purity of the film. A low pressure difference between nozzle and vacuum chamber is also beneficial to the high thermal conductivity.

Thermodynamic Study on the Formation of Acetylene during Coal Pyrolysis in the Arc Plasma Jet

Based on the principle of minimizing the Gibbs free energy, the composition of C-H-O-N-S equilibrium system about acetylene formation during the pyrolysis in arc plasma jet for four kinds of different rank-ordered coals such as Datong, Xianfeng, Yangcheng, and Luan was analyzed and calculated. The results indicated that hydrogen, as the reactive atmosphere, was beneficial to the acetylene formation. The coal ranks and the hydrogen, oxygen, nitrogen, and sulfur in coal all could obviously affect the acetylene yield. The mole fraction of acetylene is the maximum when the ratio value of atom H/C was 2. The content of oxygen was related to the acetylene yield, but it does not compete with CO formation. These agreed with the experimental results, and they could help to select the coal type for the production of acetylene through plasma pyrolysis process.

INFLUENCE OF PROCESS PARAMETERS ON STRUCTURE OF CARBON COATINGS DEPOSITED AT ATMOSPHERIC PRESSURE

Carbon coatings were deposited on the stainless steel substrates from argon-acetylene gases mixture at atmospheric pressure by arc plasma jet chemical vapor deposition (CVD). It was obtained that the increase of the torch power leads to higher growth rate and increases surface roughness. The growth rates varied in the range of 4−750 nm/s depending on the syntheses conditions. Raman spectra indicated that the bonding structure in the coatings, obtained at 600 W torch powers, changes from the typical diamond-like/graphite-like carbon to the polymer-like carbon with the increase of the distance. The FTIR spectros-copy has shown that the absorption of coatings decreases with the increase of the wave range. The IR spectra showed clear evidence of C = C and C = O sp2 bonds and presence of sp3 CH2 symmetric (2850 cm−1) and asymmetric (2920 cm−1), and sp3 CH3 asymmetric (2960 cm−1) modes in a-C:H coatings. It was obtained that the intensity of the sp2 C = C and C = O modes becomes more intense increasing the distance.

Metastable oxygen atom velocity and temperature in supersonic CO2 plasma expansions

Radial and axial velocity distribution functions of metastable oxygen atoms were obtained by way of resonant laser induced fluorescence spectroscopy at 777.19 nm in rarefied supersonic plasma jets produced from pure CO2 and CO2–N2 gas mixtures. The N2 seeded fraction is 3% in volume in order to mimic the Martian atmosphere composition. The measured lineshapes allow computation of the mean radial velocity and the perpendicular temperature, with respect to the jet axis, as well as the mean axial velocity and the parallel temperature. With an arcjet plasma source input power of 6.5 kW, the metastable O(5S) atom axial velocity is around 4500 m s−1 and the atom perpendicular temperature reaches 4500 K at the nozzle outlet. Under identical voltage and current conditions, a small addition of N2 does not change the measured values, i.e. it does not modify the overall energy balance. Distribution of flow parameters along both the radial and the axial directions reveals the existence of a barrel shock wave and a stationary shock front, which originate in shock wave regular reflexion. Flow properties, shock wave structure, departure from thermal equilibrium and impact of the applied power are debated for the two gas mixtures. Finally, the capacity of supersonic plasma expansions to simulate interplanetary probe entry into the Martian atmosphere is discussed in the light of experimental outcomes.