Argon Glow Discharge Research Articles

Modelling of non-uniform DC driven glow discharge in argon gas

Physical properties of non-uniform DC-driven glow discharge in argon at pressure 1 torr are analyzed numerically. Spatially two-dimensional axial-symmetric model is based on the diffusion-drift theory of gas discharge. Results presented compare favorably with the classic theory of glow discharges and exhibit good agreement with the experimental result. Comparison with the result of spatially one-dimensional model is performed.

Atmospheric-pressure argon/oxygen plasma-discharge source with a stepped electrode

The nonequilibrium glow discharge in argon mixed with oxygen at atmospheric pressure was generated in a parallel plate reactor with a stepped electrode powered by a 13.56MHz radio-frequency power supplier. The stepped-electrode reactor consists of a narrow and wide gap structure. A strong electric field occurred at the narrow gap region preionizes Ar∕O2 gas and assists to generate a large volumetric plasma in the wide gap region. Therefore, the stepped-electrode reactor makes it easy to operate Ar∕O2 glow discharge, providing a stable, uniform, and broad plasma jet at atmospheric pressure.

CO2 reforming of methane over argon plasma reduced Rh/Al2O3 catalyst: a case study of alternative catalyst reduction via non-hydrogen plasmas

An argon glow discharge plasma was used to reduce RhCl3 impregnated Al2O3 powder at room temperature. The obtained sample was characterized by chemisorption, X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) equipped with an energy dispersion X-ray spectrometer (EDX). XRD and EDX analyses confirmed that Rh ions were reduced into metallic Rh during the plasma reduction. TEM analysis revealed that the argon plasma reduction induces a high dispersion of Rh nano-particles. The average particle size of Rh is 1.2 nm, estimated by chemisorption. For the CO2 reforming of methane, the plasma reduced Rh/Al2O3 shows comparable activity to a conventional hydrogen reduced catalyst. The value of the standard electrode potential can be employed for the assessment of reducibility of metal ions. The catalyst reduction using argon glow discharge plasma at room temperature will provide a promising alternative to hydrogen reduction for catalyst preparation.

Characterization of Argon Glow Discharge Plasma Reduced Pt/Al2O3Catalyst

An argon glow discharge plasma was used to treat H2PtCl6 impregnated Al2O3 powder at room temperature. The obtained sample was characterized by ultraviolet−visible spectroscopy (UV−vis), X-ray photoelectron spectroscopy (XPS), CO adsorbed diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy, X-ray powder diffraction (XRD), and transmission electron microscopy (TEM) equipped with energy dispersion X-ray spectrometer (EDX). UV−vis, XPS, and CO adsorbed DRIFT confirmed that Pt ions were reduced to metallic Pt during the plasma treatment. XRD and TEM revealed that the structure of the plasma reduced Pt nanoparticles is face centered cubic. The Pt particle shape is irregular but uniformly distributed on the Al2O3. The average particle size of plasma reduced 3 wt % Pt/Al2O3 is 3.3 nm, estimated by TEM. For the partial oxidation of methane, the plasma reduced 0.5 wt % Pt/Al2O3 shows comparable activity to a conventional hydrogen reduced sample. Furthermore, the plasma reduced 0.5 wt % Pt/Al2O3 sample is more stable and more resisted to coke formation. The argon glow discharge plasma reduction at room temperature may provide an environmentally friendly, fast, and simple approach to prepare supported metal nanoparticles and also a promising alternative to hydrogen reduction at elevated temperature.

Spatial variations of non-uniform argon glow discharge

The spatial variation of a non-uniform glow discharge due to the different diameters of the same discharge tube on the plasma parameters is attracting a considerable attention. For this reason the fundamental spatial plasma parameters of an argon glow discharge have been measured by using fast three couple of Langmuir double probe (TCDP) technique. The orbital motion limited (OML) theory has been used, since the probe radius is smaller than Debye length ξ < 1. The axial and radial variation of the electron temperature and density have been investigated. The results can be summarized as follow: due to the rise in the space-charge confinement with decreasing the tube radius and discharge current, the space-charge density increases, the electron temperature decreases.

Emission spectra of titanium and argon in argon/hydrogen glow discharge

Experimental results examining the influence of hydrogen introduced into argon glow discharge on spectral line intensities are presented. The cathode was made of titanium, an element with low atomic energy levels. Spectral lines intensity of sputtered material (Ti I) and carrier gas (Ar I and Ar II) change differently with progressive addition of molecular hydrogen.

Optogalvanic effect and measurement of gas temperature in an abnormal glow discharge

Axial distribution of the gas temperature in an abnormal glow discharge in argon is simultaneously determined by laser optogalvanic and absorption spectroscopy methods. Temperature distributions obtained by two different methods are in a fair agreement except in the boundary region between the cathode fall and the negative glow. Systematically lower temperature in this region obtained by optogalvanic spectroscopy is a consequence of the nature of optogalvanic effect, which, in some circumstances, cannot be identified with spectral line profile.

Comparison between decolorization of denim fabrics with Oxygen and Argon glow discharge

In this study, we have used a low temperature plasma, produced by a DC magnetron sputtering device, for decolorizing of denim fabrics, and the effect of using different gases such as Argon and Oxygen as the discharge medium have been investigated. The results obtained under equal periods of time have been compared and the effect of washing on the treated denims has been reported.

Bacterial inactivation using a low‐temperature atmospheric plasma brush sustained with argon gas

This study investigated the bacterial inactivation/sterilization effects of a new atmospheric plasma source, which is a brush-shaped argon glow discharge created under 1 atm pressure. Such an atmospheric plasma brush requires extremely low power of less than 20 W to operate; and therefore is essentially a low-temperature discharge as confirmed by gas-phase temperature measurements. Two bacteria, Escherichia coli (E. coli) and Micrococcus luteus (M. luteus), seeded in various media were subjected to plasma treatment and their survivability was examined. It was found that such argon atmospheric plasma brush is very effective in destruction of the bacteria cells. With nutrient broth and standard methods agar as supporting media, a cell reduction in a level of 6 orders of magnitude was observed for E. coli within 3-4 min plasma treatment. A similar level of cell reduction was also observed for M. luteus in the two media with 2 or 3 min plasma treatment. The plasma treatment effects on the bacteria cell structures were also examined using scanning electron microscopy and the cell structure damages due to the plasma exposure were observed on both bacteria. The possible sterilization mechanism of the argon plasmas is also discussed in this article.

Carbon nanotube formation over plasma reduced Pd/HZSM-5

In this work, we reported a new plasma catalyst preparation method for carbon nanotube (CNT) formation. With this new method, argon glow discharge plasma was operated at room temperature and applied for the reduction of Pd/HZSM-5, instead of catalyst reduction thermally using hydrogen at elevated temperature. Such plasma reduced catalyst shows a high dispersion of metal particles. The multi-walled CNTs produced with this plasma reduced Pd/HZSM-5 exhibit structural graphene sheets in conical hollow shape, a typical structure observed in CNTs from catalytic methane decomposition. Some fiber fish bone type structures can be also observed. Compared to the hydrogen reduction (thermally), the reduction using argon plasma is feasible and effective for the preparation of catalyst for the CNTs formation. The glow discharge plasma catalyst reduction is very promising for the further development of green catalyst reduction technologies.

Electron and metastable state interactions in two-step ionization waves

We demonstrate the use of a microwave hairpin resonator to measure the time-dependent, phase-resolved electron number density in ionization waves. Under our argon glow discharge conditions, the instability was caused by two-step ionization; and the wave frequency depended on the volume quenching rate of the metastable states. We measured the 1s5 metastable state density using diode laser absorption. The peak electron number density lagged behind the peak metastable state density by 60°. This phase shift reveals the nonlocal nature of the electron kinetics due to two-step ionization.

The glow discharge plasma influence on the oxide layer and diffusion zone formation during process of thermal oxidation of titanium and its alloys

The influence of the glow discharge in argon and oxygen mixture on the effectiveness of the surface-hardening treatment of titanium and its alloys, is presented in this paper. The high solubility of oxygen in the titanium matrix is the base of the discussed technology. Interstitially placed oxygen causes significant hardness increment as well as wear resistance. The rectangular flat specimens of Ti6Al4V alloy underwent the process of plasma thermal oxidation (TO) in atmosphere Ar+O 2 which led to diffusion strengthening. The temperature of the process was 1223 K—lower than the higher temperature range of the recrystallization process. The experiments were carried out without plasma, with plasma presence during the whole process and the plasma presence only in diffusion stage. The substrates were examined with the use of scanning electron microscope. The chemical composition of formed oxides was determined. In addition to the X-ray analysis, the cross-section inspections as well as the hardness distribution in hardened layers assessment were also done. The main conclusion is that the plasma glow discharge presence during the whole process is not advantageous because the complex oxides that are difficult to dissolve in the matrix are formed. And although the surface hardness is the highest in this case, it is unfortunately connected with brittleness increase. The presence of plasma in diffusion stage is more preferable because it works “mechanically” on the oxides layer that is additionally thinner and causes the formation of thicker strengthened zone. However in both cases the use of plasma makes the process more effective than “typical” oxidation process.

Carbon dioxide reforming of methane over Ni/Al 2O 3 treated with glow discharge plasma

Ni/Al 2O 3 catalyst was first treated by argon glow discharge plasma followed by calcination in air. The catalyst prepared this way exhibits an improved low-temperature activity for carbon dioxide reforming of methane, compared to the catalyst prepared without plasma treatment. The catalyst characterization using XRD, chemisorption and TEM analyses show that the plasma treatment followed by calcination thermally induces a generation of specific nickel species on the support. This kind of “plasma” metal species is highly dispersed on the support and can remain stable during reforming reactions. The average size of the “plasma” metal particles is ca. 5 nm. The plasma treatment can also enhance the anti-carbon deposition performance of the catalyst. The formation of carbon species that is responsible for catalyst deactivation can be inhibited. The catalyst stability is therefore improved.

Computational study of plasma–solid interaction at low and medium pressures

In the last years the challenging problem for plasma science and technology started to be the surface treatment at higher pressures including the atmospheric pressure plasma. Knowledge of processes near the substrate is very important, but the possibilities of their diagnostics are limited in this pressure range. In the contribution the combination of molecular dynamics and Monte Carlo methods was used for the study of trajectories of charged particles in the sheath and presheath at low and medium pressures. The results of our simulations were compared with experimental data obtained in dc glow discharge in argon. In the discussion an attention is devoted both to the influence of gas pressure on plasma characteristics and to the technique of computer modelling at higher pressures.

Explanation of matrix effects in the GD-OES spectrum of zinc by charge transfer reactions of Ar+ ions with atoms originating from the cathode

In the analysis of Zn–Al and Zn–Cu alloys by GD-OES with the Grimm-type glow discharge in argon, emission yields of Zn II lines are higher for Zn–Al alloys than for Zn–Cu alloys. This matrix effect is explained by variations of the argon ionization degree with the analysed matrix. The variations are caused by asymmetric charge transfer (ACT) reactions of Ar+ ions with copper and zinc. ACT with Ar+ ions is an important ionization mechanism of zinc, populating the 4p 2P01/2 and 4p 2P03/2 levels of the zinc ion, and indirectly, by subsequent deexcitation/excitation, other Zn II levels also. Matrix effects of this type probably also occur for other elements that are subject to ACT reactions with argon ions and attention should be paid if ionic lines of such elements are used in analytical applications of GD-OES.

Effect of H2/Ar mixtures on the analysis of conducting and insulating materials by radiofrequency glow discharge mass spectrometry

The effect of the addition of hydrogen to a radiofrequency–argon glow discharge coupled to a time of flight mass spectrometer has been studied. Pressure and forward power conditions in the discharge were kept constant. The hydrogen concentrations added to the argon plasma gas were 0.5%, 1% and 10% v/v and two types of homogeneous samples were investigated: a conducting material (nickel-base) and two glasses. A decrease of the dc-bias voltage with increasing H2 concentration was observed at every forward power assayed. For the nickel material, the analytical signals turned out to be higher in 10% H2/Ar and 1% H2/Ar discharges than in pure Ar, while for 0.5% H2/Ar the increases were just obtained at the lowest power assayed. Concerning the glass samples, signal increases were obtained at the powers assayed for most analytical signals using 0.5% H2/Ar instead of pure Ar.

Comparative studies on excitation of nickel ionic lines between argon and krypton glow discharge plasmas

The emission characteristics of nickel ionic lines in a glow discharge plasma are investigated when argon or krypton was employed as the plasma gas. Large difference in the relative intensities of nickel ionic lines which are assigned to the 3d 84p–3d 84s transition is observed between the krypton plasma and the argon plasma. Different intense Ni II lines appear in the krypton spectrum and in the argon spectrum, such as the Ni II 231.601 nm for Kr and the Ni II 230.009 nm for Ar. The excitation energy of these Ni II emission lines can give a key in considering their excitation mechanisms. The explanation for these experimental results is that charge-transfer collisions between nickel atom and the plasma gas ion play a major role in exciting the 3d 84p excited levels of nickel ion. The conditions for energy resonance in the charge-transfer collision determine particular energy levels having much larger population; for example, the 3d 84p 4 D 7/2 level (6.39 eV) for Kr and the 3d 84p 4 P 5/2 level (8.25 eV) for Ar.

H 2/Ar direct current glow discharge mass spectrometry at constant voltage and pressure

The addition of hydrogen to a direct current (dc) - argon glow discharge (GD) coupled to a time of flight mass spectrometer has been studied using a fixed voltage between the electrodes and a fixed discharge pressure. Hydrogen contents investigated were 0.5%, 1% and 10% v/v in the argon discharge and the samples under study consisted of a copper-base, a nickel-base and an iron-base homogeneous materials. Also, the in-depth profile analysis of a tin plate was investigated. Results have shown that hydrogen addition gives rise to significant changes in the slope of the linear relationship between the electrical current and the discharge voltage. Clearly, the electrical resistance of the discharge at the typical operation voltages in the interval 600–1000 V increases with hydrogen added to pure argon. A decrease of the sputtering rates was observed the higher the hydrogen concentrations. Besides, the “reduced sputtering rates”, i.e. the sputtering rates divided by the corresponding electrical current, were also lower for the H 2/Ar discharges than for pure argon. However, the analytical ion signals observed using discharge voltages higher than 900 V turned out to be higher in a 0.5% H 2/Ar discharge than in pure argon for the copper and nickel materials. Besides, for the three samples investigated the ion yields were from 1.5 up to 3 times higher in 0.5% H 2/Ar discharges as compared to the pure argon. Finally, the effect of 0.5% H 2 addition to the Ar discharge on the in-depth profile of a tin plate has also been investigated. As compared to the use of a pure Ar GD, higher sensitivity for major and minor components of the coating were observed without loss of the relative depth resolution achieved.

Glow and pseudo-glow discharges in a surface discharge generator

The glow discharge in flowing argon at one atmospheric pressure is realized in a surface discharge generator. The discharge current presents one peak per half-cycle of the applied voltage. The duration of the discharge pulse is more than 1μs when the frequency of the applied voltage is 60kHz. For the glow discharge in argon, the power consumption increases with the increase of voltage or the decrease of gas pressure. This relation is explained qualitatively based on the theory of the Townsend breakdown mechanism. In contrast, the discharge current in one atmospheric pressure air gives many spikes in each half-cycle and correspondingly this kind of discharge is called pseudo-glow discharge. Every current spike oscillates with high-frequency damping. The pseudo-glow discharge in one atmospheric pressure air might result from the streamer breakdown mechanism.

High-ion temperature experiments with negative-ion-based neutral beam injection heating in Large Helical Device

High-Z plasmas have been produced with Ar and/or Ne gas fuelling to increase the ion temperature in Large Helical Device (LHD) plasmas heated with high-energy negative-ion-based neutral beam injection (NBI). Although the electron heating is dominant in the high-energy NBI heating, the direct ion heating power is significantly enhanced in low-density plasmas due to both an increase in the beam absorption (ionization) power and a reduction of the ion density in the high-Z plasmas. Intensive neon- and/or argon-glow discharge cleaning works well to suppress dilution of the high-Z plasmas with wall-absorbed hydrogen. As a result, the ion temperature increases with an increase in the ion heating power normalized by the ion density and reaches 10 keV. An increase in the ion temperature is also observed with the addition of centrally focused electron cyclotron resonance heating to a low-density and high-Z NBI plasma, suggesting improvement of the ion transport. The results obtained in the high-Z plasma experiments with high-energy NBI heating suggest that an increase in the direct ion heating power and improvement of the ion transport are essential to ion temperature rise, and that a high-ion temperature could be obtained as well in hydrogen plasmas with low-energy positive-NBI heating which is planned in the near future in the LHD.