Argon Gas Discharge Research Articles

Dielectric Barrier Discharge Plasma Analysis and Application for Processing Palm Oil Mill Effluent (POME)

Analysis of dielectric barrier discharge (DBD) plasma reactor electrically has been done. DBD as low-temperature plasma was used on liquid wastewater palm oil mill effluent (POME) treatment. The dielectric barrier discharge plasma reactor consists of electrodes in the stainless made of screw rod with a length of 40 cm and diameter of 1.84 cm and outer electrode as winding coil with a diameter of 2.25 cm. The outer electrode was made of copper wire windings with a diameter of 0.87 mm that was wrapped in a Pyrex tube with 0.25 cm thick, with a 20 mm inner diameter and tube length of 30 cm. Plasma reactor purged with argon gas discharge flow at 4 L/min which was connected to an AC voltage of 4 kV and frequency of 15 kHz. POME was inserted into the reactor by the time variation of 0, 30, and 60 minutes. The most optimal results in 60 minutes with a Chemical Oxygen Demand (COD) value of 115.62 mg/L or still 18% compare with an initial and TSS value of 1018 mg /L or rest 85%. We also determined the charges carrier mobility by using modified Robinson Equation, and we found that average mobility with samples is always high than average mobility without samples.

Numerical Investigation on Ion Inertia Force in Low-Temperature Plasma Using Fluid Model Considering Ion Momentum Equation

In this paper, we would like to numerically investigate the effect of ion inertia force in a typical argon gas discharge using fluid model considering the ion momentum equation, which becomes important under various operating conditions. The proposed self-consistent fluid model consists of the electron continuity equation with the drift-diffusion approximation, the ion continuity equation, the electron energy density equation, the ion momentum equation, and the Poisson equation for electric potential. We studied the plasma properties affected by the inertia force by comparing between the use of momentum equation and drift-diffusion approximation for ion momentum. The results show that the ion inertia force is significant under the low-pressure conditions (<100 mtorr) as expected, e.g., for plasma etching and radio frequency magnetron sputtering plasma. In addition, we also found when the pressure is higher than 100 mtorr, the inertia force becomes important (e.g., more than 15%) in the sheath region when the driving frequency is high enough (e.g., 60 MHz), e.g., for high-frequency plasma-enhanced chemical vapor deposition. Thus, inclusion of inertia force in the modeling of momentum equation becomes necessary under these operating conditions.

Enhanced chromium adsorption capacity via plasma modification of natural zeolites

Natural zeolites such as mordenite are excellent adsorbents for heavy metals. To enhance the adsorption capacity of zeolite, sodium-exchanged samples were irradiated with 13.56 MHz capacitively coupled radio frequency (RF) argon gas discharge. Hexavalent chromium [Cr(VI)] was used as the test heavy metal. Pristine and plasma-treated zeolite samples were soaked in 50 mg/L Cr solution and the amount of adsorbed Cr(VI) on the zeolites was calculated at predetermined time intervals. Compared with untreated zeolite samples, initial Cr(VI) uptake was 70% higher for plasma-treated zeolite granules (50 W 30 min) after 1 h of soaking. After 24 h, all plasma-treated zeolites showed increased Cr(VI) uptake. For a 2- to 4-month period, Cr(VI) uptake increased about 130% compared with untreated zeolite granules. X-ray diffraction analyses between untreated and treated zeolite samples revealed no major difference in terms of its crystal structure. However, for plasma-treated samples, an increase in the number of surface defects was observed from scanning electron microscopy images. This increase in the number of surface defects induced by plasma exposure played a crucial role in increasing the number of active sorption sites on the zeolite surface.

Conversion of the waste rapeseed oil by aerosol gliding arc discharge-assisted pyrolysis

The aerosol gliding arc discharge-assisted pyrolysis was firstly proposed to convert the waste rapeseed oil. The arc motions in pure argon gas and oil mixture discharge were compared at different total flow rate. Calculated by FLUENT software, the average flow velocity distribution along the axis direction was obtained, ranging from 8 m/s at the arc initiated gap to 0.5 m/s at the exit. The distribution of gaseous products was investigated under the effect of applied voltage and pyrolysis temperature, which indicated 74% of waste oil was converted into gaseous products at applied voltage of 10 kV and pyrolysis temperature of 800 °C, respectively. Selectivity of gaseous products (CO, H2 and C2 hydrocarbons) exhibited different sensitivity to variation of operating conditions. Optical images were captured to record the evolution of deposited carbon on copper substrate under different temperatures, while the Raman spectroscopy implied that well-organized graphitized structure was formed at rotating gliding arc regime as well as the copper surface.

Controlled Levitation of Dust Particles in RF+DC Discharges

AbstractExperiments and particle‐based kinetic simulations were performed to obtain the equilibrium levitation height of dust particles in plane parallel electrode discharges in low pressure argon gas, established by combined RF and DC excitation. The computed values were compared to experimental data. The good overall agreement of the simulation results and the experimental data verifies our gas discharge, dust charging, as well as dust force balance models. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Development of double-pulse lasers ablation system for generating gold ion source under applying an electric field

Abstract Double-pulse lasers ablation (DPLA) technique was developed to generate gold (Au) ion source and produce high current under applying an electric potential in an argon ambient gas environment. Two Q-switched Nd:YAG lasers operating at 1064 and 266 nm wavelengths are combined in an unconventional orthogonal (crossed-beam) double-pulse configuration with 45° angle to focus on a gold target along with a spectrometer for spectral analysis of gold plasma. The properties of gold plasma produced under double-pulse lasers excitation were studied. The velocity distribution function (VDF) of the emitted plasma was studied using a dedicated Faraday-cup ion probe (FCIP) under argon gas discharge. The experimental parameters were optimized to attain the best signal to noise (S/N) ratio. The results depicted that the VDF and current signals depend on the discharge applied voltage, laser intensity, laser wavelength and ambient argon gas pressure. A seven-fold increases in the current signal by increasing the discharge applied voltage and ion velocity under applying double-pulse lasers field. The plasma parameters (electron temperature and density) were also studied and their dependence on the delay (times between the excitation laser pulse and the opening of camera shutter) was investigated as well. This study could provide significant reference data for the optimization and design of DPLA systems engaged in laser induced plasma deposition thin films and facing components diagnostics.

Retardation of C2C12 myoblast cell proliferation by exposure to low-temperature atmospheric plasma.

As the first step in evaluating the possibility of low-temperature atmospheric plasma for clinical applications in the treatment of rhabdomyosarcoma (RMS), we determined the effects of plasma exposure on C2C12 myoblasts. The low-temperature atmospheric plasma was generated through an electrical discharge in argon gas. One minute of plasma exposure every 24h inhibited the cell proliferation, whereas myoblast differentiation was not affected. Plasma exposure increased the phosphorylation of ERK and JNK at 30min after the exposure, but the phosphorylation of both was decreased to less than control levels at 1 and 4h after the exposure. Plasma exposure increased the percentage of cells in the G2/M phase at 8h after the exposure. In conclusion, plasma exposure retarded the proliferation of C2C12 myoblasts by G2/M arrest. Therefore, plasma exposure can be a possible treatment for the anti-proliferative effects of malignant tumors, such as RMS, without affecting differentiated skeletal muscle cells.

Excited atoms in argon gas discharge plasma

General principles are discussed for a gas discharge plasma involving excited atoms where electron-atom collision processes dominate. It is shown that an optimal kinetic model of this plasma at not large electric field strengths can be based on the rate constants of quenching excited atom states by electron impact. The self-consistent character of atom excitation in gas discharge plasma is important and results in the tail of the energy distribution function of electrons being affected by the excitation process, which in turn influences the excitation rate. These principles are applied to an argon gas discharge plasma where excitation and ionization processes have a stepwise character and proceed via formation of argon atom states with the electron shell 3p54s.

The study of the coating adhesion on PP surface modified in different plasma/acrylic acid solution

The effect of acrylic acid deposition in the plasma-treated polypropylene surface was investigated on the surface adhesion properties. The PP sheets were examined by low frequency LF plasma treatments of the oxygen and argon gas discharge individually followed by acrylic acid dipping. The PP surface topography and hydrophilicity were characterized using surface energy measurement, attenuated total reflection spectroscopy ATR and the atomic force microscopy AFM. An evident improvement in surface energy and the coating adhesion was attributed to the creation of polar groups on PP surface in oxygen and argon plasma treatments. In comparison with argon gas plasma, the AFM images of oxygen plasma-treated specimen revealed the peak and valley structure on the PP surface. The deposition of the plasma-treated surfaces into different acrylic acid solutions resulted to surface water repellency and smoothness. Based on the AFM images, the roughness profile of the plasma treated surface changed by the concentration of acrylic acid solution. The lower surface hydrophilicity may be due to acrylic acid effect in dissolving and then removing off the formed polar groups on PP surface. However, the scanning electron microscopy SEM showed distinct regions of acrylic acid grafting on PP surface. Then, the surface adhesion properties were evaluated in pull-off adhesion test after dipping the modified sheets into an acrylic–urethane coating. The adhesion test indicated for the higher adhesion strength in oxygen plasma treatment than argon treatment and an adverse effect of acrylic acid deposition. The addition of aqueous solution of sodium hydroxide into the acrylic acid solution improved the efficiency of acrylic acid grafting on the plasma-treated PP surface. The results of ATR, water contact angle and the pull-off adhesion test showed increasing degree of acrylic acid grafting on PP surface.

Determination of cathode fall thickness in magnetized dc plasma for argon gas discharge

The thickness of the cathode fall region (dc) in magnetized dc argon plasma has been investigated using two different methods, namely the axial potential distribution and the current density distribution along the glow discharge regions. The measurements have been carried out at the edge and center of the cathode surface. Dc (cold cathode) magnetron sputtering unit has been used. The radial and axial distributions of the magnetic field B, the Ia–Va characteristic curves of the glow discharge and the axial potential distribution and the current density distribution have been investigated. The thickness of the cathode fall region was between 2 and 3.3 mm for the two methods in pressure (P) range of 0.53–4 mbar. It is concluded that a noticeable reduction of the cathode fall thickness (about 33%) has been found in the presence of a magnetic field and at the center of the cathode and stronger electric field at the edge of the cathode fall, and hence high rates of sputtering are expected.

Experimental verification of the Boltzmann relation in confined plasmas: Comparison of noble and molecule gases

Experimental verification of the Boltzmann relation is performed in argon and oxygen gas inductively coupled plasmas from the measurements of both the spatial electron currents (as a fluid approach) and the electron energy probability functions (EEPFs, as a kinetic approach). At a low gas pressure of 10 mTorr, the measured electron currents are spatially uniform, and the EEPFs in the total electron energy scale are identical, which indicate that the Boltzmann relation is valid at both the argon and oxygen gases. As the gas pressure increases to 30–40 mTorr, however, the Boltzmann relation is broken in the oxygen gas discharge, while the Boltzmann relation is still valid in the argon gas discharge. This different variation in the oxygen gas discharge is mainly due to the presence of various inelastic collisions in the entire electron energy region, which causes the transition of the electron kinetics from a non-local to a local regime.

Atmospheric Pressure Plasma: A High-Performance Tool for the Efficient Removal of Biofilms

IntroductionThe medical use of non-thermal physical plasmas is intensively investigated for sterilization and surface modification of biomedical materials. A further promising application is the removal or etching of organic substances, e.g., biofilms, from surfaces, because remnants of biofilms after conventional cleaning procedures are capable to entertain inflammatory processes in the adjacent tissues. In general, contamination of surfaces by micro-organisms is a major source of problems in health care. Especially biofilms are the most common type of microbial growth in the human body and therefore, the complete removal of pathogens is mandatory for the prevention of inflammatory infiltrate. Physical plasmas offer a huge potential to inactivate micro-organisms and to remove organic materials through plasma-generated highly reactive agents.MethodIn this study a Candida albicans biofilm, formed on polystyrene (PS) wafers, as a prototypic biofilm was used to verify the etching capability of the atmospheric pressure plasma jet operating with two different process gases (argon and argon/oxygen mixture). The capability of plasma-assisted biofilm removal was assessed by microscopic imaging.ResultsThe Candida albicans biofilm, with a thickness of 10 to 20 µm, was removed within 300 s plasma treatment when oxygen was added to the argon gas discharge, whereas argon plasma alone was practically not sufficient in biofilm removal. The impact of plasma etching on biofilms is localized due to the limited presence of reactive plasma species validated by optical emission spectroscopy.

A contribution to spectroscopic diagnostics and cathode sheath modeling of micro-hollow gas discharge in argon

In this paper, the hydrogen Balmer beta line shape from a micro-hollow gas discharge (MHGD) in argon with traces of hydrogen is used for simultaneous diagnostics of plasma and cathode sheath (CS) parameters. For this purpose, a simple model of relevant processes responsible for the line broadening is introduced and applied to the Balmer beta profile recorded from a MHGD generated in the microhole (diameter 100 μm at narrow side and 130 μm at wider side) of a gold-alumina-gold sandwich in the pressure range (100–900 mbar). The electron number density Ne in the range (0.4–4.5) × 1020 m–3 is determined from the width of the central part of the Balmer beta line profile, while, from the extended wings of the Balmer beta profile, induced by dc Stark effect, the next three parameters are determined: the average value Ea of electric field strength in the CS in the range (16–95 kV/cm), the electric field strength E0 at the cathode surface in the range (32–190 kV/cm), and the CS thickness zg in the range (18–70 μm). All four MHGD parameters, Ne, Ea, E0, and zg, compare reasonably well with results of the modeling experiment by M. J. Kushner [J. Phys. D: Appl. Phys. 38, 1633 (2005)]. The results for Ne are compared with other emission experiments.

Spectroscopic assessment of argon gas discharge induced radiolysis of aqueous adenine and thymine

Ionizing radiation influences life profoundly for it can modify genetic materials. It is a long-standing task to investigate the interaction between energetic particles and DNA together with its components such as nucleotides, nucleosides and bases so as to predict and assess the potential biological effects. In this study, argon gas discharge was employed to produce energetic ions and electrons. The gas discharge caused the radiolysis of aqueous bases and the involved reactions were analyzed by means of spectroscopic tools including UV–vis absorption, fluorescence and Fourier transformation infrared (FTIR) spectroscopy, also assisted by liquid chromatography/mass spectrometry (LC/MS). It was found that the discharge resulted in the adenine-derived lesions such as 4,6-diamino-5-formamidopyrimidine, 8-OH-Ade and 2-OH-Ade in the radiolysis of aqueous adenine, as well as the thymine-derived lesions such as thymine glycol, 5-hydroxy-6-hydrothymine and/or 6-hydroxy-5-hydrothymine, 5-hydroxymethyluracil and 5-formyluracil in the radiolysis of aqueous thymine. The study of radio-sensitivity showed that adenine was more resistant to the discharge. The mechanisms of the involved reactions were studied in detail, confirming that the hydroxyl radical played a dominant role.

Plasma parameters of a small surface-wave discharge at atmospheric pressure obtained by line-ratio method

Plasma parameters of a small surface-wave discharge in argon gas at atmospheric pressure are obtained by optical emission spectroscopy applying the line-ratio method. The microwave discharge is maintained at a frequency of 2.45 GHz in a ceramic tube with an inner diameter of 1 mm and a length of 11 mm. The discharge is ignited at power levels below 10 W. Emission spectra of the argon plasma are measured in the wavelength range 645–825 nm at different gas flows and forward microwave powers. The electron temperature and the plasma density are determined simultaneously through a ‘cross-point’ method using two line-intensity ratios and their values are Te ≅ 1.6 eV and ne = (3.6–4.5) × 1014 cm−3, respectively. The results show a stronger dependence of the plasma parameters on the gas flow rather than on the input power in the case of plasma columns longer than the tube length.

Sheath and electron density dynamics in the normal and self-pulsing regime of a micro hollow cathode discharge in argon gas

A microplasma is generated in the microhole (400 μm diameter) of a molybdenum-alumina-molybdenum sandwich (MHCD type) at medium pressure (30–200 Torr) in pure argon. Imaging and emission spectroscopy have been used to study the sheath and electron density dynamics during the stationary normal regime and the self-pulsing regime. Firstly, the evolution of the microdischarge structure is studied by recording the emission intensity of the Ar (5p[3/2]1–4s[3/2] $_{1})$ line at 427.217 nm, and Ar+ (4p′ 2P3/2–4s′ 2D $_{5/2})$ line at 427.752 nm. The maximum of the Ar+ line is located in the vicinity of the sheath-plasma edge. In both regimes, the experimental observations are consistent with the position of the sheath edge calculated with an ionizing sheath model. Secondly, the electron density is recorded by monitoring the Stark broadening of the H $_\beta$ -line. In the self-pulsing regime at 150 Torr, the electron density reaches its maximum value of 4 × 1015 cm-3, a few tens of ns later than the discharge current maximum. The electron density then decays with a characteristic decay time of about 2 μs, while the discharge current vanishes twice faster. The electron density in the steady-state regime is two orders of magnitude lower, at about 6–8 × 1013 cm-3.

Nanostructured tracers for laser-based diagnostics in high-speed flows

The potential application of aggregates of nanoparticles for high-speed flow diagnostics is investigated. Aluminum nanoparticles around 10 nm in diameter are produced by spark discharge in argon gas. Through rapid coagulation and oxidation, aggregates of small effective density are formed. They are characterized by microscopy and their aerodynamics and optical properties are theoretically evaluated. The performance of the aggregates is experimentally investigated across an oblique shock wave in a supersonic wind tunnel of 3 × 3 cm2 cross-section at Mach 2. Particle image velocimetry is used to quantify the time response of the aggregates. The investigations are also carried out on compact titanium agglomerates to provide a base for comparison. The results yield a relaxation time of 0.27 µs for the nanostructured aluminum aggregates, which is an order of magnitude reduction with respect to the compact titanium nanoparticles. This work demonstrates the applicability of nanostructured aggregates for laser-based diagnostics in supersonic and hypersonic flows.

Simultaneous plasma and electric field diagnostics of microdischarge from hydrogen Balmer line shape

Hydrogen Balmer beta line shape from a microhollow gas discharge in argon with traces of hydrogen is used for simultaneous diagnostics of plasma and cathode sheath parameters. Simple model of relevant processes responsible for line broadening is developed and results favorably compared with experiment at 500 mbar with the electron density 3.8×1020 m−3 and electric field strength of 127 kV/cm in the cathode sheath region.

Time resolved LIF with a fast-scanning diode laser

Ion phase-space resolved fluctuations carry detailed information pertaining to transport as well as to the plasma degrees of freedom. Using a 500 mW diode laser that can scan over Doppler broadened Argon ion lines in less than 50 microseconds we observe fluctutations and correlations with an adjustable bandwidth by means of a comb-filter. The high laser intensity coupled with fast scanning makes optical pumping between the Zeeman sublevels observable. This opens a new strategy for optical tagging as well as observing correlations between fluctuations at different ion velocities. The experiments are performed in a 2 meter length 0.1 meter diameter CW Argon gas discharge created by a 10 MHz inductive plasma source in a uniform 1 kG magnetic field. The plasma density is typically 109 cm−3, the electron temperature is 2 eV and the ions have a temperature of 0.1 eV. Under these conditions the ions are weakly collisional.

Influence of an acetylene impurity on the properties of a radio-frequency gas discharge in argon

The influence of an acetylene fraction in a mixture with argon on the parameters of a radio-frequency gas discharge has been investigated using the kinetic simulation by the particle-in-cell Monte Carlo collision method. Special attention has been focused on analyzing the formation of ions and radicals that are precursors for growth of nanoparticles in the gas discharge volume. It has been shown that the concentrations of electrons, positive ions, and negative ions are nonmonotonic functions of the acetylene amount in the mixture. The presence of negative ions with a concentration comparable to the electron concentration changes the parameters of the radio-frequency gas discharge only insignificantly.