Direct Current Glow Discharge Research Articles

Experimental investigation of dynamical structures formed due to a complex plasma flowing past an obstacle

We report experimental observations of the dynamical behavior of a complex plasma flowing past a spherical obstacle. The investigation has been carried out in a Π-shaped direct current glow discharge experimental device where a dust cloud of kaolin particles in a background argon plasma is made to flow in a controlled fashion by regulating the mass flow of the neutrals. A spherical metal object vertically mounted on the cathode tray acts as an obstacle to the flow. The flowing dust particles are repelled by the electrostatic field of the negatively charged sphere, and a microparticle free region (dust void) is formed surrounding the obstacle. The distant dust particles are attracted towards the floating obstacle and reflected back when they get to a certain distance, causing a ring shaped structure around the obstacle. We characterize the shape of this structure over a range of dust flow speeds and obstacle biases. For a supersonic flow of the dust fluid, a bow shock is seen to form on the upstream side of the negatively biased sphere, while the downstream side shows the generation of wave structures for a particular range of flow velocities when the Reynolds number Re≳50. The flow generated structures can be physically understood in terms of the dust dynamics under the combined influence of the ion-drag force, the neutral streaming, and the electric force.

Plasma states and carbon film deposition in glow discharge connected to dielectric barrier discharge

We developed a plasma source by connecting a direct current glow discharge (GD) with a dielectric barrier discharge (DBD) via a ground mesh (DB-GD). Based on the Langmuir probe measurements, the electron density of the DB-GD increased and the electron temperature decreased compared with those of the GD. Calculations of the electron energy distribution functions revealed that the DB-GD possessed a lower density of high-energy electrons and higher density of low-energy electrons than the GD did. We also confirmed that the DB-GD generated with methane gas was capable of producing an amorphous carbon film.

Atmospheric Pressure Plasma-Mediated Synthesis of Platinum Nanoparticles Stabilized by Poly(vinylpyrrolidone) with Application in Heat Management Systems for Internal Combustion Chambers.

Poly(vinylpyrrolidone)-stabilized Pt nanoparticles (PVP-PtNPs) were produced in a continuous-flow reaction-discharge system by application of direct current atmospheric pressure glow discharge (dc-APGD) operated between the surface of a flowing liquid anode (FLA) and a pin-type tungsten cathode. Synthesized PVP-PtNPs exhibited absorption across the entire UV/Vis region. The morphology and elemental composition of PVP-PtNPs were determined with transmission electron microscopy (TEM) and energy dispersive X-ray scattering (EDX), respectively. As assessed by TEM, PVP-PtNPs were approximately spherical in shape, with an average size of 2.9 ± 0.6 nm. EDX proved the presence of Pt, C, and O. Dynamic light scattering (DLS) and attenuated total reflectance Fourier transform-infrared spectroscopy (ATR FT-IR) confirmed PtNPs functionalization with PVP. As determined by DLS, the average size of PtNPs stabilized by PVP was 111.4 ± 22.6 nm. A fluid containing resultant PVP-PtNPs was used as a heat conductive layer for a spiral radiator managing heat generated by a simulated internal combustion chamber. As compared to water, the use of PVP-PtNPs enhanced efficiency of the system, increasing the rate of heat transfer by 80% and 30% during heating and cooling, respectively.

The formation of an oscillating system during the sputtering of sapphire single crystal with pulsed glow discharge

Sapphire (α-Al2O3, transparent corundum) single crystals were analyzed with pulsed direct current glow discharge mass spectrometry. Combined hollow cathode was used as a discharge cell. To obtain stable sputtering of dielectric material, a formation of initial surface conductivity via preliminary vacuum deposition of thin metallic layer was proposed. Al and Ta film of different thickness (30–200 nm) were considered for this purpose. The approach was found to provide the effective sputtering of dielectrics. The formation of an oscillating system was shown during the sputtering of sapphire samples in a tantalum combined hollow cathode cell. For oriented sapphire single crystals, periodic oscillations of 27Al+ intensity were acquired. This phenomenon was observed only for dielectric single crystals and not for other dielectric samples, e.g. alumina ceramic or fused quartz. The linear dependence of oscillation period on the duration of discharge pulse was found. The origin of these oscillations seems to be attributed to periodic fluctuations of surface conductivity. Oscillation periods calculated for two different orientations of sapphire single crystals (001 and 012) were found to be proportional to the main period of sapphire lattice. Therefore, an assumption that the crystal internal structure of the sample might be the cause of the oscillations is discussed.

Determination of trace impurity elements in MnZn ferrite powder by direct current glow discharge mass spectrometry

An analytical method for the determination of 26 impurity elements (such as Li, Be, Na, Mg, Al, Si, P, S, K, Ca, Sc, Ti, V, Cr, Co, Ni, Ga, Ge, Y, Nb, Mo, Ag, Cd, Sb, W and Pb) in MnZn ferrite powder by direct current glow discharge mass spectrometry (GD-MS) was established. MnZn ferrite powder was mixed with copper powder, used as a conductor, and pressed. The effects of MnZn ferrite powder preparation conditions and glow discharge parameters for the sensitivity and stability of signal analysis were investigated. By determining the choice of isotope and the application of the mass resolutions of 4000 (MR, medium resolution) and 10000 (HR, high resolution), mass spectral interference was eliminated. The contents of impurity elements in MnZn ferrite powder was calculated by subtraction after normalizing the total signal of Mn, Zn, Fe, O and Cu. The results showed that the detection limit of 26 kinds of impurity elements was between 0.002 and 0.57 μg/g, and the relative standard deviation (RSD) was between 3.33% and 32.35%. The accuracy of this method was verified by the ICP-MS. The method was simple and practical, which is applied to the determination of impurity elements in MnZn ferrite powder.

ON MECHANISMS OF INCREASING HCL DISSOCIATION DEGREE IN GLOW DISCHARGE PLASMA

The influence of initial compositions of the binary HCl+Ar and HCl+O2 gas mixtures on the hydrogen chloride dissociation kinetics in low temperature gas discharge plasma was investigated. The experiments were carried out under the conditions of direct current glow discharge at constant total gas pressure (100 Pa) and discharge current (25 mA). The data on electro-physical plasma parameters and plasma composition were obtained by modeling procedure based on the simultaneous solution of Boltzmann kinetic equation and the equations of chemical kinetics for neutral and charged species in a steady-state approximation. It was found that an increase in the second component fraction in both gas mixtures results in the sufficient increase in the HCl dissociation degree (aHCl = 23–43% for 0–80% Ar and 23–90% for 0–80% O2), which is associated with different mechanisms. Particularly, in the HCl+Ar gas mixture, an effect of increasing aHCl is provided by an increase in the electron impact dissociation frequency due to the change in electro-physical plasma parameters, such as electron mean energy and electron density. For the HCl+O2 gas mixture, such mechanism is almost negligible because of the weak disturbances in both electron energy distribution and formation/decay balance for charged species in the combination of two molecular electronegative gases. At the same time, the HCl dissociation kinetics in this gas system appears to be strongly dependent on the gas-phase interactions with ground state of oxygen atoms O(3P), metastable atoms O(1D) and OH radicals. It was found that the rates of corresponding processes begin to exceed the HCl electron impact dissociation rate at 20% O2 in HCl+O2.Forcitation:Efremov A.M., Murin D.B., Belyaev S.V. On mechanisms of increasing hcl dissociation degree in glow discharge plasma. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 61-66

Comparative investigation of the emission characteristics between 6.78-MHz radio-frequency and direct-current glow discharge plasmas for atomic emission spectrometry

This paper focused on the characteristics of emission spectra excited by a Grimm-style glow discharge plasma source in a 6.78-MHz radio-frequency (RF) power mode, in comparison to a conventional direct-current (DC) power mode. For this purpose, Boltzmann plots for atomic emission lines of iron were analyzed in detail, when the RF forward power and argon pressure in the discharge chamber were selected as the experimental parameters. The Boltzmann plot for low-lying excited levels of iron atom (3.4–4.8 eV) was on a linear relationship to provide an excitation temperature, whereas emission lines having larger excitation energies (more than 5 eV) generally deviated upwards from the linear relation. Any systematic dependence on the spin multiplicity was not found among the high-lying excited levels in the Boltzmann plot. The reason for the phenomenon was considered as follows: (1) the excitation for the low-lying emission lines would be caused by a dominant thermal collision process and (2) any non-thermal process also contributed to excitations for the high-lying emission lines to cause their over-population as a whole. The resultant excitation temperature was obtained in a narrow range of 3400–3600 K, which was hardly affected by the discharge power and the argon pressure, and further, the excitation temperature was very similar to that of a DC plasma that we had already reported. This result suggested that the glow discharge plasma could be supported by a self-stabilized negative glow region, where the kinetic energy distribution of the particles would be changed to a lesser extent as far as a stable discharge could be maintained.

Pulsed glow discharge enables direct mass spectrometric measurement of fluorine in crystal materials – Fluorine quantification and depth profiling in fluorine doped potassium titanyl phosphate

A pulsed direct current glow discharge time-of-flight mass spectrometry (GD TOF MS) method for the quantification of fluorine in insoluble crystal materials with fluorine doped potassium titanyl phosphate (KTP) KTiOPO4:KF as an example has been proposed. The following parameters were optimized: repelling pulse delay, discharge duration, discharge voltage, and pressure in the discharge cell. Effective ionization of fluorine in the space between sampler and skimmer under short repelling pulse delay, related to the high-energy electron impact at the discharge front, has been demonstrated. A combination of instrumental and mathematical correction approaches was used to cope for the interferences of 38Ar2+ and 1H316O + on 19F+. To maintain surface conductivity in the dielectric KTP crystals and insure its effective sputtering in combined hollow cathode cell, silver suspension applied by the dip-coating method was employed. Fluorine quantification was performed using relative sensitivity factors. The analysis of a reference material and scanning electron microscope-energy dispersive X-ray spectroscopy was used for validation. Fluorine limit of detection by pulsed direct current GD TOF MS was 0.01mass%. Real sample analysis showed that fluorine seems to be inhomogeneously distributed in the crystals. That is why depth profiling of F, K, O, and P was performed to evaluate the crystals' non-stoichiometry. The approaches designed allow for fluorine quantification in insoluble dielectric materials with minimal sample preparation and destructivity as well as performing depth profiling to assess crystal non-stoichiometry.

Polymerization-Driven Immobilization of dc-APGD Synthesized Gold Nanoparticles into a Quaternary Ammonium-Based Hydrogel Resulting in a Polymeric Nanocomposite with Heat-Transfer Applications.

A new method for the production of nanocomposites, composed of gold nanoparticles (AuNPs) and (vinylbenzyl)trimethylammonium chloride-co-N,N-methylene bisacrylamide (VBTAC-co-MBA) hydrogel, is described. Raw-AuNPs of defined optical and granulometric properties were synthesized using direct current atmospheric pressure glow discharge (dc-APGD) generated in contact with a solution of HAuCl4. Different approaches to the polymerization-driven synthesis of Au/VBTAC-co-MBA nanocomposites were tested. It was established that homogenous dispersion of AuNPs in this new nanomaterial with was achieved in the presence of NaOH in the reaction mixture. The new nanocomposite was found to have excellent heat-transfer properties.

Studing of Some Characteristics and parameters of Argon Glow discharge plasma Using Hollow Anode Diameter

Hollow anode argon glow discharge plasma has been investigated experimentally at different argon gas pressure from constant discharge current. A sufficient high voltage has been applied among the electrodes to obtain breakdown. Firstly, we studied the influence of hollow anode diameter on the breakdown voltage and Paschens law. The inner diameters of hollow anodes used in our work were (10, 15, 20, 25, 30, 35, and 40) mm. Secondly under the same conditions we extended our study to measure some plasma parameters in the negative glow region using direct current argon glow discharge. The temperature and density of electrons in the negative glow were measured using double probes. From the (Ip-Vp) characteristics of double probes, we obtained plasma parameters by using computer MATLAB program. The results showed that the measured Pashence's curve closes to the well-known theoretical Pashence's law. The breakdown voltage and its minimum value decreased with increasing the hollow anode diameter. The Paschen’s curve became wide and shifted to lower pressure with increasing the diameter. The reduction area of hollow anode caused dens and luminous intensity of plasma to occur in the negative glow region. Increasing the diameter resulted in decreasing the temperature and density of electron.

Rapid eradication of bacterial phytopathogens by atmospheric pressure glow discharge generated in contact with a flowing liquid cathode.

Diseases caused by phytopathogenic bacteria are responsible for significant economic losses, and these bacteria spread through diverse pathways including waterways and industrial wastes. It is therefore of high interest to develop potent methods for their eradication. Here, antibacterial properties of direct current atmospheric pressure glow discharge (dc-APGD) generated in contact with flowing bacterial suspensions were examined against five species of phytopathogens. Complete eradication of Clavibacter michiganensis subsp. sepedonicus, Dickeya solani, and Xanthomonas campestris pv. campestris from suspensions of OD600 ≈ 0.1 was observed, while there was at least 3.43 logarithmic reduction in population densities of Pectobacterium atrosepticum and Pectobacterium carotovorum subsp. carotovorum. Analysis of plasma-chemical parameters of the dc-APGD system revealed its high rotational temperatures of 2,300 ± 100 K and 4,200 ± 200 K, as measured from N2 and OH molecular bands, respectively, electron temperature of 6,050 ± 400 K, vibrational temperature of 4000 ± 300 K, and high electron number density of 1.1 × 1015 cm-1 . In addition, plasma treatment led to formation of numerous reactive species and states in the treated liquid, including reactive nitrogen and oxygen species such as NOx , NH, H2 O2 , O2 , O, and OH. Further examination revealed that bactericidal activity of dc-APGD was primarily due to presence of these reactive species as well as to UVA, UVB, and UVC irradiation generated by the dc-APGD source. Plasma treatment also resulted in an increase in temperature (from 24.2 to 40.2 °C) and pH (from 6.0 to 10.8) of bacterial suspensions, although these changes had minor effects on cell viability. All results suggest that the newly developed dc-APGD-based system can be successfully implemented as a simple, rapid, efficient, and cost-effective disinfection method for liquids originating from different industrial and agricultural settings.

Organization of the Post-Discharge Mode under Pulsed Ion-Plasma Treatment

The post-discharge processes in the electrical supply circuit of a technological system with a pulsed glow discharge used for the ion-plasma treatment of materials are analyzed, in which a direct current glow discharge is maintained in the pauses between the treatment pulses. The variants of connecting a pulse generator through a separating capacitor or a separating diode are considered and the formulas for determining the time parameters of the recovery process of the direct-current discharge after the end of the treatment pulses are obtained. Recommendations for organizing the electric mode for fast recovery of the direct-current discharge are given, as well as for preventing arc discharge at the negative electrode and extinguishing the arc if it appears.

Application of Silver Nanostructures Synthesized by Cold Atmospheric Pressure Plasma for Inactivation of Bacterial Phytopathogens from the Genera Dickeya and Pectobacterium.

Pectinolytic bacteria are responsible for significant economic losses by causing diseases on numerous plants. New methods are required to control and limit their spread. One possibility is the application of silver nanoparticles (AgNPs) that exhibit well-established antibacterial properties. Here, we synthesized AgNPs, stabilized by pectins (PEC) or sodium dodecyl sulphate (SDS), using a direct current atmospheric pressure glow discharge (dc-APGD) generated in an open-to-air and continuous-flow reaction-discharge system. Characterization of the PEC-AgNPs and SDS-AgNPs with UV/Vis absorption spectroscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction revealed the production of spherical, well dispersed, and face cubic centered crystalline AgNPs, with average sizes of 9.33 ± 3.37 nm and 28.3 ± 11.7 nm, respectively. Attenuated total reflection-Fourier transformation infrared spectroscopy supported the functionalization of the nanostructures by PEC and SDS. Antibacterial activity of the AgNPs was tested against Dickeya spp. and Pectobacterium spp. strains. Both PEC-AgNPs and SDS-AgNPs displayed bactericidal activity against all of the tested isolates, with minimum inhibitory concentrations of 5.5 mg∙L−1 and 0.75–3 mg∙L−1, respectively. The collected results suggest that the dc-APGD reaction-discharge system can be applied for the production of defined AgNPs with strong antibacterial properties, which may be further applied in plant disease management.

Relationship of Adhesive, Contact and Electret Properties of PTFE Modified by DC Discharge

The relationship between the contact, adhesive and electret properties of PTFE films modified by direct current glow discharge has been studied. The film samples of 40 μm thickness were placed at the anode and cathode and treated in the air as a working gas. The contact properties of polymer surface were characterized by the values of deionized water contact angle. The peel strength was determined using T-peel test for the Scotch®810/PTFE film contact. The electret potential was measured by the compensation technique using dynamic capacitor, and from the measured potential value the effective surface charge density was calculated. It has been found that there is an undoubted correlation between the change in the value of water contact angle, the peel strength of the DC discharge-treated film, and the magnitude of the effective surface charge.

Deuterium Removal from W-Doped Carbon Films by Thermo-Oxidation

If both carbon and tungsten were to be part of the plasma-facing armor in a future fusion reactor, it is inevitable that carbon co-deposits containing tungsten impurities will form. This work examines the effectiveness of thermo-oxidation in removing hydrogen from W-containing carbon co-deposits. Amorphous deuterated hydrocarbon (a-C:D) films were created with a CD4/Ar direct-current glow discharge and doped with W sputtered from a W mesh in front of the specimen. The W concentration in the specimens ranged from 0 to 35 at. % W/(W + C). The films were oxidized at 350°C, in 2 Torr pure O2 for time increments totaling 8 h. The D content of the films was measured before and at various stages of the oxidation exposure using laser thermal desorption spectroscopy. Essentially all deuterium was removed from films containing very little or no W doping [<0.1% W/(W + C)]. For films with more W [few percent W/(W + C)], oxidation was less effective at removing D. For two specimens with 2.4% and 35% W/(W + C), oxidation was completely ineffective at removing D.

Research progress of metal catalysts enhanced synthesized by cold plasma

Cold plasma is a kind of non-thermal plasma, and characterized by high electron temperature (1-10 eV) and low gas temperature, which can be close to room temperature. It has been proved to be a fast, facile and environmentally friendly new method for synthesizing supported metal catalysts. Enhanced synthesis of metal catalysts by cold plasma consists of complex physical and chemical reactions. On the one hand, the active environment provided by cold plasma, can not only speed up the chemical reactions, shorten the reaction time from a few hours to several minutes, but also realize the kinetically or thermodynamically infeasible chemical reactions to achieve unconventional preparation. On the other hand, the phase contact behavior on a mesoscopic scale is influenced during cold plasma enhanced preparation, thereby the metal catalysts with structure different from that synthesized by traditional method. This review summarizes the reactor structure, physical and chemical mechanism for synthesizing metal catalysts by cold plasma, as well as the structure characteristics of the obtained metal catalysts. According to the working pressure, cold plasma can be categorized into low-pressure (LP) cold plasma and atmospheric-pressure (AP) cold plasma. The LP cold plasma is often generated by radio frequency glow discharge or direct current glow discharge, while the AP cold plasma is generally generated by dielectric barrier discharge and AP cold plasma jet. Energetic electrons are deemed to be the reducing agents for LP cold plasma. However, due to the frequent collisions among the electrons and gas molecules at atmospheric pressure, the electron energy in AP cold plasma is not high enough to reduce the metal ions directly. Therefore, hydrogen-containing gases are often adopted to generate active hydrogen species to reduce the metal ions. The process of synthesizing the metal catalysts by using the cold plasma is a fast, low-temperature process, and in the preparation process there exists a strong Coulomb repulsion. Therefore, metal catalysts with small size and high dispersion of metal nanoparticles, strong metal-support interaction, as well as specific metal structures (alloying degree and crystallinity) and modified supports can be obtained. Correspondingly, metal catalysts with high catalytic activity and stability can be synthesized. In addition, the challenges of preparing the cold plasma are discussed, and the future development is also prospected.

Direct-current glow discharge in neon at cooling

The paper presents the results of the experimental measurement and the simulation of electric characteristics of dc glow discharge with the hollow cathode in neon, carried out during cooling of the discharge to the temperature of liquid nitrogen. The experiments were performed at pressure P = 18–187 Pa and discharge currents I = 0.01–3.5 mA. The behavior of the border of transition to the normal glow discharge during cooling was studied. Cooling in a subnormal discharge mode at constant current led to a change in the discharge regime. Upon cooling, the boundary of the transition to the normal glow discharge shifted to lower current, the electric field in the positive column of discharge and at the boundary of the normal glow discharge increased, but the reduced electric field decreased throughout the entire range of pressure and the discharge current.

Morphological and Structural Analysis of Polyaniline and Poly(o-anisidine) Layers Generated in a DC Glow Discharge Plasma by Using an Oblique Angle Electrode Deposition Configuration.

This work is focused on the structural and morphological investigations of polyaniline and poly(o-anisidine) polymers generated in a direct current glow discharge plasma, in the vapors of the monomers, without a buffer gas, using an oblique angle-positioned substrate configuration. By atomic force microscopy and scanning electron microscopy we identified the formation of worm-like interlinked structures on the surface of the polyaniline layers, the layers being compact in the bulk. The poly(o-anisidine) layers are flat with no kind of structures on their surfaces. By Fourier transform infrared spectroscopy we identified the main IR bands characteristic of polyaniline and poly(o-anisidine), confirming that the polyaniline chemical structure is in the emeraldine form. The IR band from 1070 cm−1 was attributed to the emeraldine salt form of polyaniline as an indication of its doping with H+. The appearance of the IR band at 1155 cm−1 also indicates the conducting protonated of polyaniline. The X-ray diffraction revealed the formation of crystalline domains embedded in an amorphous matrix within the polyaniline layers. The interchain separation length of 3.59 Å is also an indicator of the conductive character of the polymers. The X-ray diffraction pattern of poly(o-anisidine) highlights the semi-crystalline nature of the layers. The electrical conductivities of polyaniline and poly(o-anisidine) layers and their dependence with temperature are also investigated.

Probe Diagnostics of Plasma Parameters in a Large-Volume Glow Discharge With Coaxial Gridded Hollow Electrodes

Results of the experimental investigation of glow discharge plasma created in a large-volume discharge chamber are presented. The discharge configuration consists of two coaxial gridded electrodes placed in a metallic vacuum chamber. The inner electrode and the chamber housing were grounded while time-varying power up to 2 kV with frequency 20 kHz was applied on the outer electrode. The discharge was created in air at a pressure of 50 Pa and in argon at pressures of 50 and 100 Pa. Measurements of plasma parameters were carried out with a single-probe technique using the commercial Impedans Langmuir Probe system. In order to perform time-resolved measurements, an additional synchronizing device was developed. Variation in time of such plasma parameters as electron temperature, charged particle densities, and electron energy distribution function was obtained during the experiments. It is shown that both electron temperature and density change slightly in time. Obtained results indicate that the plasma created in the considered chamber configuration is similar to the negative glow region of a direct-current glow discharge.

Determination of nitrite in water samples using atmospheric pressure glow discharge microplasma emission and chemical vapor generation of NO species

In this work, a low-power (<25 W), portable direct current (dc) atmospheric pressure glow discharge microplasma (4 mm × 10 mm) molecular emission spectrometer (APGD-MES) is developed for the determination of nitrite by using chemical vapor generation. Nitrite is on-line reduced to volatile nitric oxide (NO) by 1.5% (m/v) ascorbic acid and 1.0 mol L−1 hydrochloric acid. Then, the generated NO was separated and transferred into the APGD microplasma by an argon stream (100 mL min−1) for its excitation, and NO emission was measured by a microspectrometer. The effects of operational parameters of the APGD microplasma source and vapor generation of nitrite were investigated and the analytical figures of merit for nitrite detection was evaluated. The limit of detection of the proposed method was calculated to be 0.26 μg mL−1 of nitrite by measuring NO emission at 237.0 nm. The calibration curve is linear for the nitrite concentration in the range of 2.0–100.0 μg mL−1 and good precision (2.3%, RSD) is readily achieved for 5.0 μg mL−1 nitrite. The accuracy of this procedure was demonstrated by nitrite detection in a certified reference material. Analyte recoveries test were also performed to verify the accuracy of the method for nitrite determination in a series of environmental water samples. It was found that the concentration of nitrite of these samples were all below the LOD, and the obtained recoveries were in the range of 95–117%. The proposed APGD–MES method provides an alternative useful technique for screening potential nitrite pollution of potable waters.