• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2020-01-24
Nomin Lim, Alexander Efremov, Hyun-Gyu Hwang, Sahn Nahm, Kwang-Ho Kwon

Abstract The investigation of etching kinetics and surface conditions for KNbxOy thin films in CF4 + Ar and Cl2 + Ar inductively coupled plasmas was carried out. The variable processing parameters were Ar content in a feed gas (0–75% Ar), gas pressure (4–10 mTorr) and input power (400–700 W) at constant bias power of 100 W. The combination of plasma diagnostics by Langmuir probes and plasma modeling provided the data on internal plasma parameters, gas-phase chemistry and steady-state densities of plasma active species. The compositional changes of the etched surfaces were investigated using X-ray photoelectron spectroscopy (XPS). It was found that the fluorine-based etching chemistry provides the much lower halogen atom flux together with the much higher KNbxOy etching rate under the condition of quite close ion momentum fluxes in both gas systems. The correlations between measured etching rates and model-predicted fluxes of active species suggested the neutral-flux-limited etching regime with the much lower effective reaction probability between KNbxOy and Cl atoms. The last effect may be related to lower volatility of NbClx compared with NbFx (that is confirmed by XPS data) as well as to the higher energy threshold for KNbxOy + Cl reaction.

更新日期：2020-01-24
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2020-01-22
Milos Momcilovic, Jelena Petrovic, Jovan Ciganovic, Ivana Cvijovic-Alagic, Filip Koldzic, Sanja Zivkovic

Abstract The application of an alternative laser-induced breakdown spectroscopy (LIBS) method based on transversely excited atmospheric (TEA) CO2 laser was investigated for the first time for estimating the hardness of metallic materials. The human eye-safe (TEA) CO2 laser, operating at 10.6 µm, was used for plasma generation. The LIBS spectra were recorded by employing a cost-effective CCD camera for the time-integrated and spatial resolved measurements. The cast iron and aluminum alloys samples with different hardness have been tested. The ratio between the magnesium ionic and neutral lines in LIBS spectra was applied for estimating the material hardness. In addition, the hardness of all samples included in this study was determined using the conventional method for material hardness determination, i.e. Vickers hardness test. The linear dependence of magnesium lines intensity ratio on the sample’s hardness was obtained for both kinds of materials. Profilometric measurements were used to verify that the newly-introduced method is almost nondestructive for the investigated metals. The results obtained in the present work confirmed the potential of using this original LIBS system not only for the fast elemental analysis but also for the direct estimation of the hardness of metals and alloys.

更新日期：2020-01-23
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2020-01-17
Xiajin Rao, Ju Tang, Fuping Zeng, Dajian Li, Xiaofei Xia, Yi Su, Yufeng Lu

Trace O2 significantly affects the diagnosis accuracy of decomposed components analysis method for spark discharge due to its direct participation in SF6 decomposition process. Therefore, spark discharge decomposition experiments were conducted under different proportions of SF6/O2 mixtures. The influence rules and mechanisms of φ(O2) on the content and characteristic ratio of SF6 spark discharge decomposed components were analysed quantitatively. Meanwhile, the materials on the electrode surface after spark discharge were conducted XPS analysis. Results show: no matter how much O2 adds, there exist SOF2, SOF4, SO2, and SO2F2 in the process of SF6 decomposition. The increase of φ(O2) plays a positive role in the production of SOF4 and SO2F2, but has the adverse effect on SO2. The content of SOF2 barely changes with φ(O2) increasing. Characteristic ratio φ(SO2F2 + SOF4)/φ(SOF2) gradually grows with φ(O2), but change little with discharge time extended. The X-ray photoelectron spectra show that the solid materials on the surface of the plate electrode after discharge contain Al2O3 and AlF3, and S mainly exists as metal sulfides.

更新日期：2020-01-17
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2020-01-11
S. Yu. Shadrin, P. N. Belkin, I. V. Tambovskiy, S. A. Kusmanov

This study considers some aspects of electrolytic plasma in the process of anodic carburising of steel, including the nature of the glow in a vapour gaseous envelope, its thickness under various hydrodynamic conditions; it also examines the formation patterns of a hardened layer after carburising along with quenching in the same electrolyte. The glow in a vapour gaseous envelope was examined with a spectrometer; its profile and thickness were determined by solving energy and mass balance equations in a pre-anode area. The structure of the carburised layer and hardness distribution were explored with an optical microscope and a microhardness tester. Carbon concentration in the carburised layer was determined by means of optical emission spectroscopy. The investigation has revealed that the glow in a vapour gaseous envelope under carburising is a continuous emission from heated bodies—vapour gaseous phase and the sample without any electric discharges. It has been theoretically derived, that in laminar approximation the layer has maximal thickness under certain hydrodynamic conditions. This conclusion has been confirmed by homogeneous distribution of current density throughout the surface of the sample during its carburising under condition of force hydrodynamics, i.e. the sample being flowed round with cooled electrolyte. Aerated stirring in electrolyte does not provide homogeneous current density distribution, which falls in vertical direction. Anodic carburising of steel in a glycerol electrolyte followed by quenching results in the formation of a martensitic layer up to 200 μm in thickness, within 5-min treatment, with maximal microhardness 1000 HV.

更新日期：2020-01-13
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2020-01-11
Masaya Shigeta

Abstract This article presents descriptions of theoretical models and numerical methods for simulating turbulent thermal plasma flow with nanopowder growth. Turbulence models must express turbulent and laminar states because both states co-exist with thermal plasmas showing large density variation and transport properties. Time-dependent 3D simulations are conducted based on Large Eddy Simulation using a dynamic Smagorinsky model. Results show significant difference depending on temporal and spatial discretization schemes and velocity–pressure coupling algorithms. Simulation results demonstrate that advanced numerical methods with high-order accuracy should be used for long and robust computations capturing steep gradients of nanopowder concentration and plasma temperature and 3D dynamic motions of multiscale vortices, which are turbulent features of thermal plasma flows with low Mach numbers. A thermal plasma jet generates a double-layer structure of inner high-temperature thick vortex rings and outer low-temperature thin vortex rings near the nozzle exit. Flowing downstream, these vortices interact, deform, and break up. Consequently, plasma transits to a complex thermal flow. The widely spreading distribution of multiscale vortices agrees with experimental observations, which are not simulated using conventional methods. Nanopowder is generated from material vapour by nucleation and condensation at interfacial regions between plasma and cold gas. Those regions include numerous vortices. Therefore, the vortices convey the nanopowder, producing a complex distribution of nanopowder. Simultaneously, the nanopowder diffuses and increases in size, decreasing in number by interparticle coagulation. Cross-correlation analysis suggests that a nanopowder distribution distant from a plasma jet can be controlled through temperature fluctuation control at the upstream plasma fringe.

更新日期：2020-01-13
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2020-01-10
T. Silva, M. Grofulović, L. Terraz, C. D. Pintassilgo, V. Guerra

The time-dependent evolution of the energy transfer into gas heating in the afterglow of pulsed CO2 and CO2–N2 glow discharges produced in cylindrical tubes at low pressures (1–5 Torr) is theoretically investigated, by developing a self-consistent model that couples the time-dependent gas thermal balance equation with the vibrational kinetics. The modelling predictions are in good agreement with recently published experimental data on gas temperature, obtained via time-resolved in situ Fourier transform infrared spectroscopy. The cooling of the gas in the afterglow is found to be strongly dependent on the thermal conductivity and the wall temperature. It is verified that wall and volume deactivation of CO2 vibrationally excited species influences the gas heating along the afterglow, in different proportions depending on the pressure of the gas. The time-resolved contributions of each of these cooling and heating mechanisms are discussed in detail. The new results bring an additional validation of a set of mechanisms and rate coefficients for vibrationally-energy transfers previously proposed.

更新日期：2020-01-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2020-01-06
Alireza Iranbakhsh, Zahra Oraghi Ardebili, Hedieh Molaei, Narges Oraghi Ardebili, Maryam Amini

Abstract Plasma technology as an eco-friendly efficient strategy has gained much attention in various industries, especially in food, medicine, and agriculture. This study aimed to explore the cold plasma-mediated changes in growth, anatomy, expression of a WRKY1 transcription factor, and transcription rates of four key genes involved in the biosynthesis of cannabinoids (pharmaceutically valuable secondary metabolites) in hemp (Cannabis sativa L.). The seeds were treated with cold plasma (dielectric barrier discharge; 0.84 W cm−2; exposure times of 0, 40, and 80 s). The plasma treatment of 40 s increased biomass in both shoot and roots by an average of 57%, whereas the treatment at 80 s delayed growth and reduced it by 48%. Seed priming with plasma up-regulated the WRKY1 transcription factor (mean = 11.55 folds). Besides, the plasma treatments induced the expression of olivetolic acid cyclase by 42 folds. Furthermore, the plasma-primed seedlings also exhibited higher expression rates of olivetol synthase by 19 folds. With a similar trend, exposure to plasma stimulated transcription of cannabidiolic acid synthase by 12.4 folds. Up-regulations in Δ9-tetrahydrocannabinolic acid synthase also occurred following seed priming with plasma by 25.6 folds. Seed priming with plasma exhibits high potency to up-regulate expressions of genes involved in the productions of secondary metabolites, like cannabinoids. These results imply that the plasma reception and signal transduction can alter expressions of genes at the transcriptional level through which plasma priming may improve plant protection and secondary metabolism.

更新日期：2020-01-06
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2020-01-06
Masoud Shekargoftar, Tomáš Homola

This contribution presents a new approach to rapid and low-temperature plasma-chemical crystallization of perovskite films. Chlorine-incorporated perovskite (MAPbI3–xClx) films were exposed to diffuse atmospheric hydrogen (H2) plasma immediately after their deposition. Several types of surface characterization techniques were used to investigate the effect of the H2 plasma on the surface of the perovskite films. Since the H2 plasma was generated at a low temperature (≤ 70 °C), there was no considerable damage to the plasma-treated perovskite films—although the morphology and chemistry changed significantly. H2 plasma had a range of effects on the surface of the perovskite films: (1) changes in the chemical composition of the perovskite surface without removal of lead; (2) modification of the optoelectrical band structure; (3) crystallization of the perovskite film; and (4) the grain of the surface became highly ordered. The results presented demonstrate that H2 plasma is a rapid and low-cost method for the manufacture of crystallized perovskite films. The method may be considered a significant step towards low-temperature, annealing-free crystallization of perovskite films.

更新日期：2020-01-06
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-12-16
Xi Rao, Ali Abou Hassan, Cédric Guyon, Mengxue Zhang, Stephanie Ognier, Michaël Tatoulian

The assembly of nano- and micro-scale building blocks on surface has been the focus of intense interest in materials science for years. In this work, (3-aminopropyl)triethoxysilane (APTES) carrying one primary amino group was deposited on various substrate surfaces using the plasma polymerization method. The key plasma parameters i.e. pressure and power were varied to obtained the highest density of primary amino groups. The influence of such parameters on the characteristics of deposited layers (e.g. chemical structure, adhesion strength, growth rate, etc.) was systemically investigated using various characterization methods such as XPS, FTIR, ellipsometry and so on. Meanwhile, three types of particles (AuNPs, zeolites and gold@zeolites) with sizes from nano- to submicro-range were synthesized and further used as model building blocks. Subsequently, the prepared particles were deposited onto cyclic olefin copolymer (COC) substrate surfaces, which were pre-functionalized by deposition of the plasma polymer layer using the parameters of pressure = 1.0 mbar and power = 30 W. The results confirmed the formation of membrane structures consisting of highly packed particles on the COC surface, and such immobilized structures showed high stability against flowing water, evidencing the good immobilization ability of deposited APTES layers with amino groups.

更新日期：2019-12-17
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-12-12
Duy Khoe Dinh, Dae Hoon Lee, Muzammil Iqbal, Hongjae Kang, Seongil Choi, Chan Mi Jung, Young-Hoon Song, Sungkwon Jo, Kwan-Tae Kim

The on-board reforming technique for de-NOx is attracting increasing interest because of the fast start-up and size of the device. However, due to the limited amount of energy available from the battery, a full understanding of the characteristics of the plasma reforming reaction is important to optimise this technology to achieve hydrogen production with minimal power consumption. This paper reports the relative role of the thermal effect of plasma in octane oxidation induced by rotating arc plasma. The thermal effect or gas temperature increased with increased electric power; the conversion of the electric energy to heat was estimated to be higher than 40%. The increased thermal effect was the main consequence of further increasing the plasma power, which controlled the syngas yield and was the main determinant of the energy efficiency of the reaction. In comparison, although the O2/C ratio was the main parameter determining the thermal environment in the reactor, it had only a small influence on the energy efficiency of the reaction. The optimal O2/C ratio for maximum energy efficiency depends on the electric power (e.g. the optimal O2/C was 0.8 at 80 W and 0.5 at 280 W). The results provide guidance for determining the optimal conditions for plasma-driven reforming processes.

更新日期：2019-12-13
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-12-04
Shaham Shafaei, Lanti Yang, Marcel Rudolph, Peter Awakowicz

For many applications of polycarbonate (PC) from packaging to micro-electronics improved barrier properties are necessary. In this contribution, silica thin films were deposited from hexamethyldisiloxane/oxygen (HMDSO/O2) on polycarbonate substrate in three step plasma processes by combining a microwave (MW) surface wave discharge of 2.45 GHz with an optional radio-frequency (RF) bias of 13.56 MHz. The influence of interlayer thickness, HMDSO flow and oxygen to HMDSO ratio on barrier performance for three step-coating processes was investigated. The morphology and surface properties of the coated surface of PC were studied by atomic force microscopy (AFM). The surface topography showed a silica particles distribution on the PC substrate with relatively smooth surface roughness. AFM-QNM provides more insight into the surface morphology and stiffness. The results identify the coating structure for PC film coated with and without bias. High barrier improvement of the deposited films on PC substrates was obtained after plasma silicon coating process with a barrier improvement factor up to 337. It was found that the deposition process is optimal for food packaging applications by using combined MW-RF PECVD technology.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-12-02
Yuwei Fu, Xiaohua Wang, Xinxin Wang, Aijun Yang, Mingzhe Rong

This paper thoroughly investigates the decomposition pathways of SF6 in the presence of organic insulator vapors by means of high level quantum chemistry calculations with density functional theory. Optimized molecular structures and vibrational frequencies of intermediate products (IM) and transition states (TS) are first reported in this work. Potential energy surface is then investigated with a more sophisticated CCSD method including zero-point energy corrections and the rate constants are calculated with transition state theory. The overall chemical decomposition pathways of SF6 + PTFE vapor are obtained which are consisted of 17 reactions with TS1–TS17. By analyzing the rate constants, reactions SF + C → S = CF → TS2 → F + SC, SF3 + C → TS7 → SF2CF → TS8 → SFCF2, SF4 + C → IM3 → TS11 → IM4 → SF3 + CF and SF5 + C → IM5 → TS15 → SF4 + CF are selected as main reactions in SF6 decomposition. The results are prerequisite to study the non-equilibrium compositions of SF6 + organic insulator vapor mixtures.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-11-30
Julian Held, Achim von Keudell

High power impulse magnetron sputtering (HiPIMS) plasmas produce a very energetic growth flux for the synthesis of thin films with superior properties. High power densities in the range of a few $$\hbox {kW}/\hbox {cm}^2$$ are applied to a metal target electrode in short pulses with a length of 10–$$400\,\upmu \hbox {s}$$ and duty cycles of a few percent or less in an argon plasma gas. Fast camera and probe measurements revealed the formation of very characteristic plasma patterns that become visible as rotating localized ionization zones, so called spokes. The appearance of these spokes at high plasma powers is believed to be essential for the good performance of HiPIMS plasmas. The rotation direction of the spokes is in $$\vec {E} \times \vec {B}$$ direction at high plasma powers, but in retrograde $$\vec {E} \times \vec {B}$$ direction at low plasma powers. This characteristic behavior is explained by applying a simple drift wave model from literature and comparing the dispersion relation of those waves with measured data. The pronounced rotation reversal is explained by either a change in the governing density gradient in the plasma or by the change in the direction of the streaming ions during the transition from an argon dominated regime at low powers to a metal dominated regime at high powers.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-11-28
R. Mehrabifard, H. Mehdian, K. Hajisharifi, E. Amini

In the last decades, there have been numerous reports about the separate interactions of a magnetic field and cold atmospheric plasma (CAP) with the biological systems. We have investigated the combined effect of CAP with the static magnetic field (SMF) as an effective method for cancer cells treatment. MDA-MB-231 breast cancer cells were cultured and treated with CAP with different input power and exposure times in the presence and absence of the SMF. Vitamin C was also used in medium, and cell viability was investigated in the presence and absence of this antioxidant compound. The MTT assay was employed to measure cell survival, and a T-test or one-way ANOVA was used to assess the significance level of quantitative data. In order to determine the migration rate of cancer cells, wound healing assay was carried out. Results show that the presence of the SMF and vitamin C as well as increasing the input power significantly decrease the survival and migration rate of the cells. The results of the present investigation will greatly contribute to improve the CAP efficiency in cancer therapy by using the SMF and vitamin C as a complement to conventional CAP therapies.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-11-27
Marco Krewing, Britta Schubert, Julia Elisabeth Bandow

Effects of atmospheric pressure plasmas on proteins are studied to assess the quality of plasma decontamination and to gain insights into plasma-triggered molecular events underlying observations made in plasma medicine on the cellular, organ, and systemic level. Atmospheric pressure plasma treatment has been reported to cause protein degradation. Degradation products, however, have not been characterized. Treating different model proteins in aqueous solution with a DBD plasma, we confirmed with different methods (Bradford assay, application of Lambert–Beer’s law on absorption measurements at 280 nm, ninhydrin assay, size exclusion chromatography, SDS-PAGE) that protein degradation takes place. Peptides of different sizes were detected by size exclusion chromatography. The ninhydrin assay indicated that peptide bonds are cleaved. In the presence of hydroxyl radical scavenger d-mannitol, the concentration of amino termini formed during the initial 10 min of plasma treatment was reduced by 96%, while at longer treatment times mannitol did no longer prevent the formation of amino termini, indicating that hydroxyl radicals play an important role in the initial cleaving of peptide bonds in the protein, but other mechanisms are at play in cleaving the peptide bonds in the resulting peptides. The generation of peptides has implications for plasma decontamination and plasma medicine. It is critical to verify that plasma decontamination processes do not result in protein fragments with undesired properties. In plasma medicine, plasma-generated protein fragments may act as molecular triggers in treated cells, tissues, or patients, e.g., regulating signaling cascades in a protease-like fashion.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-11-23
V. V. Chernov, A. M. Gorbachev

The paper presents the results of theoretical analysis and numerical modeling of physical processes occurring in microwave discharge supported in two intersecting wave beams in H2–CH4 gas mixture. The transformation rules are defined that allow transferring the results of self-consistent solution of system of equations describing the state of microwave discharge for selected parameters (gas pressure, microwave radiation power and frequency, reactor and wave beams geometry) to other parameters. The following parameters ranges are considered: the medium gas pressure range (100–600 Torr), the radiation power from 1 to 30 kW and radiation frequencies from 10 to 60 GHz. The results of numerical simulation confirm the proposed approach and allow comparing the energy efficiency of the systems in terms of their practical application. The optimal parameters for diamond deposition in the considered plasma-chemical reactor in given range are discussed. The limits of applicability of the microwave discharge model and the proposed transformation rules are discussed.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-11-21
Maria Guć, Edward Reszke, Michał Cegłowski, Grzegorz Schroeder

The application of an independent source of ions working with mass spectrometers and permitting generation of ions at atmospheric pressure from samples of different types is a very attractive solution allowing construction of small portable mass spectrometers. In our study two types of plasma source were used as external sources of ions to analyze the low molecular weight organic compounds by mass spectrometry. Small organic compounds and analytes on solid materials were analyzed. The application of plasma torches for analysis of organic compounds was tested by the methods of mass spectra (MS) and ion fragmentation analysis (MS2).

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-11-18
N. A. Sirotkin, A. V. Khlyustova, V. A. Titov, A. S. Krayev, D. I. Nikitin, O. A. Dmitrieva, A. V. Agafonov

An underwater impulse discharge was used for synthesis tungsten trioxide nanoparticles. The chemical composition and morphology of obtained particles were studied by using X-ray diffraction spectroscopy and electron microscopy. The dynamic light scattering was used to measure the average particle diameter and zeta-potential. It was found that a monoclinic modification of tungsten trioxide was formed with an average particle diameter of about 60 nm. The photocatalytic performance of WO3 was estimated through the degradation of Rhodamine B under dark and UV irradiation conditions. The powder of WO3 exhibited great photocatalytic activity for photodegradation of Rhodamine B of 100% under UV irradiation for 50 min.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-11-13
Avishek Kumar, Ahmed Al-Jumaili, Karthika Prasad, Kateryna Bazaka, Peter Mulvey, Jeffrey Warner, Mohan V. Jacob

Antifouling/antibacterial coating derived from a sustainable natural resource for biomedical devices have shown promising outcomes, especially in the prevention of bacterial growth. Herein, pulse-plasma chemical vapour deposition is used to fabricate antimicrobial coatings from Terpinen-4-ol, a tea tree oil-based precursor. In this manuscript, during RF plasma polymerisation, pulsed plasma is used to retain the pristine monomer structure in the developed stable coating and thereby enhance its antibacterial activity. The developed films have tunable physical and chemical properties. Diverse film surface properties were obtained by varying the plasma deposition parameters, mainly the deposition mode (pulse and continuous wave) and duty cycle. The role of film wettability on degree of bacterial attachment has been elucidated. Overall, the number of viable bacteria on all the deposited coatings (25–30%) were reduced to half with respect to the control (56%).

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-11-09
O. Živný, M. Hlína, A. Serov, A. Halinouski, A. Mašláni

Perfluorinated compounds (PFCs) increasingly utilized in electronic manufacturing represent a potent source of global warming effect. Because of extremely high stability of PFCs only very high temperature is effective for their destruction. Thermal plasma offers higher destruction and removal efficiency as compared to conventional methods allowing to reach sufficiently high temperature as well as suitable conditions, including high enthalpy and reactive environment for destruction even of the most persistent PFCs. The aim pursued by this work is to apply water and gas stabilized DC-plasma torch for generating steam plasma for efficient abatement of the most persistent PFC, i.e., CF4, and to observe a dependence of destruction and removal efficiency on operational conditions, including concentration of CF4, input arc power of the plasma torch and an influence of an additional gas. The experiments were carried out at 20 kW and 40 kW of torch power in the concentration range 1–20% of CF4 in mixture with both nitrogen and argon and total feed rate 50 L/min in plasma chemical reactor. The mixture with argon exhibit considerably higher destruction efficiency than that with nitrogen. The highest destruction efficiency was attained in the mixture CF4/argon at 40 kW of torch power. Among other gases (CO2, O2, H2) added to CF4 the only hydrogen exhibited a positive effect to destruction performance. It was found an optimal feed rate of additional hydrogen corresponding to the maximum of destruction efficiency.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-11-02
Juan Pablo Trelles

Thermal plasmas are utilized in diverse applications that require high power densities or throughputs, such as metal cutting, welding, spraying, metallurgy, and materials synthesis. Thermal plasma applications involve interactions between the highly energetic plasma and working gas streams, confining devices, or processing materials. Whereas thermal plasma implies a state of equilibrium (i.e. Local Thermodynamic Equilibrium, LTE), due to the above interactions, thermal plasma flows depict nonequilibrium phenomena of two types: kinetic and dissipative. Kinetic nonequilibrium manifests microscopically and is caused by localized imbalances between particles and fields interactions. Its occurrence is evidenced, for example, as deviations from thermal equilibrium between heavy-species and electrons or from mass-action laws. In contrast, dissipative nonequilibrium reveals macroscopically and is produced by external driving forces that incite distributed responses, such as the growth of instabilities, the occurrence of self-organization, or the establishment of turbulence. Although kinetic nonequilibrium has been increasingly incorporated in thermal plasma flow models (e.g. finite-rate chemistry, two-temperature models), it is the great advances in numerical computing that is enabling the exploration of dissipative nonequilibrium (e.g. pattern formation, small-scale turbulent features). Both types of nonequilibrium are reviewed, including their estimation and incidence, within the context of computational models and their relevance to thermal plasma sources and processes.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-11-02
D. Astanei, F. Faubert, S. Pellerin, B. Hnatiuc, M. Wartel

The ignition sparks provided by the conventional spark plug (CSP) do not always ensure a fast and complete combustion of the hydrocarbon–air mixture. For this reason, we offer a new type of spark plug with two simultaneous discharges generated by a pulsed high voltage–power supply. First, we present results concerning geometrical and electrical characteristics of plasmas produced in air and in engine combustion chamber. A more important volume of plasma is highlighted. The larger surface of interaction of plasma with the air-to-fuel mixture promotes the initiation of a greater number of chemical reactions thus increases the rate of propagation of the combustion. In addition, for long pulse durations the energy delivered by the double spark plug (DSP) to the discharge is 20% higher, as compared to a CSP. The current rise rate is more important for the DSP, which allows better ionization of the mixture. Afterwards, we present a study of two four-strokes engines ignited by this DSP, one powered with gasoline and the second one with propane. The pressure into the cylinder, measured as a function of the crankshaft angle, allowed to compute the IMEP, COVIMEP, and PPP, for both tested engines. In the case of the gasoline engine, when the ignition and flame development conditions are difficult—a high ignition angle was considered—the DSP can offer an almost 3.5 times better operation stability (considering the coefficient of variation of the indicated mean effective pressure as main indicator) and a faster development of the combustion flame (defined by the means of the pressure peak position). A study was also performed as a function of the equivalence ratio for the propane-powered engine, which confirmed the results regarding the DSP performances obtained with the first engine. In addition, this study highlighted that for very lean mixtures, the DSP can provide a better stability in operation (COVIMEP, COVPPP) is assured even for equivalence ratios in the range of 0.65, where the use of CSPs involves misfires and very high engine vibrations.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-07-31
Alexey V. Pelevkin, Alexander S. Sharipov

Multireference quantum chemical research with the aid of complete active space self-consistent field approach was performed to study the elementary reactions of $${{\text {CH}}_4}$$ with $${\text {O}}_2$$ in $${a^1\varDelta _g}$$, $${b^1\varSigma _g^+}$$, $${c^1\varSigma _u^-}$$, and $${A^{\prime 3} \varDelta _u}$$ electronically excited states highly relevant for plasma-assisted combustion and for plasma-chemical fuel reforming. The thermodynamically and kinetically favorable reaction pathways and likely intersystem crossings for the first step of the methane oxidation have been found out. The key energy values were refined based upon the extended multiconfiguration quasi-degenerate 2nd-order perturbation theory. It has been exhibited that the reaction of $${{\text {O}}_2(a^1\varDelta _g)}$$ and $${{\text {O}}_2(A^{\prime 3} \varDelta _u)}$$ with $${{\text {CH}}_4}$$ proceeds through the abstraction of hydrogen with fairly low energy barriers that led to the formation of the $$\hbox {HO}_2$$ molecule in $${^2A^{\prime \prime }}$$ and $${^2A^{\prime }}$$ electronic states, respectively. These results were compared with the findings of previous theoretical investigations. The oxygen molecule in singlet sigma b state was evinced to be nonreactive with regard to the methane. However, for $${c^1\varSigma _u^-}$$ state, the reactive interaction was nevertheless found possible due to the significant probability of the nonadiabatic transitions. Appropriate thermal rate constants for revealed channels have been calculated employing variational transition-state theory and capture approximation. Corresponding three-parameter Arrhenius expressions for the broad temperature range ($$T=300$$–3000 K) were reported.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-07-18
Linlin Zhong, Jiayu Wang, Jie Xu, Xiaohua Wang, Mingzhe Rong

C4F7N is one of the most promising candidate to replace SF6 as arc quenching medium. Some buffer gases (N2 and CO2) are usually mixed with C4F7N to reduce the operating temperature. In order to provide priori knowledge of the arc quenching performance for C4F7N mixtures, the plasma properties including equilibrium compositions, thermodynamic properties, transport coefficients, and net emission coefficients of C4F7N–N2 and C4F7N–CO2 arc plasmas are calculated and the effects of buffer gases are discussed. Taking these properties as input, a 1D arc decaying model is constructed to describe arc decaying characteristics. According to the evolution of axial temperature and arc conductance over time, the arc decaying process is divided into three stages, i.e. the thermal recovery stage, the pre-dielectric recovery stage, and the post-dielectric recovery stage. We focus on the first two stages and describe them by the thermal recovery time (or rate) and the pre-dielectric recovery time (or rate) respectively. According to the results of 1D arc decaying modelling, the descending order of the thermal recovery ability for the gases studied in this work is: SF6 > C4F7N > 75%C4F7N–25%N2 > 75%C4F7N–25%CO2 > 50%C4F7N–50%N2 > 25%C4F7N–75%N2 > 50%C4F7N–50%CO2 > CO2 > 25%C4F7N–75%CO2 > N2; and the pre-dielectric recovery ability is: N2 > SF6 > CO2 > 25%C4F7N–75%CO2 > 25%C4F7N–75%N2 > 50%C4F7N–50%CO2 > 75%C4F7N–25%CO2 > 50%C4F7N–50%N2 > 75%C4F7N–25%N2 > C4F7N.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-07-19
Hua Song, Yue Peng, Shuai Liu, Shupei Bai, Xiaowei Hong, Junhua Li

Investigating the roles of plasma active species in plasma chemical reaction process can improve understanding of the mechanism of volatile organic compounds degradation by plasma. In this work, different experimental processes were designed to distinguish the contributions of various active species of plasma in the decomposition of toluene by a dielectric barrier discharge plasma with or without the CoMnOx/TiO2 catalyst. The removal efficiency of toluene, selectivity of COx (CO2 and CO), and byproducts were detected. The results showed that within the post-plasma zone, toluene could be oxidized to organic intermediates but not completely oxidized to COx by the long-lived active species of O2 plasma; furthermore, O3 alone could not degrade toluene in the gas phase, and the active species generated by N2 discharge could not degrade toluene. In the plasma area, toluene could be decomposed by both the short- and long-lived active species, and could be oxidized to COx by the short-lived active species. The introduction of CoMnOx/TiO2 catalyst, whether within or after the plasma zone, could efficiently decompose O3 and greatly improve the utilization of the active species, thus increasing the removal efficiency of toluene and the selectivity of COx.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-08-09
Hantian Zhang, Yi Wu, Hao Sun, Fei Yang, Mingzhe Rong, Fengfeng Jiang, Chunlin Wang, Wei Huang

Arc plasmas have been extensively studied, experimentally and by means of modeling, due to their wide range of applications. In this article, a calibration-free Boltzmann plot method was applied to measure the species composition and pressure in the arc plasmas based on the assumption of local thermodynamic equilibrium and only single ionization of atoms. Experiments were performed on the argon free-burning arcs at two different pressures. Firstly, several Ar I and Ar II spectral lines were utilized to draw the Boltzmann plot. Then, the plasma temperatures were obtained by three different methods, the Boltzmann plot method, two-line Saha–Boltzmann plot method, and the Fowler–Milne method. The species concentration was calculated using the intercepts with ordinate in the Boltzmann plot. Combined with the electron number density determined from the Stark broadening of Ar I 696.54 nm, arc pressures are calculated based on the equation of state. The measured species concentration and pressures are in good agreement with the theoretical results, indicating that the used method is reliable for further arc plasma applications.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-07-30
M. Baeva, D. Loffhagen, D. Uhrlandt

Analysis of the plasma parameters of a tungsten-inert gas microarc with a length of 0.4 mm is carried out by means of a unified one-dimensional model. The model solves the fluid equations for the particle and energy conservation of the electrons and the heavy species in the plasma, and the heat conduction in the thermionic cathode. The particle transport of the electrons and the ions is coupled with the Poison’s equation. The spatial distributions of the densities of the charged particles, the electric potential and field, the components of the electric current density, the heating mechanisms and the resulting temperatures of the electrons and heavy particles are discussed in detail for an electric current density of 106 A/m2. The discharge voltage, estimates of the Debye length, the near-electrode voltage drop, and the thickness of the regions of space charge adjacent to the electrodes are obtained for current densities in the range from 5.3 × 103 up to 2.3 × 106 A/m2.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-07-13
P. Iovane, C. Borriello, S. Portofino, A. De Girolamo Del Mauro, G. Magnani, C. Minarini, S. Galvagno

A novel study about the synthesis of zirconia and calcia-stabilized zirconia powders were carried out by DC thermal plasma starting from cheap precursors as the carbonates. Different operational parameters were investigated to explore the effects of the process conditions, such as the plasma torch power and the gas flow rate on the composition and the morphology of the powders. The products phase changes from a metastable tetragonal to monoclinic/tetragonal mixture. Basically a main tetragonal phase was obtained at low torch power (7 kW) while the amount of monoclinic phase linearly rises with the power, up to 66 wt% at 26 kW of plasma power and high gas flow rate. The gas flow rate also affects the shape and the size of the powder, where high values reduce powder aggregation and enhance the spherical shape. The best results were achieved at 22 kW of plasma power and high gas flow rate, with powders of roundness about 79% and a wide particle size distribution. Adding the calcium carbonate to the zirconium carbonate (corresponding to 8 wt% CaO in the final mixture), the plasma treatment mainly produces a tetragonal phase zirconia, that at 1400 °C in furnace changes in a stable cubic phase. These powders could be made suitable for further industrial applications after proper treatments.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-07-20
Y. D. Korolev, V. O. Nekhoroshev, O. B. Frants, N. V. Landl, A. I. Suslov, A. V. Bolotov

The paper relates to the investigations of a low-current discharge in a vortex airflow with the electrode configuration corresponding to classical coaxial plasmatron. The gas flow rate is varied from 0.1 to 0.3 g/s at an inner diameter of the plasmatron nozzle of 5 mm. The discharge is powered by dc voltage via a ballast resistor. Typical averaged current is changed from 0.06 to 0.15 A so that a maximum averaged power dissipated in the discharge amounts to 160 W. In these conditions, a luminous gas region at the plasmatron exit, which in most publications is associated with a plasma jet, is observed. The method for the jet diagnostics based on a usage of the additional electrodes at the plasmatron exit has been proposed. The main idea of the experiments is the elucidation of the problem whether the jet actually represents the plasma area or we have to apply the term “plasma” with care. In particular, in the case under discussion the main charged particles in the jet are electrons that are emitted from a plasma column located in the plasmatron nozzle. The model that describes the formation of electron flow in the jet has been proposed. Typical electron density in the jet estimated with a usage of the model is at a level of 109 cm−3.

更新日期：2019-12-11
• Plasma Chem. Plasma Proc. (IF 2.768) Pub Date : 2019-08-07
Huicong Zhang, Tao Wang, Zifeng Sui, Yongsheng Zhang, Pauline Norris, Baomin Sun, Wei-Ping Pan

The mercury removal capacity of biochar can be improved by plasma modification and the functional group is an important factor affecting the mercury removal. This paper examines factors such as discharge voltages, gas flow rates, chlorine concentrations and discharge times that may affect functional groups on the surface of biochar. The mercury removal performance of the tobacco stem biochar prepared under different Cl2 plasma modification conditions was investigated using a fixed bed reactor. The number of C–Cl bonds and carboxyl increased after modification and decreased in mercury removal. Longer discharge times can destroy the biochar surface and possibly cause a decrease in the number of active sites. Increasing the discharge voltage promotes the formation of C–Cl bonds and carboxyl groups. Excessive gas flow rates cause active chlorine to be carried out of the reactor quickly which reduces the formation of C–Cl. The amount of C–Cl bonds increases with increased chlorine concentration. In the modified biochar, C–Cl and carboxyl take part in the adsorption of mercury to form HgCl2 and HgO, while the unmodified biochar is mainly physically adsorbed Hg0. C–Cl is the main functional group participated in mercury removal and the carboxyl is a secondary functional group. The proportion of HgCl2 is at least 68.2% in the used modified biochar. Under optimum conditions, the initial mercury removal efficiency of modified tobacco biochar was 99.1%, and the efficiency was still 79.1% after 100 min.

更新日期：2019-12-11
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