Search

In this work, we studied the change in the properties of powders with a core (magnesium) – shell structure (carbon and carbon/palladium) in the process of hydrogenation/dehydrogenation with hydrogen (99.995 wt%). Magnesium powders were obtained by plasma chemical synthesis in an atmosphere of argon containing a small amount of hydrogen (2–3 at.%) and nitrogen (8–9 at.%), when performing a low-frequency arc discharge between a tungsten electrode and a magnesium melt. The shell (carbon and carbon/palladium) was deposited in a plasma generator with vortex and magnetic stabilization. For all samples, a decrease in the sorption capacity of hydrogen was observed as a result of successive cycles of sorption and desorption reactions. It was found that the reason for this fall is associated with the formation of the MgO and Mg(OH)2 phase, which prevents the diffusion of hydrogen. The carbon shell provides a more complete hydrogenation of the magnesium particles, and an additional palladium shell increases the resistance to cyclic hydrogenation/dehydrogenation and reduces the temperature of these processes. According to the data obtained, powders with particles (Mg@C)@Pd can absorb the largest amount of hydrogen (6.9 wt%) for the duration of 5 cycles, after which the protective shell of the particles begins to collapse and a loss of sorption capacity is observed.

Sander Bekeschus and Sylvain Iséni equally contributed to this work as first authors.; International audience; Parameter studies of plasma treatment are informative about the optimal use of this technology in biomedical applications such as the argon radio-frequency plasma jet kINPen. However, the interdependence of the plasma-dissipated power in relation to input current and feed gas modulation on the resulting biological consequences has not been studied so far. To this end, a parameter study is presented, and the effect on human immune cell viability was investigated across different input current power and argon with oxygen/nitrogen feed gas admixture settings. It was found that with both nitrogen and oxygen admixtures, a concentration-dependent change in plasma-dissipated power emerged, which converged at 27.5 mA and 26.5 mA, respectively. The extent of cytotoxicity in immune cells confirmed the relevance of these findings, which were in congruency with the plasma dissipated powers identified. These findings underline the critical role and input parameter-dependent action of plasma sources for biomedical application.Dr Sander Bekeschus and Dr Sylvain Iséni equally contributed to this work as first authors.

The study was conducted in order to understand a mechanism of interphase mass transfer between liquid and vapor. The molecular dynamics (MD) simulation is used to examine details of condensation and evaporation from the viewpoint of molecular kinetics. First, molecular boundary conditions for condensing, reflecting, and evaporating molecules are presented for an argon molecule as a function of the surface-normal component of translation energy. The velocity distributions can be expressed by the modified Maxwellian and making use of the condensation coefficient. The condensation coefficient of water is also examined for two kinds of intermolecular potential, the Carravetta-Clementi (C-C) model and the extended simple point charge (SPC/E) model, in order to consider the effect of the surface structure of the liquid on the condensation coefficient. The results indicate that the condensation coefficient of water is close to unity for both models and its dependence on the translation energy is small compared w...

In this study, comprehensive calculations of energies, hyperfine structure constants, Landé gJ factors and isotope shifts have been performed for the lowest 71 states of Na-like Ar7+, Kr25+ and Xe43+ ions. Radiative parameters viz., wavelengths, transition rates, oscillator strengths and lifetimes are estimated for the electric dipole E1 transitions among these levels. The states under consideration include 1s22s22p6nl for n = 3–9, l = 0–6, and the fully relativistic multiconfiguration Dirac–Hartree–Fock (MCDHF) method integrated in the latest version of the general-purpose relativistic atomic structure package (GRASP2018) is used for the calculations. The additional corrections, such as the Breit interaction and quantum electrodynamics effects are included in the relativistic configuration interaction calculations, and their effects on energies and other parameters are analysed. We examined the impact of including the core–core and core–valence correlations on level energies. Furthermore, to inspect the reliability of our MCDHF results, we performed another set of calculations using the many-body perturbation theory built into the Flexible Atomic Code (FAC). Moreover, we estimated the uncertainties in the computed lifetimes and transition parameters and assigned their accuracy class. A thorough comparison between the two obtained calculations and with the previous theoretical and experimental results, wherever available, is carried out and a good agreement is observed.

In this article, the investigation has been carried out for the characterization of the proposed tapered geometry of dielectric barrier discharge (DBD)-based cold atmospheric pressure plasma jet (C-APPJ) on the basis of optical emission spectroscopy (OES) and imaging for different operating parameters, such as argon gas flow rates, applied voltages, and frequencies. The detailed characteristics for the formation of the plasma plume using argon as a working gas have been presented for a wide range of flow rates [1–3 standard liter per minute (SLM)] and frequencies (15–25 kHz). Increasing the pulse frequency, the length and the diameter of the plasma plume increase, while the length of the plasma plume increases when increasing the gas flow rate up to 2 SLM. Time-integrated images have been captured using the intensified charge couple device (ICCD) camera, which illustrates that the plasma plume comprises different emission layers of definite patterns. The propagation dynamics and formation of different emission layers of the plasma plume have also been investigated using the COMSOL Multiphysics simulation. It has been observed that the local electric field of 6 kV/cm is responsible for the propagation of the plasma bullet and the generation of the electron with an average energy of ~9 eV. OES has also been performed to understand the plasma chemistry and identify the reactive species in the C-APPJ. The discharge analysis and characteristics performed through experiment and simulation would certainly be helpful for the design and development of C-APPJ sources.

To examine the influence of radiative transitions on the performance of nonequilibrium seed-free argon plasma magnetohydrodynamic (MHD) generators, we developed MHD numerical simulation technique with a collisional-radiative (C-R) model, where neutral argon atoms with 45 discrete effective electronic excitation levels, singly ionized argon ions, and free electrons were considered under a two-temperature, low-magnetic Reynolds number MHD approximation. Furthermore, a so-called escape factor was implemented in the C-R model to consider the effects of radiation trapping by ground-state neutral atoms. Using the developed technique, we computed the performance characteristics of a nonequilibrium seed-free argon plasma MHD generator. The numerical results showed that the generator performance gets higher as the escape factor decreases, i.e., the optical thickness for radiative transitions to the ground state of neutral atoms increases. The numerical results also suggested that when the escape factor is $1.0\times 10^{-3}$ or less, the generator performance is almost the same as that for the escape factor of 0 corresponding to completely optical-thick plasma case for the radiative transitions to the ground state of neutral atoms. Furthermore, realistic escape factor values for resonance lines in the power generation channel were evaluated using a well-known estimation model. Consequently, the estimated values had the order of $10^{-4}$ . We also showed that under such relatively optically thick plasma cases, a collisional (C) model and a widely used global ionization-recombination rate model with no explicit consideration of electronically excited-state neutral atoms can reproduce the generator performance predicted by the C-R model with relatively good accuracy.

In this article, the Vlasov–Maxwell equations have been integrated by the forward semi-Lagrangian method to compute the soft X-ray (SXR) emission from a dense plasma focus device filled with pure and impure argon. The impurity has been assumed as copper of which the electrodes were made. The results have shown that, in the case of pure argon, the emission power reached up to $3.5 \times 10^{9}{\mathrm {W}}$ . However, for the impurity with a 10% volumetric fraction and with the effective charge number of 10, the emission power reduced to $4\times 10^{5}{\mathrm {W}}$ . With the further increase in the impurity amount, the emission power reduced again. However, if the impurity charge number is close to the pure gas charge number, the attenuation of the SXR emission decreases.

International audience; In this work, we investigate the influence of the molecular weight of poly (methyl methacrylate) (PMMA) thin films coated on silicon wafer on the ToF SIMS (Time of Flight Secondary Ion Mass Spectrometry) sputtering mechanisms and kinetics during depth profiling using low energy monoatomic caesium ions. The sputtering yield volumes are determined as function of molecular weight, film thickness and beam energy. The results show that the sputtering yield volume decreases with increasing molecular weight Mw down to a threshold value below which it becomes nearly constant, as previously observed with argon cluster ions. The relevance of physical parameters such as the glass transition temperature Tgdetermined here from ellipsometry measurements-and the entanglement of the polymer chains to account for this behaviour is discussed. The variation of the sputtering yield was also found to vary logarithmically with the primary beam energy. In addition, preliminary experiments carried out using a low molecular weight PMMA (4 kg/mol) evidenced a nano-confinement effect similar to that observed with argon cluster sputtering but of lower magnitude.

The concentration distribution of electrons and free radicals in remote argon plasma were studied by using a langmuir probe and electron spin resonance. The polyvinylidene fluoride (PVDF) membranes...

A control rod alloy composed of silver (Ag), indium (In), and cadmium (Cd) was heated in argon or oxygen at 1073 to 1673 K for 60 to 3600 s. Then, the release behaviors of the elements were analyze...

Optical emission spectroscopy (OES) has been used as an in-situ method to monitor the film deposition carried out using a combination of two plasma-assisted techniques; pulsed laser deposition (PLD) and magnetron sputtering (MS). In this work, the plasmas produced during the PLD ablation of a gold target in an argon atmosphere and its simultaneous use with MS of ZnO were characterized by OES. Neutral atoms of Au, Ar, and Zn and ions of Au were identified, and the temporal and spatial evolution of their emission lines was studied along the axis of the PLD plasma expansion. During the PLD of Au an increment in the emission intensity of neutral Au near the substrates, as a function of the laser pulse fluence, demonstrated resputtering of the Au deposit by the high energy species produced by PLD. When the combination of PLD of Au and MS of ZnO was performed, a similar increment was observed in the emission intensity, but in this case of neutral Zn that was caused by the preferential resputtering of Zn from the ZnO–Au deposit. The MS plasma neither significantly affect the PLD plasma expansion nor did it affect the resputtering of the films.

Chlorine-containing plasma and its mixtures with molecular and inert gases, as well as plasmas of complex polyatomic gases, such as freons, are often used to form the topology on the surface of semiconductors. This article examines the surface quality (based on the roughness data) of the semiconductor structure of GaAs after plasma-chemical etching in the plasma of mixtures of HCl/Ar, HCl/Cl2, and HCl/H2, as well as R-12 freon and its mixture with argon. Freon R-12 is often used for etching Si, Ge, and a number of other materials (GaAs, GaP, InP), providing technologically acceptable interaction rates, and also meets the requirements for anisotropy and selectivity. Also, mixtures of active gases with inert (He, Ar) gases have become widespread, which can act both as simply diluent gases and as sources of ions for the ion bombardment of the sample for the further ionic stimulation of the desorption of the interaction products, which improves the functional properties surface, with a slight decrease in the speed of interaction. Nevertheless, controlling the surface quality of samples remains an urgent task in modern electronics.

The present study investigates freely propagating methane/hydrogen lean-premixed laminar flames at elevated pressures to understand the hydrogen addition effect of natural gas on the NO formation under the conditions of industrial gas turbine combustors. The detailed chemical kinetic model which was used in the previous study on the NO formation in high pressure methane/air premixed flames was adopted for the present study to analyze NO formation of methane/hydrogen premixed flames. The present mechanism shows good agreement with experimental data for methane/hydrogen mixtures, including ignition delay times, laminar burning velocities, and NO concentration in premixed flames. Hydrogen addition to methane/air mixtures with maintaining methane content leads to the increase of NO concentration in laminar premixed flames due to the higher flame temperature. Methane/hydrogen/argon/air premixed flames are simulated to avoid the flame temperature effect on NO formation over a pressure range of 1–20atm and equivalence ratio of 0.55. Kinetic analyses shows that the N2O mechanism is important on NO formation for lean flames between the reaction zone and postflame region, and thermal NO is dominant in the postflame zone. The hydrogen addition leads to the increase of NO formation from prompt NO and NNH mechanisms, while NO formation from thermal and N2O mechanisms are decreased. Additionally, the NO formation in the postflame zone has positive pressure dependencies for thermal NO with an exponent of 0.5. Sensitivity analysis results identify that the initiation reaction step for the thermal NO and the N2O mechanism related reactions are sensitive to NO formation near the reaction zone.

In developing wettable TiB2-based cathodes for Al production, the main problem encountered for decades is the difficulty to sinter or melt this refractory material. Here, suspension plasma spray (SPS) is used as this process makes it possible to use micrometric TiB2 particles to favor a high heat transfer per particle. In addition, an argon gas shield is used to protect the inflight TiB2 particles from oxidation with air during spraying. Our results confirm the efficiency of the argon shroud to limit TiB2 oxidation when compared with a TiB2 coating obtained without shroud. The SPS TiB2 coatings show a good adhesion to the graphite substrate. However, their high porosity indicates an insufficient TiB2 melting during the spraying, suggesting that the transit time spent by the TiB2 particles in the plasma is too short. The SPS TiB2 coatings present a good wettability for molten Al. However, Al infiltration through the porous coating results in the direct contact of molten Al with the graphite substrate, which may be detrimental for its mechanical integrity.

Recycling of spent lithium-ion batteries (LIBs) for metal recovery is inevitable because of environmental and resource conservation considerations. Evaluation of the kinetics parameters is crucial for understanding the thermal response of mixed electrode material for the development of the thermal recycling process. In this study, thermal treatment of mixed electrode (anode and cathode) material resulted in an in-situ indigenous carbothermal reduction of cathode material. The thermal response of mixed electrode material was investigated at different heating rates under argon and air atmosphere. Kinetic parameters, such as the activation energy and pre-exponential factor, were evaluated using other kinetic methods. The average activation energy for the thermal dissociation of mixed electrode material under the air atmosphere is estimated as ~ 180 kJ/mol. The activation energy using different kinetic models was calculated. The product layer diffusion model was found to fit with the activation energy of 52.1, 121.4, 125.3, and 71 kJ/mol for Co, Mn, Ni, and Li recovery, respectively. The optimum product of in-situ carbothermic reduction of mixed electrode material at 900 °C, 60 minutes comprises Co, MnO, and Ni (Co: 61.6 pct, Mn: 17.8 pct, Ni: 7.1 pct, O: 13.5 pct) with a saturation magnetization of 102 emu/g.

In this study, a modified cold grid cathode penning ion source is constructed and characterized; to obtain a high stream of nitrogen ions. The effect of four samarium cobalt permanent magnet rods on the output ion beam current is studied using argon gas. The output ion beam current at different pressures and grid cathode diameters are measured using nitrogen gas. It is found that at the optimum grid cathode diameter equal to 14 mm, pressure equal to 9 × 10–4 mbar, and discharge current equal to 1.8 mA, a maximum output ion beam current is equal to 220 μA using nitrogen gas. Also, the output ion beam current is measured at different pressures and optimum grid cathode diameter using argon and hydrogen gases. The effect of applied negative extraction voltages on the extracted ion beam current at the optimum parameters was determined using argon, hydrogen, and nitrogen gases.

A high-efficiency microwave atmospheric pressure plasma jet (APPJ) has been developed in previous work. Long and stable plasma filament is excited directly in the open air with 2.45-GHz microwave power and double-channel argon flow by a double-coaxial structure. Unlike those plasma jets that strongly rely on a high flow rate to shape the plasma jet, this method produces a stable filamentous plasma jet at a low flow rate whose length and diameter are in a linear relationship with absorbed microwave power. This study aims to investigate the fundamental parameters of this special plasma filament under different power levels and gas flow rates by optical emission spectroscopy (OES), including the electron temperature and the spectrum. The electron temperature is determined to be 0.71–0.81 eV. It decreases slightly as the power increases, which is different from other high-voltage or radio frequency excited plasma jets under high power. The electron temperature does not change significantly with the change of microwave power and argon flow rate, more manifested as a change in the length, which indicates that this special plasma filament is related to the complex interaction of the microwave field and plasma. This study provides basic parameters for further investigation of this kind of plasma jet for theoretical and numerical simulation.

The spark-ignition features of premixed H2 under Ar–O2 atmospheres are essential for the development of high-efficiency and zero-emission Argon Power Cycle engines. Therefore, constant-volume combustion vessel experiments are conducted at an initial temperature of 287 K, initial pressures of 0.1, 0.3, and 0.5 MPa, with diluents of Ar/N2/CO2. Excess oxygen ratio, defined as the ratio of O2 supplied to the O2 needed for stoichiometric combustion, ranges from 1.0 to 4.7. Dilution ratios, defined as the molar fractions of diluents in the diluent-O2 mixture, were separately 70%, 79%, and 88%. Results show that both high dilution ratios and high excess oxygen ratios lengthen the flame-initiation periods. With excess oxygen ratio of 3.3, when Ar dilution ratio increases from 79% to 88%, the flame-initiation period rises by a factor of five to ten. With Ar diluent ratio of 79%, when excess oxygen ratio increases from 2.5 to 4.7, the flame-initiation period rises from under 10 ms to over 60 ms. Both the application of Ar as the diluent and high initial pressures extend the flammability limits. With Ar dilution ratio of 79% and pressure no less than 0.3 MPa, the flammability limit on excess oxygen ratio is over 4.7. Furthermore, Ar can additionally shorten the flame-initiation periods. At 0.1 MPa, excess oxygen ratio of 2.5, when diluents are respectively Ar, N2, and CO2, the flame-initiation periods are 10, 19, and 41 ms. The research reveals that a spark-ignition Argon Power Cycle engine running with ultra-lean and highly diluted mixtures may be feasible.

The primary task of this work is to clarify ammonia-oxygen explosion characteristics under nitrogen and argon atmosphere. Firstly, the flame behavior and explosion pressure are experimentally obtained. Then their correlation is revealed quantitatively. The thermal, diffusive and chemical analysis is conducted at last. The results demonstrated that the variation tendency of flame propagation velocity (FPV), maximum explosion pressure (MEP) and maximum rate of pressure rise (MRPR) is completely consistent. All index of FPV, MEP and MRPR, becomes increased and decreased with increasing equivalence ratio, continues to decrease with increasing inert gas fraction. All index of FPV, MEP and MRPR under argon atmosphere is totally larger than that under nitrogen atmosphere. By considering the state equation of ideal gas, spherically smooth flame and adiabatic compression, the flame behavior and explosion pressure under nitrogen and argon atmosphere is significantly controlled by laminar burning speed (LBS). As the inert gas fraction and equivalence ratio change, the LBS under nitrogen and argon atmosphere is significantly controlled by adiabatic flame temperature. The joint action of adiabatic flame temperature and thermal diffusivity contributes to the LBS difference.

The purpose of this article is to study the influence of different powers, pressures, frequencies, and gases on the electron density distribution in special structures. A simulation model is established, and the electronic density in a special capacitance coupled plasma (CCP) device is calculated over the power range of 0–10 kW, pressure range of 0–50 Pa, and frequency range of 13.56–300 MHz. The results show that the power is a logarithmic function of the electron density in helium and argon plasmas, and the peak value for the electron density occurs in the diffusion region. At a certain power, collisions between particles increase with increasing pressure, which leads to an increase in electron density. However, the high electron density region in the helium plasma is concentrated near the electrode, while the high density region in the argon plasma moves from the center of the device to the electrode with increasing gas pressure. At the same time, the increase in the power frequency increases the ionization rate, and energy is transferred to the electrons, which increases the electron density. However, the rate of increase in the electron density decreases with increasing power frequency at the same voltage and pressure. With increasing power frequency, the 2-D electron density distribution in the argon and helium plasmas is found to vary in a similar way to that found for increasing pressure.

Experiments were carried out to study detonation propagation through a nonuniform layer of stoichiometric hydrogen-oxygen in a narrow channel. Premixed stoichiometric hydrogen-oxygen was injected through a series of 1.3 mm diameter, 4.8 mm spaced holes into a 7 mm wide optically accessible channel initially filled with an inert gas. A Chapman-Jouguet detonation wave was transmitted into the test section from a pre-detonator of equal height. The height of the layer was varied by changing the time of hydrogen-oxygen injection relative to the arrival-time of the detonation wave. Schlieren photography was used to record the progression of the detonation wave. Soot foils mounted to the back window, were used to record the detonation cellular structure and visualization of the soot incandescence provided tracking of the reaction zone. With the channel initially filled with argon, detonation propagation was only possible when the layer height accommodated at least 8–11 detonation cells. Detonation propagation was not possible when the channel initially contained nitrogen, or carbon dioxide, indicating strong mixing with the injected premixed hydrogen-oxygen. Numerical simulations confirmed the strong mixing between the injected premixed hydrogen-oxygen with the prefilled inert gas. The simplified mixing condition, i.e., injection of premixed hydrogen-oxygen, provides a unique data set for numerical code validation and verification for a linear RDE geometry.

The eutectic FeNiCoCrTi0.6Nb0.4 high-entropy alloy coating (HEAC) is annealed in Argon at 450°C, 850°C and 1050°C to investigate the thermal stability. The results show that annealed coatings are a...

Plasma atomization (PA) is a highly recognized method for producing spherical powders for additive manufacturing and metal injection molding. It uses multiple converging plasma jets to simultaneously melt and atomize the metal wire to spherical powders. The quality of the atomized powders is highly dependent on the plasma torch for generating the plasma jet. Although the reverse-polarity plasma torch (RPT) has been commercially applied in the PA, its working characteristics relating to the high stability, high thermal efficiency, and supersonic plasma jet with high temperature desired in the PA are unclear. Therefore, experimental and numerical investigations of a self-manufactured RPT for PA were conducted to reveal its volt-ampere, thermal and jet characteristics. Results showed that the RPT works stably with the arc voltage fluctuation within 10 V ensuring the uniform quality of the produced powders. Besides, compared with the common argon plasma torch, the RPT works at high arc voltage and low arc current leading to less erosion of electrodes and purer powders. Furthermore, the thermal efficiency of the RPT and the mean enthalpy of its plasma jet is higher than 70% and 3 × 106 J/kg respectively, making it ideal for generation of the plasma jet with high energy density. Moreover, numerical results showed that the RPT with the De-Laval nozzle can generate supersonic plasma jet with temperature high enough for melting and atomizing most of materials. Finally, the PA experiment showed the effectiveness of the RPT for the production of high quality powders with smooth surfaces, high sphericity and small particle size.

In this work, the kinetics of decarburization and demanganization of Fe–15Mn–1C alloy by bubbling mixtures of Ar–O2 into the melt at 1823 K was studied. Experiments were conducted at total gas flow rates of 200 and 300 Nml/min and gas mixtures of Ar containing 6.7 to 20 pct O2. Increasing the gas flow rate and oxygen in the gas mixture resulted in higher overall rates of decarburization and demanganization. However, the experiments with the lowest oxygen concentration were the most efficient in terms of oxygen utilization for decarburization. The ratio of manganese loss to decarburization was found to be controlled by the relative mass transport of manganese and carbon in the metal. Based on the estimated mass transfer coefficient for either carbon or manganese, the reaction time for each bubble was estimated to be 0.001 seconds which is about 1 pct of the residence time of the bubble in the liquid. Although the initial competition for oxygen between manganese and carbon was controlled by relative mass transport rates, this work found no evidence that manganese and carbon repartitioned towards the equilibrium over the remaining lifetime of the bubble.

Emission spectra of argon behind the front of a strong shock wave are studied in the range of shock-wave velocities of 4.6–8.3 km/s and pressures before the wave front of 0.25–5.00 Torr. Time-integrated sweeps of radiation in a wide spectral range from the ultraviolet to infrared (190–1100 nm) and time dependences of the argon radiation intensity at wavelengths of 420, 532.8, and 740 nm are obtained. Three characteristic stages of the temporal evolution of the emission lines are defined. The dependences of the duration and intensity of the emission lines on the initial gas pressure and shock-wave velocity are established. Data are obtained on the background radiation intensity and can be used to separate the intensities of certain argon-atom lines from the total radiation.

The interaction between graphite particles and argon plasma in the arc torch is investigated by numerical simulations. The addition of carbon vapor improves the specific heat capacity, electrical conductivity and thermal conductivity of plasma, and decreases its viscosity. It is important to note that the changes in the thermodynamic and transport properties of the plasma substantially affect the arc plasma temperature and the spatial distribution of the carbon vapor concentration. As the graphite particle feed rate increases, the arc will be continuously contracted and the arc electric current density will be increased. The carbon vapor enhances the plasma electrical conductivity, but the heat absorption by the particles reduces the temperature of the plasma, eventually leading to decreased the electrical conductivity. Both result in ascent of the electric field of the arc, so that increase the arc voltage. In addition, the heat flux radial distribution of radiation-absorption of the particles is much less than the thermal conduction, but the particles near the wall absorb radiation from arc region, so that reduce energy loss of the radiation of the arc column.

A one-dimensional fluid model of a dielectric-barrier discharge (DBD) in Ar–S2 mixtures is developed, and the properties of the discharge are modeled. The discharge in a 3-mm-long gas gap between 2-mm-thick quartz layers covering metal electrodes is considered. The DBD spatiotemporal characteristics are simulated at gas pressures of 300 Torr for the case in which a 20-kHz harmonic voltage with amplitude of 8 kV is applied to electrodes. It was shown that the discharge active phase at S2 fraction of 0.1% in Ar–S2 mixture is characterized by the presence of multiple current spikes, which is explained by weak ionization waves. The cycle-averaged dissociation degree of S2 molecules is ~ 0.05–0.3% in Ar–S2 mixture with S2 fraction of 0.1–1% and degree of gas ionization is 2 × 10–8–4 × 10–7. The plasma is electronegative due to the fast attachment of electrons to sulfur molecules: e + S2 → S2–. The radiative efficiency of S2* excited molecules at S2 fraction of 0.5 and 1% is about two times higher than at S2 fraction of 0.1% and reaches about 0.8%. At S2 content in Ar–S2 mixture of 0.1% the main contribution in the discharge emission make argon resonance atoms (70%), while at 1%S2 the main contribution in the emission make sulfur excited atoms (95%), which radiative efficiency abruptly increases. The optimal S2 fraction in Ar–S2 mixture for developing DBD radiation source based on emission of S2* molecules is about 0.5%, when the 98% of discharge emission distributes between Ar* (44%), S2* (42%) and Ar2* (12%).

Nanoscale liquid film evaporation plays an essential role in many engineering applications. This study carries out molecular dynamics simulations on the effects of the depositional nanoparticle's wettability and volume in base fluid on the evaporation process to understand how the depositional nanoparticle affects the evaporation heat transfer. Increasing the nanoparticle's wettability can enhance the evaporation heat transfer process, and the enhancement effect of the hydrophobic surface is more remarkable than that of the hydrophilic surface. This because the increasing wettability causes more significant solid-liquid interaction. However, the potential energy of argon atoms at the liquid-vapor interface is almost unaffected by wettability. Moreover, when the depositional nanoparticle locates below the free liquid film, increasing the nanoparticle volume has a better heat transfer performance. As the volume increases, the heat transfer through the nanoparticle becomes more obvious, which effectively enhances the heat transfer at the solid-liquid interface and the liquid-vapor interface. The latent heat of phase change at the liquid-vapor interface is almost unchanged so that the evaporation can be enhanced. This research provides an understanding of the effects of depositional nanoparticles on nanoscale evaporation, which can impact several engineering applications, including devices' cooling and fluid transport.

There are many correlations for Nusselt numbers applied to calculate heat transfer between a fluid and a sphere. In all massive industrial processes of metal production, there is the need to calculate the melting times of metal additions during alloying operations. A multiphase mathematical model helps to assess the applicability of these correlations to actual industrial processes. This model simulates the heat transfer between solid particles and liquid steel under turbulence conditions during the tapping operation of steel with simultaneous argon bottom stirring. There are six recommendable correlations among the 16 most relevant available ones in the literature. These correlations apply to small Prandtl numbers (Pr = 0.01 to 0.2, i.e., metals) or medium magnitudes of Prandtl numbers (Pr = 1 to 10, air and water). Melting rates depend on the turbulence intensities and superheat of the metal. High superheats cause the hydrodynamic effects to have less influence on the melting time of alloying particles.

The argon power cycle is one of the most promising technologies for high efficiency and low emission hydrogen-fueled internal combustion engines. The application of coaxial injection technology in the hydrogen-fueled argon engine can improve the mixing process and the combustion performance of the H2/O2 mixture. In this study, an innovative H2–O2 coaxial injection combustion system was designed to investigate the jet flame characteristics of oxygen coaxially wrapped by hydrogen in a controllable argon thermal atmosphere. The findings of this study could provide a new perspective for designing hydrogen-fueled argon engines in the future. The influences of co-flow temperature, jet injection pressure, and excess oxygen coefficient were all determined. Observations of the flame showed a bright blue flame with a reddish glow in the far-burner region. Experimental results show that the flame length, cross-sectional area, and area/perimeter ratio first decrease with increasing jet injection pressure and subsequently increase, reaching maximum values at 0.4–0.6 MPa. When increasing the co-flow temperature from 1023 K to 1223 K, the cross-sectional area of the flame increases significantly by 61.1% at an excess oxygen coefficient of 0.4. Furthermore, the liftoff flame height shrinks when the co-flow temperature and the excess oxygen coefficient increase, while it rises along with an increasing jet injection pressure.

This article presents a systematic investigation on the behavior of electrons in the bullet in the Ar/H2O plasma jet in increasing the applied voltage and water vapor concentration based on a needle-plate discharge configuration and a 1-D particle-in-cell Monte Carlo method. The scattering angle of the electron in the bullet is described using the angle between the electron scattering direction and the bullet propagation direction. The following results are obtained. The evolution characteristic of the angle spectrum of electrons in the bullet in increasing the applied voltage is the same as that in increasing water vapor concentration, namely, the electrons scattered toward the target get increasingly less. When increasing the applied voltage, the OH density, the electron density, and the average electron energy $E_{\mathrm {ave}}$ increase. However, the increase in water vapor concentration leads to an evidently increasing OH density and a decrease in both the electron density and $E_{\mathrm {ave}}$ . In the range of electron scattering angles below 90° in the bullet, the percentage of electrons with energy above 3.27 eV (the threshold of inducing dissociative electron attachment to water molecule) increases with increasing applied voltage but presents a slight decrease in increasing water vapor concentration. The majority of electrons to most probably interact with the target are of energies higher than 3.27 eV. Finally, a notable effect of H2O admixture is that it gives rise to the decrease in not only $E_{\mathrm {ave}}$ but also the electron density in the bullet, especially the latter decreases evidently.

A plasma jet at atmospheric pressure using a dielectric barrier discharge (DBD) can be very useful in the biomedical field. In this article, a numerical simulation of such plasma jet operating in argon gas and launched in the open air was developed using COMSOL Multiphysics software. Three coupled models are considered in this study. A hydrodynamic investigation is conducted and the dilution of argon in air is considered an initial value in the plasma model. An electrostatic study is developed in order to preview the initial electric field. Finally, a plasma study is carried out and discussed in terms of electron density, electric field distribution, and plasma length. This study is validated by comparing the results to those measured in a similar system in the literature. The results are in good agreement with the literature and correspond to the physics of the plasma jet.

The characteristics of the electron beams emitted from the hydrogen ( $H$ ), nitrogen ( $N$ ), neon (Ne), and argon plasma pinches have been numerically investigated and compared by solving the Vlasov–Maxwell system with the forward semi-Lagrangian approach. Several outcomes have been obtained. For examples, it was found that, in the case of 1-mbar H, the electron current density reached a value of about $1.431\times 10^{9} \,\,\text {A}\cdot \text {m}^{-2}$ due to turbulence, while it reached ${2.554} \times {10}^{7} \,\,\text {A}\cdot \text {m}^{-2}$ due to other phenomena. For 2-mbar $N$ , the calculated voltage drops across the $m = 0$ regions ranged from about 817 kV to 4 MV. Among these gases, Ne had the biggest upstream emission current of about 9.7 kA, while $N$ emitted the least electron beam current of about 4.1 kA. Computations showed that the total charge delivered by each gas beam was of order 0.1 mC. The method of modeling, presented in this article, can be efficiently used to study the dynamics of a plasma pinch. Since the estimated electron beam currents for various gases are in good agreement with the measured ones, the proposed method can be used for designing the plasma focus devices for the electron beam source purpose.

Combustion of pyridine in rich, stoichiometric, and lean mixtures of C5H5N/O2( $$\rho_\mathrm{ Py}=0.11$$ and 0.15 mol/dm3; $$\rho_\mathrm{ O_2}=0.71$$ –1.18 mol/dm3) diluted with argon or water vapor was investigated at uniform heating of the reactor to 823 K. Analysis of the time dependences of the temperature and pressure of the reaction mixtures revealed differences in the mechanisms of pyridine oxidation at temperature measurement with a Pt-Rh/Pt or nichrosil-nisil thermocouple introduced into the center of the reaction volume. The Pt-Rh/Pt thermocouple was found to intensify the combustion of pyridine in the near-surface region and initiate detonation of the reaction mixture. Increase in the density of the water vapor prevents detonation. Increase in the oxygen content in the reaction mixture leads to decrease in the ignition temperature of pyridine and growth of the degree of carbon burnout and of the fraction of nitrogen that had transformed into N2. With a nichrosil-nisil thermocouple, which has no catalytic properties, the surface oxidation of pyridine on the reactor wall was shown to dominate. Results of mass spectrometry analysis show that in the presence of water vapor, the oxidation of pyridine proceeds through the formation of NH3 as the main intermediate.

Efficient destruction of cyanide by thermal decomposition with ferric oxide addition was proposed. The mechanism of destruction of sodium cyanide with or without ferric oxide addition under various conditions was examined by XRD, DSC−TG, and chemical analysis technologies. In the absence of ferric oxide, sodium cyanide decomposes at 587.4 °C in air and 879.2 °C in argon atmosphere. In the presence of ferric oxide, about 60% of sodium cyanide decomposes at 350 °C for 30 min in argon, while almost all sodium cyanide decomposes within 30 min in air or O2 with mass ratio of ferric oxide to sodium cyanide of 1:1. The increase of ferric oxide addition, temperature, and heating time facilitates the destruction of sodium cyanide. It is believed that with ferric oxide addition, NaCN reacts with Fe2O3 to form Na4Fe(CN)6, Na2CO3, NaNO2 and Fe3O4 in argon. NaCN decomposes into NaCNO, Na4Fe(CN)6, minor NaNO2, and the formed NaCNO and Na4Fe(CN)6 further decompose into Na2CO3, CO2, N2, FeOx, and minor NOx in air or O2.

This work is dedicated to a method for preionization of a laser medium (that is the most popular ones-CO2- and CO-lasers) using X-ray radiation created by a nanosecond sliding discharge (NSD). An experimental study has been carried out on the influence of the initial pressure and the composition of the gaseous medium on the intensity of X-ray bremsstrahlung. In order to estimate this intensity, a special sensor is used; it can measure free electron density that, in our, case is created during photoionization by X-ray radiation from an NSD. It is shown that in case an X-ray emitter is filled with argon, the photoelectron density in the vicinity of a cathode is about 15 times higher than in case the X-ray emitter is filled with helium. Moreover, when the gas volume of the X-ray emitter is filled with argon, the energy spectrum of the “runaway” electrons shifts to the region of lower values of their energy.

LiCoPO4 was synthesized in a short time by a microwave-assisted solvothermal technique at 220°C. The as-prepared samples are characterized as belonging to the Pn21a symmetry group, having poor electrochemical performance, and low specific capacity around 30 mAh/g. Further, activation at 700°C under air and argon increased the specific capacity to 57 mAh/g and 55 mAh/g, respectively. The local atomic and electronic structure of the samples before and after annealing was studied using x-ray absorption spectroscopy (XAS). The activation under air and Ar led to a phase transition from the Pn21a space group to the Pnma space group without changes in the Co oxidation state. Therefore, using myristic acid as a source for carbon coating, we found that there were no specific requirements for the activation atmosphere.

This work was inspired by a previous report (Janjua et al. J. Phys. Chem. A 113, 3576–3587, 2009) in which the nonlinear-optical (NLO) response strikingly improved with an increase in the conjugation path. Herein, the effect of donor and acceptor substitutions on the geometrical parameters, electronic, optical and reactivity of argon in organic matrices has been computed by computational methods. The 6–311 ++ g(2d,2p) basis set and second order Moller–Plesset perturbation theory are used to explore mixed-argon benzonitrile compounds (1–7) namely; hydrogen argon cyanide, methyl argon cyanide, phenyl argon cyanide, cyano-phenyl argon cyanide, hydroxy-phenyl argon cyanide, nitro-phenyl argon cyanide and methoxy-phenyl argon cyanide respectively. Mullikan population analysis, natural bonding orbital (NBO) analysis, frontier molecular orbital analysis, molecular electrostatic potential surface analysis, polarizability and hyperpolarizability of noble gases in organic matrices have been studied. The results indicate that the electron donating groups (hydroxy, methoxy, phenyl and methyl) and electron withdrawing groups (nitro and cyano) fine tune the HOMO–LUMO orbitals and nonlinear optical properties. NBO analysis confirmed that these donor–acceptor groups support the charge transfer in our investigated jack-in-the-box compounds. The linear polarizability and first hyperpolarizability results suggest that all the studied compounds are good candidates for NLO response and associated applications.

In this paper, the incorporation of auxiliary grids/electrodes into the design of the sputtering method is scrutinized by studying the impact of factors such as grid size, grid position, grid bias voltage, electrode sheath design, substrate bias voltage, reactive gas partial pressure, and magnetic trap configuration on the discharge condition and thin-film growth. In this regard, utilizing the updated Berg model for reactive sputtering, the authors obtained a formulation for the reactive grid-assisted sputtering. By the newly-developed formulation, the sputtering rate and the reactive gas partial pressure were simulated as a function of the reactive gas flow rate for various grid-to-target distances, argon partial pressures (0.67, 1.6, and 3.6 Pa), and discharge current densities (0.01, 0.015, and 0.02 A/cm2). According to the computation results, with a grid being utilized, the width of the hysteresis loops can be modified in a broader range by changing either the grid-to-target distance, the argon partial pressure, or the discharge current, resulting in better control over the deposition process. Moreover, the novel configuration of anode-spot-assisted sputtering was proposed to significantly ionize sputtered/neutral atoms near the substrate and to simultaneously deposit sputtered species and products produced as the direct result of introducing dust into the dense plasma. Finally, diverse configurations of the grid-assisted co-sputtering method were introduced for two prime purposes: deposition of composite films in any desired ratios of constituents without significantly changing the other co-sputtering parameters, and favorable alternation of a hysteresis loop for one of the guns at shared gas flow rates.

The 6-D Vlasov–Maxwell equations in the cylindrical coordinates have been solved to calculate the electron beam emission from mixtures of argon and neon. The forward semi-Lagrangian approach was used for solutions. The simulation of the electron velocity field has shown that at the early stage of the pinch evolution of a 4-mbar 90% Ar–10% Ne mixture, the sausage instabilities began to develop from the top parts of the pinch due to bigger $B_{\theta }$ with respect to $B_{z}$ . In the turbulence regions, the electrons could accelerate up to speeds of $905 \times 10^{5}$ and $2387.5 \times 10^{5} \,\,{\text {m}}/{\text {s}}$ at 90.9 and 181.82 ns, respectively. It has been observed that in the high turbulence region, $E_{z}=-2.04\times {10}^{7}\,\,{\text {V}}/{\text {m}}$ , while in the weak turbulence region, $E_{z}=-1.46\times {10}^{7}\,\,\text {V}/{\text {m}}$ . Increasing the neon percentage in the mixture changed the turbulence regions and the upstream and downstream emissions.

Transparent conductive oxides, such as aluminum-doped zinc oxide (AZO), are of substantial importance for use in a broad range of applications because of their excellent optical and electrical properties. AZO film can be deposited by using several conventional techniques, although they suffer from limitations such as long deposition time, high cost, and the requirement for complex deposition equipment. Here, we used hollow-cathode glow discharge, which produces a high-density plasma and achieves high deposition efficiency. Remarkably, instead of metallic target materials, we used Al2O3 and ZnO powders filled in the hollow cathode as a target, thus avoiding the need for specifically designed targets in this technique. The films were deposited using mixtures of argon and oxygen at various ratios (0% to 50% oxygen), to improve the film characteristics. The films deposited under all conditions exhibited hexagonal wurtzite ZnO structure, while the grain size increased with increasing oxygen content. The film was thick and porous when using low oxygen content, but became thin and dense with increasing oxygen content. The optical transmittance was found to be strongly dependent on the processing gases used, with the highest transmittance of 84% being attained when using 25% oxygen gas. The bandgap of the films lay between 3.27 eV and 3.33 eV. The highest carrier concentration and mobility were attained when using 25% oxygen, and the Hall resistivity decreased with increasing oxygen content. Besides the excellent transmittance and electrical properties of the deposited films, it is expected that the results of this study will be useful for solar cells and optoelectronic applications due to the relatively low cost of this technique and the lack of specific target requirements.

Gas aggregation and formation of interfacial nanobubbles (INBs) provide challenges and opportunities in the operation of micro-/nanofluidic devices. In the current study, we used molecular dynamics(MD) simulations to investigate the effects of hydrophobicity and various homogeneous surface conditions on gas aggregation and INB stability with a series of 3D argon-water-solid and water-solid systems. Among various signatures of surface hydrophobicity, the potential of mean force (PMF) minima exhibited the strongest correlation with the water molecular orientation at the liquid-solid interface, compared to the depletion layer width and the droplet contact angle. Our results indicated that argon aggregation on the substrate was a function of hydrophobicity as well as competition between gas-solid and water-solid PMFs. Thus, one precondition for gas aggregation on a surface is that the free energy minima of gas induced by the surface be much lower than that induced by water. We found that although the presence of gas molecules had little effect on the measures of wettability, it enhanced density fluctuations near liquid-solid interfaces. The PMF of gas along the surface tangential plane exhibited a small energy barrier between the epitaxial gas layer (EGL) in the bubble and the gas enrichment layer (GEL) in the liquid, which may benefit nanobubble stability. Much lower PMF in the EGL compared to that in the GEL indicated that gas molecules could migrate from the GEL to the nanobubble basement. However, density fluctuations enhanced by the GEL could reduce the energy barrier, thus reducing the stability of INBs.

The doped/alloyed HfO2 and ZrO2 thin films revolutionized not only the field of ferroelectric physics but also various ranges of device applications. Especially when the two oxides are combined in an 1:1 ratio, the ferroelectric polarization of the material became the most distinctive. Many researchers have investigated various different process conditions such as controlling Hf0.5Zr0.5O2 (HZO) film thickness and modifying different metal electrodes. Here, we explored the effect of additional Ar plasma treatment to the HZO film. The additional Ar plasma was exposed to the plasma-enhanced atomic layer deposition (PEALD) HZO for this study. Then, the sample was compared with a conventional PEALD and thermal ALD HZO films. By understanding the polarization–electric field (P–E), current–electric field (I–E), and electrical breakdown characteristics of the different samples, it was found that the Ar plasma treatment can control the degree of ferroelectric and antiferroelectric phases of HZO film.

Magnesium-lithium alloys are among the lightest commercially-available structural alloys. However, the reactive nature of Mg and Li makes fusion welding of this family of alloys very difficult, if ...

Silver particle-free inks are under rapid development due to their unique properties. Currently, most of the developed silver particle-free inks contain multiple components. In addition to the necessary solvents and silver precursors, these inks also contain complexing agents, reducing agents, and various additives. While such complex compositions assure good stability and printability of the inks, they hamper the sintering process as excess time and energy are often required to remove residues from various compositions to ensure high conductivities of the printed structures. Thus, a simple ink system is expected. On the other hand, plasma sintering shows its sintering potential in treating silver particle-free inks, but is only employed for the sintering of silver nitrate or silver acetate-based inks. Consequently, developing new particle-free ink systems with simple compositions and exploring the potential of plasma sintering is very meaningful. In this work, a clear and transparent silver particle-free ink was formulated, which can be treated both by low-pressure argon plasma sintering and low-temperature thermal sintering (120–160 °C). The roles of 2-amino-2-methyl-1-propanol (AMP) in the ink formulation were investigated in detail, which not only acts as the solvent but also as the complexing agent for silver oxalate to lower the sintering temperature of the ink. The electrical performance of the formulated ink was examined for both sintering processes for different conditions. The thermal sintering resulted in a resistivity value of 24.3 μΩ·cm on glass substrates after treatment at 160 °C for 60 min, while the plasma sintering yielded a resistivity value of 29 μΩ·cm at 500 W for 30 min. Compared to thermal sintering, plasma sintering achieved a similar electrical performance, but with a more nonuniform film structure. The power, sintering time, and the pressure of argon are key factors responsible for the conductivity of the produced films. Nevertheless, both resistivity values do meet the minimal electrical requirements of most electronic applications. Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347 Projekt DEAL

The effects of the atomic number of the fill gas on hard x-ray and ion beam emission from a 2.2 kJ plasma focus were studied. Hydrogen, Nitrogen and Argon gases were used in the experiment. The ano...

The synthesis, thermodynamic destabilisation and hydrogen sorption properties of the M0.2Ca0.8MgH4 hydride system, where (M = Na or Li) have been investigated. Samples were mechanically milled under argon for 5, 10 and 15 h; then characterised by X-ray diffraction (in/ex-situ), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) coupled with a mass spectrometer (MS). On Li and Na substitution into Ca–Mg–H ternary hydride, diffraction peaks shifted to higher angles. 2 and 3 endothermic reactions were observed for the Li0.2Ca0.8MgH4 and Na0.2Ca0.8MgH4. The maximum amount of hydrogen release was achieved for the 5 h milled Na0.2Ca0.8MgH4 hydride from 298 °C to 386 °C accounting for 3.5 wt % of H2.