N2 Admixture Research Articles

Influence of N2 admixture on mode transition of discharge in N2–Ar helicon plasma

Effects of N2 admixture on multiple wave modes and transitions were investigated in N2–Ar helicon plasma under fixed input power and magnetic field. The structures of helicon waves were measured by a B-dot probe to verify the different eigenmodes. The experimental results show that the plasma morphology, emission spectrum, and spatial profile change significantly during mode transitions with the N2–Ar ratio. The calculated results from the pressure balance model indicate that the densities of species N2, N+, Ar, and Ar+ will change largely during mode transition around some specific N2 percentages, which will help to improve the application of N2–Ar helicon plasma in material processing greatly.

The Influence of Selected Process Parameters on the Efficiency of the Process of Gas Nitriding of AISI 1085 Steel.

The main aim of the manuscript was to investigate the impact of modifying the parameters of the gas nitriding process of samples made from AISI 1085 steel on the course and results of the process carried out in a chemical reactor allowing for thermogravimetric measurements. The tested steel was subjected in a chemical reactor to the process of gas nitriding in the temperature range of 490-580 °C, using different sample heating rates (in the range of 1-25 °C/min) and various mixtures of nitriding gases (pure NH3, or NH3 with the addition of H2 or N2). To assess the impact of the tested process parameters on its efficiency, the thickness of the nitrided layers produced, the change in sample mass, the structure of the phases produced, the phase composition and the microhardness were examined. For the research methodology used, it was found that reducing the amount of NH3 and/or using H2 or N2 admixtures adversely affects the thickness of the nitride layers produced. At the same time, the use of a lower maximum process temperature with the same gas mixture resulted in a significant difference in the thickness of the layers. It was also found that the use of pure NH3 or a gas mixture (NH3 + H2) with higher NH3 contents resulted in higher surface microhardnesses of the samples and that for these samples, the hardness increased to a greater depth.

A surface mechanism for O3 production with N2 addition in dielectric barrier discharges

Ozone, O3, is a strong oxidizing agent often used for water purification. O3 is typically produced in dielectric barrier discharges (DBDs) by electron-impact dissociation of O2, followed by three-body association reactions between O and O2. Previous studies on O3 formation in low-temperature plasma DBDs have shown that O3 concentrations can drop to nearly zero after continued operation, termed the ozone-zero phenomenon (OZP). Including small (<4%) admixtures of N2 can suppress this phenomenon and increase the O3 production relative to using pure O2 in spite of power deposition being diverted from O2 to N2 and the production of nitrogen oxides, N x O y . The OZP is hypothesized to occur because O3 is destroyed on the surfaces in contact with the plasma. Including N2 in the gas mixture enables N atoms to occupy surface sites that would otherwise participate in O3 destruction. The effect of N2 in ozone-producing DBDs was computationally investigated using a global plasma chemistry model. A general surface reaction mechanism is proposed to explain the increase in O3 production with N2 admixtures. The mechanism includes O3 formation and destruction on the surfaces, adsorption and recombination of O and N, desorption of O2 and N2, and NO x reactions. Without these reactions on the surface, the density of O3 monotonically decreases with increasing N2 admixture due to power absorption by N2 leading to the formation of nitrogen oxides. With N-based surface chemistry, the concentrations of O3 are maximum with a few tenths of percent of N2 depending on the O3 destruction probability on the surface. The consequences of the surface chemistry on ozone production are less than the effect of gas temperature without surface processes. An increase in the O3 density with N-based surface chemistry occurs when the surface destruction probability of O3 or the surface roughness was decreased.

Impact of N2 admixture on the synthesis of graphitic carbon nanoparticles using atmospheric-pressure microwave plasma

Atmospheric-pressure microwave plasma was utilized for catalyst-free gas-phase synthesis of graphitic carbon nanoparticles by adding CH4 to a mixture of N2 and He. The impact of N2 on the formation of the graphitic carbon nanoparticles was analyzed by increasing the N2 flow rate from 0 to 20 slpm and decreasing the He flow rate from 40 to 20 slpm simultaneously. The addition of N2 altered the morphology of the carbon nanoparticles to obtain flatter and larger shapes. Furthermore, carbon nanoparticles synthesized with N2 possessed more graphitic structures with higher C/O ratios and larger crystallite sizes than those synthesized without N2. The analysis of gas compositions at thermodynamic equilibrium states demonstrated that CN and HCN were the dominant precursor species when N2 was added. The presence of N atoms or N-containing species seem to have a synergistic effect combined with H atoms on the formation of the graphitic carbon nanoparticles.

Effect of N2 on CO2-CH4 conversion in a gliding arc plasmatron: Can this major component in industrial emissions improve the energy efficiency?

Plasma-based CO2 and CH4 conversion is gaining increasing interest, and a great portion of research is dedicated to adapting the process to actual industrial conditions. In an industrial context, the process needs to be able to process N2 admixtures, since most industrial gas emissions contain significant amounts of N2, and gas separations are financially costly. In this paper we therefore investigate the effect of N2 on the CO2 and CH4 conversion in a gliding arc plasmatron reactor. The addition of 20 % N2 reduces the energy cost of the conversion process by 21 % compared to a pure CO2/CH4 mixture, from 2.9 down to 2.2 eV/molec (or from 11.5 to 8.7 kJ/L), yielding a CO2 and CH4 (absolute) conversion of 28.6 and 35.9 % and an energy efficiency of 58 %. These results are among the best reported in literature for plasma-based DRM, demonstrating the benefits of N2 present in the mix. Compared to DRM results in different plasma reactor types, a low energy cost was achieved. To understand the underlying mechanisms of N2 addition, we developed a combination of four different computational models, which reveal that the beneficial effect of N2 addition is attributed to (i) a rise in the electron density (increasing the plasma conductivity, and therefore reducing the plasma power needed to sustain the plasma, which reduces the energy cost), as well as (ii) a rise in the gas temperature, which accelerates the CO2 and CH4 conversion reactions.

On the rotational–translational equilibrium in non-thermal argon plasmas at atmospheric pressure

This work examines the rotational–translational equilibrium in non-thermal, argon-based plasmas at atmospheric pressure. In particular, rotational temperatures (T rot) and neutral gas temperatures (T g) are compared along the axis of plasma columns sustained by either radiofrequency (RF) or microwave (MW) electromagnetic fields. Water vapours or N2 admixtures are added to the high-purity argon plasmas to record the rotational temperatures from the emission spectra of either the OH(A2Σ + − X2Π i ) or the N2 +(B2Σ u + − X2Σ g + ) rovibrational systems. T g values are also deduced from the line broadening of selected Ar emission lines using an hyperfine spectrometer. In the MW Ar/H2O plasma, T g decreases from ∼2100 K close to the wave launcher to ∼1600 K near the end of the plasma column, while T rot is mostly constant in the 1500 K range. In presence of N2 admixtures instead of water vapours, T g is higher by about 300 K (from ∼2400 K to ∼1900 K), while T rot decreases from ∼3200 K to ∼2750 K along the plasma column. A discrepancy between T g and T rot is also observed in the much colder RF plasmas with T g ∼ 400 K and T rot ∼ 515 K. Such departure from the rotational–translational equilibrium in both plasmas is ascribed to the influence of electrons competing with neutrals to impose their own temperature on the distribution of rotational levels of both ground and excited states.

Monte Carlo simulation of resonance effects of electron transport in a spatially modulated electric field in Ar, N2 and their mixtures

The relaxation of the distribution function of the electrons drifting under the influence of a homogeneous electric field in noble gases is known to take place over an extended spatial domain at ‘intermediate’ values of the reduced electric field, E/N. We investigate the transport of electrons in Ar and N2 gases, as well as in their mixtures at such E/N values (∼10–40 Td). After discussing briefly the basic scenario of relaxation in a homogeneous electric field, the major part of work concentrates on the properties of transport in an electric field that is spatially modulated within a finite region that obeys periodic boundaries. The spatial distribution of the mean velocity, the mean energy, and the density of the electrons, the importance of the excitation channels, as well as the electron energy distribution function are obtained from Monte Carlo simulations for various lengths of the computational domain, at different mean values and degrees of modulation of the reduced electric field. At low modulations, the spatial profiles of the mean velocity and mean energy are nearly harmonic, however their phases with respect to the electric field perturbation exhibit a complex behaviour as a function of the parameters. With increasing modulation, an increasing higher harmonic content of these profiles is observed and at high modulations where an electric field reversal occurs, we observe trapping of a significant population of the electrons. The effect of mixing a molecular gas, N2, to Ar on the transport characteristics is also examined. Transition to local transport at high N2 admixture concentrations and long spatial domains is observed.

The Production Efficiency of Reactive Oxygen and Nitrogen Species (RONS) of AC and Pulse-DC Plasma Jet

Atmospheric pressure plasma jets driven by ac and pulsed-dc voltage were characterized, operating in helium with different admixture fractions up to 2% pure air, N2, and O2. The absolute production efficiency of nitrogen dioxide, nitric oxide, ozone, hydroxyl, and atomic oxygen was measured when plasma was processing real biological tissue. The power consumption of each power source, the effect of frequency, and gas composition were investigated. It has been found that the power consumption of 10-kHz ac-driven plasma jets increases with gas mixture increasing from 0% to 0.5% and then decreases slightly with gas mixture increasing from 0.5% to 2.0%, while 1-kHz ac-driven plasma jets are almost constant. Moreover, the average dissipated power of 10-kHz ac-driven plasma jets was about ten times more than that of the 1-kHz case, while the power consumption of P-dc-driven plasma jets was not drastically affected by gas admixture. Furthermore, O2 and air were important impurities contributing to the O, O3, and NO2 production efficiency, while N2 admixture would enable the diminution of O and O3 production efficiency. Especially, an admixture of O2, N2, and air to the main helium flow led to a reduction of OH and NO production efficiency for both ac and pulsed-dc power supply. This research may prove to be valuable both for an attainable range of RONS production efficiency and plasma medical research as a tool for assigning specific RONS or RONS mixtures.

Thermobarometric and geochronologic constraints on the emplacement of the Neoproterozoic Evate carbonatite during exhumation of the Monapo granulite complex, Mozambique

Fluid inclusion and mineral thermobarometric study supplemented by U-Th-total Pb monazite dating has been carried out in country rocks of the Evate carbonatite, which is an example of a Neoproterozoic (~590 Ma) orogenic carbonatite formed within a post-collisional tectonic setting in the Monapo granulite complex of NE Mozambique. The fluid inclusion analysis of a 573 ± 13 Ma old fenite subjacent to the Evate carbonatite revealed primary, high-density to superdense CO2-rich fluids (>1 g.cm−3) with minor admixtures of N2 (0–17.5 mol%) and CH4 (0–1.1 mol%) accompanied by alkalic hydrocarbonate melts and aqueous fluids with minor sulphates. Isochores of CO2 inclusions intersected by isopleths calculated from Ti-in-quartz and Zr-in-rutile thermometers indicate fenite formation at 480–530 °C and 2.1–5.4 kbar. The CO2-rich gas of the fenite-forming fluids/melts is similar to the anhydrous CO2 gas with traces of N2 (<1.5 mol%) trapped in granulites and paragneisses of the Monapo Complex during granulite-facies metamorphism (~850 °C, ~9 kbar) and superimposed retrogression under amphibolite-facies conditions (~550 °C, ~5 kbar) within the time interval between 680 and 590 Ma (Cryogenian to Ediacaran). Peak metamorphic conditions within the Monapo Complex are diagnostic of a hot orogen similar to that in other Pan-African Neoproterozoic HT/UHT granulite terranes. The exhumation PT trajectory of the Monapo Complex diverted from a „near-isochoric“-shaped curve to near-isothermal (~500 °C) decompression at ~590 Ma coeval with the intrusion of the Evate carbonatite into the disrupted continental crust. The pressure fluctuations during the concomitant fenitization were reflected in densities of carbonic inclusions, ranging between 1.178 and 0.773 g.cm−3. Secondary, low-density N2-rich inclusions (82–99 mol% N2, 0.8–13.7 mol% CH4, 0–4.5 mol% CO2) homogenized to vapour at temperatures below −173 °C recorded the fenite cataclasis at temperatures below 400 °C and very low pressures. The probable maximum burial depth of the Evate carbonatite, ~20 km, is estimated from the maximum fluid pressure of 5.4 kbar attributed to lithostatic load of the crust with an average density of 2.75 g.cm−3.

Effect of the admixture of N2 to low pressure, low temperature H2-CH4-CO2 microwave plasmas used for large area deposition of nanocrystalline diamond films

In a distributed antenna array reactor, microwave H2-CH4-CO2 plasmas with admixture of N2 used for the low-temperature deposition of nanocrystalline diamond (NCD) films are studied by in situ infrared laser absorption spectroscopy (LAS) and optical emission spectroscopy techniques. The experiments are carried out in order to analyze the dependence of temperatures and species densities as a function of the admixture of nitrogen. The evolution of the concentrations of the methyl radical (CH3), and of five stable molecules (NH3, HCN, CH4, C2H2, and CO), are monitored in the plasma processes by LAS using tunable lead salt diode lasers and external-cavity quantum cascade lasers (EC-QCL) as radiation sources. OES is performed simultaneously to obtain complementary information about (i) the degree of dissociation of H2 precursor gas, (ii) the gas temperature and therefore (iii) the density of atomic hydrogen, a key species in the chemistry of NCD deposition plasmas. The species temperatures are not significantly affected by the nitrogen addition. The concentrations of the various species are in the range between 1011 to 1015 molecules cm−3. HCN and CO are the major products in the plasma besides atomic hydrogen. The analysis of the nitrogen and carbon mass balances of the measured species shows that in addition to NH3 and HCN other nitrogen containing species are produced in the plasma which were not probed. It is shown that the formation of HCN consumes C atoms that can be provided from hydrocarbon species and from the deposition of carbon-containing films on the reactor walls, which results in a decrease of the measured densities of hydrocarbon species.

Temperature evolution in a pulsed CO2–N2 glow discharge measured using quantum cascade laser absorption spectroscopy

This work uses in situ narrowband quantum cascade laser (QCL) absorption spectroscopy to study the effect of N2 on the time evolution of gas temperature, rotational temperature and the vibrational temperatures of CO2 and CO in a pulsed glow discharge. Three colinear QCLs are used to scan three regions of about 1 cm−1 between 2179.20 and 2253.51 cm−1, including transitions up to the asymmetric stretch level v3 = 6, as well as (vCO) → (vCO + 1) CO transitions up to vCO = 1. A fitting routine is used to extract temperatures from the measured absorption spectra. The time resolved measurements are performed in CO2, admixed with up to 90% N2, with the plasma operated with a 5–10 ms on-off cycle, a discharge current of 50 mA and a pressure of around 6.7 mbar. The time evolution of the gas temperature has been measured and agrees well with the time evolution of the rotational temperature. The asymmetric stretch vibrational temperature T3 of CO2 reaches a maximum of 1060 K at 0.7 ms for pure CO2, while T3 goes up to 2250 K for a N2 content of 90% and stays constant until the plasma is switched off. Both T3 and the vibrational temperature of CO TCO show a clear non-equilibrium with respect to the rotational temperature Trot. Both do not equilibrate with the rotational temperature Trot between consecutive plasma cycles for a N2 content above 70%, although T3 and TCO always equilibrate with each other in the afterglow. The symmetric stretch and bending mode temperature T12 is elevated more with respect to the rotational temperature for increasing N2 content, while the maximum of the rotational temperature decreases for increasing N2 admixtures, which might be attributed to the energy stored in the vibrational modes of N2, CO2 and CO. Additionally, an indication of an increase in the total pressure during the plasma on-time due to heating and a subsequent decrease in the afterglow due to cooling was found for a pure CO2 plasma.

Gas temperature measurements in a pulsed, low-pressure inductively coupled plasma in oxygen

Optical emission spectroscopy (OES) of the magnetic dipole allowed O2(b1Σg+) to O2(X3Σg−) transition was investigated as a non-intrusive gas temperature diagnostic for E-mode and H-mode inductively coupled plasmas (ICP) in oxygen. It was compared to tunable diode laser absorption spectroscopy using Ar admixtures, and OES of the nitrogen Second Positive System with nitrogen admixtures. O2 OES provided accurate results for the E-mode ICP, 400–600 K for powers of 100–300 W, but in H-mode the method was unsuitable probably because of excitation of O2(b1Σg+) by metastable atomic oxygen. Rotational temperatures were measured, using N2 OES with N2 admixtures, for pulsed operation of the ICP with a 30 ms pulse duration and 15% duty cycle. It took 1–3 ms before the steady-state rotational temperatures were achieved. In addition, a small variation of matching network settings affects the plasma ignition delay time by several ms.

The effect of gas additives on reactive species and bacterial inactivation by a helium plasma jet

In this paper, the influences of gas doping (O2, N2, Air) on the concentrations of reactive species and bactericidal effects induced by a He plasma jet are studied. Firstly, results show that gas doping causes an increase in voltage and a decrease in current compared with the pure He discharge under the same discharge power, which might be attributed to the different chemical characteristics of O2 and N2 and verified by the changes in the gaseous reactive species shown in the optical emission spectroscopy (OES) and Fourier transform infrared (FTIR) spectroscopy. Secondly, the concentrations of aqueous reactive oxygen species (ROS) and reactive nitrogen species (RNS) are tightly related to the addition of O2 and N2 into the working gas. The concentrations of aqueous and significantly increase while the concentrations of aqueous ROS decrease with the admixture of N2. The addition of O2 has little effect on the concentrations of and and pH values; however, the addition of O2 increases the concentration of and deceases the concentrations of H2O2 and OH. Finally, the results of bactericidal experiments demonstrate that the inactivation efficiency of the four types of plasma jets is He + O2 > He + Air > He > He + N2, which is in accordance with the changing trend of the concentration of aqueous Simultaneously to the better understanding of the formation and removal mechanisms of reactive species in the plasma–liquid interaction, these results also prove the effectiveness of regulating the concentrations of aqueous reactive species and the bacteria inactivation effects by gas doping.

Reactive oxygen and nitrogen species in Ar + N2 + O2 atmospheric-pressure nanosecond pulsed plasmas in contact with liquid

In this paper, a nanosecond pulse gas-liquid discharge is generated in Ar and Ar with admixtures of N2 or O2. The discharge images and waveforms of pulse voltage and discharge current are used to characterize gas-liquid discharge characteristics; optical emission spectroscopy and Fourier-transform infrared spectroscopy are employed to diagnose the reactive species in the gas phase, and chemical probe methods are employed to investigate plasma-induced reactive species (H2O2, NO2−, and NO3−) in the liquid phase. The effects of added contents of N2 or O2 in Ar discharge on the formation of reactive species are investigated. It is found that the productions of gaseous O and O3 increase obviously with the increasing O2 ratio and the productions of gaseous N2 (C-B), NO, NO2, and N2O increase with the increasing N2 ratio. Additionally, for the reactive species measured in the liquid phase, the increase in the N2 ratio in Ar discharge is beneficial for increasing the concentrations of NO3− and NO2− and decreasing the concentrations of H2O2, while the increase in the O2 ratio in Ar discharge decreases the concentrations of H2O2 and inhibits the production of NO2−.

Systematic investigation of the effect of N2 admixture ratio on barrier discharge in helium

The influence of the N2 admixture ratio on a He–N2 uniform atmospheric pressure glow discharge (APGD) generated using an asymmetric 20 µs, 10 kHz bipolar applied voltage pulse is systematically investigated, using electrical and optical emission spectroscopic measurements as diagnostic tools. We focused our investigation on understanding the discharge characteristics of the plasma ignited after an off-voltage period of 80 µs duration. The measured breakdown voltages for various N2 admixture ratios of up to 3% are compared with a theoretically calculated breakdown voltage, taking into account the secondary electron emission coefficient of the dielectric surface. The results indicate that the value of the secondary emission coefficient should increase from 0.1 to 0.5 to realize the experimentally obtained breakdown voltage variation within a 3% N2 admixture ratio. Using experimentally obtained values of the breakdown voltage, discharge current densities for different N2 admixture ratios, and 66 reactions among electrons, helium and N2, the variations of the N2 (A), N2 (C) and (B) state densities with N2 admixture ratio are calculated. The N2 admixture ratio dependence of the calculated N2 (C) and (B) state densities are similar to the N2 admixture ratio dependences of the emission intensities of the 337 nm band of the N2 second positive system (SPS) and the 391.4 nm band of the first negative system, respectively. Experimental observation and numerical investigation indicates that below a 1% N2 admixture ratio, the He (23S) metastable state has a strong influence on the discharge characteristics, and above a 2% N2 admixture ratio, the N2 (A) metastable state influences the discharge behavior. The N2 (A) metastable state density is estimated experimentally using the emission intensity ratio of the 337 nm band of N2 SPS and the 247 nm band of a NO-γ system. The experimentally estimated and theoretically calculated value of N2 (A) metastable state density is of the same order of 1013 cm−3. The estimated N2 (A) metastable state density shows a rapid increase above a 2% N2 admixture ratio, which supports the idea that the secondary emission coefficient increases due to an increase in N2 (A) flux.

Influence of a Nitrogen Admixture on the Value and Radial Profile of the Metastable Argon Atom Density in a DC Glow Discharge in Argon

Results of measurements of the value and radial profile of the density of Ar(3P2) metastables in a dc discharge in pure argon and Ar + 0.1%N2 and Ar + 1%N2 mixtures are presented. The electric field strength in the positive column of the discharge was also measured. The experiments were performed in a 2‑cm-radius discharge tube at gas pressures of 1, 7, and 60 Torr and discharge currents in the range of 10–50 mA. It is found that, at a pressure of 60 Torr, a nitrogen admixture to argon leads to a significant decrease in the electric field strength in the diffuse discharge, while at P = 1 Torr, in contrast, the electric field increases substantially. The degree to which the nitrogen admixture affects the density of Ar(3P2) atoms on the discharge tube axis also depends on the gas pressure. At a pressure of 60 Torr, the Ar(3P2) density decreases substantially (by three orders of magnitude for the 1%N2 admixture and 1.5 orders of magnitude for the 0.1%N2 admixture), while at a pressure of 1 Torr, the Ar(3P2) densities in pure argon and in Ar + N2 mixtures differ less than twice. It is also shown that, at all gas pressures under study, a nitrogen admixture to argon leads to the broadening of the radial profile of the Ar(3P2) density. The experiments were accompanied by numerical and theoretical studies. For pure argon, the calculations were performed in a one-dimensional (along the tube radius) discharge model, while for the Ar + 1%N2 mixture, in a zero-dimensional model, which allows one to calculate the plasma parameters on the tube axis. The calculated results were used to qualitatively explain the experimentally observed effects.

Experimental and computational investigations of electron dynamics in micro atmospheric pressure radio-frequency plasma jets operated in He/N2 mixtures

The electron power absorption dynamics in radio frequency driven micro atmospheric pressure capacitive plasma jets are studied based on experimental phase resolved optical emission spectroscopy and the computational particle in cell simulations with Monte Carlo treatment of collisions. The jet is operated at 13.56 MHz in He with different admixture concentrations of N2 and at several driving voltage amplitudes. We find the spatio-temporal dynamics of the light emission of the plasma at various wavelengths to be markedly different. This is understood by revealing the population dynamics of the upper levels of selected emission lines/bands based on comparisons between experimental and simulation results. The populations of these excited states are sensitive to different parts of the electron energy distribution function and to contributions from other excited states. Mode transitions of the electron power absorption dynamics from the Ω- to the Penning-mode are found to be induced by changing the N2 admixture concentration and the driving voltage amplitude. Our numerical simulations reveal details of this mode transition and provide novel insights into the operation details of the Penning-mode. The characteristic excitation/emission maximum at the time of maximum sheath voltage at each electrode is found to be based on two mechanisms: (i) a direct channel, i.e. excitation/emission caused by electrons generated by Penning ionization inside the sheaths and (ii) an indirect channel, i.e. secondary electrons emitted from the electrode due to the impact of positive ions generated by Penning ionization at the electrodes.

Solid carbon active screen plasma nitrocarburizing of AISI 316L stainless steel: Influence of N2-H2 gas composition on structure and properties of expanded austenite

Plasma nitrocarburizing based on active screen technology using a carbon-fiber reinforced carbon active screen was applied in an industrial-scale unit for thermochemical surface treatment of austenitic stainless steel. This concept is based on the use of a solid-carbon-source for the generation of highly reactive process gases directly in the active screen plasma. In this work, plasma nitrocarburizing of AISI 316L stainless steel was performed by means of the variation of the precursor gases H2 and N2 in the range of 0% N2 up to 100% N2 without the use of any additional carbon bearing gas. For a set of H2-N2 gas mixtures, the resulting reaction gas was monitored using infrared laser absorption spectroscopy (IRLAS). The four main stable species HCN, CH4, NH3 and C2H2 were detected. A detailed analysis of the surface microstructure resulting for each specific H2-N2 precursor gas mixture was performed. This included glow discharge optical emission spectroscopy (GDOES), optical microscopy, micro hardness measurements, as well as X-ray diffraction analysis.The concentrations of hydrocarbons CH4 and C2H2 were most abundant in case of pure hydrogen plasma, and a carbon-expanded austenite layer with hardness values up to 600 HK0.01 and smooth hardness gradient resulted. The admixture of N2 to the precursor gas significantly increased the concentrations of HCN and NH3. Due to this, a duplex structure of nitrogen-expanded austenite γN and carbon-expanded austenite γC formed. With increasing content of N2 up to 50% in the precursor gas, the resulting layer thickness increased and the hardness reached values up to 1300 HK0.01. At strong nitrogen excess in the precursor gas, the nitrogen concentration in the expanded austenite significantly increased, the Fe2–3(N, C) phase was formed, and simultaneously the layer thickness decreased. Structure and properties of the expanded austenite layer significantly changed by only varying the H2-N2 ratio of the precursor gas mixture.

Ion mobility measurements in Ar-CO[formula omitted], Ne-CO[formula omitted], and Ne-CO[formula omitted]-N[formula omitted] mixtures, and the effect of water contents

A detector has been constructed for measuring ion mobilities of gas mixtures at atmospheric pressure and room temperature. The detector consists of a standard triple GEM amplification region and a drift region where ions drift. A method has been developed to measure the ions’ arrival time at a cathode wire-grid by differentiating the recorded signals on this electrode. Simulations prove that this method is accurate and robust. The ion mobility in different gas mixtures is measured while applying different drift field values ranging from 200Vcm−1 to 1100Vcm−1. From an extrapolation of a Blanc’s law fit to measurements in Ar-CO2 mixtures we find the reduced mobility of the drifting (cluster) ion species in pure argon to be 1.94±0.01 cm2V−1s−1 and in pure carbon-dioxide to be 1.10±0.01 cm2V−1s−1. Applying the same procedure to our measurements in Ne-CO2 yields 4.06±0.07 cm2V−1s−1 and 1.09±0.01 cm2V−1s−1 for the reduced mobilities in pure neon and carbon-dioxide, respectively. Admixtures of N2 to Ne-CO2 (90-10) reduce somewhat the mobility. For the baseline gas mixture of the future ALICE Time Projection Chamber, Ne-CO2-N2 (90-10-5), the measured reduced mobility of the drifting ions is 2.92±0.04 cm2V−1s−1. Ion mobilities are examined for different water content ranging from 70ppm to about 2000ppm in the gas using Ar-CO2 (90-10) and Ne-CO2 (90-10). A slight decrease of ion mobility is observed for the addition of several hundred ppm of water.

Blistering of mechanically polished molybdenum upon its exposure to deuterium-containing plasma

Recent data on the blistering process in polished polycrystalline Mo for the case of direct-current glow discharge in deuterium and D2/2–4 mol % O2 or N2 admixtures, at an energy of incident molecular ions of 70–120 eV and a pressure of 14 Pa, are reported. Depending on the method of metal surface polishing, the initial metal grains are broken up into mutually disordered regions of smaller sizes (subgrains); the chemical composition of the damaged layer changes. In the formed structure, blistering can develop easily or be impeded. Small additions of O2 or N2 to deuterium facilitate the blistering.