Gas Mixture Of Nitrogen Research Articles

Hydrogen detection using membrane-type surface stress sensor

This study shows a possibility of the application of a membrane-type surface stress sensor (MSS) with a Pd film to a hydrogen sensor. It was able to detect hydrogen concentrations from 5 to 40000 ppm in a nitrogen gas mixture. In the case of a conventional sensor using a hydrogen-occluding material, it is necessary to wait for a state of saturation. In contrast, the proposed method can detect hydrogen quickly by the initial rate of hydrogen absorption. The relationship between the initial absorption rate and hydrogen concentration is explained by considering the two-step reaction kinetics of hydrogen absorption into bulk Pd via Langmuir dissociative adsorption on surface.

Tailoring Photoluminescence from Si-Based Nanocrystals Prepared by Pulsed Laser Ablation in He-N2 Gas Mixtures.

Using methods of pulsed laser ablation from a silicon target in helium (He)-nitrogen (N2) gas mixtures maintained at reduced pressures (0.5–5 Torr), we fabricated substrate-supported silicon (Si) nanocrystal-based films exhibiting a strong photoluminescence (PL) emission, which depended on the He/N2 ratio. We show that, in the case of ablation in pure He gas, Si nanocrystals exhibit PL bands centered in the “red - near infrared” (maximum at 760 nm) and “green” (centered at 550 nm) spectral regions, which can be attributed to quantum-confined excitonic states in small Si nanocrystals and to local electronic states in amorphous silicon suboxide (a-SiOx) coating, respectively, while the addition of N2 leads to the generation of an intense “green-yellow” PL band centered at 580 nm. The origin of the latter band is attributed to a radiative recombination in amorphous oxynitride (a-SiNxOy) coating of Si nanocrystals. PL transients of Si nanocrystals with SiOx and a-SiNxOy coatings demonstrate nonexponential decays in the micro- and submicrosecond time scales with rates depending on nitrogen content in the mixture. After milling by ultrasound and dispersing in water, Si nanocrystals can be used as efficient non-toxic markers for bioimaging, while the observed spectral tailoring effect makes possible an adjustment of the PL emission of such markers to a concrete bioimaging task.

Electric Current in Rate Equation for Parallel Plate Plasma-Enhanced Chemical Vapour Deposition of SiCxNyOz Film without Heat Assistance

A 50–500 nm-thick SiCxNyOz film was formed in parallel plate plasma at room temperature using a gas mixture of monomethylsilane, nitrogen and argon at 10−30 Pa for 5 min at the electric current of 1–16 mA. The film thickness and the concentrations of the silicon, carbon, nitrogen and oxygen were expressed by equations assuming that various chemical reactions in the gas phase and at the surface were enhanced by both the electric current and the partial pressure of the gases. The obtained equations showed the influence of the electric current on the film thickness and the compositions. Using the obtained equations, the existence and the extent of the deposition and the etching by the precursors and their combinations were evaluated.

Application of a pulsed atmospheric arc plasma jet for low‐density polyethylene coating

AbstractThe development of a method for deposition of low‐density polyethylene (LDPE) on rotating three‐dimensional aluminum alloy substrates is presented. LDPE powder with an average diameter of 50 m is dispersed with nitrogen as a carrier gas. This suspension is injected into a plasma plume generated by a pulsed atmospheric arc plasma jet (PAA‐PJ). The optimized PAA‐PJ operating parameters are a pulse frequency of 63 kHz, a power of 1,500 W, a plasma gas (mixture of nitrogen with 3.3% hydrogen) flow of 54 SLM (standard litre per minute), a carrier gas flow of 9 SLM, and a powder rate of up to 5 g/min. The plasma head is moved at 200 mm/s, and the substrate is rotated at 10 rev/min. The net deposition rate reaches 2.5 g/min. A homogeneous, high‐quality film with 1‐mm thickness is deposited on an approximately 100 cm2 substrate surface.

Synthesis of Highly Transparent SiCxNyOz:H Films via Plasma-Chemical Decomposition of 1,1,3,3,5,5-Hexamethylcyclotrisilazane, Oxygen, and Nitrogen Gas Mixture

Synthesis of silicon oxycarbonitride films highly transparent over a wide spectral region (350–2500 nm) has been developed. The films have been deposited during decomposition of 1,1,3,3,5,5-hexamethylcyclotrisilazane in mixtures with oxygen and nitrogen in a high-frequency discharge plasma in the temperature range of 373–973 K. The influence of the synthesis temperature and the oxygen to nitrogen ratio in the initial gas mixtures on chemical and functional properties of SiCxNyOz:H films has been studied using IR and Raman spectroscopy, energy-dispersive spectroscopy, ellipsometry, and spectrophotometry. The composition and selected characteristics of the obtained films have been investigated.

Low-temperature ion nitriding of VT6 titanium alloy with UFG structure

This work describes the effect of low-temperature ion nitriding on the mechanical and operational properties of the titanium alloy VT6 with the ultrafine-grained structure. Ion nitriding of the alloy was carried out at T=450-600 °C and p=300 Pa in a gas mixture of argon and nitrogen during 6 hours. Low-temperature nitriding at the temperature ≥550 °C leads to a decrease in the microhardness of the material base. The optimum processing temperatures are 450-500 °C. The formation of the UFG structure and subsequent nitriding increases wear resistance by 28%.

Effect of the Channel Inclination Angle on Convective Mixing Caused by Instability of Mechanical Equilibrium of Ternary Gas Mixture at Isothermal Diffusion

The peculiarities of a convective regime aroused due to instability of mechanical equilibrium of a ternary helium–argon–nitrogen gas mixture at isothermal diffusion are experimentally investigated. The effect of the inclination angle of diffusion channel on the intensity of convective flows is considered. The intensity of the partial transport of components in the inclined channel was measured at increased pressures. The nonlinear dependence of the mixing rate of components on the inclination angle is discovered. It is established that the observed transport of components atypical for diffusion is possible at a certain composition of the gas mixture.

Diagnostics of ion fluxes in low-temperature laboratory and industrial plasmas

We studied the ion fluxes on metal surfaces in the inductively coupled plasma reactor as a test facility. The gas mixture of argon and nitrogen was used, with 0.44 Pa total pressure. The radiofrequency power was varied in a wide range (250–2000 W). The ion fluxes were sampled in situ using a specially designed electrostatic extractor and then analyzed with a custom-built magnetic sector mass-separator. The gas composition was independently monitored by the quadrupole analyzer. All measurements were accompanied by optical emission spectroscopy (OES). The correlations of measured optical and corpuscular data are discussed. The conversion function linking optical and corpuscular intensities for Ar/N2 radiofrequency discharge was determined.

Understanding Pyrolysis of PGM-Free Electrocatalysts with X-Ray Computed Tomography

Atomically dispersed Fe-N-C electrocatalyst is the emerging advanced type of PGM-free catalyst. Its activity arises from a multitude of active sites, often viewed as co-catalytic (bifunctional sites), such as atomically-dispersed iron in nitrogen coordination (FeNx) and pyridinic and pyrrolic nitrogen moieties in graphene structures. The synthesis of Fe-N-C electrocatalysts involves a pyrolysis step, for which physical and chemical transformations are not well understood. Various ramps and temperature holds are currently used to evaporate precursors and solvents and to achieve the electrocatalyst’s high electric conductivity. An additional pyrolysis step, termed second pyrolysis, is sometimes used. Recipes exist with the pyrolysis of various precursors to arrive at catalyst that contains a high content of nitrogen. Here, Fe(NO3)3 .9 H2O and an aromatic amine charge-transfer organic salt, nicarbazin, was used. Custom pyrolysis furnace built by the Advanced Light Source’s (ALS) 8.3.2 beamline scientists was used that was capable of having gas circulation, high temperature and, at the same time, a rotating stage for x-ray computed tomography (CT) imaging. After ball-milling, the sample was placed on a ceramic stage of the vertical furnace with a circulating gas mixture of nitrogen and 7 % hydrogen. The catalyst was inserted at 525°C and then furnace temperature was increased; first to 900°C in 12 min (31.25 °C/min) and then to 975°C in 8 min (9.375 °C/min). After a 45 min hold time, the catalyst was removed from the furnace. Seven X-ray CT scans were performed during this pyrolysis process. This is the first study to use micro X-ray CT to observe the morphological changes of a catalyst powder during a pyrolysis process. Figure 1 shows the schematic of the stage, the quartz tube used to seal the gases and the ceramic stage for the catalyst placement. A photograph of our mounted catalyst within the pyrolysis chamber on the rotating stage is shown by Figure 1b and a temperature profile by Figure 1c. We have found that most of the changes in the catalyst morphology happen during the temperature ramp to 975oC and during cool down. The temperature hold at 975°C did not result in significant powder morphological changes. A follow-up study was conducted where the temperature ramp was studied in more detail with X-ray CT scans taken every 100°C. Furthermore, a second pyrolysis study was conducted where morphological changes were not observed. Figure 1. a) Schematic of pyrolysis stage and gases circulation, b) a photograph of our sample mounted within the pyrolysis chamber at 8.3.2 ALS during imaging, c) the temperature ramp during pyrolysis and d) the evolution of catalyst morphology during temperature ramp. Figure 1

Nitrogen doping of carbon nanoballoons by radiofrequency magnetron plasma and evaluation of their oxygen reduction reaction activity

AbstractNitrogen‐doped carbon materials exhibit a catalytic activity, such as an oxygen reduction reaction (ORR). In this study, we performed nitrogen doping on a carbon nanoballoon (CNB), which is a nanometer‐sized carbon particle in the form of a hollow sphere made of graphite by radiofrequency (RF) magnetron plasma in a gas mixture of nitrogen and helium. Nitrogen‐doped CNBs (N‐doped CNBs) were prepared by different plasma irradiation conditions: the sample installation positions, input powers, and irradiation times. The samples were examined for chemical state by X‐ray photoelectron spectroscopy (XPS). Hydrodynamic voltammetry was used for the evaluation of the catalytic activity of a N‐doped CNB with a pyridinic N concentration of 0.4‐1.0 at.%. As a result, the onset potential was measured to be 0.13 V versus RHE (reversible hydrogen electrode), which was close to the previously reported data of highly oriented pyrolytic graphite (HOPG) with a pyridinic N concentration of 0.57 at.%, which was prepared by annealing under NH3.

Влияние угла наклона канала на конвективное смешение, вызванное неустойчивостью механического равновесия тройной газовой смеси при изотермической диффузии

The features of the convective regime that arose due to the instability of mechanical equilibrium of the ternary helium – argon – nitrogen gas mixture during isothermal diffusion were experimentally studied. The influence of the slope angle of the diffusion channel on the intensity of convective flows is considered. The intensity of partial transfer of components in the inclined channel at elevated pressures was measured. A nonlinear dependence of the mixing rate of the components on the angle of inclination was found. It has been established that the observed transfer of components, which is atypical for diffusion, is possible with a certain composition of the gas mixture.

Velocimetry during depressurized conduction cooldown events in the HTTF

Abstract The High Temperature Test Facility (HTTF) is a quarter-scale integral-effect facility designed to study pressurized and depressurized conduction cooldowns (PCC and DCC, respectively) in high temperature, gas-cooled reactors (HTGR). This study focuses on DCC and aims to characterize the gas exchange between the reactor core and the reactor cavity to assess the risk for air ingress and subsequent potential for natural circulation core cooldowns. High-resolution velocity profile measurements are performed at the coolant pipe break location over a long time-scale using molecular tagging velocimetry. This non-intrusive, laser-based technique is applied for the first time in the field of nuclear thermal hydraulics, providing new insights for understanding the underlying phenomena at play during a DCC event. Such data are also valuable for validation of numerical simulations such as Reactor Excursion and Leak Analysis Program (RELAP). Results are reported here for various gas mixtures of helium (the coolant) and nitrogen (surrogate for air) to study the effect of density ratio. The short transient (30 s) lock-exchange phase is well captured with helium flow velocity between 0.8 and 2 m/s. The flow is shown to persist over much longer time-scales (hours) at a velocity of about 0.2 m/s, a likely consequence of gas mixing in the hot leg and in the lower plenum of the reactor. Flow visualization at the exit of the hot leg shows shear instabilities, which supports the hypothesis of significant mixing.

Low-Temperature Carburization of AL-6XN Enabled by Provisional Passivation

Employing AISI-AL-6XN as example, we introduce a new method of surface activation for low-temperature carburization. This method consists of two steps: (i) removing the passivating surface oxide and a potentially existing severely plastically deformed surface layer (Beilby layer) by aqueous (liquid) hydrochloric acid, and (ii) immersion in ethanol and subsequent drying in nitrogen. Upon carburization with a gas mixture of acetylene, hydrogen, and nitrogen, this new method of surface activation enables the formation of a fully developed “case”, a uniform solid solution of interstitial carbon in austenite with carbon fractions up to 0.20 near the alloy surface. The underlying mechanism of surface activation is shown to involve the formation of a provisional passivating layer. It consists of chlorides or ethoxides that are insoluble in ethanol. It prevents the reformation of the regular Cr-rich passivating oxide layer and is readily removed upon heating and exposure to the carburizing gas. As the new activation method is quicker, more effective, and less destructive to furnace hardware than activation with hot gaseous hydrochloric acid that is currently applied in industrial manufacturing, it may have considerable technological impact.

Nucleic acid bases in Titan tholins and possible genetic systems in the Titan liquidosphere

Titan is the largest moon of Saturn and possesses a dense atmosphere composed of nitrogen and methane. Various types of organic compounds (hydrocarbons, nitriles, etc.) have been found on Titan, which were generated by reactions taking place in its atmosphere. These reactions are considered to provide crucial evidence for chemical reactions which may have occurred in the atmosphere of primitive Earth. Cassini discovered several lakes of liquid methane and ethane on Titan's surface; in addition, the presence of ammonia water in its sub-surface was implied. In order to simulate the chemical reactions in Titan's atmosphere, gas mixtures of nitrogen and methane have been exposed to plasma discharges to synthesize complex organic matters. In this study, we focused on the formation of nucleic acid bases and related compounds recovered from synthesized Titan tholins. The five nucleic acid bases that terrestrial life uses (adenine, cytosine, thymine, guanine, and uracil) have already been reported to be present in synthesized Titan tholins. Purines and pyrimidines, including the five aforementioned nucleic acid bases, were extracted from synthesized Titan tholins and analyzed by HPLC and LC/MS. As a result, the pyrimidine bases of isocytosine and 2, 4-diaminopyrimidine were detected together with the terrestrial nucleic acid bases of adenine, uracil, and cytosine. The results obtained in conjunction with those from previous studies show that some nucleic acid bases and related pyrimidine bases are found in synthesized Titan tholins, suggesting that chemical evolutions toward xenogenetic systems could occur in Titan's environment.

Synthesis of Hydrogenated Silicon Oxycarbonitride from a Gas Mixture of Methyltris(Diethylamino)Silane, Nitrogen, and Oxygen

A synthesis of thin films consisting of hydrogenated silicon oxycarbonitride using high-frequency discharge plasma from a novel organosilicon compound methyltris(diethylamino)silane (MTDEAS) mixed with oxygen and nitrogen are studied. CVD diagrams are obtained as a result of the thermodynamic modeling of the Si–C–N–H–O system in the temperature range from 300 to 1300 K, which makes it possible to optimize the synthesis of film materials such as SiCxNyOz:H. The silicon oxycarbonitride films of various compositions are experimentally obtained in the range of deposition temperatures from 373 to 973 K for different compositions of the initial MTDEAS + O2+ xN2 gas mixture. A change in the chemical composition of the gas mixtures leads to obtaining SiCxNyOz:H films having a large range of functional properties; the refractive index varies from 1.5 to 2.21; the adjustable transparency varies from 92–99.7% in the UV visible and IR spectral regions; and the tunable band gap characteristics vary in the range from 2.5 to 4.5 eV and from 2.9 to 0.7 eV for films grown from MTDEAS + O2+ N2 and MTDEAS + O2+ 2N2 mixtures, respectively. It is shown that the films contain nanocrystals of phases belonging to structures such as Si3 – xCxN4 embedded in the amorphous matrix of hydrogenated silicon oxycarbonitride layers.

Analysis of the products of a negative corona discharge in a N2–CH4 mixture with added CO2 used as a laboratory mimic of a prebiotic atmosphere

A negative corona discharge operating at atmospheric pressure has been used to initiate chemical reactions in a gaseous mixture of nitrogen, methane, and carbon dioxide. Such a mixture simulates the composition of the early Earth's atmosphere. This work extends our previous experimental studies of the chemistry of prebiotic atmospheres generated in an atmospheric‐pressure glow discharge. The present work is devoted to the study of the role of CO2 in prebiotic atmospheric chemistry. The gas mixture was composed of nitrogen with 2–4% methane and 1% CO2. The corona discharge was characterized by electrical measurements and optical emission spectroscopy. The reaction products from the discharge were further analysed by Fourier transform infrared (FTIR) spectroscopy. The composition of solid products deposited on the electrode tip was obtained by energy dispersive X‐ray (EDX) analysis. The specific input energy was altered during the experiments, and the concentration of all products was found to increase with its increase. It is further shown that while the addition of the CO2 admixture leads to the generation of CO and H2O, no other compounds containing oxygen were detected. The energy yields of products were calculated, and good agreement was found with the values obtained in previous experiments.

Effects of the dopant concentration in laser wakefield and direct laser acceleration of electrons

In this work, we experimentally study the effects of the nitrogen concentration in laser wakefield acceleration of electrons in a gas mixture of hydrogen and nitrogen. A 15 TW peak power laser pulse is focused to ionize the gas, excite a plasma wave and accelerate electrons up to 230 MeV. We find that at dopant concentrations above 2% the total divergence of the electrons is increased and the high energy electrons are emitted preferentially with an angle of ±6 mrad, leading to a forked spatio-spectral distribution associated to direct laser acceleration (DLA). However, electrons can gain more energy and have a divergence lower than 4 mrad for concentrations below 0.5% and the same laser and plasma conditions. Particle-in-cell simulations show that for dopant concentrations above 2%, the amount of trapped charge is large enough to significantly perturb the plasma wave, reducing the amplitude of the longitudinal wakefield and suppressing other trapping mechanisms. At high concentrations the number of trapped electrons overlapping with the laser fields is increased, which rises the amount of charge affected by DLA. We conclude that the dopant concentration affects the quantity of electrons that experience significant DLA and the beam loading of the plasma wave driven by the laser pulse. These two mechanisms influence the electrons final energy, and thus the dopant concentration should be considered as a factor for the optimization of the electron beam parameters.

Preparation of Carbon Molecular Sieves Used for CH4/N2 Separation

In this study, carbon molecular sieves (CMS) were prepared by chemical vapor deposition method using benzene as depositing agent based on activated carbon. The influences of deposition temperature, time, and flow rate of benzene on adsorption capacity and separation coefficient were investigated. The results show that the CH4 equilibrium adsorption capacity and CH4/N2 separation coefficient of CMS-G, which is prepared at the deposition temperature of 1023 K, time of 60 min, and flow rate of 4 mL·min–1, are at a maximum value (parametric investigation of this study is based on the parameter ranges in the text). The deposition temperatures had an obvious effect on the textural modification of CMS. CMS-G was characterized by mercury intrusion, CO2 permeation, analysis of kinetics, and pressure swing adsorption (PSA). Both kinetic and PSA results demonstrate a good CH4/N2 separation performance for the CMS-G. A very high kinetic selectivity was observed, which reached 35.26. An enrichment of 30.20% for methane in pressure swing adsorption experiment was also observed. The data demonstrate that CMS-G is a good adsorbent suitable for separating CH4 from methane and nitrogen gas mixture.

Doping Nitrogen in InGaZnO Thin Film Transistor with Double Layer Channel Structure.

This paper presents the electrical characteristics of doping nitrogen in an amorphous InGaZnO thin film transistor. The IGZO:N film, which acted as a channel layer, was deposited using RF sputtering with a nitrogen and argon gas mixture at room temperature. The optimized parameters of the IGZO:N/IGZO TFT are as follows: threshold voltage is 0.5 V, field effect mobility is 14.34 cm2V-1S-1. The on/off current ratio is 106 and subthreshold swing is 1.48 V/decade. The positive gate bias stress stability of InGaZnO doping with nitrogen shows improvement compared to doping with oxygen.

Effects of a Plasma Generated from a Gas Mixture of Nitrogen, Methane, and Hydrogen on the Reduction of Graphene-Oxide Thin Films

Effects of a Plasma Generated from a Gas Mixture of Nitrogen, Methane, and Hydrogen on the Reduction of Graphene-Oxide Thin Films