Nitrogen-hydrogen Mixture Research Articles

Protective gas in metalware-production furnaces

Three methods of producing protective gas that have been used at Cherepovets steel-rolling plant are considered; this gas contains chemically pure nitrogen and hydrogen, with a dew point no higher than −40°C. The first method was introduced at the startup of the plant’s protective-gas station. The raw materials for gas production were liquid ammonia supplied by OAO Cherepovetskii Atom and industrial-grade nitrogen (containing up to 4% oxygen). After prolonged operation, the protective-gas station became worn-out and out of date. In 2002, the production of protective gas from chemically pure nitrogen and nitrogen-hydrogen mixture was introduced. This system was used for six years. Since 2008, protective gas has been produced by mixing chemically pure nitrogen and nitrogen-hydrogen mixture in special equipment. The consequent economic savings at Cherepovets steel-rolling plant are 13.6 million rub/yr.

Nonuniform microwave discharge in a nitrogen-hydrogen mixture

The method of optical emission spectroscopy is used to investigate the influence of additions of hydrogen on the emission characteristics of a highly nonuniform electrode microwave discharge in nitrogen at a pressure of 1 torr. It is demonstrated that the pattern of the influence made by hydrogen addition (zero to 50% with respect to flow rate of hydrogen) on the intensity of emission bands of nitrogen is different in different parts of the discharge. It is further observed that the influence of hydrogen on the vibrational distribution of nitrogen molecules in the C3Πu state is different C3?uin different parts of the discharge. Analysis is made of various processes involving hydrogen, which affect the emission of nitrogen bands. An inference is made that ion conversion is an important mechanism of such influence. One-dimensional simulation is performed in view of these processes, and it is demonstrated that the experimentally observed effects may be associated with this mechanism.

Effect of Plasma Nitriding Environment and Time on Plain Fatigue and Fretting Fatigue Behavior of Ti–6Al–4V

Plasma nitriding was performed on Ti–6Al–4V fatigue test samples at 520°C in two environments (nitrogen and nitrogen–hydrogen mixture in a ratio of 3:1) for two time periods (4 and 18 h). Plain fatigue and fretting fatigue tests were conducted on unnitrided and plasma nitrided samples. Plasma nitriding degraded lives under both plain fatigue and fretting fatigue loadings. The samples nitrided in nitrogen exhibited superior lives compared with the samples nitrided in the nitrogen–hydrogen mixture, possibly due to the relatively higher hardness (and presumably lower toughness) of the nitrided layer of the samples nitrided in the nitrogen–hydrogen mixture environment. For those samples nitrided in the nitrogen–hydrogen mixture, those nitrided for 18 h exhibited superior lives compared with those nitrided for 4 h. This trend was observed for samples nitrided in nitrogen gas at lower stress levels only; the converse was true at higher stress levels of 550 MPa and 700 MPa under plain fatigue loading. However, under fretting fatigue loading, the plasma nitriding time did not influence the lives significantly.

Low power hydrogen sensors using electrodeposited PdNi–Si schottky diodes

The use of electrodeposited PdNi–Si Schottky barriers as low power Hydrogen sensors is investigated. The Palladium content of the film causes the Hydrogen molecules to dissociate and be absorbed by the film, changing the metal work function and Schottky barrier current. Electrodeposited PdNi–Si Schottky barriers exhibit very low reverse bias current and in a back to back configuration form a device that draws extremely low power when idle. The Schottky diodes were fabricated on 0.5–1.5 Ω cm 100 n-type Si by electrodeposition of PdNi followed by evaporation of Aluminium contact pads. Electrical measurements at different Hydrogen pressures were performed on back to back Schottky diodes in a vacuum chamber using pure Nitrogen and a 5% Hydrogen-Nitrogen mixture. Very low currents of ≈1nA were measured in the absence of Hydrogen. Large increases in the currents, upto a factor of 100, were observed upon exposure to different Hydrogen partial pressures. The highest sensitivity was estimated to be 17.27 nA/mbar. The low idle current, simplicity of the fabrication process and ability to easily integrate with conventional electronics proves the suitability of electrodeposited PdNi–Si Schottky barriers as low power Hydrogen sensors.

Electrical characteristics of (N2-H2) gas mixture DC glow discharge

The electrical characteristics of DC Nitrogen-Hydrogen mixture glow discharge were investigated. The discharge current-voltage (I-V) characteristic curves of the discharge were measured at different gas pressures and gas mixture percentage. The axial distribution of both potential and electric field were studied at different H2percentage. The existence of the reversal electric field in the negative glow region was confirmed. Using the axial electric field distribution, the cathode fall thickness (Xc) was calculated. Second derivative of the single Langmuir probe electron current method was used to measure the electron energy distribution function (EEDF) in (N2-H2) gas mixture DC glow discharge at different H2 percentage. In the positive column region, a Maxwellian EEDF was found at different conditions, while in both cathode fall and negative glow regions, a non-Maxwellian EEDF was observed. Two groups of electrons were detected in these two regions. Key words: Glow discharge, axial potential and electric field distributions, Paschen's curves, Langmuir probes.

BaHfO3:Ce sintered ceramic scintillators

Abstract Raw powders of BaHfO3:Ce were prepared with modified Pechini process and were calcined in the 650–1700 °C range of temperatures, at different atmospheres – air, vacuum and nitrogen–hydrogen mixture. The powders were converted into sintered ceramics by vacuum sintering. The materials were characterized by XRD, TEM, photoluminescence and radioluminescence spectroscopy. UV-VUV excitation spectra were recorded using synchrotron radiation. Excitation spectra proved that atmosphere of preparation significantly influences the host-to-activator energy transfer, which is the most efficient for materials made in reducing conditions. Also radioluminescence efficacy was found to be superior for materials prepared in such conditions.

Mechanism of oxygen poisoning of ammonia synthesis catalyst

The effect of oxygen adsorbed on the surface of a commercial catalyst from a mixture of hydrogen with water vapor on the steady-state and nonsteady-state ammonia synthesis kinetics is studied under gradientless conditions at the pressures of the stoichiometric nitrogen-hydrogen mixture below the atmospheric pressure and at the temperatures of 285 and 240°C. The results obtained are discussed on the basis of the concepts of the ammonia synthesis theory of Temkin. The poisoning effect of oxygen on the reaction rate is explained by an increase in the activation energy of the rate constant k+ in the Temkin-Pyzhev equation, i.e., an increase in the activation energy of the rate constant of nitrogen adsorption at the fixed nitrogen adsorption heat. This conclusion agrees with the concepts of Ertl et al., according to which the activation energy of nitrogen adsorption on iron changes in symbasis with the variation of the electronic work function. Oxygen adsorption on the catalyst surface increases the electronic work function. Thus, the mechanism of the catalyst poisoning by oxygen (at its low surface coverage) consists in an increase in the electronic work function. Assumptions are stated as to the role of chemical promoters of iron catalysts.

Influence of plasma nitriding on fretting wear behaviour of Ti–6Al–4V

Plasma nitriding was performed on Ti–6Al–4V samples at 520°C in two environments (pure nitrogen and a mixture of nitrogen and hydrogen in the ratio of 3:1) for two different time periods (4 and 18h). Fretting wear tests were conducted on unnitrided and nitrided samples for 50,000 cycles using alumina ball counterbody. Plasma nitriding reduced the tangential force coefficient of Ti–6Al–4V. The samples nitrided for 4h exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided for 18h. The samples nitrided in nitrogen–hydrogen mixture environment exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided in pure nitrogen. The samples plasma nitrided in nitrogen–hydrogen mixture for 4h exhibited the highest hardness and the lowest tangential force coefficient. The wear volume and specific wear rate of the plasma nitrided samples were lower than those of the unnitrided samples. A consistent trend was not observed regarding which nitriding condition would result in lower wear volume and specific wear rate at different loads.

Raising efficiency of special-purity hydrogen production from nitrogen-hydrogen gas mixtures

The results of analysis of the conditions of operation of one of Russia’s early pilot high-temperature membrane apparatuses DB-100 for producing special-purity hydrogen (99.9999–99.999999 vol. %) are reported. The interrelation of the basic technological and design parameters is expressed by a set of equations. A numerical model is used to optimize the operating parameters of the DB-100 membrane apparatus.

Fretting wear behaviour of plasma nitrided Ti-6Al-4V fretted against unnitrided Ti-6Al-4V and alumina counterbodies

Ti-6Al-4V samples were plasma nitrided at 520°C in two environments (nitrogen and a mixture of nitrogen and hydrogen in the ratio of 3:1) for two different time periods (4 h and 18 h). Fretting wear tests were conducted on unnitrided and nitrided samples for 50,000 cycles using two counterbody materials (unnitrided Ti-6Al-4V and alumina). Gross slip prevailed at a normal load of 4.9 N while mixed stick-slip prevailed at 9.8 N. Tangential force coefficient values of plasma nitrided samples were lower than those of unnitrided samples. The tangential force coefficient nearly stabilised after thousand cycles in case of samples tested against Ti-6Al-4V counterbody. On the other hand, it showed a continuously increasing trend in case of specimens tested against alumina counterbody. The samples nitrided for 4 h exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided for 18 h. The samples nitrided in nitrogen-hydrogen mixture environment exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided in nitrogen. The samples plasma nitrided in nitrogen-hydrogen mixture for 4 h exhibited the highest hardness and the lowest tangential force coefficient. The wear volume of the plasma nitrided samples was lower than that of the unnitrided samples. Owing to tribochemical reactions, the wear volume of unnitrided and nitrided samples fretted against alumina ball was higher than that of the samples fretted against Ti-6Al-4V. A consistent trend was not observed regarding which nitriding condition would result in lower wear volume at different loads.

Two-dimensional Raman mole-fraction and temperature measurements for hydrogen-nitrogen mixture analysis

A two-dimensional laser Raman technique was developed and applied to directly probe the population number of selected rotational and vibrational energy levels of hydrogen and nitrogen. Using three cameras simultaneously, temperature and mole fraction images could be detected. Three different combinations of rotational and vibrational Raman signals of hydrogen and nitrogen were analyzed to identify the combination that is most suitable for future mixture analysis in hydrogen internal combustion engines. Here the experiments were conducted in an injection chamber where hot hydrogen was injected into room temperature nitrogen at 1.1 MPa.

Particle Temperature Fluctuations in Plasma Spraying

In direct current (d.c.) plasma spray torches, the dynamic behavior of the arc attachment at the anode nozzle results in arc voltage fluctuations and correspondingly power fluctuations. The resulting plasma jet instabilities affect the treatment (heat and momentum) of particles injected in the plasma flow and, thus, the coating quality. However, it is not clear if the experimentally observed fluctuations of particle temperatures are a major phenomena and if their frequencies are always in unison with those of voltage. In this study, two online techniques are used to investigate, respectively, the time variation of particle temperatures and its correlation with voltage variations; the first technique makes it possible to analyze plasma voltage instabilities and the second one to investigate those of particle temperatures. Both allow determining the frequencies and amplitude variations of voltage and particle temperature. Experiments were carried out with three plasma torches (F4-type and two 3MB-type) using, respectively, argon-hydrogen (F4-type and 3MB) and nitrogen-hydrogen (3MB) mixtures (all with restrike mode for the voltage fluctuations) as plasma-forming gases. A good correlation between arc voltage and particle temperature fluctuations is observed when the plasma torch is operated with argon-hydrogen mixtures and high mass flow rate. However, it is not the case when the torch is operated with nitrogen-hydrogen mixtures even if the amplitudes of voltage fluctuations are two to three times higher than those obtained with Ar-H2.

하이드라진(N2H4) 아크젯 추력기의 수치적 모델링

The computational fluid dynamic analysis has been conducted for the thermo-chemical flow field in an arcjet thruster with mono-propellant Hydrazine (N2H4) as a working fluid. The Reynolds Averaged Navier-Stokes (RANS) equations are modified to analyze compressible flows with the thermal radiation and electric field. The Maxwell equation, which is loosely coupled with the fluid dynamic equations through the Ohm heating and Lorentz forces, is adopted to analyze the electric field induced by the electric arc. The chemical reactions of Hydrazine were assumed to be infinitely fast due to the high temperature field inside the arcjet thruster. The chemical and the thermal radiation models for the nitrogen-hydrogen mixture and optically thick media respectively, were incorporated with the fluid dynamic equations. The results show that performance indices of the arcjet thruster with 1kW arc heating are improved by amount of 180% in thrust and 200% in specific impulse more than frozen flow. In addition to thermo-physical process inside the arcjet thruster is understood from the flow field results.

A spectroscopic study into the decomposition process of titanium isopropoxide in the nitrogen–hydrogen 100 kHz low-pressure plasma

Optical emission spectroscopy was employed for the study of the nitrogen–hydrogen and nitrogen–hydrogen–titanium (IV) isopropoxide mixtures in the 100 kHz low pressure capacitively coupled discharge. High-energy species were identified in the plasma phase. The behavior of the excited species versus the gas composition has also been investigated. The optical actinometry technique was applied in order to evaluate the N 2, CH, CO, CN, N, C and the H relative concentrations versus the hydrogen concentration in reactive mixtures. The effect of the hydrogen concentration in the nitrogen–hydrogen mixture on the decomposition processes of titanium isopropoxide was investigated. The plasma temperature (the H excitation temperature, the CN, N 2 and N 2 + vibrational temperatures and the N 2 + rotational temperature) as well as the electron number density were determined here. The temperature magnitudes ( T exc≈5700–7400 K, T vib(CN)≈4700–8100 K, T vib(N 2)≈2700–3050 K, T vib(N 2 +)≈1500–1600 K and T rot(N 2 +)≈660–890 K) indicated a very significant deviation from the LTE state.

A numerical study of auto-ignition in turbulent lifted flames issuing into a vitiated co-flow

This paper presents a numerical study of auto-ignition in simple jets of a hydrogen–nitrogen mixture issuing into a vitiated co-flowing stream. The stabilization region of these flames is complex and, depending on the flow conditions, may undergo a transition from auto-ignition to premixed flame propagation. The objective of this paper is to develop numerical indicators for identifying such behavior, first in well-known simple test cases and then in the lifted turbulent flames. The calculations employ a composition probability density function (PDF) approach coupled to the commercial CFD code, FLUENT. The in-situ-adaptive tabulation (ISAT) method is used to implement detailed chemical kinetics. A simple k–ϵ turbulence model is used for turbulence along with a low Reynolds number model close to the solid walls of the fuel pipe. The first indicator is based on an analysis of the species transport with respect to the budget of convection, diffusion and chemical reaction terms. This is a powerful tool for investigating aspects of turbulent combustion that would otherwise be prohibitive or impossible to examine experimentally. Reaction balanced by convection with minimal axial diffusion is taken as an indicator of auto-ignition while a diffusive–reactive balance, preceded by a convective–diffusive balanced pre-heat zone, is representative of a premixed flame. The second indicator is the relative location of the onset of creation of certain radical species such as HO2 ahead of the flame zone. The buildup of HO2 prior to the creation of H, O and OH is taken as another indicator of autoignition. The paper first confirms the relevance of these indicators with respect to two simple test cases representing clear auto-ignition and premixed flame propagation. Three turbulent lifted flames are then investigated and the presence of auto-ignition is identified. These numerical tools are essential in providing valuable insights into the stabilization behaviour of these flames, and the demarcation between processes of auto-ignition and premixed flame propagation.

Variation of emission color of Y3Al5O12:Ce induced by thermal treatment at reducing atmosphere

Nanocrystalline powders of Y3Al5O12:Ce (YAG:Ce) were prepared using Pechini technique and precipitation with urea at 80–90 °C. It was shown that material obtained using Pechini procedure, after heating at 900–1000 °C is crystallographically pure, while that made with urea is contaminated with Y4Al2O9 and YAlO3. For all powders, heating at reducing atmosphere of nitrogen–hydrogen mixture at 1000 °C caused a red shift of the Ce3+ luminescence by about 20–25 nm. The effect was stronger for the powder prepared with urea. Also this powder was characterized by a longer decay time of the Ce3+ emission indicating the treatment at reducing atmosphere diminished nonradiative relaxation probability of the excited electrons.

Electron energy distribution function in plasma determined using numerical simulations of multiple harmonic components on Langmuir probe characteristic—Efficiency of the method

The method proposed to determine the electron energy distribution is based on the numerical simulation of the effect induced by a sinusoidal perturbation superimposed to the direct current voltage applied to the probe. The simulation is generating a multiple harmonic components signal over the rough experimental data. Each harmonic component can be isolated by means of finite impulse response filters. Then, the second derivative is deduced from the second harmonic component using the Taylor expansion. The efficiency of the method is proved first on simple cases and second on typical Langmuir probes characteristics recorded in the expansion of a microwave plasma containing argon or nitrogen-hydrogen gas mixture. Results obtained using this method are compared to those, which are determined using a classical Savitzsky-Golay filter.

Theoretical and experimental analysis of N2–H2 stimulated Raman spectra

The paper reports on a detailed study of the N2–H2 collisional line broadening coefficient. High resolution stimulated Raman spectra of nitrogen–hydrogen mixtures have been recorded at liquid nitrogen and room temperatures. Corresponding linewidth calculations have been performed at temperatures between 77 and 500 K using the semiclassical Robert and Bonamy model for J rotational quantum numbers varying between 0 and 11. Comparison between experimental data and calculated results shows good agreement at room temperature using an adjusted value for the kinetic diameter.

Utilization of Low-Calorific Gaseous Fuel in a Direct-Injection Diesel Engine

Low-calorific gases with a small portion of hydrogen are produced in various chemical processes, such as gasification of solid wastes or biomass. The aim of this study is to clarify the efficient usage of these gases in diesel engines used for power generation. Effects of amount and composition of low-calorific gases on diesel engine performance and exhaust emissions were experimentally investigated adding hydrogen-nitrogen mixtures into the intake gas of a single-cylinder direct-injection diesel engine. The results indicate that optimal usage of low-calorific gases improves NOx and Smoke emissions with remarkable saving in diesel fuel consumption.

Growth of non-regular a-CN x:H cluster arrays on pulse plasma nitrided hot work steel samples

Samples made of hot work steel grade H11 were pulse plasma nitrided in hydrogen nitrogen mixture and post-nitrocarburized in carbon-containing discharge. Microhardness measurements, optical microscopy, SEM, Raman, XRD and infrared spectra analyses revealed the existence of a thin epsilon + γ′ compound zone onto 150 μm thick diffusion layer after plasma nitriding, while a dense 3 μm thick amorphous hydrogenated carbon nitride overcoating was grown during plasma post-processing in carbon-containing atmosphere. On the surface of plasma deposited hydrogenated carbonitride films intended for tribological applications non-regular “arrays” of different size conductive clusters were found. Similar arrays architecture, when obtained intentionally, could be used for the resonant optical connections in nanooptics and macro optics. Some coupled arrays, like the fiberoptic waveguide in fiber optics interferometers, were also observed. Computer simulation showed that in the case of similar geometry spherical Ag clusters deposited onto dielectric substrate the resonant interaction of light beam with coupled arrays is possible resembling to the light beam coupler on nanoscale.