Nitrogen-hydrogen Mixture Research Articles

Dynamic behavior of variable-density, turbulent jets in their near development fields

Four round turbulent jets of hydrogen–nitrogen mixtures (initial density ratio ranging from 0.07 to 1) discharging into a slow air coflow are experimentally and analytically studied. The investigation is restricted to the near development field over which both buoyancy and coflow effects have negligible influence on the jet expansion. Two-color laser Doppler anemometry provides the mean and fluctuation of the velocity components, while a laser Mie scattering technique with conditional seeding provides the radial profiles of mean density. Self-similar behavior is investigated by using a local effective jet diameter that accounts for the strong density variations in the near development field. This scaling based on momentum flux conservation appears to be efficient for collapsing the centerline velocity data (mean and RMS) along a unique self-similar curve for all jets.

Dissociation of hydrogen in glow discharges in hydrogen-nitrogen mixtures

Results from a theoretical study of electron and heavy particle kinetics of H 2 in glow discharges through H 2-N 2 mixtures are presented. It is shown that for small concentrations of the additive in %N 2-%H 2, the effects on the discharge impedance are diagnostic probes providing crucial information regarding the dissociation and ionization balances. The results show that for low discharge currents (< 80 mA), medium gas pressures (> 1 Torr), and ≈10%–80%H 2-N 2 mixture composition, collisions between excited electronic states of N 2 with H 2 are the dominant dissociation channels of H 2 in %H 2-%N 2 discharges.

An experimental investigation of strain-induced extinction of diluted hydrogen-air counterflow diffusion flames

Previous studies about turbulent combustion in hydrogen-air systems for application in supersonic-combustion devices such as the National Aerospace Plane have suggested that combustion in such devices takes place in thin reaction sheets that are convoluted, distorted, and in some cases locally extinguished by turbulence. Sharing this view, a number of researchers have focused their attention on characterizing the structure and extinction properties of laminar hydrogen-air diffusion flames. Most of the research has been of a numerical or theoretical nature and only a few experiments have been performed to test the detailed numerical diffusion-flame models. The objective of the present communication is to report results of some experiments designed to characterize the extinction properties of diluted laminar counterflow diffusion flames between air and hydrogen-nitrogen mixtures.

Sintering Mechanisms of Boron Alloyed AISI 316L Stainless Steel

The effect of boron on sintering of austenitic stainless steel was studied with reference to atmosphere (nitrogen-hydrogen mixtures) and temperature conditions. Specimens were characterised by the ...

Microwave Induced Plasma (MIP) Nitriding of Titanium Alloy

ABSTRACTTitanium alloys possess several attractive properties such as light weight, high strength and excellent corrosion resistance. However, wider application of these alloys, especially for load bearing components operating under sliding conditions, are restricted due to poor tribological (friction and wear) behaviour. It has been shown previously [1] that nitriding of titanium by using DC plasma is an effective means of increasing the hardness and reducing friction and wear. In this work nitriding response of titanium alloy (Ti-6A1–4V) was investigated using a Microwave Induced Plasma (MIP). The plasma was generated in a TM012 stainless steel cylindrical cavity using 1.5 kW power supply operating at 2.45 GHz. The cavity was water cooled and tuned by two sliding shorts. Nitriding experiments in nitrogen-hydrogen mixture at 70 to 100 torr pressure established that MIP provides an excellent mass transfer medium for nitriding titanium alloy. Furthermore, significant advantages over DC plasma have been discerned. For instance, reduced sputtering, uniformity of treatment and temperature stability can be cited. In this work, preliminary results of characterisation of MIP nitrided surfaces by x-ray diffraction and optical microscopy will be presented to demonstrate the effectiveness of MIP for nitriding titanium.

Influence of methane on the nitriding gas reduction of kaolinite

A new synthesis of β′-SiAION via the reduction and nitridation of aluminosilicates in the presence of a carbon source by a hydrogen–nitrogen gas mixture is presented.The formation of β′-SiAION on surfaces (SiC, alumina) devoid of carbon was found to be impossible. Thermogravimetric analysis and mass spectrometry showed that, in a carbon crucible, methane was formed from the reaction of hydrogen with carbon. β′-SiAION was obtained in the absence of free carbon by adding a small amount of methane to the hydrogen-nitrogen gaseous mixture. The formation of β′-SiAION is thus the consequence of reduction by methane rather than by hydrogen. Parasitic reactions of hydrogen lead to silicon elimination as SiO in the gas phase, and to a Si/Al ratio lower than in the starting kaolinite.

Interaction of Zr+Nb with carbon, nitrogen, and hydrogen in the combustion mode

Systematic investigations of combustion of heterogeneous systems based on zirconium, niobium, and nonmetals, viz., carbon, nitrogen, and hydrogen, are conducted. The combustion regularities of three-, four-, and five-component systems and the dependences of the combustion temperatures and rates and the chemical composition of the final products on the process parameters are studied. Changes in the gasless and filtration modes of combustion in multicomponent systems are revealed. The basic factor influencing the formation of single-phase multicomponent compounds are ascertained. Concentration triangles are constructed, which are pseudophase diagrams of the Zr−Nb−C system for combustion in argon, nitrogen hydrogen, and a nitrogen-hydrogen mixture that represent the evolution of the phase composition of the combustion products, depending on the reaction medium.

Thermal nonequilibrium in a low-power arcjet nozzle

Emission spectroscopy measurements were made of the plasma flow inside the nozzle of a 1-kW-class arcjet thruster. The thruster propellant was a hydrogen-nitrogen mixture used to simulate fully decomposed hydrazine. Several 0.25-mm-diam holes were drilled into the 12-mm-long diverging section of the tungsten thruster nozzle to provide side-on optical access to the internal flow. Electron excitation for atomic species and molecular vibrational and rotational temperatures were determined for the expanding plasma using relative line ratio techniques. The atomic excitation temperature decreased from 18,000 K at a location 3-mm downstream of the constrictor to 9000 K at a location 9 mm from the constrictor, while the molecular vibrational and rotational temperatures decreased from 6500 to 3000 K and 8000 to 3000 K, respectively, between the same locations. The electron density, measured using H^ line Stark broadening, decreased from ~1021 m~3 to 2 x 10 20 m~3 during the expansion in the nozzle. The results show that the plasma is in a nonequilibrium state throughout most of the nozzle, with relaxation times close to or larger than the particle residence time.

Determination of overall mass transport coefficients in gas diffusion electrodes

Gas diffusion electrodes are used for many purposes, for example in fuel cells, in synthesis and as anodes in electrodeposition processes. The behaviour of gas diffusion electrodes has been the subject of many studies. In this work the transport of gas in the gas diffusion electrode, characterized by the overall mass transport coefficient, has been investigated using hydrogen-nitrogen mixtures. A reactor model for the gas compartment of the gas diffusion electrode test cell is proposed to calculate the concentration of hydrogen in the gas compartment as a function of the input concentration of hydrogen and the total volumetric gas flow rate. The mass transport coefficient is found to be independent of variations in hydrogen concentration and volumetric gas flow rate. The temperature dependence of the mass transport coefficient has been determined. A maximum was found at 40°C.

Thermodynamic equilibrium of a gas mixture with a solution in the condensed phase

A thermodynamic analysis is made of the equilibrium of a gas mixture (using a nitrogen-hydrogen mixture as an example) with a solid solution of its components. The processes occurring in the surface layer and interphase exchange are taken into account. The equilibrium characteristics are determined in terms of the equilibrium constants of the intermediate stages of the surface reactions.

プラズマ窒化によるＴｉ‐６Ａｌ‐４Ｖ合金の表面改質

Ion nitriding is widely used as an important surface hardening method for various metals. In this method, the sample to be treated is served as a cathode in a d. c. glow diacharge. In our study, what is called "plasma nitriding" was tried in place of ion-nitriding for titanium alloy (Ti-6Al-4V). In this plasma nitriding, the sample generally maintained in an electrically floating state was placed in an r. f. glow plasma generated inductively using pure nitrogen or nitrogen-hydrogen mixture. By addition of hydrogen into nitrogen, the nitriding rate was promoted and δ-TiN phase was preferentially formed at relatively lower temperatures. It is probable that active ions and N-H radicals in the plasma can attribute to such phenomena. According to SEM observation, it was made clear that the change of the nitrided surface morphology became more remarkable with the elapsed time and the increase of hydrogen content in the gas mixture. We also attempted to impose a d. c. bias voltage to the alloy sample in the r. f. plasma. The promotion of nitriding and other interesting phenomena, such as phase transition from ε to δ and increase of surface hardness, were observed in such r. f. plasma nitriding assisted by charged particle bombardment. Thermal nitriding of the same sample without plasma was tried to confirm the characteristics of plasma nitriding.

Rated reliability of compressors with corrosion taken into account

This paper attempts to examine various types of compressor component corrosion in moist gases and liquids. Moist gas moves through the main compressor channel and the air cooling system; when the cooling system is water-fed, its components interact with the liquid. Various gases (air, nitrogen-hydrogen mixtures, ethylene, nitrogen, oxygen, helium, hydrogen, chlorine, etc.) are compressed in piston compressors. The air in industrial regions is polluted with sulfur dioxide and nitrogen oxides [i], which form acids in the presence of moisture; this is responsible for occurrence of moist acidic gases in the working channels of air compressors and in air-fed compressor cooling systems. Operating experience has shown that the components of a multistage piston compressor most affected by corrosion are the cylinders, pistons, piston rings, valves, coolers, pipelines, and water/oil separators. The main compressor components are now fabricated from the following materials: pistons from grey iron or aluminum alloys, cylinders from cast iron (grey, high-strength, or alloy) and steel (carbon and alloy), piston rings from grey iron; valves from grey iron, type 45 steel, types 40Kh, 30KhMA, 30KhGSA, 50KhFA, and 65S2VA low alloy steels, and types !2KhlSN9T and 30Kh13 high-alloy steels, and coolers from cast iron, steel (carbon and alloy), copper, brass, and clad metals. These compressor components differ substantially from one another in terms of exogenous and endogenous factors promoting corrosion. The choice of materials for fabricating compressor components that meet specified reliability requirements is an important problem, and its solution can begin at the working. design stage. It is suggested that test calculations of main compressor component working characteristics be made with the influence of corrosion taken into account. These are guideline calculations and can in no way substitute for serious materials selection studies in the stages following working design. Allowance for the influence of corrosion makes computation of compressor reliability at the design stage more complete. The term "standing" corrosion used throughout the remainder of this paper (by analogy with the term employed for turbines) refers to corrosion of compressor components during shutdowns. The recommendations below may be useful in making design-level compressor reliability calculations with permissible corrosion rate taken into account [2]. The corrosion rate for metals in the active state in acidic media containing no oxidizing agents (hydrogen depolarization) can be computed from the following relationships:

Some properties of amorphous hydrogenated silicon nitride prepared by ion-beam-assisted deposition

Thin films of a-SiNx:H were deposited using the ion-beam-assisted deposition technique. Silicon was evaporated from a resistively heated carbon crucible while the substrate was bombarded with low-energy ions (100 eV). The feed gas used for the ion source was primarily ammonia (NH3), but a 90% nitrogen, 10% hydrogen mixture was also tried. The nitrogen–hydrogen mixture resulted in nonhydrogenated films. Both the absence of absorption in the IR spectrum owing to oxygen, and the increase in slope of the Tauc plots are evidence of an improvement in film morphology owing to the ion bombardment. The wide band-gap films photoconduct when exposed to UV light. The photoconducting property is lost when the films are exposed to air, and is restored when the samples are thermally annealed in a vacuum.

PVT data from burnett and refractive index measurements for the nitrogen—hydrogen system from 270 to 353 K and pressures to 30 MPa

The P, ϱ and T behaviour of four nitrogen—hydrogen mixtures (0.8505 N 2, 0.7501 N 2, 0.4998 N 2 and 0.2503 N 2) was measured in the temperature range 270–353 K and pressures up to 30 MPa. Measurements were carried out with a Burnett apparatus and an optical device, also termed a grating interferometer. The experimental results were used to obtain tables of compressibility factors for each mixture. The compressibility factors obtained by the two methods, the Burnett and optical experiments, are accurate to ±0.1%. For pressures below 10 MPa the accuracy of the Burnett data is estimated to be ±0.07%. The P, ϱ and T data were used to determine the second and third virial coefficients, B and C, for each mixture. Unlike interaction virial coefficients, B 12, C 112 and C, 122 were determined from the mixture virial coefficients by using the like interaction virial coefficients, B 11, B 22, C 111 and C 222, of the pure components from Jaeschke and Hinze. The deduced values of B 12 are accurate to ±0.4 cm 3 mol −1. These values agree excellently with the B 12 results determined from the P, ϱ and T data of Michels and Wassenaar.

Effect of nitriding on the oxidation kinetics of niobium

1. The oxidation of niobium in air under, atmospheric pressure in the 600–700°C interval proceeds linearly; in this case, the process begins from a stage of parabolic oxidation to 650°C. 2. The nitriding of niobium specimens in a nitrogen-hydrogen mixture at 900°C significantly improves their oxidation resistance in air.

Degradation of LaNi 5 by thermobaric cycling in hydrogen and hydrogen-nitrogen mixture

The dynamics of LaNi 5 degradation by thermobaric cycling up to 7000 cycles in hydrogen and hydrogen-nitrogen mixture has been studied. The quantitative X-ray analysis and the study of desorption isotherms of the samples subjected to cycling have been carried out. It has been shown that the dynamics of change of the hydrogen capacity is identical in the cases of technical hydrogen, pure hydrogen and hydrogen-nitrogen mixtures at an absorption temperature of less than 40°C and at decomposition temperatures of 100°C and 150°C. It has been shown that one can distinguish the irreversible loss of hydrogen capacity conditioned by the hydrogenolysis reaction and the restorable loss conditioned by the formation of LaNi 5H 4 phase in a kinetically immobilized form.

Effect of pressure on the reduction rate of a fused iron catalyst for ammonia synthesis

The reduction kinetics of an iron catalyst for ammonia synthesis of the KM I type with a grain size of 1.00–1.20 mm was studied at 773 K within the pressure range 0.1–3.8 MPa in a thermo-balance flow system using a hydrogen-nitrogen (3:1) mixture. With a 40-fold increase in the pressure, the initial reduction rate is approximately doubled. The reduction rate is also doubled with a 4-fold increase in the flow-rate. The flow-rate effect is due to a build-up of the water content (ca. 700–1700 ppm, v/v) in the thermobalance chamber during the reduction. It is well know that water vapour results in a dramatic decrease in the reduction rate. At higher flow-rates, a decrease in water content accelerates the reduction. On the above basis, the rate of reduction of an iron catalyst can be determined at an a priori fixed temperature and pressure and at an a posteriori experimentally determined humidity of the gas phase.

Structure and extinction limits of counterflow diffusion flames of hydrogen-nitrogen mixtures in air

The paper describes the results of a numerical investigation of the structure and properties of counterflow diffusion flames in three fuel-air mixtures, in which the fuels are respectively pure hydrogen, an equimolar mixture of hydrogen and nitrogen, and a mixture of 21 percent hydrogen and 79 percent nitrogen. Realistic chemistry and detailed formulation of the transport fluxes are employed. The extinction limits of all three flames are examined, and occur at velocity gradients of 13000, 8600 and 1520 s −1 , with maximum temperatures of 1422, 1308 and 1214 K respectively. An additional property of diffusion flames is that there is a minimum oxygen content of the nitrogen-oxygen mixture (or “air”) below which no flame can be established. When the fuel is pure hydrogen, this minimum mole fraction is found numerically to be 0.052. Both the value of the limit and the computed properties of the limit flame agree excellently with experiment, and this provides validation for the reaction mechanism in the diffusion flame context. The properties of all the flames are discussed in relation to their chemical mechanism. The major radical production in all the flames is centred more or less on the stoichiometric position, and near the position of maximum temperature. The dominant heat release is always on the fuel-lean side of the flame, and occurs by way of the HO 2 cycle of reaction in the hydrogen-oxygen system. These heat release rates increase with increasing strain rate or velocity gradient, and this is related with increased concentrations of hydrogen and oxygen in the reaction zone, at the expense of lower reactedness and lower temperatures. Eventually the temperature becomes so low that the radical production mechanism fails and the flame extinguishes.

Librations of hydrogen in stage II caesium graphite, C24Cs

Neutron spectra of hydrogen and hydrogen–nitrogen mixtures in the second-stage caesium graphite intercalation compound C24Cs(H2)1, C24Cs(H2)2 and C24Cs(H2)1(N2)x, where x= 0.18, 0.45 and 1.00, in the librational energy region 10< ΔE/meV <200 (80–1600 cm–1) are reported. The results confirm the two-site absorption model deduced from earlier tunnelling data, but indicate a cos 2θ potential with axial symmetry. The barriers to rotation are 51 and 78 meV (4.9 and 7.5 kJ mol–1) in the A and B sites. The librational spectra using HD and D2 show isotopic shifts which are largely in agreement with this model.

Influence of hydrogen on the carburizing of steel in nitrogen-hydrogen mixtures with the addition of pure methane

1. An increase in hydrogen partial pressure in an N2−H2−CH4 gaseous mixture promotes an increase in the flow of carbon into the steel as a result of the increase in the diffusion mobility of methane in the Nernst layer. 2. The effective diffusion coefficient of carbon in unalloyed austenite in carburzing of steels in nitrogen-hydrogen mixtures with pure methane significantly exceeds the actual diffusion coefficient of it and increases with an increase in the partial pressures of hydrogen and methane. 3. In carburizing in an N2−H2−CH4 mixture there is observed the mutual influence of carbon and hydrogen on the kinetics of establishment of equilibrium with the steel with respect to hydrogen, which is probably caused by the existence of C−H complexes. 4. Carburizing in nitrogen-hydrogen mixtures with additions of pure methane may be intensified by increasing the partial pressures of methane and hydrogen and also by increasing the frequency of change as the result of the use of higher capacity centrifugal blowers.