Gas Mixture Of NH3 Research Articles

Investigation of a Fuel-Flexible Diffusion Swirl Burner Fired with NH3 and Natural Gas Mixtures

Investigation of a Fuel-Flexible Diffusion Swirl Burner Fired with NH3 and Natural Gas Mixtures

Comparison оf Secondary Nucleation Processes during Diamond Synthesis in Microwave Plasma in H2–CH4–N2 and H2–CH4–NH3 Gas Mixtures

Comparison оf Secondary Nucleation Processes during Diamond Synthesis in Microwave Plasma in H2–CH4–N2 and H2–CH4–NH3 Gas Mixtures

One-step amination of MWCNTs in RF-dielectric barrier discharge Ar–N2-H2 plasmas

Plasmas technology is a simple way to functionalize the surface of multi-wall carbon nanotube MWCNT. Homogenous plasma of Ar–N2-H2 gas mixture was generated in radio frequency RF dielectric barrier Discharge DBD at discharge power of 60 W and total pressure of 500 Pa. The active plasma species was monitored by optical emission spectroscopy OES. While the untreated and treated MWCNTs were investigated with various techniques. The result from OES shows complex spectrum with spectral line/bands related various species such as OH, N2, CN, C2, Hα and Are I, confirming the rich plasma environment, as well as possible active interaction between the MWCNTs and the plasma species. The TEM images of the treated samples revealed the roughness of the CNT outer surface. The X-ray photo electron emission XPS results confirm the presence of nitrogen-based functional groups (C–NC, C–NHO and (CO)–N-(CO)) on the plasma treated MWCNTs. Raman spectrum analysis confirms the functionalization of the treated MWCNTs as the ID/IG ratio increased for the treated sample. The Ar–N2-H2 plasma treatment of MWCNTs undamaged the MWCNTs structure and preserved integrity as observed by XRD result and SEM image.

Magnetoresistance in Pd–Co/Cu/Pd–Co trilayer under hydrogen–nitrogen gas mixture

The magnetoresistance of three Pd–Co(1)/Cu/Pd–Co(3) trilayers with different Pd–Co(3) thicknesses were evaluated in a H2–N2 gas mixture. The resistance of Pd–Co/Cu/Pd–Co increased with increasing hydrogen concentration in the gas phase, which is similar to the behavior observed in the Pd metal. The peak structure was shown in the magnetoresistance under a nitrogen atmosphere and was associated with magnetic scattering at the interface between the Pd–Co and Cu layers. In the H2–N2 gas mixture, the peak position and width in the resistance profiles were independent of the hydrogen concentration for all the prepared trilayers, and the peak intensity decreased with increasing hydrogen concentration for the trilayer containing a 4.2 nm thick Pd–Co(3) layer. The decrease in intensity was due to the reduction in magnetization in the Pd–Co layer after hydrogen absorption. The change in the resistance ratio by hydrogen absorption in the trilayer was larger under a high external magnetic field of 170 mT than under a low magnetic field of 10 mT. These results confirmed that the multilayered structure of the Pd–Co/Cu enhances the resistance response to hydrogen under a high magnetic field.

Laser absorption spectroscopy for plasma-assisted thermochemical treatment. Part II.: Impact of the carbon and water contaminants on a low-pressure N2–H2 discharge

The density evolution of , , and molecules over time was monitored by laser absorption spectroscopy in a low pressure DC pulsed discharge in N2–H2 gas mixtures with addition of CH4 or O2. The discharge was maintained in an industrial-scale, active screen (AS) plasma nitrocarburizing (ASPNC) reactor with a steel AS. The measured species densities were analysed using a simplified kinetic model that includes three characteristic times for chemical processes in the ASPNC reactor. The shortest time (1–4 min) was associated with the gas residence time in the reactor, the middle one (about 20 min) was assigned to surface reactions on the AS and workload, whereas the largest one (about 3–5 h) was assigned to surface reactions on the cold reactor walls. The work highlights the importance of monitoring the gas composition during plasma nitrocarburizing processes in order to maintain defined treatment conditions and compensate for continuously changing chemical kinetics at the internal reactor surfaces.

Study on etch characteristics of magnetic tunnel junction materials using rf-biased H2/NH3 reactive ion beam

In order to etch CoFeB and MgO constituting the magnetic tunnel junction (MTJ) layer of magnetic random access memory, rf-biased reactive ion beam etching (RIBE) with a H2:NH3 gas mixture was introduced and the etching characteristics were investigated. The H2:NH3 gas mixture of 8:1 was used for rf-biased RIBE because the etch selectivity is increased with H2 percentage in the H2:NH3 gas mixture while the etch rates of MTJ materials are the highest between 2:1 and 1:1 ratio of H2:NH3 due to the synergy effect of H2 and NH3 in the etching of MTJ materials. When a high rf power was applied to the substrate (high rf-biasing) during RIBE, even though etch rates of MTJ materials were increased, the etch selectivities of MTJ materials over hard mask materials were decreased possibly due to the high physical sputtering effect. However, when small rf-biasing was added to the substrate during RIBE, improved etch characteristics such as higher etch selectivity of MTJ over the top electrode (TE) material, improved etch anisotropy of the MTJ pattern masked with TE, and a thinner sidewall residue on the MTJ pattern could be observed. The improvement in etch characteristics by the addition of small rf-biasing during RIBE is believed to be related to the increased chemical etching effect through H2/NH3 gas dissociation and the increased H/NH ratio in the plasma generated just above the substrate without increasing the physical sputtering effect. Specifically, for the substrate located on the insulating substrate holder, the charging of the substrate could be removed without using an electron emitting neutralizer by supplying electrons from the plasma generated by rf-biasing during RIBE.

Improvement on pitting wear resistance of gears by controlled forging and plasma nitriding

In the present investigation, the use of a bainitic steel for forged gears applications and the suitability of different plasma nitriding treatments is discussed. The gears were forged, machined, ground, polished, and nitrided at 500 °C with three sets of N2–H2 gas mixtures, containing 5, 24, and 76 vol.% N2, to develop a nitrided case of approximately 300 μm depth. Gears were characterized before and after the nitriding concerning the phase composition, microstructure, microhardness, fracture toughness, and residual stresses states. Pitting wear tests were performed on a standard Forschungsstelle für Zahnräder und Getriebebau (FZG) test rig. The nitrided gears with 24 and 76 vol.% N2 formed a biphasic compound layer of ε-Fe2-3(C)N and γ′-Fe4N. As the volume fraction of nitrogen in the gas mixture was decreased, the detected content of γ′-Fe4N in the compound layer increased, but a monophasic compound layer was only reached with 5 vol.% N2. The nitrogen rich gas composition increased the surface hardness and decreased the fracture toughness of the compound layer, as they have more ε-Fe2-3(C)N. The diffusion zone of the different nitrided surfaces showed residual compressive stresses. The best performance was obtained in the nitrided gears with 24 vol.% N2, due to the better combination between the surface hardness, fracture toughness, residual stresses, and compound layer thickness. The nitrided gears with 24 vol.% N2 have ten times improvement over the non-nitrided gears, while the nitrided gears with 5 and 76 vol.% N2 have an improvement of three point seven and five point four times.

Effect of N2–H2 Ratio during Conventional Plasma Nitriding of Intermetallic FeAl40 Alloy on Electrochemical Corrosion Parameters in Sulphuric Acid

The intermetallic alloy FeAl40 was plasma nitrided at 575 ∘C for 4 h while varying the N2–H2 gas mixture with nitrogen contents fN2 between 0.1 and 0.9. The effect of the gas mixture on the resulting structure of the nitrided FeAl40 and the associated electrochemical corrosion behaviour in a 0.25 M H2SO4 (pH = 0.3) electrolyte were investigated using different complementary analytical methods such as scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray spectroscopy, electron probe microanalysis (EPMA), electrochemical polarisation and electrochemical impedance spectroscopy. Nitriding significantly changed the corrosion mechanism of FeAl40 alloys in acidic environments, ranging from consistently high material loss in untreated base material to strongly inhibited material loss. This phenomenon was the result of a corrosion product layer formed on nitrided FeAl40 during the corrosion process. Therefore, plasma nitriding reduced the corrosion rate to about 5–7 mm/year compared with 22 mm/year of the untreated FeAl40 base material. A high nitrogen content in the N2–H2 plasma of more than fN2 = 0.3 ensured the formation of protective nitrided layers on FeAl40. In addition, an approach to explaining the effect of the nitrided layer on FeAl materials was presented on the basis of thermodynamic considerations.

High Density RF-DC Plasma Nitriding under Optimized Conditions by Plasma-Diagnosis

This paper is concerned with plasma diagnosis on a N2-H2 gas mixture to determine the optimum parameters for the nitriding process. Plasma parameters such as pressure, RF-voltage, and DC-bias were varied for optimization. The active species such as N2+ and NH were identified in plasma diagnosis. In the N2-H2 gas mixture, hydrogen imposed a great influence on plasma generation. The small addition of a hydrogen molecule into the gas mixture resulted in the highest yield of N2+ ions and NH radicals; the optimum hydrogen content was 20% in the mixture. The austenitic stainless-steel type AISI304 was nitrided at 673 K and 623 K to experimentally demonstrate that hydrogen gas content optimization is necessary to improve the surface hardness and to describe low temperature nitriding under high nitrogen flux at the surface.

Microstructure and Wear Properties of a Low Carbon Bainitic Steel on Plasma Nitriding at Different N2-H2 Gas Mixtures

For the first time, the influence of gas mixture on first damage resistance of a plasma nitrided DIN 18MnCrSiMo6-4 bainitic steel was investigated. Samples were nitrided at 500 °C with three different N2-H2 gas mixtures, containing 5, 24, and 76 vol.% N2. Samples were characterized concerning the resulting roughness, microstructure, compound layer’s phase composition, residual stresses in the diffusion zone, and surface hardness. Tribological ball-on-flat tests were carried out in reciprocal mode using zirconia as ball material for friction coefficient and the compound layer resistance until the first damage. The test results were evaluated statistically by analysis of variance (ANOVA). As the amount of nitrogen in the gas mixture decreases, the ε-Fe2-3(C)N content in the compound layer decreases. A γ’-Fe4N monophasic compound layer was achieved at 5 vol.% N2 gas mixture. The diffusion zone as expected presented compressive residual stresses with the highest values near the surface. In the tribological tests, better results were obtained for 5 and 24 vol.% N2 in the gas mixture as higher amounts of γ’-Fe4N were formed. The 76 vol.% N2 gas mixture led to a brittle behavior, due to the biphasic compound layer (γ’-Fe4N and ε-Fe2-3(C)N) with a predominant content of ε-Fe2-3(C)N.

Experimental investigations on rotation–vibration energy transfer in H2–N2 collisions

We investigated the rotational–vibrational impact energy transfer processes in a H2–N2 gas mixture system. The stimulated Raman pumping technique was used to excite H2 molecules to the (1, 7) high rotational states. The population of the H2(1, 7) level was verified by the coherent anti-Stokes Raman (CARS) spectra, the total pressure of the mixture was maintained at 500 Torr and nitrogen with different molar ratios was filled in the sample cell. The collisional deactivation rate coefficients of the excited state H2(1, 7) with H2 and N2 were obtained by fitting the experimental data with the Stern–Volmer equation. The multi-quantum near-resonant rotational relaxation process of H2(1, 7) colliding with N2 was confirmed by the time-resolved CARS profile measurements of H2(v = 1, J = 7, 5, 3) after the excitation of H2(1, 7). The results can provide data reference for atomic and molecular physics, atomic and molecular collisions, rotation and vibration excitation calculation, etc.

Inspection of contamination in nitrogen plasmas by monitoring the temporal evolution of the UV bands of NO-γ and of the fourth positive system of N2

In this study, contamination by oxygen species in nitrogen plasmas produced by the active screen system used for plasma nitriding has been investigated by optical emission spectroscopy in the spectral range of 200–900 nm. Temporal evolution of emission intensity of different species (N2, N2+, NO, OH, H, NH, and Fe) was monitored, as well as electrical characteristics (current and voltage) of the discharge produced by a pulsed unipolar power supply. In nitrogen plasma, it was found that the emission of oxygen-containing species (NO and OH) decreases with time, while Fe emission intensity increases. Such behavior is observed only when the discharge is initiated immediately after venting the reactor. Starting from the hypothesis of contamination of the reactor walls by water vapor, we propose an explanation based on the synergistic effect between the temperature and the reactive nitrogen created by the plasma. Such a long decay of NO emission was not observed in N2–H2 gas mixtures. After decontamination, the fourth positive system of N2 could be observed. Such a not commonly observed system can be used as a tool to control reactor cleanliness in pure nitrogen discharge for nitriding applications.

Effects of deposition parameters on the microstructure and mechanical properties of Ti(C,N) produced by moderate temperature chemical vapor deposition (MT-CVD) on cemented carbides

Using an industrial-scale chemical vapor deposition (CVD) system, a series of Ti(C,N) films were deposited from a TiCl4–CH3CN–H2–N2 gas mixture at 850–950 °C and 70–700 mbar with N2/H2 molar ratio varying from 0.27 to 3.77. Within the investigated temperature range, it is found that the growth rate of Ti(C,N) films is strongly dependent on the total pressure. Such behavior agrees with a diffusional limitation step. The lowest growth rate is measured at the N2/H2 molar ratio of 3.77, because of the low reduction rate of TiCl4 in a H2 deficient atmosphere. No significant influence of processing conditions on the carbon content of Ti(C,N) films could be found, as determined by X-ray diffraction and EPMA. The microstructure and mechanical properties were investigated and chiefly influenced by deposition conditions. In this work, the Ti(C,N) films deposited at 850 °C and 70 mbar with N2/H2 molar ratio of 0.27 exhibit a mixed texture with laminated facetted grains, the superior hardness reaching 30 GPa and the Young's modulus of 394 ± 32 GPa were measured. Furthermore, experimental results reveal that residual stresses could be thickness-dependent, due to the evolutionary film microstructure during film growth, and the stress relaxation is particularly attributed to cooling cracks.

Investigation of admixed gas effect on plasma nitriding of AISI316L austenitic stainless steel

The influence of discharge gas composition on the plasma nitriding of AISI316L austenitic stainless steel was investigated using a laboratory-made apparatus consisting of a DC diode and a plasma monitoring system. H2-N2 and Ar-N2 gas mixtures with various mixture ratios were introduced in the apparatus, and nitriding was performed without auxiliary substrate heating. A >4 μm-thick surface layer, consisting of an expended austenitic phase, γN, was formed on the AISI316L substrate when the optimized H2-N2 plasma was used. The thickness and maximum nitrogen content of the surface layer increased with an increase in the population of N2+ species in the plasma; the N2+ population in the plasma is considered an underlying parameter for the optimization. Conversely, the penetration of nitrogen into the AISI316L surface was scarce when Ar-N2 plasma was used, irrespective of the gas mixture ratio. Such a phenomenon indicates that Ar-N2 plasma is ineffective for nitriding. However, the effects of H2-N2 plasma, which are not limited to the surface reaction, are beneficial to facilitate nitriding.

Development of a selective ammonia YSZ-based sensor and modeling of its response

In the present study, Au-V2O5 sensing material was tested as a sensing electrode for developing mixed-potential ammonia gas sensors. The results of gas sensing measurements indicated selective responses to NH3 while this selectivity was highly dependent on the temperature. Different V2O5 contents were tested in the sensing electrode. The results showed that by increasing V2O5 content from 15 wt.% to 50 wt.%, selective ammonia sensors could be achieved at 550 °C. The selectivity of Au-50 %V2O5 sensor was also confirmed in gas mixtures of CO, NH3, NO, and NO2 gases. Modeling of the sensor responses in the ammonia concentration range 2–40 ppm at four oxygen concentrations was performed based on mixed-potential theory. Nernst and Butler-Volmer equations with an electron transfer assumption were used for data modeling.

Hollow Co3O4-x nanoparticles decorated N-doped porous carbon prepared by one-step pyrolysis as an efficient ORR electrocatalyst for rechargeable Zn-air batteries

Composites of cobalt oxides and nitrogen-doped porous carbon, as electrocatalysts for oxygen reduction reaction (ORR), offer considerable potential in new-style energy conversion and storage devices. Herein, a straightforward method for production of N-doped porous carbon (Co3O4-‍x@N–C) decorated by hollow Co3O4-x nanoparticles with oxygen vacancies has been studied by one-step pyrolysis of Co-doped quinone-amine polymer in gas mixture of NH3 and Ar. The nanosized CoO/Co3O4 heterostructure can boost the electron transport, while the hollow structure can ensure the structural and chemical stability of the catalyst, and the oxygen vacancy can change the surface electron structure and lower the activation energy barrier for oxygen reduction. Consequently, the as-prepared catalyst Co3O4-x@N–C exhibits excellent ORR catalytic performance (E1/2 = 0.845 V vs. RHE), exceeding that of Pt/C and most recently reported ORR catalysts. The Zn-air batteries assembled with Co3O4-x@N–C present a high open circuit potential (1.524 V), a large peak power density (105.2 mW cm−‍2) and great discharge-charge cycling performance, superior to the Zn-air batteries assembled with Pt/C. The excellent electrocatalytic performances of Co3O4-x@N–C make it an ideal alternative for precious metal catalyst (Pt/C) in rechargeable Zn-air batteries.

Etch characteristics of magnetic tunnel junction materials using H2/NH3 reactive ion beam

Magnetic tunneling junction (MTJ) materials such as CoFeB, Co, Pt, MgO, and the hard mask material such as W and TiN were etched with a reactive ion beam etching (RIBE) system using H2/NH3. By using gas mixtures of H2 and NH3, especially with the H2/NH3( 2:1) ratio, higher etch rates of MTJ related materials and higher etch selectivities over mask materials (>30) could be observed compared to those etching using pure H2( no etching) and NH3. In addition, no significant chemical and physical damages were observed on etched magnetic materials surfaces and, for CoPt and MTJ nanoscale patterns etched by the H2/NH3( 2:1) ion beam, highly anisotropic etch profiles >83° with no sidewall redeposition could be observed. The higher etch rates of magnetic materials such as CoFeB by the H2/NH3( 2:1) ion beam compared to those by H2 ion beam or NH3 ion beam are believed to be related to the formation of volatile metal hydrides (MH, M = Co, Fe, etc) through the reduction of M-NHx( x = 1 ∼ 3) formed in the CoFeB surface by the exposure to NH3 ion beam. It is believed that the H2/NH3 RIBE is a suitable technique in the etching of MTJ materials for the next generation nanoscale spin transfer torque magnetic random access memory (STT-MRAM) devices.

Exhaust energy recovery via catalytic ammonia decomposition to hydrogen for low carbon clean vehicles

The work presented here, demonstrates the on-board exhaust assisted catalytic ammonia (NH3) conversion to H2-N2 using either only exhaust heat (decomposition) or by direct reaction with part of the exhaust gas (reforming). The resultant H2-N2 gas mixture from the exhaust heat driven thermochemical energy recovery processes contains up to 15% more energy than the reactant NH3 (i.e. for 1 kW of NH3 used in the reaction up to 1.15 kW of H2 is produced). Experimental studies using a rhodium-platinum (Rh-Pt) catalyst and equilibrium calculations in Chemkin using Konnov’s 0.6 and Nozari’s reduced mechanisms have revealed that complete NH3 conversion occurs at typical gasoline direct injection (GDI) engine exhaust gas temperatures (450 °C–550 °C).By partially replacing gasoline in GDI engine with the resultant (H2-N2 products, up to 30% reduction in CO2 and fuels consumption can be achieved. Additional benefits can be gained under real engine operation when the benefits of reduced pumping losses, due to intake dilution with H2-N2 gas, are also considered. Furthermore, the work demonstrates additional benefits in CO2 life cycle for the NH3 use as an energy carrier in transportation and broader combustion power generation systems.

Direct conversion of NO and SO2 in flue gas into fertilizer using ammonia and ozone

This study focused on the simultaneous removal of NO and SO2 from an industrial flue gas stream. To evaluate the removal efficiency of NO and SO2 using O3 and NH3, the consumption of two reactants (O3 and NH3) in line with the conversion of NO and SO2 was quantified experimentally. In addition, NO and SO2 were converted to valuable fertilizers, NH4NO3 and (NH4)2SO4. To identify a principle strategy to enhance the generation of fertilizer, Fourier transform infrared spectroscopy was used to examine the reaction mechanisms for the formation of NH4NO3 and (NH4)2SO4. Acceleration of SO2 oxidation could be achieved effectively by adding NO to a gas mixture of SO2, NH3, and O3. The formation of HNO3 might be enhanced by the simultaneous feeding of NO and SO2. Particle generation was also 10 times higher for NH3/(NO + SO2) than for NH3/NO and for NH3/SO2, which is a prominent feature of this study. Moreover, the introduction of steam had a positive influence on particle generation. This method offers dual applications for NO and SO2 removal from a flue gas stream and direct fertilizer generation.

The Influence of Hollow Cathode Geometry and N2-H2 Gas Mixture on the 2 MHz RF-DC Plasma Species and Density

RF-DC plasma combined with the hollow cathode effect is used to generate plasma inside a hollow cavity. A high-density plasma was formed inside a vacuum chamber using a 2 MHz RF generator. A hollow cathode was utilized to focus the power at the voltage of 150 V with DC bias of -500 V. The plasma system was specially designed for titanium nitriding process at low temperature using N2-H2 gas mixture. The N2-H2 gas with a flow rate of 90-10 mL/minute was conducted at pressure 20 to 150 Pa. The cylindrical and rectangular hollow cathodes are used to make the discharge containing attractive atoms or molecules inside the hollow cavity. The trapped electrons could trigger the secondary electron emission that induced high-density plasma. The geometry components such as gap size, diameter, and cavity depth combined with variations of chamber pressure have been studied to produce high-density plasma. The species inside of N2-H2 plasma were detected by OES based on light emission. The high-intensity peaks of N2 * molecules from the second positive system and N2 + ions from the first negative system at the wavelength range of 300 to 500 nm were detected to obtain effective plasma species for the nitriding process.