Dilute Nitrogen Research Articles

Composition-dependent transformation-induced plasticity in Co-based complex concentrated alloys

While the mechanically-induced martensitic transformation and transformation-induced plasticity (TRIP) effects have various known benefits, transformation of blocky martensite can also accelerate ductile damage nucleation and growth. Some complex-concentrated alloys (CCAs) with negative stacking-fault energy (SFE) demonstrate a rare faulting plasticity behavior with high strain hardening capability, that sets them apart from conventional low, positive SFE alloys that exhibit the TRIP effect. This study investigates the influence of dilute nitrogen on the TRIP mechanisms in a Co-rich CoCrNi CCA, and reveals, among other findings, that nitrogen interstitials can effectively reduce the extension of stacking faults and deformation-induced phase transformation, resulting in higher strain hardenability at early deformation levels and ductility. Thermodynamic calculations are coupled to various experimental analyses based on atom-probe tomography, scanning transmission electron microscopy, electron backscattered diffraction, electron-channeling contrast imaging, in situ high-energy synchrotron X-ray diffraction, and stress relaxation testing, to explore the origins of the observation. This work provides insights into the future design of CCAs with desirable TRIP, faulting plasticity, and mechanical properties.

Tuning the Microstructures of ZnO To Enhance Photocatalytic NO Removal Performances

Effective removal of kinetically inert dilute nitrogen oxide (NO, ppb) without NO2 emission is still a challenging topic in environmental pollution control. One effective approach to reducing the harm of NO is the construction of photocatalysts with diversified microstructures and atomic arrangements that could promote adsorption, activation, and complete removal of NO without yielding secondary pollution. Herein, microstructure regulations of ZnO photocatalysts were attempted by altering the reaction temperature and alkalinity in a unique ionic liquid-based solid-state synthesis and further investigated for the removal of dilute NO upon light irradiation. Microstructure observations indicated that as-tuned photocatalysts displayed unique nucleation, diverse morphologies (spherical nanoparticles, short and long nanorods), defect-related optical characteristics, and enhanced carrier separations. Such defect-related surface-interface aspects, especially Vo″-related defects of ZnO devoted them to the 4.16-fold enhanced NO removal and 2.76 magnitude order decreased NO2 yields, respectively. Improved NO removal and toxic product inhabitation in as-tuned ZnO was disclosed by mechanistic exploitations. It was revealed that regulated microstructures, defect-related charge carrier separation, and strengthened surface interactions were beneficial to active species production and molecular oxygen activation in ZnO, subsequently contributing to the improved NO removal and simultaneous avoidance of NO2 formation. This investigation shed light on the facile regulation of microstructures and the roles of surface chemistry in the oxidation of low concentration NO in the ppb level upon light illumination.

Bulk Viscosity of Dilute Gases and Their Mixtures

In this work, we use the Green–Kubo method to study the bulk viscosity of various dilute gases and their mixtures. First, we study the effects of the atomic mass on the bulk viscosity of dilute diatomic gas by estimating the bulk viscosity of four different isotopes of nitrogen gas. We then study the effects of addition of noble gas on the bulk viscosity of dilute nitrogen gas. We consider mixtures of nitrogen with three noble gases, viz., neon, argon, and krypton at eight different compositions between pure nitrogen to pure noble gas. It is followed by an estimation of bulk viscosity of pure oxygen and mixtures of nitrogen and oxygen for various compositions. In this case, three different composition are considered, viz., 25% N2 + 75% O2, 50% N2 + 50% O2, and 78% N2 + 22% O2. The last composition is aimed to represent the dry air. A brief review of works that study the effects of incorporation of bulk viscosity in analysis of various flow situations has also been provided.

On the estimation of bulk viscosity of dilute nitrogen gas using equilibrium molecular dynamics approach

In this work, we present a study for the estimation of bulk viscosity using the equilibrium molecular dynamics-based Green–Kubo method. We have performed a parametric study to find optimal hyper-parameters to estimate bulk viscosity using the Green–Kubo method. Although similar studies exist for shear viscosity, none has been reported so far specifically for bulk viscosity. The expected uncertainty in bulk viscosity for a given length and number of molecular dynamics trajectories used in statistical averaging is determined. The effect of system size, temperature, and pressure on bulk viscosity has also been studied. The study reveals that the decay of autocorrelation function for bulk viscosity is slower than that for shear viscosity and hence requires a longer correlation length. A novel observation has been made that the autocorrelation length required for convergence in the Green–Kubo method for both shear and bulk viscosity of dilute nitrogen gas is of the same mean collision time length units irrespective of simulation pressure. However, when the temperature is varied, the required autocorrelation length remains unaffected for shear viscosity but increases slightly with temperature for bulk viscosity. The results obtained from the Green–Kubo method are compared with experimental and numerical results from the literature with special emphasis on their comparison with the results from the nonequilibrium molecular dynamics-based continuous expansion/compression method. Although the primary focus and novelty of this work are the discussion on bulk viscosity, a similar discussion on shear viscosity has also been added.

The grey water footprint of milk due to nitrate leaching from dairy farms in Canterbury, New Zealand

ABSTRACT The Canterbury Region of New Zealand has undergone rapid and significant land use intensification over the last three decades resulting in a substantial increase of nitrate-nitrogen leached to the environment. In this article, we determined the nitrate grey water footprint of milk, which is the amount of water needed to dilute nitrogen leached past the root zone to meet different receiving water nitrate standards per milk production unit. Our analysis revealed the nitrate grey water footprint for Canterbury ranged from 433 to 11,110 litres of water per litre of milk, depending on the water standards applied. This footprint is higher than many estimates for global milk production, and reveals that footprints are very dependent on inputs included in the analyses and on the water quality standards applied to the receiving water. The extensive dairy farming in Canterbury is leading to significant pollution of the region’s groundwater, much of which is used for drinking water. Dairy farming at this intensity is unsustainable and if not reduced could pose a significant risk to human health and the market perception of the sustainability of the New Zealand dairy industry and its products.

Ti6Al4V matrix composites fabricated by laser powder bed fusion in dilute nitrogen

In situ synthesised TiN reinforced Ti6Al4V matrix composites were fabricated via laser powder bed fusion (L-PBF) in an atmosphere of 10vol.-% N2 and 90vol.-% Ar based on novel gas–liquid reaction between N2 and Ti6Al4V melt pool. With lower laser energy density (LED), the microstructures of the composites mainly consisted of acicular α′ martensites, while the martensites were shortened and coarsened with increasing LED. The X-ray diffraction analysis demonstrated that the interstitial solid solution of N was formed in the Ti lattice. High-resolution transmission electron microscopy analysis confirmed the generation of TiN. The microhardness, yield strength, ultimate strength and plasticity of the composites initially increased and then decreased with increasing LED. The strengthening mechanisms of the composites were elucidated.

Residual oxygen driven defect mediated room temperature magnetism in dilute nitrogen incorporated amorphous Al-N-O alloy thin film

In the present work, the effect of residual oxygen during reactive sputtering of Al target in a dilute nitrogen environment has been investigated. We have deposited a thin film by reactive sputtering of high purity Al target (99.999%) using a mixture of ultra-high pure Ar & N2 gas in a percentage ratio of 95% and 5%, respectively. The characterization of as-deposited film using Grazing Incidence X-ray Diffraction (GIXRD), X-ray Photoelectron Spectroscopy (XPS), and Energy-Dispersive X-ray (EDX) spectroscopy reveals that in dilute nitrogen environment Al preferred to react with residual oxygen to form amorphous Al2O3 (a-Al2O3) along with aluminum vacancies (AlV). The dilute nitrogen incorporated in the film occupies the AlV sites in Al2O3 and bonded with nearby oxygen to form Al(NOy)x phase. The bulk of the film mainly consists of Al(NOy)x phase, which decreases as we move towards the film surface. At close to the film surface the oxygen vacancies are significantly present. Magnetic and electrical transport properties measurement of the film shows room temperature (RT) magnetism along with n-type semiconducting behaviour. The origin of RT magnetism and observed transport properties have been investigated using a first-principle calculation based on density functional theory (DFT). The residual oxygen driven defects present in the film are found to play a critical role and discussed in detail. The current study is significant in the sense that it provides a new insight to explore the potentials of Al-N-O alloy-based materials as an n-type magnetic semiconductor at room temperature by manipulating defects and optimizing nitrogen concentration.

In-situ laser additive manufacturing of Ti6Al4V matrix composites by gas–liquid reaction in dilute nitrogen gas atmospheres

Processing titanium (Ti)-based materials in high-concentration nitrogen gas (N2) atmosphere is credited with reducing ductility/plasticity arising from the excessive formation of brittle agglomerated TiN. However processing these materials in dilute N2 may reduce the risk. In this study, a novel method is developed for laser additive manufacturing of in-situ synthesized TiN and AlN co-reinforced Ti6Al4V matrix composites (NTMCs) by the gas–liquid reaction in low-concentration N2 atmospheres. The manufacturing process of the NTMCs involves melting Ti6Al4V powders followed by laser-induced pyrolysis of N2 near the melt pool. The process is facilitated by the reaction between the decomposed nitrogen and molten Ti6Al4V, dissolution and precipitation of nitrides, and formation of the composites layer-by-layer. The formation of the nitride precipitates was verified by XRD, SEM, EDS, and HR-TEM. Such in-situ synthesized nanoscale reinforcements exhibited good dispersion and strong interfacial bonding with the matrix alloy in the composites. The microhardness, 0.2% compressive yield strength, and ultimate compressive strength of the NTMCs significantly increased with increasing N2 concentration in additive manufacturing; their maxima were 511 HV, 1721 MPa, and 2010 MPa, respectively, increased by 36.3%, 67.9%, and 16.8% from those of the Ti6Al4V alloy. The formation and strengthening mechanisms of the NTMCs were elucidated.

High-temperature treatments of niobium under high vacuum, dilute air- and nitrogen-atmospheres as investigated by in situ X-ray absorption spectroscopy.

Niobium metal foils were heat-treated at 900°C under different conditions and in situ investigated with time-resolved X-ray absorption fine-structure (EXAFS and XANES) measurements. The present study aims to mimic the conditions usually applied for heat treatments of Nb materials used for superconducting radiofrequency cavities, in order to better understand the evolving processes during vacuum annealing as well as for heat treatments in controlled dilute gases. Annealing in vacuum in a commercially available cell showed a substantial amount of oxidation, so that a designated new cell was designed and realized, allowing treatments under clean high-vacuum conditions as well as under well controllable gas atmospheres. The experiments performed under vacuum demonstrated that the original structure of the Nb foils is preserved, while a detailed evaluation of the X-ray absorption fine-structure data acquired during treatments in dilute air atmospheres (10-5 mbar to 10-3 mbar) revealed a linear oxidation with the time of the treatment, and an oxidation rate proportional to the oxygen (air) pressure. The structure of the oxide appears to be very similar to that of polycrystalline NbO. The cell also permits controlled exposures to other reactive gases at elevated temperatures; here the Nb foils were exposed to dilute nitrogen atmospheres after a pre-conditioning of the studied Nb material for one hour under high-vacuum conditions, in order to imitate typical conditions used for nitrogen doping of cavity materials. Clear structural changes induced by the N2 exposure were found; however, no evidence for the formation of niobium nitride could be derived from the EXAFS and XANES experiments. The presented results establish the feasibility to study the structural changes of the Nb materials in situ during heat treatments in reactive gases with temporal resolution, which are important to better understand the underlaying mechanisms and the dynamics of phase formation during those heat treatments in more detail.

NOx scrubbing with H2O2/HNO3 solutions achieved with a laboratory bubble contactor

In this work, the removal of dilute nitrogen oxides NOx from the gaseous effluents of Tunisian nitric acid plant by absorption into aqueous hydrogen peroxide solutions containing or not nitric acid was studied. All semi-continuous absorption tests were carried out at ambient conditions and at 40 Pa as NOx partial pressure. The effects of the gas flow rate, the initial H2O2 concentration and the presence of HNO3 on the NOx absorption efficiency (ANOx) were studied. The tests results revealed that ANOx increases with an increase in initial H2O2 concentration in the scrubbing liquid, but decreases with an increase of gas flow rate. Furthermore, the presence of nitric acid in the aqueous hydrogen peroxide solution has a positive effect on ANOx. These results confirmed that the removal of NOx liberated from the plants of the Tunisian Chemical Group (TCG) by absorption into H2O2 solution is a feasible and an effective solution.

Estimation of bulk viscosity of dilute gases using a nonequilibrium molecular dynamics approach.

A method is proposed for the calculation of bulk viscosity, μ_{b}, of dilute gases using nonequilibrium molecular dynamics (NEMD) simulations. The method uses measurement of mechanical (P_{mech}) and thermodynamic pressure (P_{thermo}) in a NEMD simulation of an expanding fluid and then relates the bulk viscosity to them by the relation μ_{b}=(P_{mech}-P_{thermo})/∇·u[over ⃗], where ∇·u[over ⃗] is the controlled rate of expansion of the fluid per unit volume. A special emphasis is given to the fundamental physical understanding of bulk viscosity in this work. The proposed method is demonstrated for the estimation of bulk viscosity of dilute nitrogen gas in the temperature range of 200-800K. Variation of bulk viscosity with temperature is reported in the above-mentioned temperature range and is found to be in a reasonably good agreement with the data available in the literature. Furthermore, variation of bulk viscosity with pressure and volumetric expansion rate is obtained. A weak linear dependency of bulk viscosity with pressure is observed, which increases with temperature. However, no significant effect of the rate of volumetric expansion is observed until 10^{8}s^{-1}. Moreover, the effect of the direction of volumetric change (expansion vs. compression) is also demonstrated in this work.

Effects of a thin nitrogen-doped layer on terahertz dynamics in GaAs containing InAs quantum dots

The transient terahertz signal generated by electron diffusion that was excited by an ultrashort pulse was observed to vary with the potential structure around the surface. The formation of InAs quantum dots caused the strain field and the nitrogen atoms to further modify the potential structure around the quantum dots. The terahertz signal that was observed for various pump energies exhibited an interesting phase change. Further, the change in terahertz dynamics originated from the formation of a dilute nitrogen layer around the quantum dots. Furthermore, this change depends on the position of the nitrogen-doped layer. The results of this study provide important information for controlling the optical properties of quantum dots.

Power-to-protein: converting renewable electric power and carbon dioxide into single cell protein with a two-stage bioprocess

To prevent an environmental collapse while feeding a population of 10 billion people, dilute nitrogen in waste streams as a nitrogen source and carbon dioxide as a carbon source should be converted into edible protein as part of the circular economy.

Nitrogen oxides absorption into aqueous nitric acid solutions containing hydrogen peroxide tested using a cables-bundle contactor

This work aims to study the removal of dilute nitrogen oxides from gaseous effluents by absorption into aqueous nitric acid solutions containing or not hydrogen peroxide. NOx absorption tests (pNOx = 50 Pa with a varying composition) were performed in a cables-bundle contactor at ambient conditions. Tests runs were carried out with the recycling of the absorbent solution (0–8 mol/l for HNO 3 and 0–2 mol/l for H 2 O 2 ) allowing to observe the temporal evolution of the absorption efficiency. The effects of the different operating conditions on the NO, NO 2 and NOx absorption performances (A) were investigated. Results revealed in all the cases that A NOx increases when increasing the proportion of more oxidized species in NOx. Without H 2 O 2 A NOx decreases when the HNO 3 concentration of the solution is increased and also with the recycling of the scrubbing liquid, leading to NOx desorption phenomena. When hydrogen peroxide is added to the nitric acid solution the NOx absorption performances are much higher and increase with the initial H 2 O 2 concentration and the HNO 3 concentration. • A NOx increases when increasing the proportion of more oxidized species in NOx. • Without H 2 O 2 , A NOx decreases when the HNO 3 concentration of the solution is increased and also with the recycling of the scrubbing liquid, leading to NOx desorption phenomena. • When H 2 O 2 is added to HNO 3 solution, A NOx is much higher and increases with the initial concentration of H 2 O 2 and HNO 3 .

An application of the water footprint assessment to optimize production of crops irrigated with saline water: A scenario assessment with HYDRUS

Agriculture, due to a growing scarcity of fresh water resources, often uses low-quality waters for irrigation, such as saline waters. However, unmanaged applications of such waters may have negative environmental and economic consequences. Based on the concept of the water footprint (WF), a measure of the consumptive and degradative water use, the field-calibrated and validated HYDRUS (2D/3D) model was applied to find optimal management scenarios (from 1980 different evaluated scenarios). These scenarios were defined as a combination of different salinity rates (SR), irrigation levels (IL, the ratio of an actual irrigation water deth and a full irrigation water depth), nitrogen fertilization rates (NR), and two water-saving irrigation strategies, deficit irrigation (DI) and partial root-zone drying (PRD). The consumptive WF was defined as the crop water consumption divided by the crop yield. The grey WF was calculated for the N fertilizer and defined as the volume of freshwater required to dilute nitrogen (N) in recharge so as to meet ambient water quality standards. Simulated components of water and solute dynamics were used to calculate criteria indices, which were divided into two groups: (a) environmental indices, including the degradative grey water footprint (GWF) and the apparent N recovery rate efficiency (ARE), and (b) economic indices, including economic water (EWP) and land (ELP) productivities. While significant improvements of 3.9–59.2%, 0.1–165.8%, and 0.01–166.5% in ARE, EWP, and ELP, respectively, were obtained when NR varied within the range of 0–200 kg ha−1, changes in these indices were relatively minor when NR was higher than 200 kg ha−1. At a given NR, GWF tends to increase considerably by up to 180% when DI-crops are subject to low-intermediate salt (SR < 7 dS m−1) and water (IL > 70%) stresses. This is at the expense of up to a 55% reduction in ELP and up to a 120% increase in EWP. With N uptake 0.2–17.3% higher, PRD seems to be a more viable agro-hydrological option than DI in reducing a pollutant load into regional aquifers as well as in sustaining farm economics. The entire analysis reveals that the PRD strategy with N-fertilization rates of 100-200 kg ha−1, a moderate salinity stress (SR < 5 dS m−1), and irrigation levels of 60–90% represents the best management scenario. It can be concluded that, while there is a substantial need for rescheduling irrigation and fertilization managements when crops are irrigated with saline waters, HYDRUS modeling may be a reliable alternative to extensive field investigations when determining the optimal agricultural management practices.

The OVAL experiment: a new experiment to measure vacuum magnetic birefringence using high repetition pulsed magnets

A new experiment to measure vacuum magnetic birefringence (VMB), the OVAL experiment, is reported. We developed an original pulsed magnet that has a high repetition rate and applies the strongest magnetic field among VMB experiments. The vibration isolation design and feedback system enable the direct combination of the magnet with a Fabry-P\'erot cavity. To ensure the searching potential, a calibration measurement with dilute nitrogen gas and a prototype search for vacuum magnetic birefringence are performed. Based on the results, a strategy to observe vacuum magnetic birefringence is reported.

Novel nitrogen/gallium precursor [Ga(bdma)H2] for MOVPE

Dilute nitrogen (N) containing III/V semiconductors are promising candidates for solar cell and laser applications. The N incorporation efficiency of 1,1-dimethylhydrazine (UMDHy) in metal organic vapor phase epitaxy (MOVPE), however, happens to be only in the one percentage range and below. This leads to an extremely high offer of UDMHy in the MOVPE reactor and, therefore, a drastic change in the growth conditions. Furthermore, the device efficiency of dilute nitride materials is currently hampered by carbon (C) incorporation, which is believed to be incorporated either jointly with the N from the dimethylamine radical of the UMDHy or from short hydrocarbon radicals originating from the decomposition of the other metal organics. Therefore, this work presents a novel N precursor N,N'-Bis(dimethylamino)acetamidinato-galliumdihydride [Ga(bdma)H2], which provides not only N but also gallium (Ga) during MOVPE. The direct N–Ga bond in this molecule might facilitate the N incorporation and hence increase the efficiency. For a systematic N incorporation study Ga(NAs)/GaAs heterostructures were grown by MOVPE. The N content was determined via high resolution X-ray diffraction and photoluminescence (PL) studies. Good structural quality and as grown room temperature PL were obtained. It will be also shown that the N incorporation efficiency in GaAs using [Ga(bdma)H2] is significantly higher than for growths using UDMHy under comparable conditions, making this class of molecules promising candidates for the growth of dilute nitride materials.

Voltage limitation analysis in strain-balanced InAs/GaAsN quantum dot solar cells applied to the intermediate band concept

Several attempts have been carried out to manufacture intermediate band solar cells (IBSC) by means of quantum dot (QD) superlattices. This novel photovoltaic concept allows the collection of a wider range of the sunlight spectrum in order to provide higher cell photocurrent while maintaining the open-circuit voltage (VOC) of the cell. In this work, we analyze InAs/GaAsN QD-IBSCs. In these cells, the dilute nitrogen in the barrier plays an important role for the strain-balance (SB) of the QD layer region that would otherwise create dislocations under the effect of the accumulated strain. The introduction of GaAsN SB layers allows increasing the light absorption in the QD region by multi-stacking more than 100 QD layers. The photo-generated current density (JL) versus VOC was measured under varied concentrated light intensity and temperature. We found that the VOC of the cell at 20K is limited by the bandgap of the GaAsN barriers, which has important consequences regarding IBSC bandgap engineering that are also discussed in this work.

Exciton-related nonlinear optical response and photoluminescence in dilute nitrogen [formula omitted] cylindrically shaped quantum dots

An investigation of the effects of the dilute nitrogen contents in the exciton states of cylindrical InxGa1−xNyAs1−y/GaAs quantum dots is presented. The exciton states in the system are obtained within the effective mass theory and the band anti-crossing model. Exciton-related nonlinear optical absorption and refractive index change, as well as excitonic photoluminescence are studied with the help of the calculated exciton states.

First‐principles study on the conduction band electron states of GaAsN alloys

AbstractWe have analyzed the electronic states of the lowest conduction band of GaAsN alloys based on the first‐principles calculation. In order to study the nitrogen concentration dependence of the electron effective mass, we calculated the electronic structure of GaAsN alloys using a full‐potential density functional theory program. The calculated effective mass of GaAsN with a dilute nitrogen concentration is about twice as heavy as that of GaAs. In addition, the effective mass is found to decrease with increasing nitrogen concentration although it is always heavier than that of GaAs. In addition, we calculated the density of states of GaAsN to examine what the cause of the decrease in the effective mass is. Our calculations suggest the discontinuity of the physical property from GaAs to GaAsN and provide an important insight into the formation of the conduction band states of GaAsN alloys. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)