N2 Flow Research Articles

Compound-specific amino acid 15N-stable isotope probing for the quantification of biological nitrogen fixation in soils

Biological nitrogen fixation (BNF) performed by diazotrophs is vital to our understanding of ecosystem functions, as plant nitrogen (N) is commonly a limiting nutrient for primary productivity. However, significant limitations have remained in our knowledge of the controls and rates of this process, due to technical difficulties in directly quantifying nitrogen (N2) fixation rates. To address this, we developed a novel compound-specific 15N-stable isotope probing method involving analysis of acid hydrolysable soil amino acids (AAs) by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) for the quantification of BNF in soils. By analysing 15N-enriched AAs (as N-acetyl, O-isopropyl derivatives), this new approach aimed to provide greater specificity compared to existing methods, and to contribute previously unobtainable quantitative information on the capture and flow of N2 fixed in soils. Laboratory incubations using 15N2 gas were carried out on surface peat over 15 days to obtain quantitative measures of N2 fixation by the microbial community. Longer incubations with the addition of a glucose energy source significantly increased the level of 15N enrichment, i.e. N fixed. The enhanced detection limits of 15N-AAs by GC-C-IRMS, compared to bulk soil δ15N value determinations, was key to assessments of N2 fixation. Valuable insights into the assimilation pathway of the applied 15N2-substrate were revealed; for peat soils, 15N incorporation into glutamate dominated over other AAs.

A novel criterion to identify coatings’ adhesion

ABSTRACT A novel criterion, plastic/elastic deformation work (Wp/We), was introduced to identify the co-deformation capacity of chromium–nitrogen (Cr–N) coating and titanium alloy system, which can be related to the coating/substrate adhesion. By changing the N2 flow (f N2), the Cr–N coatings were deposited on Ti6Al4V (TC4) alloy substrate to obtain Cr(N), Cr2N and/or CrN coatings, which could be related to the various deformation capacities. It indicated that the high Wp/We ratios of the metallic Cr(N)/TC4 systems deformed coordinately and attached well. Among the ceramic CrNx/TC4 systems, the single-phase CrN/TC4 exhibited higher Wp/We ratio of 1.71 than 1.52 and 1.61 of the Cr2N or Cr2N@CrN/TC4 and better adhesion. As a novel criterion, Wp/We ratio indicates the co-deformation capacity of a coating/alloy system, related to the failure mechanism and the adhesion of a coating to the substrate.

Temperature and Tumor Microenvironment Dual Responsive Mesoporous Magnetic Nanospheres for Magnetothermal Effect-Induced Cancer Theranostics

Temperature and Tumor Microenvironment Dual Responsive Mesoporous Magnetic Nanospheres for Magnetothermal Effect-Induced Cancer Theranostics

Surface Conductivity and Preferred Orientation of TiN Film for Ti Bipolar Plate

The properties of thin films are often influenced by the crystal’s preferred orientation. In the present study, we report the strong dependence of surface conductivity on the preferred orientation of TiN film that acts as the coating material for Ti bipolar plate. The preferred orientation of TiN film is successfully controlled along the (111) or (200) planes by adjusting the N2 flow rate or Ti substrate temperature during the deposition process via DC (direct current) reactive magnetron sputtering. Small N2 flow rate of 3 to 6 sccm or low substrate temperature (e.g., 25 °C) facilitates the growth of TiN films along the (111). The (111) preferred orientated TiN films show much lower interfacial contact resistance (ICR) than the (200) preferred orientated films. A considerably low ICR value of 1.9 mΩ·cm2 at 140 N/cm2 is achieved at the N2 flow of 4 sccm and the substrate temperature of 25 °C.

Effect of reactive gas condition on nonpolar AlN film growth on MnS/Si (100) by reactive DC sputtering

The effects of reactive gas flow conditions on nonpolar AlN film growth on MnS/Si (100) substrates using reactive DC magnetron sputtering were investigated. During AlN deposition at a substrate temperature of 750 °C, the MnS surface can be unintentionally nitrided, resulting in a decrease in the crystallinity of the AlN. Low-temperature growth of the AlN layer at 300 °C prevents this nitridation and results in the crystallization of nonpolar AlN. A N2 flow equal to 30% of the Ar sputtering gas flow was found to improve the crystallinity of the nonpolar AlN and to reduce nitrogen defects, which play an important role in interfacial reactions. Nitrogen defects promote the formation of alloys such as AlMn and MnSi that degrade the interface and can significantly decompose the MnS. A higher proportion of N2 improves the nonpolar AlN crystallinity, reduces the concentration of defects and suppresses reactions at the AlN/MnS interface.

Epitaxial growth of TiN on (0001) semi-insulating 4H-SiC substrate by reactive sputtering

Growth of epitaxial TiN film on a semi-insulating single crystal (0001) SiC substrate has been achieved by DC magnetron reactive sputtering deposition. The effects of growth temperature and N2 flow ratio in Ar on film quality and growth rate were investigated. X-ray diffraction (XRD) characterization shows that all the deposited TiN films at 550 and 700 °C are heteroepitaxially grown on SiC with the epitaxial relationship between TiN and 4H-SiC in (111)TiN//(0001)SiC and [11¯0]TiN//[112¯0]4H-SiC. Increasing the N2 flow ratio from 4 to 8% results in improvement of the film quality and a decrease in the growth rate. The width of the X-ray rocking curve of TiN (111) reflection can reach a value as small as 249 arcsec and the resistivity of TiN film can be 21 μΩ·cm for deposition at 700 °C with 8% N2 flow ratio. Measurements by atomic force microscopy show that the surface roughness of the TiN film can be 1.1 nm. X-ray photoelectron spectroscopy reveals that TiN composition is nearly in stoichiometry for all the grown TiN films. Examinations by cross-sectional transmission electron microscopy show that TiN is directly grown on SiC and verify the epitaxial relationship from XRD.

Micro-current excitation for efficient diagnosis of membrane electrode assemblies in fuel cell stacks: Error analysis and method optimization

The inconsistency of membrane electrode assemblies (MEAs) greatly restricts the development of high-performance and long-lifetime fuel cell stacks. Micro-current excitation (MCE) method has promising prospects in consistency evaluation due to its capacity in MEA component diagnosis at the stack level. In this study, the ohmic resistance is identified with the initial voltage jump characteristic upon MCE and then introduced into the excitation-response model for precision upgrading. A detailed error analysis is then conducted concerning the decoupling algorithm, the simplified model, and the stack state, demonstrating the significance of error revision for degraded stacks. Based on the updated method, the condition sensitivity of inconsistency identification is further investigated, involving the operating temperature, the gas humidity, and the gas flow rate. It is essential to ensure the same hydration state of fuel cells for simultaneous component inconsistency diagnosis. Heating and minor gas humidification are sufficient and necessary. The MCE is proven to be very sensitive to the N2 flow rate in the cathode. An extremely low N2 flow rate enables a relatively uniform gas distribution and hydrogen adsorption saturation, and is thus recommended. Finally, the updated MCE is validated to adapt to a single excitation for inconsistency diagnosis, which means great progress in test efficiency.

Numerical study of discharge characteristics of an atmospheric pressure plasma jet with a coaxial dual-channel inlet

A two-dimensional axisymmetric fluid model was applied to investigate the influence of N2 flow velocity on the discharge characteristics of a He plasma jet with a coaxial dual-channel inlet. Helium working gas flowed in the annular space of a coaxial tube and N2 flowed in a central stainless steel tube powered by a DC voltage. When N2 flow velocity increases from 0 m/s, the jet appears to be stratified, forming the outer side and inner side of the jet, and the electron density on the outside of the jet is much higher than that on the inside. For different N2 flow velocities, the peak densities of He+ and N2(c3π) appear in the jet head, while the peak densities of He* and N2+ both appear at the dielectric nozzle and the jet head. When N2 flow velocity is low, the Penning ionization rate is lower than the electron impact ionization rate, but when N2 flow velocity is high, it is just the opposite, which can increase the concentration of reactive species and contribute to the practical application of the jet. N2 flow velocity not only changes the length and structure of the jet but also controls the uniformity of the distribution of reactive species in the jet, which indicates that there is an optimal N2 flow velocity to make the jet longer and more uniform in space, which will greatly promote the practicality and flexibility of the plasma jet and also provide meaningful insights for optimizing and controlling the characteristics of the plasma jet.

Permeability characteristics of CH4, CO2, and N2 during the whole process of adsorption in coal with accumulated pressure under triaxial stresses

This study aimed to explore the seepage characteristics of N2, CH4, and CO2 in coal during the whole process of adsorption with cumulative gas pressure. A self-developed device was utilized to conduct the adsorption isotherm experiment, and the theoretical method based on the gas state equation was utilized to calculate the real-time permeability of gases during adsorption. The gas flow and velocity at the inlet and outlet were calculated on the basis of the pressure and time change law. Results showed that, during adsorption with accumulated pressure, the average pore pressure of N2 increased, whereas that of CO2 decreased. As cumulative pressure increased, the gas flow at the inlet gradually decreased, whereas that at the outlet increased. The flow and velocity of CO2 at the inlet were the largest, followed by CH4. On the contrary, the flow and velocity of N2 at the outlet were the smallest, followed by CH4. On the basis of the gas flow and velocity at the inlet and outlet, the adsorption amount and permeability of gases in coal were calculated. Gas adsorption isotherm conformed to Langmuir characteristics. Under certain gas pressure, the real-time permeability showed a quadratic form with adsorption amount, and the real-time gas permeability decreased with the increase of cumulative pressure. The real-time permeability of N2 was greater than that of CH4 and CO2, followed by CH4. The research can provide theoretical basis for deep coalbed methane development and carbon sequestration in coal seam, even gas flow in porous media.

Influence of the carbonization atmosphere on the development of highly microporous adsorbents tailored to CO2 capture

Two microporous activated carbons (ACs) tailored to CO2 capture were developed from Prosopis ruscifolia sawdust. The ACs were obtained through a two-stage process. The first consisted in the carbonization of the precursor, while the second involved chemical activation employing KOH solution as activating agent. The influence of the atmosphere involved in the carbonization stage (N2 flow at 773 K or air flow at 573 K) on the chemical and textural-morphological characteristics of the resulting ACs and on their CO2 removal capacity was analyzed. The ACs presented similar properties with a predominance of microporous structures, BET surface areas slightly larger than 1000 m2 g−1, and micropore volumes of ∼0.43 cm3 g−1 on average. Both ACs also showed a predominance of surface acidic functionalities over basic ones. The adsorbed amounts of CO2 as determined from the isotherms were 5.6 and 5.3 cm3 g−1, for the ACs developed from the precursor carbonized under N2 and air flow, respectively. From thermogravimetric tests to assess adsorption kinetics, values of the CO2 removal (101.325 kPa and 303 K) reached at equilibrium conditions were 1.15 and 1.04 mmol g−1, respectively. Present results demonstrated that the carbonization atmosphere did not have a pronounced effect on chemical and textural characteristics of the resulting ACs and, consequently, on their CO2 adsorption capacity. Accordingly, the use of air instead of N2 in the carbonization stage of the activation process may represent an interesting alternative because of the lower operating temperature involved, leading to reduce energy consumption and operating costs without sensibly affecting ACs performance.

Predicting bio-oil yield obtained from lignocellulosic biomass pyrolysis using artificial neural networks

ABSTRACT The prediction of bio-oil yield from pyrolysis of lignocellulosic biomass is important for processes optimization, modeling, and installation’s design. This work models the bio-oil of lignocellulosic biomass yield by Artificial Neural Networks (ANN), being the inputs: cellulose, hemicellulose, lignin, pyrolysis temperature, heating rate, N2 flow rate, and particle size. A database was created with 34 biomass types, modeling with 329 samples, training with 80%, and validating with 20%. A previous stage of screening was carried out with 100% of data for choosing the algorithm of the second phase and the number of neurons in the hidden layer; the selection criteria were the mean absolute error (MAE) and the correlation coefficient. The best performance was for backpropagation/Levenberg-Marquardt with 7:13:1 as ANN architecture. All ANN with less than 1% of MAE were tested for validating and the weight’s matrix of the best one is shown. The selected network with a correlation coefficient of 0.9739 and MAE of 1.7159% for validation, only had four outlier values between 5 and 6%, the remaining 62 samples with all 263 used in training, had less than 5% of difference compared to the experimental values, thus representing a very accurate model for predicting bio-oil yield.

Experimental Investigation of Vitrification Process for the Disposal of Hazardous Solid Waste Containing Chlorides

Vitrification has attracted much attention as an efficient method for solidifying heavy metals in hazardous solid wastes, but its effect is limited when hazardous solid wastes contain chlorides. Aiming at fly ash, a normal chlorine-containing solid waste, a novel process of chlorination melting and glass curing was developed to completely realize the harmlessness of heavy metals. Melting temperature, time, and auxiliary agent were adequate to realize the harmlessness, and their influence on the migration and transformation of Cl, Na, Pb, and Zn and the leaching of slag were studied. The results showed that the majority of Cl, Na, Pb, and Zn in the fly ash had been transferred to the soot, and the residual part in the slag had been solidified in glass by controlling the process conditions. Under the optimized conditions (12 wt.% CaO and 5 wt.% SiO2 was added, the N2 flow ratio was at 1 L/min, and the melting temperature was 1300 °C for 2 h), the leaching index was determined, including the acid dissolution ratio, the Pb and Zn content of the water leaching solution, and the acid leaching solution, which all met the requirements of the relevant standards. Furthermore, the novel process provided a simple and efficient approach for the disposal of other similar solid wastes containing chlorides and heavy metals.

Slow pyrolysis of cork granules under nitrogen atmosphere: by-products characterization and their potential valorization

Cork granules (Quercus suber L.) were slowly pyrolyzed at temperatures between 400-700 °C and under N2 flow. While preserving its structure, some cells of the cork biochar became interconnected, allowing such carbon residue to be used as templates for manufacturing ceria redox materials. The pyrolytic char morphology was similar to that of the natural precursor. The produced cork biochar belonged to Class 1 (C > 60%) and possessed a high heating value of 32 MJ kg−1. Other pyrolysis-derived compounds were identified and quantified through GC-FID and GC-MS analyses. The yield of gases released during cork pyrolysis was strongly dependent on the temperature used due to the thermal decomposition reactions involved in the degradation of cork. In particular, rising pyrolysis temperature from 500 to 700 ºC resulted in reducing the total hydrocarbon gases from 74 to 24 vol%. On the other hand, the yield of H2 increased from 0 to 58% by increasing the pyrolysis temperature from 400 to 700 ºC. Due to the presence of suberin in cork, the composition and yield of bio-oil could be regulated by the pyrolysis temperature. Cork bio-oil was found to consist of long-chain hydrocarbons (from C11 to C24). The bio-oil resulting from the slow pyrolysis of cork residues is suitable as an appropriate feedstock for producing aliphatic-rich pyrolytic biofuels or as a source of olefins. Overall, the findings of this study suggest that Quercus suber L. could be a promising feedstock for biochar and biofuel production through the pyrolytic route and could contribute to the environmental and economic sustainability of the cork production industry.

Explorations on Growth of Blue-Green-Yellow-Red InGaN Quantum Dots by Plasma-Assisted Molecular Beam Epitaxy.

Self-assembled growth of blue-green-yellow-red InGaN quantum dots (QDs) on GaN templates using plasma-assisted molecular beam epitaxy were investigated. We concluded that growth conditions, including small N2 flow and high growth temperature are beneficial to the formation of InGaN QDs and improve the crystal quality. The lower In/Ga flux ratio and lower growth temperature are favorable for the formation of QDs of long emission wavelength. Moreover, the nitrogen modulation epitaxy method can extend the wavelength of QDs from green to red. As a result, visible light emissions from 460 nm to 622 nm have been achieved. Furthermore, a 505 nm green light-emitting diode (LED) based on InGaN/GaN MQDs was prepared. The LED has a low external quantum efficiency of 0.14% and shows an efficiency droop with increasing injection current. However, electroluminescence spectra exhibited a strong wavelength stability, with a negligible shift of less than 1.0 nm as injection current density increased from 8 A/cm2 to 160 A/cm2, owing to the screening of polarization-related electric field in QDs.

Improved interface and dark current properties of InGaAs photodiodes by high-density N2 plasma and stoichiometric Si3N4 passivation

The interface and dark current properties of mesa-structure In0.83Ga0.17As photodiodes with improved passivation processes are investigated. Inductively coupled plasma chemical vapor deposition (ICPCVD) is used to continuously perform high-density N2 plasma treatment of InGaAs epitaxial material and then SiNx passivation film deposition. The bonding efficiency between Si and N can be effectively improved when close-to-stoichiometric SiNx films are synthesized by precisely controlling the N2 and SiH4 flow rates. Metal-insulator-semiconductor (MIS) capacitors are fabricated to study the interface properties, and C-V analysis shows that the interface state density significantly decreases to 5.3 × 1012 cm−2eV−1. Then, the process is applied to mesa-structure In0.83Ga0.17As photodiodes, and the results show a low dark current density (13 nA/cm2, @ 190 K) and negligible surface current (@ room temperature), indicating the ideal passivation effect. The method of increasing the deposition temperature to promote chemical bonding of SiNx films is studied, and both the interface and dark current properties can be improved. Our work is of important significance to the development of low-noise and large-format InGaAs arrays.

Influence of residual dopants to net doping concentration in N-type 4H-SiC films grown using high-speed wafer rotation vertical CVD method

In this study, the influence of residual dopants on the net doping concentration in n-type 4H-SiC epitaxial films grown at different N2 flow rates and C/Si ratios were investigated. By reducing the N2 flow rate, the influence of the residual donors on the net doping concentration was observed to become dominant for the films grown at low C/Si ratios and that of the residual acceptors on the net doping concentration becomes dominant for the films grown at high C/Si ratios. For the films grown at the middle C/Si ratio, an apparent proportional relation due to the compensation balance between the residual and intentional donors and the residual acceptors was observed in the N2 flow rate dependence of the net doping concentration. Furthermore, the decay curve of the net doping concentration observed in the C/Si ratio dependence is affected by the compensation balance between the intentional dopant concentration and the residual dopant concentration.

Effect of Immobilization of Phenolic Antioxidant on Thermo-Oxidative Stability and Aging of Poly(1-trimethylsilyl-1-propyne) in View of Membrane Application.

The effect of phenolic antioxidant Irganox 1076 on the structure and gas permeation behavior of poly(1-trimethylsilyl-1-propyne) (PTMSP) was investigated. Isotropic films as well as thin film composite membranes (TFCM) from pure PTMSP and with added antioxidant (0.02 wt%) were prepared. PTMSP with antioxidant has a significantly higher thermal degradation stability in comparison to pure polymer. The thermal annealing of isotropic films of PTMSP with antioxidant was carried out at 140 °C. It revealed the stability of gas permeation properties for a minimum of up to 500 h of total heating time after a modest permeation values decrease in the first 48 h. X-ray diffraction data indicate a decrease in interchain distances during the heat treatment of isotropic films and indicate an increase in the packing density of macromolecules during thermally activated relaxation. Isotropic films and TFCMs from pure PTMSP and with antioxidant stabilizer were tested under conditions of constant O2 and N2 flow. The physical aging of thick and composite PTMSP membranes point out the necessity of thermal annealing for obtaining PTMSP-based membranes with predictable properties.

An Investigation of Thermal Air Degradation and Pyrolysis of Per- and Polyfluoroalkyl Substances and Aqueous Film-Forming Foams in Soil

In this study, we found that thermal decomposition of per- and polyfluoroalkyl substances (PFAS) in soil was rapid at moderate temperatures of 400–500 °C, regardless of whether the soil was contaminated by a single PFAS compound or a PFAS mixture in aqueous film-forming foams. Substantial degradation (>99%) of PFAS in soil, including perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), short-chain homologues, cationic and zwitterionic precursors, and PFOA and PFOS alternatives, occurred in 30 min at 500 °C in both a sealed reactor in air and a horizontal reactor under a continuous flow of N2. The effect of the initial PFAS level in soil (0.001–10 μmol/g) and soil texture was insignificant, provided a sufficiently high temperature was applied. Furthermore, this study showed, for the first time, that kaolinite dramatically decreased the apparent yield of F from PFAS heated at >300 °C, likely due to the chemisorption of F radicals on kaolinite. This phenomenon was not observed when kaolinite and an inorganic fluoride salt (NaF) were thermally treated. Lastly, various nonpolar thermal degradation products of PFOA and PFOS were reported for the first time. The profile of fluorinated volatiles, particularly perfluoroalkenes, was similar between these two chemicals. The results support a radical-mediated degradation pathway of PFAS.

The effect of particle content and sintering time on the properties of Al-Al9Co2-Al13Co4 composites, made by powder metallurgy

In the current study, aluminum matrix composites made of Al-Al9Co2-Al13Co4 are developed using powder metallurgy with a flow of N2 at a temperature of 600 °C. In this study, the impacts of process variables such cobalt concentration (0.5, 1, 3, and 5 %at.) and sintering time (4, 8, 24, 48, and 72 h) on hardness were examined. X-ray diffraction analysis, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy were used to evaluate the crystalline phase and microstructure of the composites made using the powder metallurgy process. A micro Vickers hardness tester was used to test the mechanical properties. During heat treatment, mixed products Al13Co4 and Al9Co2 were generated in the aluminium matrix through reactive diffusion in solid state. The results show, on the one hand, that the obtained alloys have microhardness values that are significantly higher than those of pure aluminum (49 ± 4 HV). In contrast, the microhardness of alloys based on the compositions ‘Al-0.5%Co’ and ‘Al-1%Co’ increases with the sintering time and achieves a maximum value of 153.89 ± 4.85 HV and 141.49 ± 7.81 HV, respectively, at a sintering time of 72 h. Nevertheless, the microhardness decreases with longer sintering times of 72 h for the higher compositions that were studied ‘Al-3%Co’ et ‘Al-5%Co’. After 48 h of sintering, the microhardness of the ‘Al-3%Co’ alloy falls from 131.88 ± 2.50 HV to 102.67 ± 4.33 HV. For the alloy ‘Al-5%Co’, it decreases from 93.87 ± 2.50 HV to 64.65 ± 2.50 HV after 24 h of sintering. This decrease in hardness is explained by the generation of a large amount of pores during the sintering of the alloys with large compositions.

Production of Niobium Nitride Via Nitrogen-Based Solid-Gas Reaction

Nanostructured niobium nitride was synthesized through a solid-gas reaction in an atmosphere of nitrogen and hydrogen using an oxalic niobium precursor. Crystal phases evolution throughout the reactive processes were evaluated using X-Ray Diffraction, reaction parameters modifications were performed in isotherm time, gas flow, and precursors’ mass. It was verified the synthesis of a stable NbN material with a hexagonal structure under the following conditions: 1g of precursor, 300 min of isotherm at 1100 °C and, the gas flow of N2 = 40% (v/v), and H2 = 60% (v/v). The increase in gas phase flow and the decrease of solid load favored the process, and a pure and single-phase powder was obtained. This set indicates the importance of physical resistance in the fluid-particle interaction process. Under these conditions, the solid obtained had a crystallite size of 30 - 50 nm.