High Purity Nitrogen Research Articles

One-pot synthesis of NiO/C composite nanoparticles as anode materials for lithium-ion batteries

Nanostructured NiO/C composite particles with controlled carbon content for lithium-ion battery anode were prepared via a one-pot hydrothermal approach and subsequent calcination in a high purity nitrogen atmosphere. The composites were composed of amorphous carbon and nanocrystalline NiO. The structure of the NiO crystals was determined with X-ray diffraction (XRD) analysis and the content of carbon was calculated from the energy dispersive spectroscopy (EDS) results. Scanning electron microscopy (SEM) images showed a relatively narrow distribution of particle size for both the neat NiO and NiO/C nanoparticles. Electrochemical performance measurements demonstrated that, after 50 cycles, NiO/C nanocomposites maintained a high reversible capacity of 585.9 mAh g−1, much higher than that of 356.1 mAh g−1 of the neat NiO nanoparticles without carbon. The NiO/C nanoparticles also exhibited a remarkable discharge capacity, a high charge/discharge rate and an excellent cycle stability. The improvements can be attributed to the even carbon coating on the NiO particles, which significantly enhances the conductivity and improves the structural stability of the electrode.

Influence of Trace Impurities on Oxygen Activity for High Purity Nitrogen Gas Processed by Zirconia Oxygen Pump

Influence of Trace Impurities on Oxygen Activity for High Purity Nitrogen Gas Processed by Zirconia Oxygen Pump

Zero gas reference standards

High purity nitrogen or air, often referred to as zero gas, is essential for calibrating instrumentation used in a wide variety of measurements, such as air quality monitoring.

Investigation of novel integrated air separation processes, cold energy recovery of liquefied natural gas and carbon dioxide power cycle

Cryogenic air separation unit (ASU) consume high amount of energy to produce oxygen and nitrogen with high purity. Liquefied natural gas (LNG) regasification process provides low temperature cryogenic refrigeration source which can be used in ASU with high efficiency. In this study two cryogenic air separation processes for production of high purity nitrogen and oxygen with low energy consumption are proposed and analyzed. The first proposed process is a two-column configuration which power consumption per oxygen production is 16.6% lower, compared to a convectional cryogenic air separation process. In the second one, liquefied natural gas cold energy is used for pre-cooling the feed air. This greatly reduces the energy consumption of the compressors located before the columns by more than 55.6% compared to the first proposed process, without much change in purity of the products. In the second process, energy saving in the air separation unit and power generation cycle is 2715 kW and 17,810 kW respectively. Both processes use an integrated heat exchanger which is both condenser of the high pressure column and reboiler of the low pressure column. With this integration latent heat of the pure nitrogen and pure oxygen can be exchanged in a two-column process configuration. The second proposed process is a hybrid with a carbon dioxide trans-critical power cycle. The liquefied natural gas cold energy is used for cooling the power cycle condenser. Energy and exergy analysis are carried out on the air separation unit and power generation cycle.

Complete Equation-Oriented Approach for Process Analysis and Optimization of a Cryogenic Air Separation Unit

A cryogenic air separation unit produces large volumes of high-purity oxygen, nitrogen, and argon through distillation. Such a complex process with a heat-coupling design, a high purity requirement, and a large-scale feature is difficult to analyze and optimize. In this study, a complete equation-oriented (EO) model, which includes a unit model and a thermodynamic model, is developed for cryogenic air separation involving a low-pressure column, a high-pressure column, and an argon side arm column. The EO approach is then applied to deal with the following three issues in air separation: thermodynamic parameter estimation, process analysis with heat-coupling design, and process optimization with varying load demands. The proposed EO method is superior to traditional sequential modular based commercial software in terms of convergence performance.

New Technology of Base Metals Precipitation by Hydrogen Sulfide Obtained Using <i>Desulfurella</i> <i>acetivorans</i> and <i>Desulfurella</i> <i>kamchatkenis</i>

Nowadays, efficient recovery of base metals from the solutions when processing gold ores is a topical issue. In this connection, the focus is on the use of hydrogen sulfide produced in bioreactors using sulfate-reducing (SRB) and sulfur-reducing bacteria. A new technology of biogenic hydrogen sulfide production followed by the precipitation of base metals from the solutions as sulfides was developed. The strains of anaerobic sulfidogenic thermophilic microorganisms: Desulfurellaacetrivans and DesulfurellaKamchatkensis which were obtained at S.N.Vinogradsky Institute of Microbiology RAS, Moscow were used for these tests. They have anaerobic respiration using sodium acetate as an electron donor and elemental sulfur as an electron acceptor. In order to cut costs for biogenic hydrogen sulfide production, the possibility of using acetic acid as an electron donor was studied. Scaled-up test work was conducted in a 1.5L bioreactor at the temperature of 55°C, pH of 5.0, redox of-250mV and using POX solution with the content of C2+=5700.0 mg/L, Fe2+=4890.0 mg/L and Zn2+=1200.0 mg/ L. Selective precipitation of copper (at pH of ≤0.5), zinc (pH=1.0-2.0) and iron (II) (pH≥5.5) was carried out. Recycled gas contacted with the metals solutions (in a series of reactors for the precipitation of metals) coupled with the removal of hydrosulfuric acid from the recycled gas and the recovery of metals from the solution as sulfides. The precipitate was separated from the solutions by filtering. Then the filtrate was directed to the next stage. Carbon dioxide was removed from the recycled gas by filtrating through alkaline solution. After that, about 10% of ultra high purity nitrogen was added from the balloon and the recycled gas was again directed to the bioreactor. The average hydrogen sulfide reactor throughput was 1 g/L per day of culture medium. The total consumption of hydrogen sulfide was 1.28 g/L of the process solution. Results showed that this process can selectively recover metals from POX solutions with generation of high grade copper (50%), zinc (45%) and iron sulfide (45%) concentrates.

Determination of Dicarboxylic Acids in Fine Atmospheric Particles by Micro-Pressurized Liquid Extraction Coupled with Gas Chromatography-Mass Spectrometer

Abstract The method of micro-pressurized liquid extraction (μ-PLE) coupled with gas chromatography-mass spectrometer (GC-MS) for analysis of 4 dicarboxylic acids (DCAs, including malonic acid, succinic acid, glutaric acid, and adipic acid) in fine atmospheric particles was developed. PM2.5 filter sample was extracted by μ-PLE at a pressure of 8 MPa and temperature of 80 °C using methanol as extraction solution. After two static 5-min extractions and a rinsing step with 100 μL methanol, about 500 μL of extraction solution was obtained. The extraction solution was then blown to dry with high purity nitrogen and submitted to a silylation reaction at 60 °C for 30 min. After internal standard (IS) was added, the derivatization solution was directly injected for GC-MS analysis. For quantification of 4 normally DCAs in fine atmospheric particles, the calibration curve was obtained with a good linear relationship in the range of 0.2–20 ng μL−1. The limits of quantification (LOQs, S/N = 10) were in the range of 0.15–0.47 ng m−3. The relative recoveries were between 92% and 122% with the RSDs between 2.6% and 11.8% for spiked filter samples. The method developed here was used to determine malonic acid, succinic acid, glutaric acid, and adipic acid in real PM2.5 samples collected from Xinghai Bay of Dalian city, and the results were determined to be 64.6, 50.0, 41.8 and 20.2 ng m−3, respectively.

Paramagnetism of cobalt-doped ZnO nanoparticles obtained by microwave solvothermal synthesis.

Zinc oxide nanopowders doped with 1–15 mol % cobalt were produced by the microwave solvothermal synthesis (MSS) technique. The obtained nanoparticles were annealed at 800 °C in nitrogen (99.999%) and in synthetic air. The material nanostructure was investigated by means of the following techniques: X-ray diffraction (XRD), helium pycnometry density, specific surface area (SSA), inductively coupled plasma optical emission spectrometry (ICP-OES), extended X-ray absorption fine structure (EXAFS) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and with magnetometry using superconducting quantum interference device (SQUID). Irrespective of the Co content, nanoparticles in their initial state present a similar morphology. They are composed of loosely agglomerated spherical particles with wurtzite-type crystal structure with crystallites of a mean size of 30 nm. Annealing to temperatures of up to 800 °C induced the growth of crystallites up to a maximum of 2 μm in diameter. For samples annealed in high purity nitrogen, the precipitation of metallic α-Co was detected for a Co content of 5 mol % or more. For samples annealed in synthetic air, no change of phase structure was detected, except for precipitation of Co3O4 for a Co content of 15 mol %. The results of the magentometry investigation indicated that all as-synthesized samples displayed paramagnetic properties with a contribution of anti-ferromagnetic coupling of Co–Co pairs. After annealing in synthetic air, the samples remained paramagnetic and samples annealed under nitrogen flow showed a magnetic response under the influences of a magnetic field, likely related to the precipitation of metallic Co in nanoparticles.

Rutherford backscattering spectroscopy and structural analysis of DC reactive magnetron sputtered titanium nitride thin films on glass substrates

Titanium nitride thin films were deposited on sodalime glass substrate using DC reactive magnetron sputtering technique with 99.99 % pure titanium target. High purity nitrogen and argon gases were used as the reactive and sputtering gases respectively. The sputtering deposition time was fixed at 10 min for all samples, while the chamber sputtering pressure was varied from 0.80 to 11.33 Pa with corresponding change in the nitrogen partial pressure. The films were characterized using Rutherford backscattering (RBS) spectroscopy, UV–visible spectrophotometry, scanning electron microscopy and optical microscopy. The RBS studies revealed disparity in film thicknesses and stoichiometry with respect to the deposition sputtering pressure. Up to 10 % oxygen concentration was observed in films deposited at relatively low sputtering pressures of 0.80 and 1.07 Pa, while no oxygen was detected in the films deposited at higher sputtering pressure. High pressure sputtered TiNx films showed distinct optical properties reminiscent of indium tin oxide with high transmission of 86.74 % maximum in the visible range and wide band gap energy of 3.78 eV.

Streamer knotwilg branching: sudden transition in morphology of positive streamers in high-purity nitrogen

We describe a peculiar branching phenomenon in positive repetitive streamer discharges in high purity nitrogen. We name it knotwilg branching after the Dutch word for a pollard willow tree. In a knotwilg branching a thick streamer suddenly splits into many thin streamers. Under some conditions this happens for all streamers in a discharge at about the same distance from the high-voltage electrode tip. At this distance, the thick streamers suddenly bend sharply and appear to propagate over a virtual surface surrounding the high-voltage electrode, rather than following the background electric field lines. From these bent thick streamers many, much thinner, streamers emerge that roughly follow the background electric field lines, creating the characteristic knotwilg branching. We have only found this particular morphology in high purity nitrogen at pressures in the range 50 to 200 mbar and for pulse repetition rates above 1 Hz; the experiments were performed for an electrode distance of 16 cm and for fast voltage pulses of 20 or 30 kV. These observations clearly disagree with common knowledge on streamer propagation. We have analyzed the data of several tens of thousands of discharges to clarify the phenomena. We also present some thoughts on how the ionization of the previous discharges could concentrate into some pre-ionization region near the needle electrode and create the knotwilg morphology, but we present no final explanation.

Simultaneous determination of three organic fluorides in workplace air by portable gas chromatography-mass spectrometer

To establish a method for rapid determination of organic fluorides in the air of a fluorine chemical plant using portable gas chromatography-mass spectrometer (GC-MS). Standard samples of monochlorodifluoromethane, tetrafluoroethylene, and hexafluoropropylene of different concentrations were prepared by static volumetric method with high-purity nitrogen as the diluent gas. The samples were injected into the GC-MS by a hand-held probe. Retention time and characteristic ion were used for qualitative analysis, and the area of selected ion peak was used for quantitative analysis. The standard curves were then created for quantitative determination of the three organic fluorides. The linear ranges for monochlorodifluoromethane, tetrafluoroethylene, and hexafluoropropylene by the method were 0.39-7.72, 0.45-8.84, and 0.61-12.20 mg/m3, respectively, the average recovery rates for the three concentrations were 102.8%, 96.0%, and 106.5%, respectively, and the average deviations were 2.1%, 5.1%, and 2.4%, respectively. The portable GC-MS can be used for the simultaneous qualitative and quantitative analysis of monochlorodifluoromethane, tetrafluoroethylene, and hexafluoropropylene in the workplace air, and the method is simple, fast, and accurate.

Effect Of SiC Particles On Sinterability Of Al-Zn-Mg-Cu P/M Alloy

Abstract Premix Al-5.5Zn-2.5Mg-0.5Cu alloy powder was analyzed as matrix in this research. Gas atomized powder Al-9Si with 20% volume fraction of SiC particles was used as reinforcement and added into the alloy with varied concentration. Mix powders were compacted by dual action press with compaction pressure of 700 MPa. High volume fraction of SiC particles gave lower green density due to resistance of SiC particles to plastic deformation during compaction process and resulted voids between particles and this might reduce sinterability of this mix powder. Sintering was carried out under ultra high purity nitrogen gas from 565°-580°C for 1 hour. High content of premix Al-5.5Zn-2.5Mg-0.5Cu alloy powder gave better sintering density and reached up to 98% relative. Void between particles, oxide layer on aluminum powder and lower wettability between matrix and reinforcement particles lead to uncompleted liquid phase sintering, and resulted on lower sintering density and mechanical properties on powder with high content of SiC particles. Mix powder with wt90% of Alumix 431D and wt10% of Al-9Si-vf20SiC powder gave higher tensile strength compare to another mix powder for 270 MPa. From chemical compositions, sintering precipitates might form after sintering such as MgZn2, CuAl2 and Mg2Si. X-ray diffraction, DSC-TGA, and SEM were used to characterize these materials.

Non-isothermal pyrolysis characteristics of giant reed (Arundo donax L.) using thermogravimetric analysis

A constructed wetland plant waste, Arundo donax L. (AD), was pyrolyzed from room temperature to 1000 °C under a dynamic high-purity nitrogen atmosphere at different heating rates. Results show that three stages occur during thermal degradation of AD. Mass loss rates associated with lignocellulose degradation were not affected by heating rates. Physical and chemical characterization of ADs pyrolyzed under different temperatures indicated that simultaneous pyrolysis occurred during the lignocellulose devolatilization process. The non-isothermal method indicated that the pyrolysis reaction should conform to a single-step reaction model with average E (activation energy) of 163 kJ mol−1, calculated by partial least squares linear regression. The most probable mechanism of thermal degradation of AD, determined by the Malek method with the calculated E as the initial value, is described with the random nucleation and later growth (Johnson–Mehl–Avrami (J–M–A) model). It can be written as f(α)=0.28(1−α)[−ln(1−α)]−2.57. Finally, E = 163.44 ± 3.50 kJ mol−1, the reaction order n = 0.28 ± 0.031, and the decimal logaritm of pre-exponential factor lg(A) = 13.13 ± 0.096 lg(s−1) were estimated.

Determination of residual organic solvents and macroporous resin residues in Akebia saponin D

According to ICH, Chinese Pharmacopoeia and supplementary requirements on the separation and purification of herbal extract with macroporous adsorption resin by SFDA, hexane, acetidine, ethanol, benzene, methyl-benzene, o-xylene, m-xylene, p-xylene, styrene, diethyl-benzene and divinyl-benzene of residual organic solvents and macroporous resin residues in Akebia saponin D were determined by headspace capillary GC. Eleven residues in Akebia saponin D were completely separated on DB-wax column, with FID detector, high purity nitrogen as the carry gases. The calibration curves were in good linearity (0.999 2-0.999 7). The reproducibility was good (RSD < 10%). The average recoveries were 80.0% -110%. The detection limit of each component was far lower than the limit concentration. The method is simple, reproducible, and can be used to determine the residual organic solvents and macroporous resin residues in Akebia saponin D.

Nanosecond repetitively pulsed discharges in N2–O2 mixtures: inception cloud and streamer emergence

We evaluate the nanosecond temporal evolution of tens of thousands of positive discharges in a 16 cm point-plane gap in high purity nitrogen 6.0 and in N2–O2 gas mixtures with oxygen contents of 100 ppm, 0.2%, 2% and 20%, for pressures between 66.7 and 200 mbar. The voltage pulses have amplitudes of 20 to 40 kV with rise times of 20 or 60 ns and repetition frequencies of 0.1 to 10 Hz. The discharges first rapidly form a growing cloud around the tip, then they expand much more slowly like a shell and finally after a stagnation stage they can break up into rapid streamers. The radius of cloud and shell in artificial air is about 10% below the theoretically predicted value and scales with pressure p as theoretically expected, while the observed scaling of time scales with p raises questions. We find characteristic dependences on the oxygen content. No cloud and shell stage can be seen in nitrogen 6.0, and streamers emerge immediately. The radius of cloud and shell increases with oxygen concentration. On the other hand, the stagnation time after the shell phase is maximal for the intermediate oxygen concentration of 0.1% and the number of streamers formed is minimal; here the cloud and shell phase seem to be particularly stable against destabilization into streamers.

AlxGa1−xN/GaN/AlN heterostructures grown on Si(1 1 1) substrates by MBE for MSM UV photodetector applications

AlxGa1−xN/GaN/AlN heterostructures on silicon (Si) substrate was developed by nitrogen plasma-assisted molecular beam epitaxy (MBE) and their properties were investigated by scanning electron microscopy (SEM), electron dispersive X-ray (EDX), atomic force microscopy (AFM), high resolution X-ray diffraction (XRD), Raman spectroscopy and Hall effect measurements. High purity gallium (7N) and aluminum (6N5) were used in the Knudsen cells. High purity nitrogen with 7N purity was supplied to radio frequency (RF) source to generate reactive nitrogen species. The nitrogen pressure and a discharge power were kept at 1.5×10−5Torr and 300W, respectively. From SEM measurements, the surface morphology of samples presented 2- and 3-dimensional growth modes. The EDX measurements showed that there were no foreign elements in the grown samples. The HR-XRD measurement has confirmed that the AlxGa1−xN/GaN/AlN heterostructures samples were epitaxially grown on Si substrate. All the dominant E2 phonon modes were found in Raman spectra results. Lastly, AlxGa1−xN/GaN/AlN heterostructures based metal–semiconductor–metal (MSM) UV photodetectors were fabricated and the electrical characteristics of the devices were investigated by using current–voltage (I–V) and photo-conductivity measurements. The devices presented good I–V and photoconductivity characteristics.

Long Plasma Jet Generated by DC Discharge in N&lt;sub&gt;2&lt;/sub&gt; at Atmospheric Pressure: Impact of Trace Admixtures on Composition of Reactive Species in Far Afterglow

The object under study is a long plasma jet (up to 15 cm) generated by a steady-state dc discharge in N2 at atmospheric pressure. Successful usage of long afterglow plasma jet for distant treatment of 3-D object of a complicated shape with deep slots was demonstrated. This paper focuses on a role of trace impurities in plasma-forming gas on chemical composition of reactive species in far afterglow plasma. This role was studied numerically by example of the additives in high-purity nitrogen contained in high-pressure N2 tank. It is shown that small oxygen admixtures (at 10 ppm level) to N2 can be more effective in production of atomic oxygen than ambient air. Besides, trace admixtures of water vapor and hydrocarbons (at parts per million level) lead to full change in a composition of reactive species in far afterglow in comparison with the set of primary species generated by plasma source.

Occurrence state of SiO2 in hercynite synthesized by reaction sintering

Sample was prepared using Fe2O3, Al2O3 and Si O2 powders as raw materials according to mass ratio Fe O:Al2O3 of 40.8:59.2 and adding a percent of Si O2 in the synthetic system, and being sintered under high purity nitrogen atmosphere at 1 600 ℃for 4 h. The sample was analyzed and characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy and transmission electron microscope. Based on Fe O-Al2O3-Si O2 ternary phase diagram, the existence of silicon dioxide was investigated. The results indicate that silicon dioxide didn't enter into hercynite crystals, but existed among hercynite crystals as amorphous phase. When a percent of Si O2 was added into the synthetic system, amorphous phase containing Si O2 was discontinuously distributed and the direct contact among hercynite crystals wasn't changed.

Evaluation of Sintering Behavior of Premix Al-Zn-Mg-Cu Alloy Powder

Sintering of light aluminium alloys powder has been investigated as a way to substitute steels in automotive and aerospace industries. Premix Al-5.5Zn-2.5Mg-0.5Cu composite powder called Alumix 431D was analyzed in this research. Sintering was carried out under ultra high purity nitrogen gas and before reaching sintering temperature, green samples were delubricated at 400°C for 30 min. The powder possesses high sinterability by reaching 96% relative density at 580°C sintering temperature. Formation of liquid phase seems to support achieving high sintering density. Optimum mechanical properties also were obtained under those conditions. T6 heat treatment was done to improve the mechanical properties by formation of precipitation strengthening, and MgZn2appears to be dominant strengthening precipitate. X-ray diffraction, optical microscopy, and SEM-EDS were used to characterize powder, and sintered and heat treated samples.

Co-pyrolysis of lignite and Shendong coal direct liquefaction residue

To utilize the coal direct liquefaction residue (DLR) and improve the tar yield and quality, experimental studies on co-pyrolysis of lignite and DLR were conducted with a fixed-bed reactor under atmospheric pressure in high purity nitrogen. In-situ micro-Raman experiments, Soxhlet extraction, scanning electron microscope, and X-ray energy spectra analysis were also performed to explore the interaction mechanisms during the co-pyrolysis process. The results indicated that there was an interactive effect between lignite and DLR, which increased the tar yield. This interaction was attributed to the hydrogenation of organic components in the DLR and mass transfer process in pyrolysis of DLR. Also, the co-pyrolysis of DLR and lignite with ratio of 0.15, pyrolysis temperature of 550°C and particle size range of 0.425–0.85mm resulted in the most pronounced interactive effect on the high tar yield. Under optimal operational conditions, the tar yield of co-pyrolysis reached 8.8wt.% and the yield of n-hexane soluble was 61.4wt.%.