Nitrogen-rich Atmosphere Research Articles

Laboratory Experiments of Titan Tholins formed by Photochemistry of Cyanopolyynes

Tholins are complex organic materials produced by irradiation of several carbon and nitrogen rich atmosphere. It has been proposed that Tholins could have played an important role in the origin of life on Earth [1]. We investigate the formation of polymer (Tholins) from the photolysis of dicyanoacetylene. As of today, nitriles molecules have been identified in Titan atmosphere. Among these nitriles, the cyanopolyynes (HCnN) are very important since they are the essential constituents in building block amino acids. It is known that a rich phochemistry takes place in the Titan aerosols, and contributes to the evolution of molecular diversity in this atmosphere. These compounds evolve through polymerization processes in aerosol particles, which grow by coagulation and rain down to the surface of Titan containing water ice. We present photochemical processes of larger cyanopolyyne formation from small precursor molecules submitted to long wavelength photons. Under UV irradiation cyanopolyynes are known to induce izomerization process (figure 1) [2] and formation of longer cyanopolyynes [3].

Structurally-Tuned Nitrogen-Doped Cerium Oxide Exhibits Exceptional Regenerative Free Radical Scavenging Activity in Polymer Electrolytes

The regenerative free radical scavenging activity of cerium oxide (CeO2) nanoparticles was improved by tuning its microstructure via nitrogen doping (N-doping). Commercially available CeO2 (60 m2/g) and high-surface-area CeO2 (synthesized in-house; 220 m2/g) were doped with nitrogen by annealing in a nitrogen rich atmosphere. The evolution of CeO2 microstructure in Nitrogen doped (N-doped) commercial CeO2 (20 m2/g) and N-doped high-surface-area CeO2 (90 m2/g) was studied. XPS and Raman measurements revealed that N-doping of CeO2 enhanced Ce3+ surface concentration and concomitantly increased surface non-stoichiometry (surface oxygen vacancy concentration). XRD analysis of the doped samples confirmed that the nitrogen atom replaced the oxygen atom in the CeO2 lattice, yielding a lower electron density region around the N-doped sites. The high-surface-area CeO2 and its N-doped version had significantly larger lattice parameters than that of commercial CeO2 and its doped version. XAS studies revealed that the N-doped high-surface-area CeO2 had more Ce3+ active clusters than its counterparts, and effectively retained its active Ce3+ active clusters upon exposure to reactive oxygen species (ROS). To confirm, the regenerative ROS (hydroxyl radical) scavenging ability of N-doped CeO2 nanoparticles within the polymer electrolyte membrane (PEM) of an operating polymer electrolyte fuel cell (PEFC) was evaluated using in-situ fluorescence spectroscopy. The N-doped high-surface-area CeO2 showed at least 100 hours of efficient and quantitative ROS scavenging under harsh conditions - a 15-fold improvement over previous reports. This study unequivocally demonstrates that N-doping increases both the number of Ce3+ active clusters in the lattice and the Ce-O bond distance; these structural attributes enhance regenerative ROS scavenging activity of CeO2.

Dunes on Saturn’s moon Titan as revealed by the Cassini Mission

Dunes on Titan, a dominant landform comprising at least 15% of the surface, represent the end product of many physical processes acting in alien conditions. Winds in a nitrogen-rich atmosphere with Earth-like pressure transport sand that is likely to have been derived from complex organics produced in the atmosphere. These sands then accumulate into large, planet-encircling sand seas concentrated near the equator. Dunes on Titan are predominantly linear and similar in size and form to the large linear dunes of the Namib, Arabian and Saharan sand seas. They likely formed from wide bimodal winds and appear to undergo average sand transport to the east. Their singular form across the satellite indicates Titan’s dunes may be highly mature, and may reside in a condition of stability that permitted their growth and evolution over long time scales. The dunes are among the youngest surface features, as even river channels do not cut through them. However, reorganization time scales of large linear dunes on Titan are likely tens of thousands of years. Thus, Titan’s dune forms may be long-lived and yet be actively undergoing sand transport. This work is a summary of research on dunes on Titan after the Cassini Prime and Equinox Missions (2004–2010) and now during the Solstice Mission (to end in 2017). It discusses results of Cassini data analysis and modeling of conditions on Titan and it draws comparisons with observations and models of linear dune formation and evolution on Earth.

Thermal analysis of magnesium reactions with nitrogen/oxygen gas mixtures

The thermal behavior and kinetic parameters of magnesium powder subjected to a nitrogen-rich atmosphere was investigated in thermogravimetric (TG) and differential scanning calorimeter (DSC) experiments with oxygen/nitrogen mixtures heated at rates of 5, 10, 15, and 20°C/min. At higher temperature increase rates, the observed oxidation or nitridation steps shifted toward higher temperatures. The comparison of mass gain and heat of reaction in different nitrogen concentrations is helpful in interpreting the inerting effect of nitrogen on magnesium powder explosion in closed vessels. Activation energies for oxidation in air calculated by the Kissinger–Akahira–Sunose (KAS) method are generally consistent with previously published reports, but the method was not successful for the entire nitridation process. The change of activation energy with temperature was related to protective properties of the corresponding coating layer at particle surfaces. Two main coating layer growth processes were found in magnesium oxidation and nitridation using a modified Dreizin method which was also employed to determine activation energy for both magnesium oxidation and nitridation. For magnesium powder oxidation, activation energy calculated by the Dreizin method was close to that by KAS. Variation in activation energies was a function of different mechanisms inherent in the two methods.

VUV photochemistry simulation of planetary upper atmosphere using synchrotron radiation

The coupling of a gas reactor, named APSIS, with a vacuum-ultraviolet (VUV) beamline at the SOLEIL synchrotron radiation facility, for a photochemistry study of gas mixtures, is reported. The reactor may be irradiated windowless with gas pressures up to hundreds of millibar, and thus allows the effect of energetic photons below 100 nm wavelength to be studied on possibly dense media. This set-up is perfectly suited to atmospheric photochemistry investigations, as illustrated by a preliminary report of a simulation of the upper atmospheric photochemistry of Titan, the largest satellite of Saturn. Titan's atmosphere is mainly composed of molecular nitrogen and methane. Solar VUV irradiation with wavelengths no longer than 100 nm on the top of the atmosphere enables the dissociation and ionization of nitrogen, involving a nitrogen chemistry specific to nitrogen-rich upper atmospheres.

Active upper-atmosphere chemistry and dynamics from polar circulation reversal on Titan

Saturn's moon Titan has a nitrogen atmosphere comparable to Earth's, with a surface pressure of 1.4 bar. Numerical models reproduce the tropospheric conditions very well but have trouble explaining the observed middle-atmosphere temperatures, composition and winds. The top of the middle-atmosphere circulation has been thought to lie at an altitude of 450 to 500 kilometres, where there is a layer of haze that appears to be separated from the main haze deck. This 'detached' haze was previously explained as being due to the co-location of peak haze production and the limit of dynamical transport by the circulation's upper branch. Here we report a build-up of trace gases over the south pole approximately two years after observing the 2009 post-equinox circulation reversal, from which we conclude that middle-atmosphere circulation must extend to an altitude of at least 600 kilometres. The primary drivers of this circulation are summer-hemisphere heating of haze by absorption of solar radiation and winter-hemisphere cooling due to infrared emission by haze and trace gases; our results therefore imply that these effects are important well into the thermosphere (altitudes higher than 500 kilometres). This requires both active upper-atmosphere chemistry, consistent with the detection of high-complexity molecules and ions at altitudes greater than 950 kilometres, and an alternative explanation for the detached haze, such as a transition in haze particle growth from monomers to fractal structures.

INFLUENCE OF HEAT TREATMENT CONDITION ON PHOTOCATALYTIC PROPERTIES OF OXIDIZED TiN FILM

Nitride doped titanium oxide ( TiOxNy ) is a photocatalytic material which acts under visible light, while conventional titanium oxide acts only in ultra violet light. In this study, we tried to make nitride doped titanium film by oxidizing of TiN film. The TiN films were deposited on the quartz substrate by DC magnetron sputtering. The film structure was analyzed by X-ray diffraction. The photocatalytic decomposing rate was measured using methylene blue solution under black light and fluorescent lamp. As a result, post annealing process after oxidizing process is unsuitable to realize a high photocatalytic activity for oxidized TiN . On the other hand, the samples oxidized in nitrogen rich atmosphere showed the obvious photocatalytic activity under visible light irradiation. This reason is that the oxidation of the film surface is controlled and nitrogen atom left in film surface by nitrogen gas supplying. In conclusion, oxidizing of TiN film in nitrogen rich atmosphere is suitable to realize a high photocatalytic activity.

Synthesis of High Purity- Sicand- Si 3N4Fromricehulls

Silicon carbide and silicon nitride were synthesized from ashes obtained by heating rice hulls at 800C for 3 hours in argon. -SiC was produced from the ashes by reheating them at l 400C for 8 hours in argon, whereas -Si,N, was obtained by heating the ashes at temperatures ranging from 1250C to l 400C for periods of 3 to 6 hours in a nitrogen rich atmosphere. Toe products were characterized by infrared spectroscopy, X-ray and scanning electron microscopy. High purity -SiC and -Si,N, compounds with whisker type morphology were obtained. It was possible to obtain -Si,N, without SiC by heating the ashes for 6 hours at 1250C.

Statistical analysis of the energetic ion and ENA data for the Titan environment

The MIMI experiment (Magnetosphere Imaging Instrument) onboard Cassini is dedicated to the study of energetic particles, with in particular LEMMS analyzing charged particles, or the INCA detector which can image the Energetic Neutral Atoms produced by charge exchange collisions between cold neutrals and energetic ions. The MIMI experiment is thus well adapted to the study of the interaction between the Titan nitrogen rich atmosphere and the energetic Saturnian magnetospheric plasma. We analyze here the energetic protons at the Titan orbit crossings before January 2008 (MIMI-LEMMS data; 27–255 keV), which are very dynamic, with tri-modal flux spectra and probably quasi-isotropic pitch angle distributions. We provide statistical parameters for the proton fluxes, leading to estimates of the average energy deposition into Titan's atmosphere, before we discuss the possible influence of Titan on the magnetopause. We then analyze the H ENA images (24–55 keV) during the Titan flybys before June 2006 to obtain a better diagnostic of the Titan interaction: the ENAs variability is mostly related to the magnetospheric variability (the exosphere being roughly stable) or the distance from the moon, the ENAs halo around Titan is very stable (corresponding to a lower limit for ENAs emission at the exobase), and strong asymmetries are observed, due to finite gyroradii effects for the parent ions.

Aeronomical evidence for higher CO 2 levels during Earth’s Hadean epoch

According to recent simulations of the Earth’s thermosphere, the exospheric temperature is not expected to rise above 7000–8000 K even under extreme solar EUV conditions anticipated for the early Earth. Rather, when the solar EUV flux exceeds some critical value, the escaping flow of the bulk upper thermosphere starts cooling it due to adiabatic expansion, which results in a decrease of the exobase temperature. Under these extreme conditions, the exobase might have expanded above the magnetopause and the magnetosphere had not been able to protect the upper atmosphere against strong non-thermal erosion by the solar wind. This study shows that a nitrogen-rich terrestrial atmosphere with a present-day composition would have been removed within a few million years during the extreme EUV and solar wind conditions that are expected to have prevailed before the late heavy bombardment period ∼3.8 Ga ago. Our results suggest that a CO 2 amount in the early nitrogen-rich terrestrial atmosphere of at least two orders of magnitude higher than the present-time level was needed to confine the upper atmosphere after the onset of the geodynamo within the shielding magnetosphere and thus might have protected it from complete destruction.

Electron impact processes in nitrogen rich atmospheres of the outer solar system

Electron collisions with N2 are predominant components of the interaction between outer solar-system atmospheres and solar photons, solar wind, and magnetospheric electrons. Our collaboration between the Jet Propulsion Laboratory (JPL) and the California State University, Fullerton (CSUF), has devoted a significant effort over the last few years to improving the knowledge base of electron-N2 excitation phenomena. Here, we highlight the lack of Franck-Condon behaviour in excitation of the Rydberg-valence states, using excitation of the C 3Πu state as a case in point. Further, we briefly introduce ongoing work measuring vibrationally-resolved emission cross sections for the Lyman-Birge-Hopfield (LBH) band system of the a 1Πg (v′) → X 1Σ+g (v′′) transitions. Specifically, we present preliminary results for the relative (3,0) emission cross section, which calls the currently accepted LBH shape function of Ajello and Shemansky (1985 J. Geophys. Res.-Space 90 9845) into question.

Investigation of energetic proton penetration in Titan's atmosphere using the Cassini INCA instrument

Saturn's largest moon, Titan, provides an interesting opportunity to study how dense atmospheres interact with the surrounding plasma environment. Without an intrinsic magnetic field, this satellite's nitrogen-rich atmosphere is relatively unprotected from plasma interactions. Therefore, the energy-deposition rate is important for understanding chemistry and dynamics in Titan's atmosphere. Since the plasma environment can vary significantly we focus here on the T18 Titan encounter using in-situ data from instruments on board the Cassini spacecraft. These instruments cannot provide in-situ information below the spacecraft closest approach altitude (∼>960 km) so we use the Cassini magnetospheric imaging instrument (MIMI) ion-neutral camera (INCA) to remotely image energetic hydrogen particle fluxes (20–80 keV) at altitudes below Titan closest approach. We also use the MIMI low-energy magnetosphere measurements system (LEMMS) to measure the incident ion fluxes as the spacecraft approaches Titan and combine these data sets with an atmospheric model to first reproduce INCA images. We then use this model to calculate the energy-deposition profiles for the observed incident proton flux. Our model is able to reproduce the INCA observations and give the energy density deposited vs. altitude in Titan's atmosphere; however, we find that the incident fluxes and energy-deposition profiles vary significantly during the encounter.

Titan's exosphere and its interaction with Saturn's magnetosphere

Titan's nitrogen-rich atmosphere is directly bombarded by energetic ions, due to its lack of a significant intrinsic magnetic field. Singly charged energetic ions from Saturn's magnetosphere undergo charge-exchange collisions with neutral atoms in Titan's upper atmosphere, or exosphere, being transformed into energetic neutral atoms (ENAs). The ion and neutral camera, one of the three sensors that comprise the magnetosphere imaging instrument (MIMI) on the Cassini/Huygens mission to Saturn and Titan, images these ENAs like photons, and measures their fluxes and energies. These remote-sensing measurements, combined with the in situ measurements performed in the upper thermosphere and in the exosphere by the ion and neutral mass spectrometer instrument, provide a powerful diagnostic of Titan's exosphere and its interaction with the Kronian magnetosphere. These observations are analysed and some of the exospheric features they reveal are modelled.

CH 4/N 2/H 2 spark hydrophilic tholins: A systematic approach to the characterization of tholins

Tholins are complex organic materials produced by irradiation of several carbon and nitrogen rich atmospheres. They could have played a key role in the origin of life on Earth because their ability to release important bioorganics, which are nowadays present in proteins, nucleic-acid bases and other important biostructures. Usually, the yield of these compounds is higher after acid hydrolysis, however little is known about the structure and chemical composition of the tholins. In this work, we propose the use of different spectroscopic and separation techniques, which are not usually applied in this field, in order to obtain complete information about the tholin structure and behavior. Two different simulation experiments of prebiotic synthesis were carried out in CH 4/N 2/H 2 atmosphere out from spark discharge activation of aqueous aerosols and liquid water, respectively. In both cases, a hydrophilic tholin and a hydrophobic tholin were obtained. Herein, we report the application of this methodology to our hydrophilic tholins and we review, briefly, some astrobiological aspects related to these complex substances.

Annealing of evaporated and sputtered niobium films in oxygen and nitrogen rich atmospheres by Rapid Thermal Processing (RTP)

AbstractThin films of niobium were deposited on thermally oxidized Si‐(100)‐wafers by two different methods: electron beam evaporation and direct current reactive magnetron sputtering. The thicknesses of as‐deposited niobium films were 200 and 500 nm. 200 nm evaporated niobium films were nitridated in nitrogen and ammonia using rapid thermal processing (RTP). In these investigations the reactivity of N2 and NH3 with Nb‐films was compared. 500 nm sputtered Nb‐films were annealed in several steps. At first niobium films were nitridated under ammonia atmosphere at 1000 °C for 1 min using an RTP. After that nitridated niobium films were oxidized in molecular oxygen at temperatures ranging from 400 to 600 °C. Before and after reactions with ammonia, oxygen and nitrogen evaporated and sputtered samples were characterized by several complementary analytical methods. X‐ray diffraction (XRD) was used for phase analysis after annealing. Determination of the elemental depth profiles of the films was realized by secondary ion mass spectrometry (SIMS). Microstructure and spatial distribution of the elements were imaged by transmission electron microscopy (TEM) and energy‐filtered TEM (EFTEM). Electron energy loss spectra (EELS) were taken at selected positions to discriminate between different nitride, oxynitride and oxide phases. Investigation by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed differences of the film morphology depending on the reactive agent and reaction temperature. Investigations of sputtered films show that surface roughness of the samples after oxidation of niobium films nitridated in ammonia before is lower then after direct oxidation of as deposited films in oxygen, in spite of the same phase of niobium pentoxide formed after annealing in both cases. We explain this due to large expansion of niobium lattice during direct oxidation of Nb‐film in molecular oxygen. By incorporation of oxygen in the crystal lattice of niobium and formation of niobium pentoxide substantial intrinsic stress was built up in the film frequently resulting in delamination of the film from the substrate. The possibility of the formation of niobium oxynitride phase after three steps annealing in ammonia, oxygen and finally in ammonia was investigated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Sintering Stainless Steels with Boron Addition in Nitrogen Base Atmosphere

Stainless steel has become increasingly used in the nuclear industry recently. Thus, this study is aimed at investigating stainless steel 316L with boron addition and the possibility of sinter these materials in nitrogen rich atmospheres. By analyzing the final product, the properties of the stainless steel 316L (good mechanical properties and high corrosion resistance) with the boron neutron absorption properties were found to unify. The P/M technologies enable higher boron quantities to be added to the steel. This was not possible with the solidification conventional technologies, as segregation is produced in the latter. Mixtures with 0.75 and 1.5% boron were prepared. Uniaxial compaction (at 700 MPa) was carried out to study the green density of compacted materials. The sintering atmosphere used was N2-10%H2-0.1%CH4, and was used to form boron nitrides instead of chromium nitrides. Although some boron nitride was formed, not all chromium nitride formation was avoided. The sintered samples were characterized through their physical properties (density and dimensional change), chemical analysis (carbon and nitrogen contents), mechanical behavior (bending strength and hardness) and wear behavior. To finish the materials characterization, a microstructural study is proposed. Lastly, the wear tracks were observed by SEM. Boron nitride has precipitated in grain boundaries, making more difficult the sintering of the material and reducing the properties of the stainless steel.

Starch Consolidation as a New Process for Manufacturing Powder Metallurgy High-Speed Steels

The development of a new method called “starch consolidation,” suitable for the production of powder metallurgy (P/M) high-speed steel (HSS) components has been studied. Samples have been consolidated using 1.5, 3.5, and 5vol pct starch and up to 60vol pct powder. The high solid loading was achieved by stabilizing the repulsive forces with a small addition (0.01wt pct) of a dispersant (polyacrylic acid) that resulted in accurate fluidity and consolidation of the prepared slurries. After shaping of the samples, the bending strength of the green bodies was evaluated. Debinding cycles were optimized by comparing carbon and oxygen content in argon, in N2-5H2, and in pure hydrogen. The three atmospheres showed no significant differences in carbon elimination. To determine the influence of H2 in a nitrogen-rich atmosphere during sintering, tests were performed at 1230°C in a N2-5H2 and in a nitrogen atmosphere. Pure nitrogen resulted in a microstructure formed by smaller carbides. Heat treatments were performed on the samples with the compositions that gave the best combination of properties. A hardness of 800HV and a bending strength of 1475MPa were obtained.

The Effect of Chemical Composition of Sintering Atmosphere on the Structure and Mechanical Properties of PM Manganese Steels with Chromium and Molybdenum Additions

The effect of chemical composition of the sintering atmosphere on the density, microstructure and mechanical properties of Fe-3%Mn-(Cr)-(Mo)-0.3%C is described. Pre-alloyed Astaloy CrM and CrL, ferromanganese and graphite powders were the starting powders. Following the pressing in rigid dies, compacts (green density approx. 6.8-7.1 g/cm3) were sintered at 1120 and 1250°C in atmospheres with different H2 and N2 content. The dew point of the sintering atmospheres was below -60°C. Subsequently samples were furnace cooled to room temperature. Tensile and transverse rupture strengths, elongation, R0.2 yield offset, impact toughness and apparent surface hardness were examined. Following the mechanical tests, to investigate microstructure optical microscopy was employed. As the results show, sintering in nitrogen-rich atmospheres allow to achieve comparable properties of the specimens with those of the specimens sintered in hydrogen-rich atmosphere. It means that it is possible to produce sintered Fe-Mn-Cr-Mo-C PM steels in safe and cheaper nitrogen-rich atmosphere.

Laser spray cladding of porous NiTi coatings on NiTi substrates

Laser spray cladding in N 2-rich atmosphere is a competitive technique for manufacture of porous NiTi shape memory alloy (SMA) and TiN surface film. In order to gain expected porous coating and porosity size, TiH 2 powder was considered to be used as porosity initiating agent, and nitrogen was used for shielding and active nitriding gas. A 2 kW continuous wave Nd:YAG laser equipped with a 3-way coaxial nozzle was used for laser spraying. NiTi alloy powder and TiH 2 powder were used as additive materials. The mixed powder of NiTi and TiH 2 was conveyed by a powder feeder, congregated at the laser interacting zone and sprayed onto the substrate with molten droplets. In order to improve the corrosion resistance of the surface of coating layer, a gas nitriding process is facilitated simultaneously during the laser spraying and cladding process in nitrogen-rich atmosphere. A gradient porous coating of NiTi alloy had been manufactured by laser spraying. The investigation shows that there are pores with size of 100–200 μm near the surface. XRD analysis shows that the coating consists of intermetallic compounds NiTi, NiTi 2 and nitrides TiN, Ti 2N. Corrosion test was carried out in Hank's balanced salt solution (H9269) by potentiostat/galvanostat model 273A. The polarization curves of the test result demonstrates the porous coating with TiN presents better corrosion resistance than NiTi substrate.

The exosphere of Titan and its interaction with the kronian magnetosphere: MIMI observations and modeling

Titan's nitrogen-rich atmosphere is directly bombarded by energetic ions, due to its lack of a significant intrinsic magnetic field. Singly charged energetic ions from Saturn magnetosphere undergo charge exchange collisions with neutral atoms in Titan's exosphere, being transformed into energetic neutral atoms (ENAs). The ion and neutral camera (INCA), one of the three sensors that comprise the magnetosphere imaging instrument on the Cassini/Huygens mission to Saturn and Titan, images the ENA emissions from various ion/gas interaction regions in the Saturnian magnetosphere. During Cassinis second orbit around Saturn the spacecraft performed the Ta Titan flyby (26 October 2004), at an altitude of only 1174 km. INCA data acquired during this targeted close flyby not only confirm model predictions of dominant finite ion gyroradii effects, but also reveal a much more complex interaction. These observations are analyzed and compared to simulations. A new Titan exosphere model is then proposed.