Gas Nitrogen Content Research Articles

Parameter Optimization of Nitriding Process Using Chemical Kinetics

Using the dynamics of chemical kinetics, an investigation to search for an optimum condition for a gas nitriding process is performed over the solution space spanned by the initial temperature and gas composition of the furnace. For a two-component furnace atmosphere, the results are presented in temporal variations of gas concentrations and the nitrogen coverage on the surface. It seems that the exploitation of the nitriding kinetics can provide important feedback for setting the model-based control algorithms. The present work shows that when the nitrogen gas concentration is not allowed to exceed 6 pct, the Nad coverage can attain maximum values as high as 0.97. The time evolution of the Nad coverage also reveals that, as long as the temperature is above the value where nitrogen poisoning of the surface due to the low-temperature adsorption of excess nitrogen occurs, the initial ammonia content in the furnace atmosphere is much more important in the nitriding process than is the initial temperature.

Impact of sputter deposition parameters on molybdenum nitride thin film properties

Molybdenum and molybdenum nitride thin films are presented, which are deposited by reactive dc magnetron sputtering. The influence of deposition parameters, especially the amount of nitrogen during film synthesization, to mechanical and electrical properties is investigated. The crystallographic phase and lattice constants are determined by x-ray diffraction analyses. Further information on the microstructure as well as on the biaxial film stress are gained from techniques such as transmission electron microscopy, scanning electron microscopy and the wafer bow. Furthermore, the film resistivity and the temperature coefficient of resistance are measured by the van der Pauw technique starting from room temperature up to 300 °C. Independent of the investigated physical quantity, a dominant dependence on the sputtering gas nitrogen content is observed compared to other deposition parameters such as the plasma power or the sputtering gas pressure in the deposition chamber.

Conductive Transparent TiNx/TiO2 Hybrid Films Deposited on Plastics in Air Using Atmospheric Plasma Processing

The successful deposition of conductive transparent TiNx/TiO2 hybrid films on both polycarbonate and silicon substrates from a titanium ethoxide precursor is demonstrated in air using atmospheric plasma processing equipped with a high‐temperature precursor delivery system. The hybrid film chemical composition, deposition rates, optical and electrical properties along with the adhesion energy to the polycarbonate substrate are investigated as a function of plasma power and plasma gas composition. The film is a hybrid of amorphous and crystalline rutile titanium oxide phases and amorphous titanium nitride that depend on the processing conditions. The visible transmittance increases from 71% to 83% with decreasing plasma power and increasing nitrogen content of the plasma gas. The film resistivity is in the range of ∼8.5 × 101 to 2.4 × 105 ohm cm. The adhesion energy to the polycarbonate substrate varies from ∼1.2 to 8.5 J/m2 with increasing plasma power and decreasing plasma gas nitrogen content. Finally, annealing the film or introducing hydrogen to the primary plasma gas significantly affects the composition and decreases thin‐film resistivity.

Hysteresis, structural and composition characteristics of deposited thin films by reactively sputtered titanium target in Ar/CH4/N2 gas mixture

Hysteresis, crystal structure and chemical composition of thin films deposited through reactive sputtering of titanium metal target in Ar/CH4/N2 gas mixture have been investigated. The transition from metallic to compound sputtering mode was clearly seen as the reactive gases (CH4 and N2) flowrate concentration first increased and subsequently decreased. Abrupt cathode current drop from 273 mA to reach a minimum value of 195 mA was observed upon addition of nitrogen gas from 0 to 10% flowrate concentration to the Ar/CH4 gas mixture. This was also accompanied by an abrupt change in reactive gas partial pressure. Exploration of the deposition rate and film thickness showed that it decreased from 4·5 to 1·5 nm min−1 and from 140 to 40 nm as the N2 flowrate concentration increased from 1·5 to 7·5% at 5·5%CH4 flowrate concentration respectively. X-ray diffraction and X-ray photoelectron spectroscopy analyses of the deposited films confirmed the formation of titanium carbide and carbonitride phases as the methane and nitrogen gas concentrations in the sputtering gas were increased.

Surface Morphology and Structural Investigation of TiN Nanocrystal Thin Films Grown with Different N<sub>2</sub> Concentration

In this work, new information on surface morphology, phase and local structure of titanium nitride (TiN) nanocrystal thin films grown with different nitrogen gas concentration by direct current (DC) magnetron sputtering is provided. Surface morphology of the thin films was studied by field emission scanning electron microscope (FE-SEM). Phase and local structure of the TiN nanocrystals were determined by X-ray diffraction spectroscopy (XRD) and X-ray absorption fine structure (XAFS). The TiN nanocrystals were prepared on silicon substrates. N2/Ar gases were used as reactive gases for sputtering Ti target. The amount of these two reactive gases was varied at different ratios (N2/Ar), i.e. 100:0, 75:25, 50:50 and 25:75 respectively. Our results suggested that sputtering Ti target with high N2/Ar gas raSubscript texttio (higher than 75%) provides good TiN layer while sputtering with low N2/Ar gas ratio (lower than 25%) gives Ti layer instead of TiN. In addition, sputtering with 50% N2/Ar gas ratio gives a multiphase system between TiN and Ti. Local structure parameters of these nanocrystal thin films are reported.

Bacterial Community Dynamics during Swine In vitro Fermentation Using Starch as a Substrate with Different Feed Additives for Odor Reduction.

The experiment was conducted by in vitro fermentation and bacterial community analysis to investigate the reduction of odorous compounds in response to the use of feed additives (FA) during carbohydrate overload in growing pigs. Soluble starch at 1% (control) and various FA at 0.1% Ginseng meal (FA1); Persimmon leaf (FA2); Gingko nut (FA3) and Oregano lippia (FA4) were added to fecal slurry and incubated anaerobically for 12 and 24 h. In vitro parameters and microbial diversity of the dominant bacteria following fermentation were analyzed using Denaturing Gradient Gel Electrophoresis (DGGE), band cloning and sequencing of the V3 region. Results showed that total gas production increased with the advancement of incubation (p<0.05). pH values of FAs and control groups were decreased except the FA4 group which increased somewhat from 12 to 24 h (p<0.05). Ammonia nitrogen (NH3-N) and H2S gas concentrations were comparatively lower in both stages in FA4 treatment than in the other groups (p<0.05). Hence, NH3-N concentrations in liquid phases were increased (p<0.05) from 12 to 24 h, but the trend was lowest in FA4 than in the other groups at both stages. The total VFA production was comparatively lower and butyrate levels were moderate in FA4 group than in the the other groups during both stages (p<0.05). Indirect odor-reducing compounds such as NO2, NO3 and SO4 concentrations were higher in the FA4 and FA3 than in the other groups at 24 h (p<0.05). After fermentation, ten dominant bands appeared, six of which appeared in all samples and four in only the FA4 treated group. The total number of DGGE bands and diversity was higher in the FA4-group compared to other groups. Additionally, similarity indices were lowest (71%) in the FA4, which represented a different bacterial community compared with the other groups. These findings indicate that NH3-N, H2S and VFA production was minimal, and pH was also better in the FA4 group than in the other groups. Furthermore, the conversion of odor-reducing indirect compounds or their intermediates was higher in the FA4 group in compared to the other groups. FA4 group generated less odorous products and more indirect products by in vitro fermentation at 24 h, and their microbial pattern appeared to differ from that of the other groups. These findings suggest that this particular FA could change the microbial population, which may have a beneficial effect on odor reduction. It is recommended that the oregano lippia may be supplied to growing pigs as FA along with excess carbohydrate sources to reduce the production of odorous compounds.

Deposition of Amorphous Hydrogenated Carbon Nitride Films with a Dielectric Barrier Discharge

AbstractThin amorphous carbon nitride (CNx) films have been deposited by DBD plasma. Deposition experiments have been performed on flat silicon (100) substrates using a C2H6/N2 gas mixture and deposition times of up to 6 h. The C2H6/N2 gas ratio has been varied between 1:1 and 1:5 to observe the influence of the feeding gas mixture on the chemical composition of the deposited films. The experiments were performed at gas pressures of 300 and 500 mbar. The chemical composition and bond structure of the deposited CNx films were evaluated by X‐ray photoelectron spectroscopy and by attenuated total reflectance‐Fourier transform infrared spectrometry. The results show that the chemical composition of amorphous CNx thin films depends on the working gas composition. Films deposited with higher nitrogen gas concentrations show a larger N/C ratio, an increase of C=N and C≡N bonds, and become harder.magnified image

A Swine Model of Neonatal Asphyxia

Annually more than 1 million neonates die worldwide as related to asphyxia. Asphyxiated neonates commonly have multi-organ failure including hypotension, perfusion deficit, hypoxic-ischemic encephalopathy, pulmonary hypertension, vasculopathic enterocolitis, renal failure and thrombo-embolic complications. Animal models are developed to help us understand the patho-physiology and pharmacology of neonatal asphyxia. In comparison to rodents and newborn lambs, the newborn piglet has been proven to be a valuable model. The newborn piglet has several advantages including similar development as that of 36-38 weeks human fetus with comparable body systems, large body size (~1.5-2 kg at birth) that allows the instrumentation and monitoring of the animal and controls the confounding variables of hypoxia and hemodynamic derangements. We here describe an experimental protocol to simulate neonatal asphyxia and allow us to examine the systemic and regional hemodynamic changes during the asphyxiating and reoxygenation process as well as the respective effects of interventions. Further, the model has the advantage of studying multi-organ failure or dysfunction simultaneously and the interaction with various body systems. The experimental model is a non-survival procedure that involves the surgical instrumentation of newborn piglets (1-3 day-old and 1.5-2.5 kg weight, mixed breed) to allow the establishment of mechanical ventilation, vascular (arterial and central venous) access and the placement of catheters and flow probes (Transonic Inc.) for the continuously monitoring of intra-vascular pressure and blood flow across different arteries including main pulmonary, common carotid, superior mesenteric and left renal arteries. Using these surgically instrumented piglets, after stabilization for 30-60 minutes as defined by Z<10% variation in hemodynamic parameters and normal blood gases, we commence an experimental protocol of severe hypoxemia which is induced via normocapnic alveolar hypoxia. The piglet is ventilated with 10-15% oxygen by increasing the inhaled concentration of nitrogen gas for 2h, aiming for arterial oxygen saturations of 30-40%. This degree of hypoxemia will produce clinical asphyxia with severe metabolic acidosis, systemic hypotension and cardiogenic shock with hypoperfusion to vital organs. The hypoxia is followed by reoxygenation with 100% oxygen for 0.5 h and then 21% oxygen for 3.5 h. Pharmacologic interventions can be introduced in due course and their effects investigated in a blinded, block-randomized fashion.

Quantifying the flux of CaCO3and organic carbon from the surface ocean using in situ measurements of O2, N2, pCO2, and pH

[1] Ocean acidification from anthropogenic CO2 has focused our attention on the importance of understanding the rates and mechanisms of CaCO3 formation so that changes can be monitored and feedbacks predicted. We present a method for determining the rate of CaCO3 production using in situ measureme nts of fCO2 and pH in surface waters of the eastern subarctic Pacific Ocean. These quantities were determined on a surface mooring every 3 h for a period of about 9 months in 2007 at Ocean Station Papa (50°N, 145°W). We use the data in a simple surface ocean, mass balance model of dissolved inorganic carbon (DIC) and alkalinity (Alk) to constrain the CaCO3: organic carbon (OC) production ratio to be approximately 0.5. A CaCO3 production rate of 8 mmol CaCO3 m−2 d−1 in the summer of 2007 (1.2 mol m−2 yr−1) is derived by combining the CaCO3: OC ratio with the a net organic carbon production rate (2.5 mol C m−2 yr−1) determined from in situ measurements of oxygen and nitrogen gas concentrations measured on the same mooring (Emerson and Stump, 2010). Carbonate chemistry data from a meridional hydrographic section in this area in 2008 indicate that isopycnal surfaces that outcrop in the winter in the subarctic Pacific and deepen southward into the subtropics are a much stronger source for alkalinity than vertical mixing. This pathway has a high enough Alk:DIC ratio to support the CaCO3:OC production rate implied by the fCO2 and pH data.

Life at the Frontier

Life at the Frontier

Deposition Rate Control of Ag Thin Films Deposited by Sputtering in Argon and Nitrogen Mixed Gases

The nitrogen addition to argon gas during the Ag deposition was investigated to lower the deposition rate. As a result, it was found that the deposition rate systematically decreased with the increase of nitrogen gas concentration; furthermore, the Ag thin films deposited with nitrogen gas exhibited sufficient optical reflectance. It can be considered that the nitrogen gas addition leads to the decrease of sputtering yield and positive ions accelerated to the target, hence, the deposition rate of the Ag thin films decreases.

Net biological oxygen production in the ocean—II: Remote in situ measurements of O 2 and N 2 in subarctic pacific surface waters

Net community biological production in the euphotic zone of the ocean fuels organic matter and oxygen export from the upper ocean, which has a large influence on the atmospheric pressure of carbon dioxide and is the driving force for metabolite distributions in the sea. We determine the net annual biological oxygen production in the mixed layer of the northeast subarctic Pacific Ocean from in situ O 2 and N 2 measurements. Temperature, salinity, total gas pressure and O 2 were measured every 3 h for 9 months in 2007 at about 3 m depth on a surface mooring at Station P (50°N, 145°W). The concentration of nitrogen gas, N 2, determined from separate total gas pressure and pO 2 measurements, was used as an inert tracer of the physical processes that induce gas departure from thermodynamic equilibrium with the atmosphere. We use a simple model of the ocean’s mixed layer along with the nitrogen concentration to constrain the importance of bubbles, gas exchange and horizontal advection, which are then used in the oxygen mass balance to derive net biological oxygen production. The mixed-layer oxygen mass balance is dominated by exchange with the atmosphere, and we determine a mean summertime oxygen production of 24 mmol O 2 m −2 d −1. The annual pattern in the difference between the supersaturation of oxygen and nitrogen in the surface waters reveals very little net oxygen production during the winter at this location. The calculated annual net community production (NCP) of carbon from this new method, 2.5 mol m −2 yr −1, agrees to within its error of about×40% with previous determinations at this location from oxygen mass balance, NO 3 − draw down and 234Th measurements. This value is either indistinguishable from or lower than annual NCP measurements in the subtropical North Pacific, indicating that there is no experimental evidence for differences in annual NCP between the subarctic and subtropical North Pacific Ocean.

Microstructure and Thermal Diffusivity of Gd&lt;sub&gt;2&lt;/sub&gt;Zr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt; Powders

The selection of new TBC materials is restricted by few basic requirements such as: high melting point, no phase transformation between room and the operation temperatures, low thermal conductivity, chemical inertness to the combustion gases and environment, thermal expansion match with the metallic substrate, good adherence to the metallic substrate and low sintering rate of the porous microstructure. Among these properties, one of the most important is thermal diffusivity. The number of material that can be used as TBCs is limited and so far only a few materials have been found to basically satisfy these requirements. Recent research has shown that certain rare-earth zirconates, such as Gd2Zr2O7, have even lower thermal conductivities than 7YSZ, and this has spurred an intensive research in discovering alternative TBC materials. The results of microstructure tests performed on the powders intended for thermally sprayed TBCs with APS method were presented in this article. The tests of phase and chemical composition of the analysed powder were performed. The carbon, sulphur and gas nitrogen contents were, among other things, determined during those tests. The x-ray powder diffraction phase identification in as received material was determined. The tested material showed the presence of Gd2Zr2O7 compound as the predominant one and Gd2O3 and ZrO2 oxides. The surface morphology analysis of the powder was carried out and its internal structure was characterized. The tested material shows porous structure typical for agglomerated powders. The second testing area applied to analysis of the powder thermal properties. The thermal diffusivity of the compressed samples with density similar to the solid material was determined with the laser flash (LF) method. The measurement results show that requirements for the materials used for new generation TBCs are met.

Microstructure and Thermal Diffusivity of Micro- and Nano-Sized YSZ

The thermal barrier coatings (TBC) enable to lower temperature (at approx. 170°C) of operating elements in a hot section of gas turbine to a range, which enables to operate for a long time in conditions of high temperature influence and prolongs operation of them even three or four times. Usually, the TBC coverings are constructed of four layers: • superalloys on a base of nickel; • outer ceramic zone, from which low thermal conduction is required. It is, in most cases, ZrO2 oxide stabilized with Y2O3 (YSZ – yttria stabilized zirconia), material of one of lowest values of thermal conductivity in high temperature of a rank 2.3 Wm-1K-1 in 1000°C for 100% density and thermal expansion of a rank 11×10-6°C-1, what enables to reduce thermal stresses. Usually, thickness of an outer ceramic layer is within a range 250-375μm; • bond coat of a type Ni(Co)CrAlY or diffusion layer of a type (Ni,Pt)Al; • layer of barrier oxides, accrueting as a result of temperature growth TGO (thermally grown oxide). In the present study characterization of conventional micro-sized YSZ powders stabilized by 8% of yttria and in comparison nano-sized YSZ will be presented. The tests performed showed that the monoclinic phase content in the nanocrystalline powder is approx. 8.8%, and approx. 7.5% in the conventional powder. The chemical composition analysis and test of powder microstructure were also performed. Carbon, sulphur and gas nitrogen contents were determined and the results received were similar. The surface morphology and powder microstructure on the cross-sections were also characterized. The standard powder with spherical shape and relatively smooth surface is predominant. The internal structure is characterized by the presence of tiny sintered particles and low porosity. The nanocrystalline powder tests showed the presence of particles in the form of tiny polyhedrons with bimodal size distribution of particles (approx. 1μm and 10μm).

Effects of shielding gas composition and activating flux on GTAW weldments

This study investigated the effects of shielding gas composition and activating flux on weld morphology, angular distortion, retained delta-ferrite content, mechanical properties and hot cracking susceptibility. An autogenous gas tungsten arc welding process was used on austenitic stainless steel to produce a bead-on-plate weld. The nitrogen content in the argon-based shielding gas was in the range of 2.5–10 vol.%. Activating flux materials consisted of a manganese oxide powder and zinc oxide powder mixture. The results showed that the penetration and cross-sectional area of the weld increased with the increase of nitrogen added to the argon-base shielding gas. An increase in shielding gas nitrogen content had markedly reduced the angular distortion of the weldment. Increasing the nitrogen increased the tensile strength and hardness but reduced the retained delta-ferrite. The hot cracking susceptibility of the austenitic stainless steel welds increased as the nitrogen content increased. Activating flux plays a major role than nitrogen added in argon shielding gas, which influenced the various properties of austenitic stainless steel TIG welds.

Structural and optical properties studies of sputtered a-SiCN thin films

Amorphous silicon carbonitride (a-SiCxNy) thin films were deposited by reactive sputtering from SiC target and N2/Ar mixtures. Their structural study was carried out by mean of RBS, FTIR, Raman and electron spin resonance analysis. The optical properties were determined by UV-visible spectroscopy. The fact to introduce different amounts of nitrogen with argon in the gas phase induced structural changes which are visible since 5 % of N2. For more than 30 % of nitrogen in the gas mixture, a N-saturated Si–C–N film were formed. The increase of nitrogen gas concentration induced the appearance of C-C sp2 character, an increase of the C≡N and dangling bonds densities. All these structural variations leaded to an increase of optical band gap from 1.75 to 2.35 eV.

Denitrification rates and excess nitrogen gas concentrations in the Arabian Sea oxygen deficient zone

Rates of canonical, i.e. heterotrophic, water-column denitrification were measured by 15N incubation techniques at a number of coastal and open ocean stations in the Arabian Sea. Measurements of N 2:Ar gas ratios were also made to obtain independent estimates of N 2 excess resulting from denitrification. Measured denitrification rates ( 15NO 3 − → 15 − 14N 2) at open ocean stations averaged 9.1±1.0 nmol N l −1 d −1 ( n = 15 ), and coastal rates averaged 33.2±12.4 nmol N l −1 d −1 ( n = 18 ). When extrapolated to the entire Arabian Sea, deep measurements within the offshore perennial suboxic zone indicate an overall denitrification rate of 41 Tg N a −1±18 Tg N a −1, which is within the range (10–44 Tg N a −1) of previous estimates for canonical denitrification in the region based on stoichiometric calculations and electron transport system activity. Nitrogen excess gas measurements predict a larger nitrogen anomaly than estimated by classical stoichiometric methods (maximum anomaly=23 μg at N l −1 vs. 13 μg at N l −1, respectively). This mismatch may result from incorrect assumptions of Redfield stoichiometry inherent in the nitrate deficit calculation, inputs of new nitrogen through N-fixation, N 2 contributions from sedimentary denitrification along continental margins, the anammox reaction, and metal catalyzed denitrification reactions. Nevertheless, if denitrification is defined as the conversion of combined nitrogen to a gaseous end product, then the data suggest that denitrification in the Arabian Sea may have been underestimated so far.

Gas mixture ratio dependence of ion temperature in ECR plasma

The ion temperature in N 2/Ar and O 2/Ar electron cyclotron resonance (ECR) plasma is measured by high-resolution optical emission spectroscopy for pressure of 0.27 Pa and microwave power of 2.4 kW. It is found that as the nitrogen gas concentration is increased, the ion temperature in N 2/Ar ECR plasma decreases drastically and the uniformity of the radial electron density distribution improves. It is considered that the decrease of the ion temperature in N 2/Ar ECR plasma is caused by the decrease of the radial electric field. In the case of O 2/Ar ECR plasma, the ion temperature increases as the oxygen gas concentration is increased. It is considered that the increase of the ion temperature in O 2/Ar ECR plasma is caused by energy exchange between electrons and ions because the electron temperature considerably increases with increasing of the oxygen concentration.

Amorphous molybdenum nitride thin films prepared by reactive sputter deposition

Amorphous molybdenum nitride thin films were prepared by pulsed direct current (dc) reactive sputter deposition. The effect of the sputtering gas nitrogen content on the structure of as-deposited thin film was investigated. The nitrogen content in the sputtering gas affected the crystallinity of deposited thin films. When the sputtering gas contained from 10 to 30% nitrogen, crystalline γ-Mo 2N was observed. A decrease in the γ-Mo 2N peak intensity along with peak shifting and broadening was observed in X-ray diffraction (XRD) spectra as the deposition nitrogen content increased. An amorphous molybdenum nitride thin film was obtained as the nitrogen content in the sputtering gas increased to 50%. X-ray photoelectron spectroscopic analysis (XPS) of the as-deposited thin films showed that the binding energy of Mo 3d 3/2, Mo 3d 5/2 and Mo 3p 3/2 peaks as well as the amount of nitrogen in thin film increased as the nitrogen content in sputtering gas increased. Thermal treatment of the amorphous thin film showed that the amorphous film had survived 700 °C thermal annealing with no evidence of crystallization and reaction. However, crystallization of amorphous film and reaction of the amorphous thin film with Si substrate were observed after thermal annealing at 800 °C.

Measurement of ion temperature in N2/Ar and O2/Ar ECR plasma

Ion temperatures in N2/Ar and O2/Ar electron cyclotron resonance (ECR) plasmas have been measured with high-resolution optical emission spectroscopy. It was found that the Ar ion temperature in N2/Ar plasma decreased drastically as the nitrogen gas concentration was increased, while the electron temperature slightly increased. The uniformity of the radial electron density distribution also increased with increasing the nitrogen gas concentration. These results suggest that the radial electric field decreased with increasing the nitrogen gas concentration, and as a result, the transverse ion temperature in N2/Ar plasma decreased. On the other hand, the ion temperature in O2/Ar ECR plasma increased as the oxygen gas concentration was increased and the electron temperature considerably increased. This increase in the electron temperature may be caused by generation of negative ions. As the negative ion generation affects the electron density and hence the electron temperature, the ion temperature in O2/Ar plasma is increased with increasing the oxygen gas concentration.