Increasing N2 Partial Pressure Research Articles

Improvement of Erosion-Corrosion Behavior of AISI 420 Stainless Steel by Ion-Assisted Deposition ZrN Coatings

In this paper, a pragmatic technique has been developed to evaluate the erosion-corrosion behavior of three kinds of ZrN coatings (i.e., monolayer, multilayer, and gradient layers) which were deposited on AISI 420 martensitic stainless steel using an ion-assisted deposition technology. Among them, the monolayer coating refers to the coating with no change in composition and structure, the multilayer coating refers to the coating with alternating change of Zr/ZrN, and the gradient coating refers to the ZrN coating by increasing N2 partial pressure gradually. The morphology, composition, and microhardness of these ZrN coatings were examined by means of integrating the scanning electron microscopy (SEM), X-ray diffraction (XRD), and Knoop hardness measurements, while anodic polarization tests and salt fog spray tests in a simulated industrial environment have been performed to evaluate and identify the corrosion mechanisms of these coatings. The surface microhardness and corrosion resistance of the AISI420 martensitic stainless steel is found to be significantly improved by depositing the ion-assisted deposition ZrN coatings. The study indicates that the erosion-corrosion behavior in the slurry is the result of the synergistic effect of small-angle erosion and acid solution corrosion. Three ZrN coatings hinder the slurry erosion-corrosion behavior from two aspects (i.e., erosion resistance of small-angle particles as well as corrosion resistance of the substrate), thereby significantly improving the erosion-corrosion resistance of AISI 420 stainless steel. In addition, the ZrN gradient coatings show a much better erosion-corrosion resistance than that of the monolayer/multilayer ZrN coating because they have excellent crack resistance, bearing capacity, and electrochemical performance.

Influence of N2 partial pressure on the microstructure, hardness, and thermal stability of CrZrSiN nanocomposite coatings

The effects of N2 partial pressure in the unbalanced magnetron sputtering process on the microstructure, hardness, and thermal stability of the CrZrSiN nanocomposite coating were investigated. A typical nanocomposite structure, composed of a crystalline phase and an amorphous phase was obtained and the distribution of these phases changed with increasing N2 partial pressure. The N1s spectra revealed the presence of two-peak characteristic of nitrogen in the CrZrN and SiN x phases, and the ratio of the peak’s SiN x to CrZrN intensity increased with increasing N2 partial pressure, indicating an increase in the amorphous phase in the nanocomposite microstructure. As N2 partial pressure increased, the CrZrSiN coating hardness decreased from 38 to 30 GPa due to the increasing amount of the SiN x amorphous phase. After the thermal stability test, the hardness values of the CrZrSiN coatings were maintained at approximately 30 GPa up to 800°C, but the hardness decreased rapidly to 18 GPa after annealing at 900°C. This drastic change of hardness over 900C was due to the formation of a Cr2O3 phase in the CrZrSiN coating.

N2-associated surface warming on early Mars

Early Mars may have had a warmer and denser atmosphere allowing for the presence of liquid water on the surface. However, climate model studies have not been able to reproduce these conditions even with a CO2 atmosphere of several bars. Recent 3D simulations of the early Mars climate show that mean surface temperatures only slightly below 273K could be reached locally.We want to investigate the effect of increased partial pressures of N2 on early Mars’ surface temperature by including pressure broadening of absorption lines and collision-induced N2–N2 absorption.A 1D radiative–convective cloud-free atmospheric model was used to calculate temperature profiles and surface conditions. We performed a parameter study varying the N2 partial pressures from 0 to 0.5bar at CO2 partial pressures between 0.02bar and 3bar. These values are consistent with existing estimates of the initial, pre-Noachian reservoir for both species. Solar insolation was set to be consistent with the late Noachian, i.e. around 3.8 billion years ago.Our 1D global mean simulations clearly show that enhanced N2 content in the Martian atmosphere could have increased surface temperatures. An additional greenhouse warming of up to 13K was found at a high N2 partial pressure of 0.5bar. Still, even at this N2 partial pressure, global mean surface temperatures remained below 273K, i.e. the freezing point of water. However, given the magnitude of the N2-induced surface warming and the results of recent 3D studies which show that local mean surface temperatures are not much lower than 273K, our results imply that the presence of atmospheric N2 could have led to almost continuously habitable mean surface conditions in some regions. In addition, atmospheric water column amounts increased by up to a factor of 6 in response to the surface warming, indicating that precipitation might also increase upon increasing N2 partial pressure.

Influence of the N<SUB>2</SUB> Partial Pressure on the Characteristics of CrZrN Coatings Synthesized Using a Segment CrZr Target

In this study, CrZrN films were synthesized by unbalanced magnetron sputtering (UBM) under various N2 partial pressures and their characteristics such as crystalline structure, surface morphology, microstructure and mechanical properties as a function of the N2 partial pressures were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation, wear tests, and corrosion tests. Results revealed that, with increasing the N2 partial pressure from 0.05 to 0.21 Pa, the nitrogen content of the films increased from approximately 40.9 to 53.7 at%, the deposition rate decreased from approximately 100 to 59 nm/min and the surface roughness (Rms value) was increased from approximately 0.57 to 1.79 nm. The Cr37.3-Zr9.0-N53.7 film has the highest hardness, elastic modulus, and plastic deformation resistance of 36 GPa, 380 GPa, and 0.41, respectively. The Cr37.3-Zr9.0-N53.7 film also has the lowest friction coefficient and wear rate of 0.19 and 3.01 (10(-6)m3/Nm) at room temperature. In addition, the potentiodynamic test results showed the corrosion resistance of the CrZrN films became increased significantly and their corrosion current density (i(corr)), corrosion potentials (Ecorr) and corrosion rate decreased with increasing N2 partial pressure.

Trapping an Intermediate of Dinitrogen (N2) Reduction on Nitrogenase

Nitrogenase reduces dinitrogen (N2) by six electrons and six protons at an active-site metallocluster called FeMo cofactor, to yield two ammonia molecules. Insights into the mechanism of substrate reduction by nitrogenase have come from recent successes in trapping and characterizing intermediates generated during the reduction of protons as well as nitrogenous and alkyne substrates by MoFe proteins with amino acid substitutions. Here, we describe an intermediate generated at a high concentration during reduction of the natural nitrogenase substrate, N2, by wild-type MoFe protein, providing evidence that it contains N2 bound to the active-site FeMo cofactor. When MoFe protein was frozen at 77 K during steady-state turnover with N2, the S = 3/2 EPR signal (g = [4.3, 3.64, 2.00]) arising from the resting state of FeMo cofactor was observed to convert to a rhombic, S = 1/2, signal (g = [2.08, 1.99, 1.97]). The intensity of the N2-dependent EPR signal increased with increasing N2 partial pressure, reaching a maximum intensity of approximately 20% of that of the original FeMo cofactor signal at > or = 0.2 atm N2. An almost complete loss of resting FeMo cofactor signal in this sample implies that the remainder of the enzyme has been reduced to an EPR-silent intermediate state. The N2-dependent EPR signal intensity also varied with the ratio of Fe protein to MoFe protein (electron flux through nitrogenase), with the maximum signal intensity observed with a ratio of 2:1 (1:1 Fe protein:FeMo cofactor) or higher. The pH optimum for the signal was 7.1. The N2-dependent EPR signal intensity exhibited a linear dependence on the square root of the EPR microwave power in contrast to the nonlinear response of signal intensity observed for hydrazine-, diazene-, and methyldiazene-trapped states. 15N ENDOR spectroscopic analysis of MoFe protein captured during turnover with 15N2 revealed a 15N nuclear spin coupled to the FeMo cofactor with a hyperfine tensor A = [0.9, 1.4, 0.45] MHz establishing that an N2-derived species was trapped on the FeMo cofactor. The observation of a single type of 15N-coupled nucleus from the field dependence, along with the absence of an associated exchangeable 1H ENDOR signal, is consistent with an N2 molecule bound end-on to the FeMo cofactor.

Synthesis and characterization of Cr–B–N coatings deposited by reactive arc evaporation

Nanocomposite Cr–B–N coatings were deposited from CrB0.2 compound targets by reactive arc evaporation using an Ar/N2 discharge at 500 °C and −20 V substrate bias. Elastic recoil detection (ERDA), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED) were used to study the effect of the N2 partial pressure on composition and microstructure of the coatings. Cross-sectional scanning electron microscopy (SEM) showed that the coating morphology changes from a glassy to a columnar structure with increasing N2 partial pressure, which coincides with the transition from an amorphous to a crystalline growth mode. The saturation of N content in the coating confirms the formation of a thermodynamically stable CrN–BN dual-phase structure at higher N2 fractions, exhibiting a maximum in hardness of approximately 29 GPa.

NANOSTRUCTURED CARBON NITRIDE FILMS DEPOSITED USING THE LOW-COST PENNING DISCHARGE PLASMA-SPUTTERING TECHNIQUE

Nanostructured carbon nitride films have peen synthesized by using a low-cost Penning discharge (PD) plasma-sputtering source. The influences of different working gas pressures on the surface morphologies, chemical compositions, bond structures, and mechanical properties of deposited carbon nitride thin films have been investigated using Scanning probe microscope (SPM), X-ray photoelectron spectroscopy (XPS) measurements, Raman spectroscopes, and nanoindentation measurements, respectively. SPM and XPS data indicate the variations of the root-mean-square roughness (R RMS ) of the samples surfaces from 7.5 nm, 11.4 nm, to 17.7 nm, and an increase of sp2 fraction inside the films from 22.8% to 26.9% with an up-shift of the deposition gas pressures. In contrast, the sp3 content decreases from 17.5% to 11.8%. The shifts of D and G peaks and variations of band intensity (ID/IG) have been observed in Raman spectra. The hardness of samples is reduced with increasing N2 partial pressure applied during film deposition.

Effects of nitrogen partial pressure on titanium oxynitride films deposited by reactive RF magnetron sputtering onto PET substrates

Titanium oxynitride (TiNxOy) films have been deposited onto polyethylene terephthalate (PET) substrates by reactive radio frequency (RF) magnetron sputtering. The influence of the nitrogen (N2) partial pressure in the discharge atmosphere, with a set pressure of 0.133 Pa, was examined. Other deposition conditions were held constant. The deposition rate of the films, which exhibit an island-type morphology, was found to decrease with increasing N2 partial pressure. This concurred with an increase in the surface roughness at higher N2 partial pressure. The TiNxOy films deposited at N2 partial pressures from 0.26×10−1 Pa to 0.8×10−1 Pa possess Ti:N:O ratio of about 1:0.9:0.8 to 1:1.2:0.7. At the lowest N2 partial pressure of 0.26×10−1 Pa, the water vapor (WV) and oxygen transmission rates (OTR) of the TiNxOy films reached values as low as 0.31 g/m2-day-atm and 0.62 cc/m2-day-atm, respectively; these values are about 16 and 50 times lower than those of the uncoated PET substrate.

Optical properties of amorphous GaAs1−xNx film sputtering with different N2 partial pressures

We study the optical properties of amorphous GaAs1−xNx films grown by radio frequency magnetron sputtering method with different N2 partial pressures. The surface morphology, the optical absorption, the Raman spectra, and optical constants of the films with different N2 partial pressures are reported. The appearance of the Raman peak at 245cm−1 of “GaAslike” and a shoulder at about 750cm−1 related to GaN indicates the formation of GaN clusters in GaAs matrix. The roughness decreases and the optical band gap of amorphous GaAs1−xNx films moves to short wavelength with increasing N2 partial pressure. The refractive index and the extinction coefficient of the films decrease with increasing N2 partial pressure, and it has been found that the amorphous GaAs1−xNx films with nonzero N2 partial pressure are transparent in red and near infrared wavelength regions.

Structure and magnetic properties of N-doped L10-ordered FePt–C nanocomposite films

As-deposited and annealed N additive FePt–C nanocomposite films fabricated using facing-target sputtering were investigated systemically. Structure analyses reveal that the as-deposited films are composed of ∼3nm amorphous metal granules buried in a-CN matrix, and transform into L10-ordered FePt particles followed by an increase of particle size after being annealed. The N atomic fraction increases, and the size of FePt particles in the 650°C annealed films reduces, with increasing N2 partial pressure (PN). The diffusion of Fe and Pt atoms into the positions of the ordered L10 lattice was improved by the decompounding of Fe–N bonds and the escape of N atoms from the film during the annealing. Magnetic measurements indicate that high-temperature annealing turns the superparamagnetism (at PN<10%) and paramagnetism (at PN⩾10%) of the as-deposited films into ferromagnetism. The coercivity of the 650°C annealed N-doped films decreases with increasing PN due to the particle size reduction.

Sm-Fe薄膜の磁歪特性に及ぼす窒素ガス添加の影響

Sm-Fe thin films as giant magnetostrictive materials were prepared by d.c. magnetron sputtering process with Ar or mixed Ar-N2 gas. Diffraction peaks of Sm nitride and Fe nitride were observed at 3.8×10-3 Pa N2 partial pressure. With increasing N2 partial pressure, saturated magnetostriction of the Sm-Fe thin films decreased from 1400 ppm to 600 ppm. The maximum value of magnetostrictive susceptibility was showed at 2.3×10-3 Pa of N2 partial pressure. A compression stress with a small addition of N into Sm-Fe thin films may lead to increase of magnetostrictive susceptibility.

Pathways of atomistic processes on TiN(001) and (111) surfaces during film growth: an ab initio study

Density functional methods were used to calculate binding and diffusion energies of adatoms, molecules, and small clusters on TiN(001) and TiN(111) surfaces in order to isolate the key atomistic processes which determine texture evolution during growth of polycrystalline TiN layers. The surface energy for nonpolar TiN(001), 81 meV/Å2, was found to be lower than that of both N- and Ti-terminated TiN(111) polar surfaces, 85 and 346 meV/Å2. While N2 molecules are only weakly physisorbed, Ti adatoms form strong bonds with both TiN(001), 3.30 eV, and TiN(111), 10.09 eV. Ti adatom diffusion is fast on (001), but slow on (111) surfaces, with calculated energy barriers of 0.35 and 1.74 eV, respectively. The overall results show that growth of 111-oriented grains is favored under conditions typical for reactive sputter deposition. However, the presence of excess atomic N (due, for example, to collisionally induced dissociation of energetic N2+ ions) leads to a reduced Ti diffusion length, an enhanced surface island nucleation rate, and a lower chemical potential on the (001) surface. The combination of these effects results in preferential growth of 001 grains. Thus our results provide an atomistic explanation for the previously reported transition from 111 to 001 texture observed for sputter deposition of TiN in Ar/N2 mixtures with increasing N2 partial pressure PN2 and at constant PN2 with increasing N2+/Ti flux ratios incident at the growing film.

Effect of N2 partial pressure on the structure of MgO thin films deposited by radio frequency-magnetron sputtering with single-crystal MgO target

We report the effect of N2 partial pressure on the structure of MgO thin films deposited on Si(100) substrates by radio frequency-magnetron sputtering in Ar+N2 mixture. The films were evaluated using x-ray diffractmeter. As increasing N2 partial pressure, the intensity of (200)MgO reflection increased and saturated above partial pressure of 4.4×10−1 Pa, which corresponds to N2 flow rate of 3 sccm. Effect of N2 gas on the structure of MgO thin films were investigated by plasma emission spectroscopy. The increase of the optical emission intensity of NH spectrum results in the increase of intensity of (200)MgO reflection. We found the strong relationship between the emission intensity of NH spectrum and intensity of (200)MgO reflection.

Search for high moment soft magnetic materials: FeZrN

FeN materials exhibiting high moment, low coercivity and small magnetostriction have previously been reported. Zr has been known to reduce the magnetostriction in other Fe alloys. The criteria for an ideal recording head pole material as well as shields for magnetoresistive sensors include high moment, low coercivity, high permeability, and zero magnetostriction. We present here the properties of 0.3 μm thick rf sputtered FeZrN films measured as a function of the N2 partial pressure. The films were deposited at a pressure of 3 mT using a Perkin Elmer sputtering system. The target was composed of Fe with Zr chips covering approximately 2% of the surface area. The easy axis and hard axis coercivities show minima of 1.8 and 0.6 Oe, respectively, at 7–10 % N2 partial pressure with a saturation magnetization of about 18 kG. The magnetic anisotropy field is approximately 5 Oe yielding a dc permeability of approximately 4000 along the hard axis. X-ray data reveal a systematic change in the ratio of α–Fe and γ–Fe4 N; the amount of the γ–Fe4N phase increasing with increasing N2 partial pressure. The magnetostriction increases with increasing N2 content crossing zero at approximately 6%. The grain size, as probed by atomic force microscopy, is an increasing function of the N2 partial pressure; from a few nm for N2 partial pressures of 5% to being as large as 50 nm for a partial pressure of 15%. The surface roughness is about 1 nm.

Anomalous Pressure Dependence of Infrared Spectra Due to the Combination of Collisional Broadening and Instrument Resolution

The combination of collisional line broadening and limited instrumental resolution can have peculiar and unexpected effects on the intensities of infrared spectra. An illustrative example is provided by the series of Q branches in the v7 band of ethane. Conventional FT-IR spectra, with a resolution of ∼0.25 cm−1, show a dramatic increase in the absorbance of these branches as a function of increasing N2 partial pressure, an effect which could be construed as collisional narrowing. In contrast, high-resolution diode laser spectroscopy reveals a monotonie increase in branch width (0.14 cm−1/atm), and a concomitant decrease in intensity, as the N2 pressure is raised. The present work shows that absorption measurement of the inherently very narrow ethane Q branches with limited instrumental resolution and collisional line broadening conspire to give the appearance that the absorbance increases with N2 pressure. This effect in general, as well as its implications for the use of FT-IR spectroscopy to measure molecular concentrations in gaseous mixtures, is discussed.

Measurement of the ionisation coefficients in binary and ternary mixtures of CO2, N2 and He

The Townsend first ionisation coefficient alpha T and the secondary coefficients gamma T have been measured in binary and ternary mixtures of CO2, N2 and He gases by the steady-state Townsend method for E/p0 values from 54 to 215 V cm-1 Torr-1. The results show that the alpha T/p0 value in mixtures of CO2 and N2 increases monotonically with increasing N2 partial pressure whereas in binary mixtures of He and N2, or of He and CO2 there is a maximum value of alpha T/p0 as the partial pressure of He is increased for E/p0>or=108 V cm-1 Torr-1. The alpha T/p0 values of ternary mixtures of these gases are shown on a trigonal prism plot. The value of gamma T is found to decrease rapidly with increase of the component having a small value of gamma T.

Glow discharge mass spectrometry of sputtered tantalum nitride

It is well known that the properties of reactively sputtered thin films of tantalum nitride are dependent upon the partial pressure of N2 in the sputtering gas. In this study, a Ta target was rf diode sputtered using various Ar/N2 gas mixtures. Glow discharge spectrometry was used to monitor the positive ions present in the sputtering plasma. Electrical and x-ray diffraction measurements on the resulting films related their crystallography and resistivity to the composition of the plasma, in particular to the relative number of Ta and TaN ions. The results are discussed in terms of the change in the target surface with increasing N2 partial pressure.