Abstract: A single-layer graphene is synthesized on Cu foil in the absence of H(2) flow by plasma enhanced chemical vapor deposition (PECVD). In lieu of an explicit H(2) flow, hydrogen species are produced during the methane decomposition process into their active species (CH(x<4)), assisted with the plasma. Notably, the early stage of growth depends strongly on the plasma power. The resulting grain size (the nucleation density) has a maximum (minimum) at 50 W and saturates when the plasma power is higher than 120 W because hydrogen partial pressures are effectively tuned by a simple control of the plasma power. Raman spectroscopy and transport measurements show that decomposed methane alone can provide a sufficient amount of hydrogen species for high-quality graphene synthesis by PECVD.

Abstract: A new method to measure oxygen concentration in air-saturated organic solvents and binary mixtures has been developed. The methodology relies on the ability of HPLC columns to retain the molecular oxygen contained in different types of solvents which are injected into the system at 298.15 K. The outlet of the HPLC is coupled with an optical oxygen sensor which continuously measures changes in oxygen partial pressure.

Abstract: Composite membranes with enhanced oxygen permeability and unprecedented stability in oxyfuel-like gas environments are reported. Specifically, 60 vol% NiFe2O4 - 40 vol% Ce0.8Tb0.2O2-δ (NFO-CTO) composite has been successfully obtained by one-pot fabrication method showing both spinel and fluorite pure phases. Narrow grain size distribution centered around 1 μm and homogeneous distribution of grains is attained, as well as percolative pathways from side to side of the dual-phase membranes. The composite resisted a stability test in wet SO2 and CO2 containing gas at 800 °C for 170 h, which represents a step forward toward its use in oxyfuel power plants. The conductivity of both phases is investigated as a function of temperature and oxygen partial pressure (pO2). Oxygen separation in this kind of NFO-doped-ceria composite membranes occurs via the separate ambipolar transport through the two distinct percolating networks. Oxygen permeation flux values of 0.17 mL·min–1·cm–2 and 0.20 mL·min–1·cm–2 are achieve...

Abstract: We initiated a self-adjusted oxygen-partial-pressure approach to prepare high-performance Li2MnO3–LiMO2 cathode material. Four different lithium resources, lithium acetate, lithium hydrate, lithium carbonate, and lithium nitrate were used to create the local oxygen partial pressure over the samples. Since the melting points or decomposition temperatures for these lithium resources decrease in a sequence, Li2CO3 ≈ LiOH > LiNO3 > CH3COOLi, the oxygen partial pressure of the four crucibles that contain these lithium salts increases in a sequence, S4 ≈ S3 < S2 < S1 ≈ air in muffle furnace (S1: CH3COOLi·2H2O, S2: LiNO3, S3: LiOH·H2O, and S4: Li2CO3). Regardless of the lithium resources, the decomposed gases reduced the local oxygen partial pressures, leading to an incomplete oxidation of Mn ions in the final product Li[Li0.14Mn0.47Ni0.25Co0.14]O2. That is, some of the Mn3+ ions existed in the final product Li[Li0.14Mn0.47Ni0.25Co0.14]O2, and the amount of Mn3+ ions was closely related to the oxygen partial pressure. The lower oxygen partial pressure gave rise to a larger amount of Mn3+ in the final products, as confirmed by X-ray photoelectron spectroscopy. Electrochemical tests showed that the products prepared using lithium carbonate exhibited the best electrochemical performance: the initial discharge capacity was 279.4 mA h g−1 at a current density of 20 mA g−1, which remained as high as 187.2 mA h g−1 even at a much higher current density of 500 mA g−1. Such excellent electrochemical performance could be ascribed to the presence of Mn3+ that decreased the surface layer resistance and charge transfer resistance, and that further increased the conductivity and Li+ ion diffusion coefficient.

Abstract: Insects and spiders rely on gas-filled airways for respiration in air. However, some diving species take a tiny air-store bubble from the surface that acts as a primary O2 source and also as a physical gill to obtain dissolved O2 from the water. After a long history of modelling, recent work with O2-sensitive optodes has tested the models and extended our understanding of physical gill function. Models predict that compressible gas gills can extend dives up to more than eightfold, but this is never reached, because the animals surface long before the bubble is exhausted. Incompressible gas gills are theoretically permanent. However, neither compressible nor incompressible gas gills can support even resting metabolic rate unless the animal is very small, has a low metabolic rate or ventilates the bubble's surface, because the volume of gas required to produce an adequate surface area is too large to permit diving. Diving-bell spiders appear to be the only large aquatic arthropods that can have gas gill surface areas large enough to supply resting metabolic demands in stagnant, oxygenated water, because they suspend a large bubble in a submerged web. * A : surface area BL : boundary layer K G : Krogh's coefficient of diffusion of a gas L : distance M b : body mass ![Graphic][1] : molar rate of flow of a gas Δ P G : difference in partial pressure of a gas V G : volume of gas * Book lungs : Internal gas exchange organs of arachnids, consisting of broad, hemolymph-filled leaves alternating with air-spaces that are connected to the atmosphere through a small hole. Boundary layer (effective, hydraulic) : A layer of fluid (water or air) next to a surface in which the velocity of fluid is less than that in the surrounding bulk medium. The effective boundary layer is the thickness of a layer in which velocity is theoretically zero, and the diffusion rate across the stagnant layer is equivalent to that which occurs naturally by a combination of diffusion and convection between the free medium and the surface. The hydraulic boundary layer occurs in that thickness in which velocity is less than an arbitrary 99% of that in the free medium. Convection : The movement of a substance by being carried in a moving fluid (water or air). Diffusion : The movement of a substance down a gradient in concentration or partial pressure without bulk movement of the medium. Fick's first law of diffusion : A mathematical expression describing that the rate of gas diffusion depends on the product of the gas partial pressure difference and the gas conductance (a measure of the ease of diffusion through a barrier). Gas gill (compressible, incompressible) : A gas space (bubble) on the external surface of an animal that permits respiratory gas exchange through its surface. If the bubble is free and unsupported, it is compressible and continually collapses. If the bubble is supported (by a plastron), it is incompressible and potentially permanent. Gill factor : The ratio of the potential total amount of O2 delivered by a collapsible gas gill and the amount originally present upon renewal at the water surface. The amount delivered is that originally in the gas gill plus the amount taken up from the water before total collapse of the bubble. Theoreticalgill factors are approximately eight, meaning that seven times the amount of O2 can be taken up from the water as originally present after renewal. Partial pressure : The pressure (measured in Pascals) exerted by each gas of a mixture independently of the others. The sum of the partial pressures equals the total pressure of the mixture. Thus barometric pressure of dry atmospheric air at sea level is ~101.3 kPa=21 kPa P O2, 79 kPa P N2, plus 1.3 kPa trace gases. The partial pressures of gases dissolved in water are equal to the partial pressures of the gases in air when in equilibrium, but the concentrations of dissolved gases are much lower in water than in air. Plastron : A layer on the surface of an animal or plant containing gas and protected against collapse by hydrophobic supporting structures that press against the air-water interface. Snorkel : A tube connecting a gas store on an insect to the surface of the water to admit atmospheric O2. Spiracles : The openings of the tracheal system of insects or spiders. There may be several through the exoskeleton, exposed or under other structures, and their apertures may be controlled by spiracular valves. Trachea : The larger tubes of the tracheal system. Tracheal gills : External extensions of the tracheal system of insects that are closed, but covered with a broad, thin chitinous barrier that nevertheless allows gas exchange with the water. Tracheal system : A branching system of air-filled tubes that permit O2 and CO2 exchange between the atmosphere and cells of insects and spiders. The system opens to the atmosphere at the spiracles and ends in the tracheoles. Tracheoles : The smallest, blind-ended tubes of the tracheal system that approach or enter cells. [1]: /embed/inline-graphic-10.gif

Abstract: Among the many techniques for the deposition of Mo–N coatings, AC and DC magnetron sputtering, ion implantation and cathodic arc evaporation, the latter is the most comprehensive, owing to the high degree of particle ionisation in the plasma, high density and coating quality. The phase structure of Mo–N coatings strongly depends on the deposition technology, mainly on the pressure of nitrogen in the working chamber, and the substrate bias voltage. Coatings deposited at four nitrogen pressures: 0.6, 1.0, 1.8 and 3.0 Pa, and four negative substrate bias voltages U B : 10, 70, 150 and 250 V, were widely tested. EDS and WDS were used to evaluate the chemical composition, XRD to determine the phase composition, scanning and an optical microscopy to assess the morphology and surface quality, the scratch test and Daimler-Benz test to estimate the coatings adhesion, and ball-on-disc test to define the specific wear rate. The increase in the nitrogen pressure changes the phase structure of the body-centred cubic lattice of molybdenum Mo, through cubic γ-Mo 2 N to the hexagonal δ-MoN. Due to the different structures of the crystal lattice, the given phases exhibit different physical properties. The substrate bias voltage rise initiates the resputtering of the coating, causing a reduction in nitrogen atoms in the coating. This affects the changes in the chemical composition and the coating morphology. It can be the cause of the cubic γ-Mo 2 N phase existing in the deposition conditions of the hexagonal δ-MoN phase. The relatively large amount of macroparticles on the coating surface depends on the nitrogen pressure and the substrate bias voltage. The surface roughness Ra of the coating deposited at substrate bias voltages of more than − 70 V is relatively small and almost independent of the nitrogen pressure. The coatings deposited at low substrate bias voltages (U B = − 10 V) are characterised by more than twice the surface roughness Ra, decreasing as the partial pressure of nitrogen increases. The mechanical parameters of the deposited coatings depend on their phase composition due to the different properties of Mo, Mo 2 N and MoN.

Abstract: The effect of surface finish on the scaling behavior of Super 304H was investigated in steam and supercritical water (SCW). The oxide scales were analyzed using scanning electron microscope with an energy dispersive X-ray detector, X-ray diffraction, and Raman spectroscopy. The results showed that surface deformation improved the oxidation resistance by promoting the preferable formation of chromia and improving the scale adhesion. In SCW, the absence of hematite may be ascribed to the low oxygen partial pressure; while the whisker growth on the sandblasted sample may have resulted from the low oxygen partial pressure and the increased chromium diffusion flux.

Abstract: In this work, the results of the electrocoloration of strontium titanate single crystals with different iron concentrations are presented. The samples of SrTiO3(100) doped with 0.06 at. % and 0.13 at. % of iron were electroreduced at low pressure (10−8 mbar) and elevated temperature (250 °C) using a DC voltage of 200 V. This led to the migration of oxygen vacancies and subsequent electrocoloration of the samples, which was confirmed by optical analysis and electrical measurements. Evolution of the color front was compared with finite element calculations of electric potential indicating good agreement. Both macroscopic and nanoscopic measurements showed insulator-metal transition at several hundreds of seconds (0.06%Fe) and resistive switching behavior. We found that the resistive switching is clearly modified by the oxygen partial pressure of the ambient atmosphere. Moreover, after electroreduction, in the region between the electrodes, stripes can be found following simple crystallographic directions connected with the extended defects and easy diffusion paths also observed in the single crystals of undoped strontium titanate. Furthermore, migration of negatively charged oxygen ions towards the anode led to the formation of oxygen bubbles trapped between the surface of the crystal and the electrode. Using atomic force microscopy, we were able to measure the geometry of a bubble and calculate the oxygen pressure necessary for the formation of such bubbles and the total amount of oxygen ions trapped within.

Abstract: This article is an attempt to elucidate the role of lattice oxygen mobility in catalytic activity of Sr-substituted ferrites at high temperatures. For this goal, three catalysts with close element (La, Sr, Fe) content but different phases and surface compositions: LaSrFeO 4 (surface)–La 0.4 Sr 0.6 FeO 3 ( LSF-N ), La 0.15 Sr 0.85 FeO 3 –La 0.7 Sr 0.3 FeO 3 ( LSF-C ) and LaSrFeO 4 have been studied in high temperature reactions of N 2 O decomposition, ammonia oxidation and methane combustion. The kinetics of 18 O/ 16 O oxygen exchange have been analyzed at 800 °C and 0.005 atm oxygen partial pressure, which is closely corresponding to the reaction conditions, and the rates of surface oxygen exchange and the coefficient of lattice oxygen diffusion have been evaluated. It allowed us to reveal the direct correlation between the surface exchange rate constant and the rate of N 2 O decomposition. For NH 3 oxidation, evidence of the same order of the samples activity both in surface oxygen exchange and ammonia oxidation reaction was shown. In methane oxidation it was found that activity correlates with the rate of exchange for 20 monolayers of oxygen atoms indicating the growing influence of lattice oxygen mobility. The results show that improvement of catalytic properties can be achieved when synthesizing “LaSrFeO 4 (surface)–La 0.4 Sr 0.6 FeO 3 ” composites. Such composites exhibit increased rate of surface oxygen exchange on retention of high lattice oxygen mobility, which can be attributed to formation of heterostructured interfaces.

Abstract: The mechanisms of char gasification in the mixture of H2O and CO2 are not clear, and some problems are yet to be solved. The Langmuir–Hinshelwood (L–H) model of char gasification in the mixture of H2O and CO2 and the inhibition effect between char–H2O and char–CO2 reactions are two controversial issues among these problems. This paper presented new data to elucidate these two issues. Experiments were carried out at atmospheric pressure using a modified thermogravimetric analyzer (TGA) system at various reactant partial pressures and within a temperature range of 1173–1273 K. The kinetic parameters in the L–H model were determined from pure H2O and CO2 gasification (N2 as a diluent). The experimental results showed that the L–H model based on common active site assumption is applicable to describe the experimental data and the pressure is not the reason leading to different results in validity experiments of common or separate active site assumptions. Including H2 and CO in the reactant gas does not change...

Abstract: We grew highly textured phase pure VO2 thin films on c-plane Al2O3 substrates with different oxygen partial pressure. X-ray absorption and photoemission spectroscopy confirm the identical valence state of vanadium ions despite the different oxygen pressure during the deposition. As the O2 flow rate increases, the [010] lattice parameter for monoclinic VO2 was reduced and coincidently distinctive changes in the metal-semiconductor transition (MST) and transport behaviors were observed despite the identical valence state of vanadium in these samples. We discuss the effect of the oxygen partial pressure on the monoclinic structure and electronic structure of VO2, and consequently the MST.

Abstract: Technical divers use gases other than air and advanced equipment configurations to conduct dives that are deeper and/or longer than typical recreational air dives. The use of oxygen-nitrogen (nitrox) mixes with oxygen fractions higher than air results in longer no-decompression limits for shallow diving, and faster decompression from deeper dives. For depths beyond the air-diving range, technical divers mix helium, a light non-narcotic gas, with nitrogen and oxygen to produce 'trimix'. These blends are tailored to the depth of intended use with a fraction of oxygen calculated to produce an inspired oxygen partial pressure unlikely to cause cerebral oxygen toxicity and a nitrogen fraction calculated to produce a tolerable degree of nitrogen narcosis. A typical deep technical dive will involve the use of trimix at the target depth with changes to gases containing more oxygen and less inert gas during the decompression. Open-circuit scuba may be used to carry and utilise such gases, but this is very wasteful of expensive helium. There is increasing use of closed-circuit 'rebreather' devices. These recycle expired gas and potentially limit gas consumption to a small amount of inert gas to maintain the volume of the breathing circuit during descent and the amount of oxygen metabolised by the diver. This paper reviews the basic approach to planning and execution of dives using these methods to better inform physicians of the physical demands and risks.