Varying Oxygen Partial Pressure Research Articles

The consequences of daily cyclic hypoxia on a European grass shrimp: From short‐term responses to long‐term effects

Abstract Salt marshes are a key coastal environment for their important role as nursery habitats for marine and estuarine fish and crustaceans. Salt marshes are variable environments where species can experience daily cyclic hypoxic stress, characterised by profound variations in oxygen partial pressure (pO2) from supersaturated conditions (~42 kPa) to extremely hypoxic conditions (~3 kPa) in ~12‐hr. Here, under laboratory conditions, we assessed the physiological consequences of exposing the shrimp Palaemon varians, a species commonly found in the salt marshes of northern Europe, to the daily cyclic hypoxic regime currently experienced in its habitat in August (7.1 ± 1.8 hr/day below 4.0 kPa). In the laboratory, adults were kept at water pO2 < 4.5 kPa for 7 hr each night and in normoxic conditions for the rest of the time. We recorded an acceleration of P. varians’ moult cycle, which was 15% shorter in animals kept in cyclic hypoxia compared to animals in normoxia. Similarly, the pattern of expression of two cuticular proteins over an entire moult cycle indicated an effect of cyclic hypoxia on moult stage‐related genes. After 16 days, morphological changes to the gills were detected, with shrimps in cyclic hypoxia having a 13.6% larger lamellar surface area (measured in μm2/mg animal) than normoxic animals, which could improve gas exchange capacity. Overall, phenotypic and morphological data indicate that faster moulting is triggered in response to cyclic hypoxia, with the benefit that gill modifications can be prompted more rapidly in order to meet oxygen requirements of the body. On the first experimental day, in cyclic hypoxic‐exposed animals, we recorded a 50% decrease in feeding rates (during hypoxic conditions) in comparison with normoxic animals. Similarly, ammonium excretion was reduced by 66%–75% during the 1st and 21st experimental day. Body size was reduced by ~4% after 28 days. Females that reproduced in cyclic hypoxic conditions reduced the amount of yolk in each egg by ~24%. Overall, results underline how, in a decapod shrimp living in a key coastal environment, many physiological parameters are impaired by a cyclic hypoxic regime that is currently found in its natural habitat. A plain language summary is available for this article.

Effects of bias pulse frequencies on reactively sputter deposited NbOx films

Within the current work, niobium oxide thin films have been deposited by reactive d.c. magnetron sputtering from cold gas sprayed niobium targets, applying a systematic variation of oxygen partial pressure, bias pulse frequency and substrate temperature. The films grown without additional substrate heating are amorphous. X-ray photoelectron spectroscopy shows the Nb5+ oxidation state, characteristic for the Nb2O5 phase, for films grown at the highest oxygen partial pressure applied, while the Nb4+ state of NbO2 is additionally present at lower oxygen partial pressures. With increasing oxygen partial pressure, an optical shift from non-transparent to nearly fully transparent was observed, whereby the higher bias pulse frequency leads to a transition already at lower oxygen partial pressures. The transparent films are characterized by a maximum transparency of ~80% and a refractive index of ~2.5. Increasing the substrate temperature up to 600 °C results in the formation of well crystalline coatings consisting of the orthorhombic Nb2O5 phase, which are whitish and semi-transparent.

Effect of substrate temperature and oxygen partial pressure on RF sputtered NiO thin films

Nickel oxide (NiO) thin films were deposited by RF sputtering process and the physical properties were investigated for varying substrate temperatures and oxygen partial pressure. The variation of the crystallographic orientation and microstructure of the NiO thin films with an increase in substrate temperature were studied. It was observed that NiO thin films deposited at 350 °C shows relatively good crystalline characteristics with a preferential orientation along (111) plane. With the optimum substrate temperature of 350 °C, the NiO thin films were deposited under various oxygen partial pressures at the same experimental conditions. The structural, optical and electrical properties of NiO thin films under varying oxygen partial pressure of 10%–50% were investigated. From XRD it is clear that the films prepared in the pure argon atmosphere were amorphous while the films in oxygen partial pressure exhibited polycrystalline NiO phase. SEM and AFM investigations unveil that the higher substrate temperature improves the microstructure of the thin films. It is revealed that the NiO thin films deposited at oxygen partial pressure of 40% and a substrate temperature of 350 °C, showed higher electrical conductivity with p-type characteristics.

On the defect chemistry of BaFe0.89Al0.01Ta0.1O3‐δ, a material for temperature independent resistive and thermoelectric oxygen sensors

The Seebeck-coefficient (aka thermopower) is a less wide-spread parameter to determine constants for defect chemical models of semiconductor oxides. It is a measure for the charge carrier concentration. In contrast to the often investigated electrical conductivity, it has the benefit of being independent of the material geometry. BaFe0.7Ta0.3O3‐δ is known as a temperature-independent conductometric oxygen sensor material with perovskite crystal structure. The present work considers the Seebeck-coefficient as well as the electrical conductivity of bulk and thick-film BaFe0.89Al0.01Ta0.1O3‐ δ (BFAT10). Seebeck-coefficient and electrical conductivity were measured simultaneously between 600 and 950°C under varying oxygen partial pressures from 10−24 to 1bar. BFAT10 thick films have been successfully deposited by the novel Aerosol Deposition Method (ADM) at room temperature on a special transducer. The electrical conductivity of thick-film sensors shows almost no temperature dependency but depends strongly on the oxygen partial pressure in the temperature range from 600 to 800°C. An n-to-p-type transition was observed in the investigated oxygen partial pressure and temperature range. The defect parameters were derived from the experimental results and an initial defect model for BFAT10 is discussed. A hopping-type conduction mechanism is assumed due to the very low charge carrier mobility.

Flight metabolic rate of Locusta migratoria in relation to oxygen partial pressure in atmospheres of varying diffusivity and density.

Flying insects have the highest mass-specific metabolic rate of all animals. Oxygen is supplied to the flight muscles by a combination of diffusion and convection along the internal air-filled tubes of the tracheal system. This study measured maximum flight metabolic rate (FMR) during tethered flight in the migratory locust Locusta migratoria under varying oxygen partial pressure (PO2 ) in background gas mixtures of nitrogen (N2), sulfur hexafluoride (SF6) and helium (He), to vary O2 diffusivity and gas mixture density independently. With N2 as the sole background gas (normodiffusive-normodense), mass-independent FMR averaged 132±19 mW g-0.75 at normoxia (PO2 =21 kPa), and was not limited by tracheal system conductance, because FMR did not increase in hyperoxia. However, FMR declined immediately with hypoxia, oxy-conforming nearly completely. Thus, the locust respiratory system is matched to maximum functional requirements, with little reserve capacity. With SF6 as the sole background gas (hypodiffusive-hyperdense), the shape of the relationship between FMR and PO2 was similar to that in N2, except that FMR was generally lower (e.g. 24% lower at normoxia). This appeared to be due to increased density of the gas mixture rather than decreased O2 diffusivity, because hyperoxia did not reverse it. Normoxic FMR was not significantly different in He-SF6 (hyperdiffusive-normodense) compared with the N2 background gas, and likewise there was no significant difference between FMR in SF6-He (normodiffusive-hyperdense) compared with the SF6 background gas. The results indicate that convection, not diffusion, is the main mechanism of O2 delivery to the flight muscle of the locust when demand is high.

Thermodynamic investigations on the growth of CuAlO2 delafossite crystals

Simultaneous differential thermal analysis (DTA) and thermogravimetric (TG) measurements with copper oxide/aluminum oxide mixtures were performed in atmospheres with varying oxygen partial pressures and with crucibles made of different materials. Only sapphire and platinum crucibles proved to be stable under conditions that are useful for the growth of CuAlO2 delafossite single crystals. Then the ternary phase diagram Al2O3–CuO–Cu and its isopleth section Cu2O–Al2O3 were redetermined. Millimeter sized crystals could be obtained from copper oxide melts with 1–2mol% addition of aluminum oxide that are stable in platinum crucibles held in oxidizing atmosphere containing 15–21% oxygen.

Experiments on Condensation of Calcium Sulfide Grains To Demarcate Environments for the Formation of Enstatite Chondrites

To achieve a better understanding of material evolution in the early solar system, experiments have been performed to constrain the environments in which many of the dust grains formed. Sulfur is an element whose chemical processes and mineralization of related grains are poorly understood. The high reactivity of sulfur makes it difficult to perform experiments in conventional metallic chambers, because these become heavily contaminated. Nevertheless, sulfur is expected to be a key element to understand processes in the early solar system. Here, we performed experiments on the condensation of calcium sulfide (CaS) in a glass chamber in an attempt to identify constraints on the possible formation environments of components of enstatite chondrites in terms of the effects of oxygen. Condensation experiments showed that calcium sulfate (CaSO4) or solid-solution particles of CaS and calcium oxide (CaO), i.e., [Ca(S,O)], were formed at various partial pressures of oxygen. Our results expand the range of possibl...

Luminescence Quenching of Ligand‐Substituted Molybdenum and Tungsten Halide Clusters by Oxygen and Their Oxidation Electrochemistry

Cluster compounds (TBA)2[Mo6I8(CF3SO3)6], (TBA)2[W6I8(CF3SO3)6], and (TBA)2[W6Br8(CF3SO3)6] are prepared and structurally characterized from single‐crystal X‐ray diffraction data. All compounds show red emission on photoexcitation at 400 nm. However, the phosphorescence of crystalline samples is quenched in the presence of oxygen, depending on the partial pressure of oxygen. The distinct phosphorescence‐quenching behavior of compounds containing trifluoromethanesulfonato (CF3SO3–) ligands is compared with corresponding compounds with trifluoroacetato (CF3COO–) and p‐toluolsulfonato (CH3C6H4SO3–) ligands. By studying these compounds, we investigate the relationship of more‐ or less‐electron‐withdrawing ligands (L) of (TBA)2[M6X8L6] halide (X) clusters, their redox potentials (E0), and their phosphorescence‐quenching behavior under variable oxygen partial pressures.

Evaluation of electrical conductivity and oxygen diffusivity of the typical Ruddlesden-Popper oxide Sr3Fe2O7-δ

The electrical conductivity (σ) and oxygen diffusivity of the typical Ruddlesden-Popper oxide Sr3Fe2O7-δ were investigated with the variation of oxygen partial pressure, P(O2), and temperatures, and thus the results were discussed based on its defect structure. The σ increases with the increase of P(O2) and a positive slope of log σ depend on P(O2) is close to 1/4 with the small polaron conduction, where the mobility μP are between 0.01 and 0.02cm2V−1s−1 regardless of temperature and P(O2). Oxygen diffusivity derived from the electrical conductivity relaxation (ECR) after an abrupt change of P(O2) increased with the increase P(O2) and temperature. A new pulse isotope 18O-16O exchange (PIE) at 623–773K was carried in order to rapidly determine the tracer oxygen surface reaction coefficient. The numerical relationship of oxygen diffusivity measured by ECR and PIE measurements was successfully established by the ambipolar diffusion theory and defect chemical analysis.

Phase pure epitaxial growth of BiFeO3 films: An effect of oxygen partial pressure

We report the growth of bismuth ferrite, BiFeO3 (BFO), thin films by varying oxygen partial pressure (230, 100 and 10mTorr) in pulsed laser deposition system using 10% bismuth excess BFO target on SrTiO3 (001) [STO] substrates at 700°C each for 15min duration. X-ray diffraction shows the presence of an impurity phase along with BFO peaks for 230mTorr film, whereas oriented BFO film is observed for 100mTorr film with a small impurity phase. Importantly, epitaxial growth of BFO is observed without any impurity phase and with sufficiently increased strain for the 10mTorr film, confirmed by the reciprocal space mapping of (002) and (103) reflections. UV-Raman measurements have been performed on as grown films and the 10mTorr BFO film after annealing up to 500°C to check its thermal stability. Atomic force microscopic (AFM) study reveals that the 10mTorr BFO film shows a lower roughness as compared to 100mTorr and 230mTorr films. Fast Fourier Transform (FFT) analysis in AFM shows a fourfold symmetric structure suggesting the presence of both modes of pattern-orientation in 230mTorr BFO film whereas an elongated bright spot along the y-direction in the FFT of 10mTorr BFO film suggests the growth tendency to be along the y-direction.

Mechanical Properties of SOFC Anode Support Materials at Operating Conditions

The mechanical properties of solid-oxide fuel cells (SOFCs) and the materials they are fabricated from play an important role in manufacturability, durability and lifetime of the devices. Functioning cells must maintain a gas-tight seal though the cell, with no cracks or pores from anode or cathode, through a range of temperatures and oxygen partial pressures. The cell must be able to withstand intrinsic stresses in addition to those introduced by the stacking and sealing of the cells. It is known that the environmental conditions can affect the mechanical properties of materials. It has been shown that point defect concentration and temperature change the elastic modulus and strength of fluorite-structured oxides, but these tests were done using quenched samples or at high temperature in air, not at operating conditions. In this work the flexural modulus and strength of SOFC support materials are investigated under varying oxygen partial pressures at elevated temperatures, under the same conditions SOFCs experience during operation. This is achieved by using a three-point bend fixture on a universal testing machine, with a chamber and furnace to control the environmental conditions. From this information, relationships are built relating materials’ modulus and strength to the defect concentrations and temperatures that it would experience during operation.

Structure Stability and Mechanical Property of Y<sub>2</sub>O<sub>3</sub> Thin Films Deposited by Reactive Magnetron Sputtering

Y2O3 has a great application potential at reaction barrier coating of high-temperature composites due to its high thermodynamic stability and high melting point, and the phase structure stability at high temperature and structure dependent mechanical property are key parameters for this application. Y2O3 thin films were deposited on silicon (100) wafers by DC magnetron sputtering with various oxygen partial pressure and substrate bias, and then vacuum annealing at 1000°C was performed to investigate the phase structure stability. The microstructure, stress and hardness of as-deposited and annealed Y2O3 thin films were explored by X-ray diffraction, transmission electron microscope, and nanoindenter. The result showed that as-60 bias voltage was applied to substrate, cubic-c phase formed regardless of variation of oxygen partial pressure, and the cubic-c phase remains stability and crystallinity became better after annealing at 1000 °C.In addition, the hardness and modulus also just had minor changes as a function of oxygen partial pressure. As oxygen partial pressure was kept at 0.043 Pa, phase transition from cubic-c to monoclinic-b phase took place with increasing substrate bias, accompanying by the increment of hardness and modulus, and 1000 °Chigh-temperature annealing resulted in that as-deposited monoclinic-b phase transforms to cubic-c phase.

Mechanical Properties of SOFC Anode Support Materials at Operating Conditions

The mechanical properties of solid-oxide fuel cell (SOFC) materials play an important role in manufacturability, durability and lifetime of the devices. Environmental conditions can affect the mechanical properties of materials. It has been shown during testing of quenched samples that point defect concentration and temperature change the elastic modulus and strength of fluorite-structured oxides. In this work, the flexural modulus and strength of pressed Ce0.90Gd0.10O2-x (GDC) bars are investigated under varying oxygen partial pressures at 675℃, under the same conditions SOFCs experience during operation. This is achieved by using a three-point bend fixture on a universal testing machine, with a chamber and furnace to control the environmental conditions. At operating conditions, the strength and modulus of polycrystalline bars do not follow the expected trends of quenched single grains tested by other methods.

Kinetic study and modelling of char combustion in TGA in isothermal conditions

The purpose of this work is the kinetic study of biomass char combustion in isothermal conditions in TGA. This char was obtained from fast pyrolysis of beech bark pellet in a fluidized bed reactor at 850°C and atmospheric pressure. Kinetic study of isothermal char combustion was performed for temperatures up to 400°C, oxygen partial pressures ranging from 5065 to 21,273Pa and a char particles size of 25μm. Mass transfer effects around and within the crucible were thoroughly characterized by naphthalene vaporization. Oxygen diffusion was found to have no effect on char combustion for temperatures below 400°C. A novel method including the transfer function of the TGA which describes the variation of oxygen partial pressure just after switching the gas from inert to reactive in the TGA was taken into consideration in the kinetic modelling. Two kinetic models (the Grain Model and the Random Pore Model) were used to determine kinetic parameters. The Grain Model was found to be in very good agreement with experimental data. Values of activation energy and reaction order with respect to oxygen are respectively equal to 124kJ/mol and 0.74. Besides, the maximum combustion rate commonly observed in the literature during char combustion was found to be the result of the non-uniform oxygen partial pressure in the TGA at the initial stage of the char combustion.

Mechanism of active and passive oxidation of reaction-bonded Si3N4-SiC refractories

Abstract The mechanism of the active and passive oxidation of reaction-bonded Si 3 N 4 -SiC refractories used for six-month in silicon nitridation shuttle has been analyzed. The change of morphology and component of reaction-bonded Si 3 N 4 -SiC block of saggar have been analyzed. The results show that in Si 3 N 4 -SiC, Si 3 N 4 has a higher activity and is more easily oxidized than SiC in both active and passive oxidation modes. All the fibrous α-Si 3 N 4 which exists in a substantial amount in Si 3 N 4 -SiC before use has transformed to β-Si 3 N 4 or was oxidized. The burning side of Si 3 N 4 -SiC block, which operates in high oxygen partial pressure, is oxidized in passive mode generating SiO 2 , Si 2 N 2 O and carbon. The working side of Si 3 N 4 -SiC block, who works in low oxygen partial pressure, is oxidized in the active mode generating gaseous SiO. In another stage of service, SiO generated by silicon nitridation in the saggar infiltrates into the block and reacts with nitrogen forming small rods of Si 3 N 4 that fill pores, which leads to lower apparent porosity. In the middle section of the block, two different oxidation modes coexist, since there is a gradually variation of oxygen partial pressure.

Symmetrical solid oxide fuel cells fabricated by phase inversion tape casting with impregnated SrFe0.75Mo0.25O3-δ (SFMO) electrodes

The new phase inversion tape casting method is explored to fabricate the “porous|dense|porous” La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) with aligned straight pores. Symmetrical fuel cells are obtained by impregnating nano-scale SrFe0.75Mo0.25O3-δ (SFMO) catalysts into both porous LSGM scaffolds. Operation on hydrogen and air oxidants produces 401, 521, 602 and 703 mW cm−2 at 650, 700, 750 and 800 °C, respectively. Impedance measurements show that the overall interfacial polarization resistances are 0.17, 0.20, 0.25 and 0.36 Ω cm2 for such symmetrical fuel cells at 800, 750, 700 and 650 °C, respectively. Impedance analysis under varied oxygen partial pressures indicates that the symmetrical SFMO-LSGM electrodes exhibit lower polarization resistances for phase-inversion casted LSGM scaffolds than for the traditionally casted LSGM scaffolds.

Modeling study of oxygen permeation through an electronically short‐circuited YSZ‐based asymmetric hollow fiber membrane

Here, oxygen fluxes through an electronically short‐circuited asymmetric Ag‐YSZ|YSZ|LSM‐YSZ hollow fiber prepared via a combined spinning and sintering route were tested and correlated to an explicit oxygen permeation model. The average oxygen permeation through such asymmetric hollow fiber with a 27 μm‐thick YSZ dense layer reached 0.52 mL (STP) cm−2 min−1 at 1173 K. From the model results, we can obtain the characteristic thickness, the effects of the temperature, and the effect of He sweep gas flow rate to the individual step contribution. The oxygen partial pressure variation in the permeate side, the local oxygen flux, and the three‐different resistance distribution along the axial direction of the asymmetric hollow fiber are theoretically studied; providing guidelines to further improve the membrane performance for oxygen separation. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3491–3500, 2017

Formation of intrinsic and silicon defects in MoO3 under varied oxygen partial pressure and temperature conditions: an ab initio DFT investigation

DFT simulations predict how varied MoO3 preparation conditions could change intrinsic defect concentrations and avoid silicon contamination in photovoltaic applications.

Insight into the synthesis and electrical properties of alkali-earth-substituted Gd3GaO6 oxide-ion and proton conductors

Novel ionic conductors were prepared by substituting Ca2+ and Sr2+ for Gd3+ in Gd3GaO6. A microwave-assisted combustion technique was used to synthesize these compounds at 900 °C. SEM observations showed that both substituents promote grain growth during sintering. XRD proved that the Gd3-x(Ca,Sr)xGaO6-x/2 solid solutions are formed up to x = 0.10. Below 600 °C, the level of conductivity under wet Ar is higher than that of measured under dry atmospheres, thereby demonstrating the contribution of proton defects to the overall conductivity. The highest level of proton conduction, i.e. σ600°C = 1 × 10−3 S cm−1, was measured for Gd2.9Sr0.1GaO5.95 at 600 °C in wet Ar. At higher temperatures, only oxygen ions contribute to the conductivity. At 800 °C, a total oxide-ion conductivity of σ800°C = 1 × 10−2 S cm−1 was measured for the highest substitution level, i.e. x = 0.10. In both temperature ranges, activation energy associated with ionic transport decreases with the Me content as a result of an increase in grain size. Stability tests were successfully achieved as the structure of materials remains unchanged after different treatment under severe conditions. Conductivity measurements under varying oxygen partial pressures demonstrated that materials are purely oxide-ion conductors up to pO2 = 1 × 10−5 atm. At higher pO2, a p-type contribution appears.

Investigation of Copper Losses to Synthetic Slag at Different Oxygen Partial Pressures in the Presence of Colemanite

Copper losses to slag are crucial for copper matte smelting and converting stages. One factor affecting the copper losses to slag during these processes is partial pressure of oxygen. In this study, theoretical and experimental investigations of oxygen partial pressure effect on copper losses to fayalite type slag in the presence of colemanite were investigated. Theoretical considerations include liquidus temperatures and phase diagrams of the fayalite type slag calculated by the FactSage software program. In the experiments, a synthetic matte–slag (SM–SS) was produced by melting certain amounts of reagent grade Fe2O3-SiO2 and metallic Fe as starting materials. Experiments were carried out with SM–SS pair by the addition of calcined colemanite (from 0% to 6%) under various partial pressures of oxygen (10−7, 10−9, 10−11 atm) at 1250°C for 2 h. From the experimental results, it was found that the amount of copper in slag decreased slowly when colemanite was increased under all oxidizing atmospheres. The lowest copper content in synthetic slag was obtained as 0.38% after 6% colemanite addition.