Oxygen Flux Research Articles

Oxygen consumption during digestion in Anodonta anatina and Unio pictorum in response to algal concentration

The metabolic activity of unionid mussels influences the oxygen fluxes and other physical and chemical characteristics in aquatic systems. Unionid oxygen consumption rate during digestion and its dependency on food availability is understudied. In laboratory conditions, we quantified the oxygen consumption rate of Anodonta anatina and Unio pictorum in response to algal concentration—0.05, 6.0 and 12.0 mg of Ash Free Dry Mass of Chlorella vulgaris L−1—and mussel dry soft-tissue mass at 19 ± 1°C. Following a 5-h feeding-period, the oxygen consumption rate (mg O2 h−1) increased with algal concentration and mussel dry mass in both species during a 2-h digestion-period. The mean oxygen consumption per gram of dry mass (mg O2 gDM−1 h−1) increased with the algal concentration in both species. The oxygen consumption rate of A. anatina was significantly greater than that of U. pictorum at a given algal concentration. The A. anatina oxygen consumption per gram of dry mass decreased with increasing dry mass. Oxygen consumption rate during digestion shows inter-specific differences and is dependent on food availability. The findings inform the species-specific quantification of oxygen consumption, and validation is required in in situ conditions.

Ce0.9Gd0.1O2-δ-based multi-phase membranes with high CO2-tolerance

In this work, the oxygen ionic conductor Ce0.9Gd0.1O2-δ was paired with the electronic/mixed conductive oxides, including NiFe2O4 (NFO), La2NiO4+δ (LNO) and Ba0·5Sr0·5Co0·8Fe0·2O3-δ (BSCF), forming three kinds of dual-phase membranes. The performance of the membranes was compared in terms of oxygen flux and CO2 tolerance. The CGO/BSCF provided the highest permeation flux among the three composites with either helium or CO2 fed as the sweep gas, although a sharp decrease of the permeation value was observed for the CGO/BSCF when CO2 was in contact with the membrane. Based on the results for the dual-phase membranes, some CGO/BSCF/NFO triple-phase membranes were developed. The triple-phase membranes were found be less sensitive to the presence of CO2 in the sweep gas than the CGO/BSCF, and the application of the two triple-phase composites instead of the dual-phase ones promoted the oxygen permeation fluxes when the membranes were swept with pure CO2. The results provide valuable information for the material selection and performance optimization of CGO-based multi-phase membranes for oxygen permeation.

Nitrogen removal processes in lakes of different trophic states from on-site measurements and historic data

Freshwater lakes are essential hotspots for the removal of excessive anthropogenic nitrogen (N) loads transported from the land to coastal oceans. The biogeochemical processes responsible for N removal, the corresponding transformation rates and overall removal efficiencies differ between lakes, however, it is unclear what the main controlling factors are. Here, we investigated the factors that moderate the rates of N removal under contrasting trophic states in two lakes located in central Switzerland. In the eutrophic Lake Baldegg and the oligotrophic Lake Sarnen, we specifically examined seasonal sediment porewater chemistry, organic matter sedimentation rates, as well as 33-year of historic water column data. We find that the eutrophic Lake Baldegg, which contributed to the removal of 20 ± 6.6 gN m−2 year−1, effectively removed two-thirds of the total areal N load. In stark contrast, the more oligotrophic Lake Sarnen contributed to 3.2 ± 4.2 gN m−2 year−1, and had removed only one-third of the areal N load. The historic dataset of the eutrophic lake revealed a close linkage between annual loads of dissolved N (DN) and removal rates (NRR = 0.63 × DN load) and a significant correlation of the concentration of bottom water nitrate and removal rates. We further show that the seasonal increase in N removal rates of the eutrophic lake correlated significantly with seasonal oxygen fluxes measured across the water–sediment interface (R2 = 0.75). We suggest that increasing oxygen enhances sediment mineralization and stimulates nitrification, indirectly enhancing denitrification activity.

Bottom Boundary Layer Oxygen Fluxes During Winter on the Oregon Shelf

AbstractIn this study, lander‐based eddy covariance measurements made 30 cm above a sandy seafloor are combined with ocean‐observing and ship‐based measurements to evaluate magnitudes of oxygen fluxes within the bottom boundary layer (BBL) during winter on the Oregon shelf. The total oxygen fluxes observed at a mid‐shelf station were −12.3 ± 7.6 and −18.6 ± 16.9 mmol m−2d−1 during February 2018 and January 2019 deployments, respectively, and −51.8 ± 34.9 mmol m−2d−1 during a deployment on the inner shelf in January 2019. These mean (±SD) flux derivations are greater than fluxes determined previously at nearly the same locations during the summer upwelling season, which points to the activation of benthic respiration by winter wave‐dominated BBL dynamics. To determine the direct flux contributions (or potential bias) at wave frequencies, a phase‐based method of spectral decomposition was applied to separate wave‐induced and turbulence‐induced components of velocity and dissolved oxygen time‐series. This approach identified 25.4, 18.6, and 23.3% of the average total EC oxygen fluxes from the three deployments as carried by waves or possibly turbulence stretched by waves. Additionally, we observed evidence of large waves regularly resuspending sediments and transporting entrained particles past the EC sensors. We apply this evidence to infer that wave frequencies must also contribute significantly to the real spectral domain of benthic oxygen fluxes and that the total fluxes of this study reflect elevated oxygen consumption rates without artifacts. This assessment may not be true for all data sets and may be dependent on wave properties and the quality and treatment of the measurements.

A refined model on flow and oxygen consumption in the human cornea depending on the oxygen tension at the interface cornea/post lens tear film during contact lens wear

The study of oxygen consumption rate under” in vivo” human cornea during contact lens wear has been technically a challenge and several attempts have been made in the last 20 years to model the physiology of the human cornea during contact lens wear. Unfortunately, some of these models, based on a constant corneal oxygen consumption rate, produce areas on the cornea where the oxygen tension is negative, which has no physical sense. In order to avoid such inconsistency, different researchers have developed alternative models of oxygen consumption, which predict the likely oxygen metrics available at the interface cornea/post lens tear film by determination of oxygen flux, oxygen consumption, and oxygen tension through the different layers (endothelium, stroma, and epithelium). Although oxygen deficiency produces corneal edema, corneal swelling, hypoxia, acidosis, and other abnormalities, the estimation of the oxygen distribution below the impact of a contact lens wear is interesting to know which lens transmissibility was adequate to maintain the cornea and avoid epithelial and stromal anoxia. The estimation of minimum transmissibility for a lens for extended wear applications will be very useful for both clinicians and manufacturers. The aim of this work is to present a complete discussion based on Monod kinetics model that permits give an estimation of oxygen partial pressure distribution, the profile distribution of corneal flux and oxygen consumption rate, and finally the estimation of the relaxation mechanism of the cornea depending on the oxygen tension at the interface cornea/post lens tear film. Relaxation time in this context can quantify the capability of the corneal tissue to adapt to increasing concentrations of oxygen. It is proposed this parameter as a biological meaningful indicator of the interaction between contact lens polymers and living tissues such as the corneal cellular layer.

Oxygen budget of the north-western Mediterranean deep- convection region

Abstract. The north-western Mediterranean deep convection plays a crucial role in the general circulation and biogeochemical cycles of the Mediterranean Sea. The DEWEX (DEnse Water EXperiment) project aimed to better understand this role through an intensive observation platform combined with a modelling framework. We developed a three-dimensional coupled physical and biogeochemical model to estimate the cycling and budget of dissolved oxygen in the entire north-western Mediterranean deep-convection area over the period September 2012 to September 2013. After showing that the simulated dissolved oxygen concentrations are in a good agreement with the in situ data collected from research cruises and Argo floats, we analyse the seasonal cycle of the air–sea oxygen exchanges, as well as physical and biogeochemical oxygen fluxes, and we estimate an annual oxygen budget. Our study indicates that the annual air-to-sea fluxes in the deep-convection area amounted to 20 molm-2yr-1. A total of 88 % of the annual uptake of atmospheric oxygen, i.e. 18 mol m−2, occurred during the intense vertical mixing period. The model shows that an amount of 27 mol m−2 of oxygen, injected at the sea surface and produced through photosynthesis, was transferred under the euphotic layer, mainly during deep convection. An amount of 20 mol m−2 of oxygen was then gradually exported in the aphotic layers to the south and west of the western basin, notably, through the spreading of dense waters recently formed. The decline in the deep-convection intensity in this region predicted by the end of the century in recent projections may have important consequences on the overall uptake of atmospheric oxygen in the Mediterranean Sea and on the oxygen exchanges with the Atlantic Ocean, which appear necessary to better quantify in the context of the expansion of low-oxygen zones.

Defining a biogeochemical baseline for sediments at Carbon Capture and Storage (CCS) sites: An example from the North Sea (Goldeneye)

Injection of carbon dioxide (CO2) into subseafloor reservoirs is gaining traction as a strategy for mitigating anthropogenic CO2 emissions to the atmosphere. Yet, potential leakage, migration and dissolution of externally-supplied CO2 from such reservoirs are a cause for concern. The potential impact of CO2 leakage on the biogeochemistry of sediments and overlying waters in the North Sea was studied during a controlled subsurface CO2 release experiment in 2019 at a potential carbon capture and storage site (Goldeneye). This study describes the natural (unperturbed) biogeochemistry of sediments. They are classified as muddy sand to sandy mud with low organic carbon content (∼0.6 %). Distributions of dissolved inorganic carbon (DIC) and total alkalinity (TA) in sediment porewaters are reported in addition to in situ benthic fluxes of dissolved nutrients and oxygen between the sediments and the overlying water. Oxygen fluxes into the sediment, measured using benthic chambers and eddy covariance, were 6.18 ± 0.58 and 5.73 ± 2.03 mmol m−2 d-1, respectively. Diagnostic indicators are discussed that could be used to detect CO2 enrichment of sediments due to reservoir leakage at CCS sites. These include the ratio TA and ammonium to sulfate in sediment porewaters, benthic fluxes and chloride-normalized cation distributions. These indicators currently suggest that the organic carbon at Goldeneye has an oxidation state below zero and is mainly degraded via sulfate reduction. Carbonate precipitation is apparently negligible, whereas decreases in Mg2+ and K+ point toward ongoing alteration of lithogenic sediments by reverse weathering processes.

Measure microbial activity driven oxygen transfer in membrane aerated biofilm reactor from supply side

This short communication demonstrates for the first time a solely microbial activity driven oxygen influx across a microporous hollow fibre membrane via tracking changes in volume and gas composition of entrapped air supply. A U-shape manometer was used to directly reflect gas influx due to microbial activities. A pressure difference of several hundred pascal was created to draw oxygen while 25 mg-N/L of ammonium was oxidized into nitrite by active biofilm at a hydraulic retention time of 6 h. Calibrated and normalized gas compositions before and after the experiment were processed to unveil the gas exchange and estimate the actual oxygen influx across the membrane. A solely microbial activity driven oxygen influx of 10.7 mg O2/m2/h was observed. Measuring oxygen transfer from supply side provides a more straight-forward perspective on the role of active biofilm in membrane aerated biofilm reactor. The capability of the microbial activity to uptake oxygen on its own could potentially lead to greater energy savings in some MABR applications when strict aeration control is not needed.

Eddy correlation measurements of benthic oxygen fluxes in a stratified and operated reservoir

Benthic oxygen fluxes at the sediment-water interface (SWI) regulate the process and even direction of biochemical interfacial reactions; thus, they are crucial to the water quality. However, many medium- and large-sized reservoirs suffer from thermal stratification and human operations, lead to a significant impact on SWI oxygen exchanges. A 3-month-long noninvasive measurement of SWI oxygen fluxes was conducted in the Daheiting Reservoir using the eddy correlation method. Its result shows that reservoir stratification markedly affects the benthic boundary layer environment factors such as temperature, dissolved oxygen (DO) concentration, and hydrodynamics. In contrast, reservoir operations determine the benthic flow directions and its correlation to velocities in the mixed stage. A further discussion suggests that benthic temperatures mainly participate in the thermal structure rather than directly affecting the benthic fluxes. Conversely, it is DO concentrations coupled with hydrodynamics that control SWI oxygen fluxes. The flux is inhibited by DO shortage in anoxic conditions, but it is mainly controlled by hydrodynamics with redundant DO. Likewise, the hydrodynamics affects the fluxes by changing the diffusive boundary layer thickness, but this effect is also restrained by the DO field. These results indicate that a long-term and in-situ measurement of SWI oxygen fluxes in drinking reservoirs is of considerable significance to forecast water quality disasters, optimize operation plans, and ensure water security.

Comprehensive analysis of oxygen transport properties of a BaFe0.7Zr0.2Y0.1O3–δ-based mixed ionic-electronic conductor

Mixed ionic-electronic conductors (MIECs) represent a convenient means for separating oxygen from air, simultaneously combining high efficiency, low energy consumption and an environmentally safe electrochemical process. In the framework of this study, we propose two effective strategies for fabricating MIEC-based membranes: from a materials science viewpoint, a new perovskite-type BaFe0.7Zr0.2Y0.1O3–δ (BFZY) material was prepared as an alternative to Co-free oxides; from the technological viewpoint, the very simple tape-calendaring method was used to obtain a symmetrical-type membrane with a 150 μm-thick dense BFZY layer separating two porous and well-adhered layers of the same composition. According to experimental results, this membrane achieves maximal oxygen fluxes of 0.13- and 0.28-ml min−1 cm−2 at 750 °C and 850 °C, respectively, which are comparable with those obtained for related Fe- and even Co-containing MIEC membranes. A comprehensive analysis of transport properties conformed that bulk oxygen diffusion is a predominant process in the overall permeation process for the BFZY membrane. These findings provide a fresh approach for the rational design of MIEC materials and membrane cells for supporting the oxygen permeation process, including oxygen separation, oxygen production and electrochemical conversion.

Warm fish eggs gasp for oxygen

Breathing underwater is tough. Fish get by thanks to their elaborate gills, which have a large surface area to efficiently extract oxygen from the water. However, eggs don't have this luxury and must rely entirely on whatever oxygen seeps in through their jelly-like shells. The situation worsens the larger the egg, where the influx of oxygen must supply a greater volume. Benjamin Martin at the University of Amsterdam in The Netherlands wondered whether the largest aquatic eggs, like those of Chinook salmon, may struggle at times to get the oxygen they need.With an international team of collaborators, Martin set about investigating how developing salmon eggs respond to an increase in oxygen demand due to higher temperatures, or a limited supply when oxygen in the water is depleted; both of these scenarios afflict the river beds where wild salmon spawn and are becoming increasingly frequent as our planet warms. In a super-sized experiment, the team reared thousands of salmon eggs in the lab at nine different combinations of temperature and oxygen levels and monitored how much oxygen the embryos consumed throughout development.It turns out that for an embryo encased in jelly, everything depends on oxygen: the rate at which they develop, their tolerance of higher temperatures, the size of the hatchlings and, importantly, survival. A decrease in the amount of oxygen in the water has dire consequences, increasing mortality of the brood, but it was especially devastating when it occurred late in development, when the embryos’ need for oxygen was highest. An increase in temperature generally led to faster embryo growth, but also a greater need for oxygen, making them even more vulnerable to a depletion of oxygen in the water. The team then fed these results into a mathematical model that illuminated the egg's inner oxygen supply. Salmon embryos were surprisingly tough and tolerated an 80% cut in oxygen within the egg. However, in late development, the embryos were always oxygen starved, which constrained their growth, and even a small decrease in the oxygen level in the water or an increase in temperature could push them over the edge and decrease survival.But nature is messy in ways that lab experiments and mathematical models cannot capture. Therefore, the team reared additional eggs in artificial gravel beds that naturally mimicked the salmons’ spawning grounds. The slow water flow through the pebbles meant that the oxygen consumed by the eggs wasn't replenished as quickly as in the lab, making them even more vulnerable to higher temperatures. In addition, the hapless eggs sitting downstream of the bunch suffered most, as their greedy siblings upstream had already gobbled up all the oxygen in the water, resulting in smaller hatchlings and lower survival. Even eggs sitting right next to one another would experience vastly different levels of oxygen, because the water flow through the egg–gravel mix was random. As if braving low oxygen and high temperatures wasn't enough, in the wild, the survival of a salmon egg is also a lottery.While some adult fish seem to handle the whims of climate change quite well, their embryos typically do not. In the long term, a species is only as resilient as its most sensitive life stage. The high vulnerability of fish embryos is rooted in their precarious oxygen supply within the egg. Even under optimal conditions, growing fish embryos become starved of oxygen, which leaves only razor-thin margins to tolerate any increase in temperature or decrease in oxygen level. The life of a fish embryo is like a reckless tightrope act where survival depends on walking a delicate balance between oxygen supply and demand.

Aquatic Biogeochemical Eddy Covariance Fluxes in the Presence of Waves

AbstractThe eddy covariance (EC) technique is a powerful tool for measuring atmospheric exchange rates that was recently adapted by biogeochemists to measure aquatic oxygen fluxes. A review of aquatic biogeochemical EC literature revealed that the majority of studies were conducted in shallow waters where waves were likely present, and that waves biased sensor and turbulence measurements. This review identified that larger measurement heights shifted turbulence to lower frequencies, producing a spectral gap between turbulence and wave frequencies. However, some studies sampled too close to the boundary to allow for a spectral turbulence‐wave gap, and a change in how EC measurements are conducted and analyzed is needed to remove wave‐bias. EC fluxes have only been derived from the time‐averaged product of vertical velocity and oxygen, often resulting in wave‐bias. Presented is a new analysis framework for removing wave‐bias by accumulation of cross‐power spectral densities below wave frequencies. This analysis framework also includes new measurement guidelines based on wave period, currents, and measurement heights. This framework is applied to sand, seagrass, and reef environments where traditional EC analysis resulted in wave‐bias of 7.0% ± 9.2% error in biogeochemical (oxygen and H+) fluxes, while more variable and higher error was evident in momentum fluxes (10.5% ± 21.0% error). It is anticipated that this framework will lead to significant changes in how EC measurements are conducted and evaluated, and help overcome the major limitations caused by wave‐sensitive and slow‐response sensors, potentially expanding new chemical tracer applications and more widespread use of the EC technique.

Oxygen semi-permeation properties of Ba1-xSrxFeO3-δ perovskite membranes

This work is focused on the evaluation of oxygen semi-permeation performances of free cobalt perovskite membrane materials, Ba1-xSrxFeO3-δ perovskites. A wide range of Ba and Sr contents was studied. The best performances were obtained for Ba0.9Sr0.1FeO3-δ perovskite membranes with oxygen fluxes of 4.1 10−3 mol.m−2.s−1 at 850 °C. For a better understanding of the rate determining step of oxygen transport through Ba1-xSrxFeO3-δ perovskite membranes (with x = 0.1, 0.5, and 0.7), the oxygen diffusion and oxygen desorption coefficients were determined using a specific method based on oxygen semi-permeation.

Atomic oxygen generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and O2

Absolute atomic oxygen densities measured space resolved in the active plasma volume of a COST microplasma reference jet operated in He/O2 and driven by tailored voltage waveforms are presented. The measurements are performed for different shapes of the driving voltage waveform, oxygen admixture concentrations, and peak-to-peak voltages. Peaks- and valleys-waveforms constructed based on different numbers of consecutive harmonics, N, of the fundamental frequency f 0 = 13.56 MHz, different relative phases and amplitudes are used. The results show that the density of atomic oxygen can be controlled and optimized by voltage waveform tailoring (VWT). It is significantly enhanced by increasing the number of consecutive driving harmonics at fixed peak-to-peak voltage. The shape of the measured density profiles in the direction perpendicular to the electrodes can be controlled by VWT as well. For and peaks-/valleys-waveforms, it exhibits a strong spatial asymmetry with a maximum at one of the electrodes due to the spatially asymmetric electron power absorption dynamics. Thus, the atomic oxygen flux can be directed primarily towards one of the electrodes. The generation of atomic oxygen can be further optimized by changing the reactive gas admixture and by tuning the peak-to-peak voltage amplitude. The obtained results are understood based on a detailed analysis of the spatio-temporal dynamics of energetic electrons revealed by phase resolved optical emission spectroscopy.

Modification of Ruddlesden-Popper-type Nd2-xNi0.75Cu0.2M0.05O4±δ by the Nd-site cationic deficiency and doping with Sc, Ga or In: Crystal structure, oxygen content, transport properties and oxygen permeability

Nd2-xNi0.75Cu0.2M0.05O4±δ (x ​= ​0 and 0.1; M ​= ​Sc, Ga, and In) Ruddlesden-Popper-type oxides are obtained by a sol-gel route and characterized concerning phase composition and crystal structure. It is found that the largest In3+ cannot be effectively introduced into the structure, while Nd stoichiometric and cation-deficient Nd2-xNi0.75Cu0.2Sc0.05O4±δ and Nd2-xNi0.75Cu0.2Ga0.05O4±δ (x ​= ​0; 0.1) can be obtained as single-phase materials. Systematic characterization of the crystal structure at high temperatures, oxygen content, as well as transport properties reveals that while the Nd-site deficiency has rather negligible influence on the structure, it causes a substantial decrease of the oxygen content, which at high temperatures leads to a change of the dominant type of defects from the oxygen interstitials to the vacancies for Nd1.9Ni0.75Cu0.2Sc0.05O4±δ and Nd1.9Ni0.75Cu0.2Ga0.05O4±δ. The Nd-site deficiency also causes a decrease of the total conductivity. Importantly, all the examined materials exhibit full chemical stability in CO2 atmosphere, which together with moderate thermal expansion makes them good candidates for the oxygen transport membranes, which can be used e.g. in the air separation technologies. The selected Sc- and Ga-doped compounds evaluated as ceramic membranes show relatively high oxygen fluxes, with the highest value of 0.78 ​mL ​cm-2 min-1 at ca. 880 ​°C registered for 0.9 ​mm thick, dense Nd1.9Ni0.75Cu0.2Ga0.05O4±δ membrane.

How Does Mangrove Expansion Affect Structure and Function of Adjacent Seagrass Meadows?

Temperatures are increasing globally and causing species-specific geographic range expansions. In the Gulf of Mexico, mangroves are encroaching regions historically dominated by temperate salt marshes, changing animal communities and nutrient cycling in the intertidal zone. Marine systems are highly connected; therefore, we expect that changes in the intertidal will alter functions of adjacent subtidal seagrass meadows. We surveyed seagrass meadows adjacent to mangroves, salt marshes, and a mixture of the two and asked, do changes in intertidal plant composition influence (1) environmental conditions (subtidal water and sediment characteristics); (2) biogeochemical cycling (net oxygen and nitrogen gas fluxes); (3) seagrass meadow cover, biomass, and productivity; and (4) invertebrate community assemblage? There are clear differences in sediment organic matter and net nitrogen gas (N2) fluxes between adjacent intertidal habitats, but the magnitude or direction of change differs seasonally. We hypothesize that this seasonal pattern is due to outwelling from the intertidal, as mangroves senesce in fall, and marshes senesce later in winter. Therefore, changes in adjacent intertidal habitat can impact the timing of organic matter delivery. This also has implications for seagrass biomass. Thalassia testudinum belowground biomass adjacent to mangroves substantially decreased over the winter, suggesting vulnerability to stressors as the intertidal plant community shifts from marsh to mangrove dominance. Epifauna density and diversity did not vary among seagrass meadows based on adjacent intertidal habitats, but subtle differences in community assemblages associated with shifts in intertidal plant community were detected. This work demonstrates that impacts of species range expansions are far-reaching due to connectivity in marine systems.

Optimum heat treatment to enhance the weak-link response of Y123 nanowires prepared by Solution Blow Spinning

Although the production of YBa2Cu3O7-δ (Y123) has been extensively reported, there is still a lack of information on the ideal heat treatment to produce this material in the form of one dimension nanostructures. Thus, by means of the Solution Blow Spinning technique, metals embedded in polymer fibers were prepared. These polymer composite fibers were fired and then investigated by thermogravimetric analysis. The maximum sintering temperatures of heat treatment were chosen in the interval 850 °C–925 °C for 1 h under oxygen flux. SEM images allowed us to determine the wire diameter as approximately 350 nm for all samples, as well as to map the evolution of the entangled wire morphology with the sintering temperature. XRD analysis indicated the presence of Y123 and secondary phases in all samples. Ac magnetic susceptibility and dc magnetization measurements demonstrated that the sample sintered at 925 °C/1 h is the one with the highest weak-link critical temperature and the largest diamagnetic response.

Bubble nucleation in core-shell structured molten oxide-based membranes with combined diffusion-bubbling oxygen mass transfer: experiment and theory.

Oxygen-selective membranes are likely to play a leading part in the future separation processes relevant to energy engineering. A newly developed molten copper and vanadium oxide-based diffusion-bubbling membrane with core-shell structure and fast combined oxygen mass transfer is a promising candidate for efficient oxygen separation. In this work, the oxygen bubble nucleation and transport properties of the diffusion-bubbling membrane were experimentally and theoretically studied. Bubble size distribution and cumulative oxygen flux have been plotted as functions of oxygen partial pressure. The relationship between the bubble density, oxygen partial pressure, and oxygen permeation flux was established. The oxygen flux and bubble density vary in the ranges of 3.2 × 10-8-1.4 × 10-7 mol cm-2 s-1 and 1.3 × 1013-5.8 × 1013 m-3 at ΔPO2 = 0.1-0.75 atm, respectively. The mechanisms of homogeneous, heterogeneous, pseudo-classical and non-classical nucleation are reviewed within the framework of the Cahn-Hilliard model. It is shown that the homogeneous nucleation mechanism is most likely in the membrane core. The estimated values of the interfacial tension, energy barrier, and rate nucleation are 0.02 J m-2, 5 kT, and 4 × 1029 m-3 s-1, respectively.

Керамические композиционные мембраны на основе Bi3Ru3O11 – Bi1,6Er0,4O3 для получения кислорода

Using hot uniaxial pressing in an argon atmosphere with a stress of 35 MPa and with a holding at 800 °C for 1 hour, ceramic composites of Bi3Ru3O11 – 50, 65 wt % Bi1,6Er0,4O3 were obtained. It was found that phase composition of the composites does not change during gas chromatographic testing at 800 °C and well corresponds to the specified one. Microstructure of the obtained composites was tested and the formation of dense composites with a total porosity of less than 1% and with a uniform distribution of the Bi3Ru3O11 and Bi1,6Er0,4O3 components in bulk of material was demonstrated. Transport properties (total conductivity, oxygen fluxes and selectivity of separating oxygen over nitrogen) of the obtained composites at 600 – 800 °C had been investigated. Thus, at 800 °C the electrical conductivity of Bi3Ru3O11 – 50, 65 wt % Bi1,6Er0,4O3 was about 200 and 50 Ohm–1∙cm–1, respectively, while the metallic nature of their temperature dependence of conductivity is correlated to that for the Bi3Ru3O11. The value of oxygen permeability for the obtained ceramic composites of about 7∙10–9 mol·cm–1·s–1 at 800 °C, which is compared to other membrane materials based on bismuth oxide, demonstrated the potential of their further use in the tasks for obtaining of pure oxygen from air.

Study on Preparation and Ns-Laser Damage of HfO<sub>2 </sub>Single Layers

The effects of the main parameters of argon flux, oxygen flux and beam voltage on the surface morphology, transmittance spectrum and laser damage of the HfO2 single layers prepared by ion beam sputtering are studied. The HfO2 amorphous single layers have porous surface morphologies. Different processes will cause differences in coatings absorption and surface morphology, which in turn will cause changes in the spectral transmittance curve. The ion beam sputtering HfO2 single layers have high content of argon (4.5% - 8%). The laser damage of HfO2 single layers is related to argon inclusions and non-stoichiometric defects. The changes of argon flux and beam voltage have a greater impact on argon content and O/Hf ratio. When the argon content in the coatings is lower and the O/Hf ratio is higher, the laser damage thresholds of the HfO2 single layers are higher.