Variation Of Oxygen Content Research Articles

Study on eutectic-oxidation coupling reaction of Cr-Zr system in high temperature steam environment

The isothermal steam oxidation behavior of Cr-coated Zr-1Nb alloy at 1350 ℃ and 1400 ℃ was investigated. The temperatures are above the Cr-Zr eutectic temperature. The reliability of the experimental setup and methodology was confirmed by conducting isothermal steam oxidation experiments on bare Zr-1Nb specimens at 1100∼1400 ℃, and the corresponding oxidation kinetics correlation was obtained. After the eutectic-oxidation reaction, the surface of the coated specimens exhibited a “crocodile skin” morphology composed of “ridges” and “hollows”, which was attributed to the non-uniform eutectic reaction. Due to the much higher O affinity of Zr compared to Cr, and the higher solubility of Cr in β-Zr compared to α-Zr(O) and ZrO2, the ZrO2 and α-Zr(O) layers initially grew on the Cr-Zr eutectic during oxidation. Cr continuously diffused inward and eventually precipitated as Cr-rich phases within the metallic matrix. Three types of Cr-rich phases were observed, with varying oxygen content and reflecting the oxidation process of the Cr-rich phases. The Cr-rich phases were ultimately oxidized into a mixture of Cr2O3 and ZrO2. The parabolic weight gain rates for the oxidation of Cr-Zr eutectic are compared with the oxidation kinetics correlation derived from the bare Zr-1Nb specimens, and the model applicability of the oxidation kinetics correlations of Zr alloys in the simulations of Cr-Zr eutectic-oxidation reaction is discussed.

Integrating full fan morphology and configuration in three-dimensional simulation of air-cooled proton exchange membrane fuel cell stack

The internal water and thermal state and performance of an air-cooled proton exchange membrane (PEM) fuel cell stack are strongly determined by the fan arrangement and operational characteristics. This study presents an innovative method to investigate the influence of fan on stack performance through integration of fan’s full morphology, including the fan blade, grill between the fan and stack, etc. into a three-dimensional (3D) multiphase stack model. The multiple reference frame (MRF) model is implemented to simulate the air flow field caused by the rotation of fan and the multiple transfers coupled with electrochemical reactions is considered in the 3D stack model in detail. Through this integrated model, the influence of the air supply mode, fan number and duty ratio on stack performance and the distribution characteristics are investigated in detail. It is found that the air flowing into each cell in the fan-cooled stack is highly non-uniform, which increases the variations of oxygen concentration, temperature, and voltage in the stack. In comparison with the blowing mode, the suction mode helps to promote the uniformity of air supply with a lower air flow velocity.

Numerical Analysis of Thermal Flow Dynamics of Arc Plasma and Molten Pool in Hollow Cathode Arc Welding with Oxygen Content

The mechanism of the pulsed hollow cathode arc welding (HCAW) process was revealed using a fully coupled model with a hollow cathode. We solved the governing equations with the Marangoni effect to study the dynamic behaviors of a molten pool with a square pulsing current (200~400 A, 900 Hz) and varying O2 content; the dynamics of the arc plasma and the weld pool in the HCAW process were investigated quantitatively. The results show that the intensity of the arc plasma was more significantly weakened by the design of the hollow cathode in HCAW than that in GTAW with a solid hollow cathode. We could obtain a stable molten pool even with a large pulsing current section (200 A–400 A) at higher frequencies. The flow dynamics of the molten pool were mainly dominated by the Marangoni effect with varying oxygen content, and we could promote penetration by increasing O2 content in HCAW.

Exposure to Non-Steady-State Oxygen Is Reflected in Changes to Arterial Blood Gas Values, Prefrontal Cortical Activity, and Systemic Cytokine Levels.

Onboard oxygen-generating systems (OBOGSs) provide increased inspired oxygen (FiO2) to mitigate the risk of neurologic injury in high altitude aviators. OBOGSs can deliver highly variable oxygen concentrations oscillating around a predetermined FiO2 set point, even when the aircraft cabin altitude is relatively stable. Steady-state exposure to 100% FiO2 evokes neurovascular vasoconstriction, diminished cerebral perfusion, and altered electroencephalographic activity. Whether non-steady-state FiO2 exposure leads to similar outcomes is unknown. This study characterized the physiologic responses to steady-state and non-steady-state FiO2 during normobaric and hypobaric environmental pressures emulating cockpit pressures within tactical aircraft. The participants received an indwelling radial arterial catheter while exposed to steady-state or non-steady-state FiO2 levels oscillating ± 15% of prescribed set points in a hypobaric chamber. Steady-state exposure to 21% FiO2 during normobaria produced arterial blood gas values within the anticipated ranges. Exposure to non-steady-state FiO2 led to PaO2 levels higher upon cessation of non-steady-state FiO2 than when measured during steady-state exposure. This pattern was consistent across all FiO2 ranges, at each barometric condition. Prefrontal cortical activation during cognitive testing was lower following exposure to non-steady-state FiO2 >50% and <100% during both normobaria and hypobaria of 494 mmHg. The serum analyte levels (IL-6, IP-10, MCP-1, MDC, IL-15, and VEGF-D) increased 48 h following the exposures. We found non-steady-state FiO2 levels >50% reduced prefrontal cortical brain activation during the cognitive challenge, consistent with an evoked pattern of neurovascular constriction and dilation.

Microstructural Evolution and Mechanical Properties of Ti-6Al-4V Alloy through Selective Laser Melting: Comprehensive Study on the Effect of Hot Isostatic Pressing (HIP)

This study explores the profound impact of varying oxygen content on microstructural and mechanical properties in specimens HO and LO. The higher oxygen concentration in specimen HO is found to significantly influence alpha lath sizes, resulting in a size of 0.5-1 μm, contrasting with the 1-1.5 μm size observed in specimen LO. Pore fraction, governed by oxygen concentration, is high in specimen HO, registering a value of 0.11%, whereas specimen LO exhibits a lower pore fraction (0.02%). Varied pore types in each specimen further underscore the role of oxygen concentration in shaping microstructural morphology. Despite these microstructural variations, the average hardness remains consistent at ~370 HV. This study emphasizes the pivotal role of oxygen content in influencing microstructural features, contributing to a comprehensive understanding of the intricate interplay between elemental composition and material properties.

Enhanced corrosion resistance and mechanical properties of CrAlON coatings under alternating hydrostatic pressure

CrAlN coatings and CrAlON coatings with varying oxygen content were prepared on the surface of TC4 using multi-arc ion plating. Oxygen introduction resulted in the formation of a (CrAl)(ON) solid solution, leading to finer coating grains and enhanced corrosion resistance. Following a 240-hour immersion in an alternating hydrostatic pressure (AHP) environment, the coatings retained strong adhesion to the substrate. Moreover, they displayed varied improvements in surface hardness and corrosion resistance. The CrAlN coating's improved performance is due to the formation of a surface passivation film, while the high‑oxygen CrAlON coating's enhancement is primarily attributed to filling surface defects with corrosion products under static water pressure.

Oxygen dynamics in a deep‐silled fjord: Tight coupling to the open shelf

AbstractOxygen is declining globally in subsurface seawater. Fjords are particularly susceptible to hypoxia, because entrance sills restrict water circulation. We studied the oxygen dynamics of the Kitimat Fjord System on the west coast of Canada, using 3 yr of data from moored sensors and water column profiles. Subsurface oxygen within the fjord system is principally controlled by the connection to Hecate Strait on the outer shelf. Variations in oxygen concentration in Hecate Strait are reflected in the water that is drawn into the fjord system year‐round at mid‐depth (50–150 m). Deep water is renewed annually, beginning in May/June. Remineralization results in a seasonal decline in oxygen at depth. In the absence of deep‐water renewal, the bottom water in the system could become hypoxic in 1–2 yr. Mixing over a shallow inner sill (100 m) replenishes the oxygen in the deep water of Gardner Canal year‐round. The decadal trends in oxygen concentration show an increase from the 1950s to a maximum in the late 1970s, followed by a decline through 2016. The decline over the period 1977–2016 is 0.018 mL L−1 yr−1 (~ 0.83 μmol L−1 yr−1), which is consistent with the decline observed over the upper continental shelf over the same period.

Research regarding oxygen content reduction in steels

Actual paperwork reflects obtained results of technological analyse of reducing oxygen content in steel for pipe manufacturing, enterprised in a steel furnance equipped with a triple aggregate EAF-LF-VD. Oxygen content was measured during manufacturing process in Loading Furnance and Vacuum Degasing and has been analysed in comparison with several parameters. The results are presented using Matlab through regression surfaces and correlation equations and highlights the influence of analysed factors on oxygen content variation in steel.

Oxidative Modification, Structural Conformation, and Gel Properties of Pork Paste Protein Mediated by Oxygen Concentration in Modified Atmosphere Packaging

The objective of this study was to investigate the effect of pork oxidation through modified atmosphere packaging (MAP) on gel characteristics of myofibrillar proteins (MP) during the heat-induced gelation process. The pork longissimus thoracis (LT) was treated by MAP at varying oxygen concentrations (0, 20, 40, 60, and 80% O2) with a 5-day storage at 4 °C for the detection of MP oxidation and gel properties. The findings showed the rise of O2 concentration resulted in a significant increase of carbonyl content, disulfide bond, and particle size, and a decrease of sulfhydryl content and MP solubility (p &lt; 0.05). The gel textural properties and water retention ability were significantly improved in MAP treatments of 0–60% O2 (p &lt; 0.05), but deteriorated at 80% O2 level. As the concentration of O2 increased, there was a marked decrease in the α-helix content within the gel, accompanied by a simultaneous increase in β-sheet content (p &lt; 0.05). Additionally, a judicious oxidation treatment (60% O2 in MAP) proved beneficial for crafting dense and uniform gel networks. Our data suggest that the oxidation treatment of pork mediated by O2 concentration in MAP is capable of reinforcing protein hydrophobic interaction and disulfide bond formation, thus contributing to the construction of superior gel structures and properties.

Thermodynamic analysis of defect equilibration in highly nonstoichiometric perovskites LnBaMn2O6–δ (Ln=Nd, Sm)

Double-ordered manganites LnBaMn2O6–δ (Ln = Nd, Sm) were shown to possess a variable oxygen content from δ = 0 to 1 while maintaining a tetragonal structure within the temperature range of 973–1223 K and under partial oxygen pressure 10−22 – 1 atm. Coulometric titration technique was successfully utilized to reveal three separated phase in these materials depending on oxygen content. Thermodynamic analysis based on experimentally obtained isothermal functions δ=f(pO2) enabled one to develop a defect formation model suggesting a coexistence three main processes of defect formation in the studied oxides. Thus oxidation and partial disproportionation of manganese supplemented by intrinsic oxygen disordering were demonstrated to govern defect equilibrium. Different influence of activity coefficients involved in the thermodynamic model was considered. Moreover, a reduction in the radius of lanthanide was found to be favorable to expand oxygen homogeneity region and to decrease in the enthalpy of oxidation reaction.

Effect of Size Fractions of Foraminifera on Reconstructing the Paleoceanography of Cretaceous Oceanic Anoxic Event 2

Abstract The globally recognized Cretaceous Oceanic Anoxic Event 2 was recorded at Integrated Ocean Drilling Program Site U1407 in the North Atlantic in sediments that were deposited under varying oxygen concentrations, conditions often associated with decreased foraminiferal test size. A &amp;gt;63-µm size fraction is typically used for collecting foraminifera that live in low-oxygen and deep-sea settings, particularly for paleoceanographic reconstructions where key environmental indicator species may be under-represented or absent in coarser sizes. Using 31 sediment samples from the site, we test the best size fraction to utilize when exploring biotic responses to an oceanic anoxic event. Counts of benthic and biserial (heterohelicid) planktic foraminifera from the standard &amp;gt;63-µm and finer 38–63-µm sieve sizes are compared to determine if critical information is lost if the smaller size fraction is not used. Results show similar trends in relative abundances for both size fractions. There are higher abundances in 38–63-µm residues, but species identification and counts are overly time-consuming for obtaining the general trends. We recommend the use of &amp;gt;63-µm sieves for foraminifera collected from low-oxygen sediments but encourage examination of the 38–63-µm fraction to verify intervals recognized as barren are truly absent of foraminifera.

The burning rate of wood cribs under forced flow and variable oxygen concentration: A B-number approach

Wood cribs are used in a multitude of fire testing and research capacities including the certification of inert gas extinguishing systems. In these standardized tests, a wood crib is subjected to the joint effects of a variable forced flow through the crib and a systematic reduction of oxygen concentration. These joint effects increase the wood crib burning rate, even at reduced oxygen concentrations, before extinction is achieved by oxygen depletion. Currently, no theoretical frameworks exist for studying these coupled effects simultaneously. To address this problem, the in-depth heat and mass transfer phenomena are examined, and a general mass transfer B-Number is proposed for wood cribs. The methodology presented in this work encapsulates the oxygen reduction effects through the B-Number and the forced flow effects through the heat transfer coefficient. The theoretical burning rate with inputs of experimental flow velocities and oxygen concentrations demonstrates that the initial increase in flow drives the observed burning rate increase in the experimental results. Following the initial increase, the reduction in the oxygen concentration dominates and leads to a decrease in the wood crib burning rate. The combined B-number and heat transfer coefficient approach provides a good representation of the competing flow and O2 depletion effects and correctly captures experimental trends. A more accurate wood crib Nusselt number correlation for the heat transfer coefficient is required to better account for the heat transfer in the complex crib geometry.

Effects of Different Oxygen Levels and Time Points on Mitochondrial Respiratory Functional Analysis of Placental Tissue

The placenta plays an important role in fetal growth and development. The Oxygraph-2k mitochondrial function respirometer provides an accurate and realistic quantitative analysis of mitochondrial respiratory function and the energy metabolism of organisms. However, this machine is used less frequently in placental tissues, which consume do not consume as much oxygen as the heart, brain, or skeletal muscle tissues, therefore, it is crucial to develop a standard respiratory measurement protocol for placental tissues. For this, we tested varying oxygen concentrations (150–160 (ambient air), 200, 250, and 300 μM) and time tissue remains viable in respiratory medium (1.5~3, 3~4.5, 4.5~6, and 6~7.5 hour) to determine the optimal experimental conditions. As a result, we found no significant changes in mitochondrial respiratory capacity at different oxygen levels, whilst there was a decrease in mitochondrial respiratory capacity more than 3 hour after delivery.

Combined flow, temperature and soot investigation in oxy-fuel biomass combustion under varying oxygen concentrations using laser-optical diagnostics

In pulverized oxy-fuel biomass combustion, intricate interaction of complex fluid-mechanical, particle-dynamical, and chemical processes manifests even at intermediate scales. This study performs a comprehensive analysis aimed to understand the processes of flame stabilization, pollutant formation, and combustion behavior of biomass particles, while evaluating the impact of varying oxygen concentration on combustion. The investigation is conducted with a comprehensive data set, encompassing various oxy-fuel operation conditions ranging from 27vol.% to 36vol.% in O2 concentration, along a comparable air flame. These conditions are realized in an optically accessible gas-assisted solid fuel combustor designed to generate flames up to 70kWth. Advanced laser-optical diagnostics are employed to capture the combustion process. These techniques include the use of two-phase PIV/PTV for simultaneous measurements of flow and particle velocities, the application of tomographic absorption spectroscopy to elucidate three-dimensional gas temperature distributions, and the establishment of a quasi-simultaneous LII and LIF experimental setup to capture both PAH and soot occurrences. Additionally, chemiluminescence imaging of CH∗ is incorporated. The analysis extends to both single-phase and two-phase combustion, revealing a pronounced influence of oxygen concentration on both regimes. The inner recirculation zone, characteristic of a swirl flame, decreases with increasing oxygen content, coupled with an acceleration of the main flow downwards due to heightened heat release proximate to the nozzle. In two-phase combustion, a significant combustion delay is observed compared to single-phase combustion. Furthermore, the occurrences of PAHs and soot are clearly separated, and a pronounced influence of local gas composition on soot formation is evident. Comparative examination between oxy-fuel and air combustion show that an oxy-fuel condition with an oxygen concentration just below 33vol.% closely mirrors the flame characteristics of air combustion.

Numerical Simulation Study on the Dynamics of Bluff-Body Flames under Oxygen-Lean Conditions

As modern aeroengine combustors advance towards high temperatures, afterburners are inevitably affected by diminished oxygen content in incoming flows, thus affecting combustion efficiency, instability, and flammability limits. In this study, the dynamic combustion characteristics of V-shaped bluff body-stabilised diffusion flames were investigated using a large eddy simulation method with an oxygen mass fraction range of 14–23% and temperatures ranging from 900 to 1100 K. The results show the significant effects of oxygen content and inflow temperature on the flame/flow behaviours downstream of the bluff-body flame holder. In a separated shear layer, two distinct modes of flow/flame shedding are observed when varying the oxygen content and inflow temperature. The results show that BVK instability governs the far-field wake flow/flame features, whereas the oxygen concentration and temperature significantly affect their oscillation amplitudes. In addition, variations in the incoming oxygen content and temperature shift the axial position of the transition from KH instability to BVK instability. Finally, a spectral analysis is conducted to investigate the characteristics of pressure and heat release pulsations under different scenarios. This study highlights the importance of oxygen content on the combustion dynamics of bluff body-stabilised diffusion flames at various temperatures, which is essential for optimising combustion efficiency and stability in practical applications.

Mechanisms behind the environmental sensitivity of carbon fiber reinforced polytetrafluoroethylene (PTFE)

AbstractCarbon fiber reinforced polytetrafluoroethylene (CF/PTFE) composites are known for their exceptional tribological performance when sliding against steel or cast iron in inert gas environments. Compared to experiments in humid air, about an order of magnitude lower wear rate and several times lower coefficient of friction have been reported for tests conducted in dry nitrogen and hydrogen. Moreover, trace moisture has been shown to affect the friction and wear significantly of this tribosystem, although a possible effect of oxygen cannot be ruled out due to uncertainties regarding the oxygen concentrations. While several studies have pointed out the environmental sensitivity of CF/PTFE, the understanding of the underlying mechanisms are very limited. The objective of this research is to investigate the individual and combined effect of oxygen and moisture on the tribological behavior of CF/PTFE sliding against steel. Additionally, this study aims to elucidate the underlying mechanisms that govern the environmental sensitivity of the system. Climate-controlled three-pin-on-disc experiments were conducted in nitrogen atmospheres at various concentrations of oxygen and moisture. The tribological results clearly demonstrate that both moisture and oxygen contribute to increased friction and wear. However, the adverse effect was much more pronounced for oxygen than moisture. A qualitative method was developed to estimate the tribofilm coverage on the CF/PTFE surface. Results showed strong correlation between high coverage of strongly adhered tribofilm and low wear rate. Moreover, a loosely adhered tribofilm was observed on top of the CF/PTFE surface in presence of moisture. FTIR analysis indicated that the loosely adhered tribofilm found in the moisture-enriched environment contained a significant amount of adsorbed water, which may explain the lower coefficient of friction in presence of moisture compared to oxygen. The adsorbed water in the loosely adhered tribofilm could be an indication of moisture-driven lubrication by the non-graphitic carbon in the tribofilm.

Radiative flamelet/progress variable modelling of the UMD turbulent line fires under varying oxygen concentrations

Advanced combustion models for fire simulations remain challenging due to the complex interaction of turbulence, combustion and radiation. Among these models, the flamelet-based model is a promising candidate to incorporate detailed chemistry at low computational cost. To this end, flamelet large-eddy simulations (LES) are performed to investigate extinction characteristics of a turbulent line fire, which is a target case in the Measurement and Computation of Fire Phenomena (MaCFP) workshop and has been experimentally studied at the University of Maryland. Two radiative flamelet formulations are investigated: (a) the radiative laminar flamelet model (RLFM-u) and (b) the radiative flamelet/progress variable (RFPV-u) model. In the normal air case where XO2 = 21%, RLFM-u and RFPV-u perform similarly, both yield reasonable agreement with experimentally measured temperature. However, in the under-ventilated case (XO2 = 13%), RFPV-u outperforms RLFM-u as it manages to capture the local flame extinction. Two dimensionless indices are introduced to quantify the role of radiation heat loss and local strain in flame weakening. It is revealed that radiative heat loss dominates the flame weakening in the normal air case while strain-induced local extinction contributes significantly to flame weakening in under-ventilated conditions, which is only captured by RFPV-u, highlighting its advantages in predicting fires with strong extinction.

Integrated experimental assessment and validation of oxidation with real-scale SiC fuel compact in HTGR

Air ingress is a critical accident in HTGR design, caused by a rupture in the coolant pipe. It leads to the oxidation of hot graphite at high temperatures, resulting in mechanical degradation of graphite structures. To address this issue, the authors propose a novel approach of substituting graphite fuel compacts with polycrystalline reaction-sintered SiC (RS-SiC) fuel compacts due to their superior oxidation resistance. The adoption of SiC based fuel compact will eliminate the graphite sleeves currently used in the pin-in-block type HTGR designs. It will also make it possible to achieve the high-power density due to the absence of graphite sleeves. There is limited understanding of the oxidation kinetics and transition behavior in RS-SiC. To address this knowledge gap, integrated experiments are conducted to investigate the thermal and oxidation behavior of SiC under varying oxygen concentrations. These experiments aim to provide insights into SiC's performance in HTGR environments using similar temperature and flow velocity conditions. Experimental data obtained will be utilized to develop a numerical model for enhanced understanding. In this study, both experimental and computational fluid dynamics (CFD) analyses were performed to compare the temperatures obtained from simulations with experimental measurements. The results demonstrated good agreement between experimental and numerical data. Passive oxidation was observed in real scale SiC fuel compacts at both 900 °C and 1100 °C, with slightly lower weight gain at the higher temperature. This suggests the possibility of damage to the SiO2 oxide layer at elevated temperatures. These results are important as the experiments are done in an integrated test facility using the air ingress accident boundary conditions of HTGR with the SiC fuel compact of real scale. These experiments validate the earlier findings from thermogravimetry differential thermal analysis (TG/DTA) conducted in a smaller-scale facility. They play a role in extending our understanding of SiC oxidation behavior, thereby assisting in the advancement of HTGR designs for enhanced safety and performance.

On the importance of nano-oxide control in laser powder bed fusion manufactured Ni-based alloys to enhance fracture properties

In this study, a series of Ni-Cr-Mo based alloys (IN625, C22 and NA282), sourced from various powder suppliers and having varying oxygen concentrations (200 ppm to 800 ppm), were printed under similar conditions using laser powder bed fusion (LPBF). Nano-oxides in the range of 20–50 nm were observed in each alloy in the as-printed state, albeit with different number densities. Room temperature tensile tests and liquid nitrogen (LN2, -196 °C) Charpy impact tests were performed to assess the mechanical response of each alloy. The IN625 and C22 samples showed considerably lower impact energy values than the NA282, as well as lower room temperature post-necking tensile elongations, despite showing similar yield strengths and strain hardening behaviours. Fracture surface dimple sizes were shown to correlate with nano-oxide particle spacings. Nano-oxides were found in the middle of most dimples on fracture surfaces suggesting that the nano-oxides are the sites of void nucleation during fracture, despite being only 20–50 nm in size. The precursor metal powders were identified as the primary origin of the nano-oxide particles. This study highlights the critical, detrimental role that nano-oxides, typically present in LPBF metals, have on the fracture properties of these materials. In the case of the Ni-Cr-Mo alloys examined here, limiting oxide formation is critical to achieving optimal fracture properties.

Cell membrane dysfunction in postharvest spinach leaves increases water permeability through parallel pathways involving the lipid bilayer and aquaporins

Leafy greens, such as spinach, are susceptible to postharvest deterioration. Understanding factors underlying freshness loss, particularly related to cell membrane function and water permeability, is crucial for improving postharvest handling and preservation techniques. This study aimed to investigate changes in membrane water permeability in spinach mesophyll cells during storage and to identify the factors that affect these changes. We examined three properties of the cell membrane: lipid peroxidation, which triggers cell membrane deterioration; membrane rupture strength, reflecting the viscosity and fluidity of the cell membrane; and the expression of four aquaporin (AQP) genes: SoPIP1;1, SoPIP1;2, SoPIP2;1, and SoδTIP. To analyze their relationship with membrane water permeability, we conducted a protoplast shrinking assay under a hyperosmotic challenge. Our findings revealed that lipid peroxidation increased and membrane rupture strength weakened in response to varying oxygen concentrations during storage, correlating with an increase in membrane water permeability. Interestingly, the expression of SoAQPs markedly decreased during storage, regardless of the oxygen concentration. These observations suggest that membrane peroxidation and embrittlement promote packing imperfections in the lipid bilayer and induce AQPs to adopt an open conformational state, thereby contributing to the overall increase in membrane water permeability, even when the expression of SoAQPs decreases.