Increasing Oxygen Content Research Articles

Characteristics of lean oxygen combustion and dynamic microreaction process of water-soaked coal

Oxidative spontaneous combustion is likely to occur after long-term water immersion in the gob area of coal mines. Mostly, the oxidation process is slowly carried out under different air leakage conditions. This paper summarizes the four stages of the low-temperature oxidation of water-soaked coal samples through temperature-programmed experiments. Using infrared spectroscopy and thermal analysis experiments, the migration laws of the functional groups and the thermal reaction characteristics of the four stages were investigated. The results show that as the oxygen concentration increases, the gas product concentration increases, and the activation energy of the deep oxidation stage decreases. With the progress of the heating stage, when the oxygen concentration is higher than 10%, the change in each functional group is larger, and the conversion of the functional group and the intermediate complex is relatively closer at an oxygen concentration of 21%. The low-temperature oxidation reaction is a parallel process of the pyrolysis and micro-oxygen absorption, and the DTG size is not affected by the oxygen concentration at the critical temperature. The higher the oxygen concentration is, the lower the initial exothermic temperature is, which promotes the exothermic process in the deep oxidation and oxidation-limited stages. The microreaction mechanism among coal, oxygen and water molecular chemisorption is constructed. By controlling the coal oxidation reaction stages under different air leakage conditions, the spontaneous combustion of water-soaked coal in the goaf is avoided.

Decarburization and ash characteristics during melting combustion of fine ash from entrained-flow gasifier

Disposal of gasification fine ash (GFA), a by-product of coal gasification, is still dominated by stockpiles, increasing land and environmental problems. To explore ways to reduce and reuse GFA through combustion, our research team used the circulating fluidized bed to modify the less reactive GFA through preheating and achieved the secondary use of GFA under high-oxygen and high-temperature reaction conditions. Through this experiment, we explored the effects of equivalent ratio and oxygen concentration in a melt furnace on carbon conversion and ash characteristics. The increase of oxygen concentration in the melt furnace unit benefited decarbonization of the preheated GFA. The increased oxygen concentration in the melting furnace unit was not conducive to the generation of mineral phase structures and pore structures in the products. The mineral phase structures and elemental contents of the coarse slag, fine slag and fly ash produced by the melt furnace unit differed. Reduction of the equivalent ratio did not significantly affect the morphology of the coarse slag products. However, the morphology of the fine slag and fly ash changed more significantly. Moreover, the carbon conversion capacity decreased significantly along with the drop of equivalent ratio and the change of the reaction atmosphere.

Neuroprotective Treatments for Ischemic Stroke: Opportunities for Nanotechnology

AbstractStroke is one of the major causes of death and severe disability worldwide. At present, intravenous thrombolysis to restore blood flow at the ischemic part of the brain is the main treatment for ischemic stroke. However, even if patients are treated in time during the therapeutic window of thrombolytic drugs, thrombolysis causes a sharp increase in oxygen concentration at the injury site after ischemia–reperfusion, leading to the outbreak of free radicals, which further aggravates the brain injury. Neuroprotective therapy, which is combined with thrombolytic therapy, is an important treatment for ischemic stroke and metabolic disorders caused by ischemic brain injury. It can inhibit various types of cell necrosis, increase cell viability, delay neuronal death, and promote the recovery of neural functions. This review summarizes novel neuroprotective treatments for stroke, especially nanotechnology‐assisted advanced targeted therapies. Future prospects and challenges are also discussed for the development of neuroprotective nanomaterials.

Direct laser-assisted fabrication of turbostratic graphene electrodes: Comparing symmetric and zinc-ion hybrid supercapacitors

Lasers offer a versatile means towards the single-step, binder-free synthesis of three-dimensional graphene-like porous networks, providing an enticing alternative over energy intensive, multi-step traditional synthesis protocols creating unwanted waste streams. Here, we report on a novel laser-assisted method for the one-step preparation of the electrode component, not solely the active material, based on the simultaneous synthesis of turbostratic graphene-like structures on a carbon precursor and its transfer/deposition on the selected current collector. The performance of the graphene-based electrodes was electrochemically evaluated for both electric double layer capacitor (EDLC) and zinc-ion hybrid capacitor (ZIC) configurations. The performance of the EDLC devices was found to be superior to that of the current state-of-the-art devices prepared by laser-grown graphene. The ZIC exhibited higher areal energy density than the symmetric devices by one order of magnitude. The devices showed very low equivalent series resistance, good rate performance and high long-term cycling stability. Notably, the EDLC with the KOH electrolyte demonstrated an unexpected ∼20% increase in capacitance during the stability test of 10,000 cycles. This result was attributed to the substantial increase of oxygen content of the graphene electrodes, which act as sites for redox activity.

Biodiesel Exhaust Toxicity with and without Diethylene Glycol Dimethyl Ether Fuel Additive in Primary Airway Epithelial Cells Grown at the Air-Liquid Interface.

Biodiesel usage is increasing steadily worldwide as the push for renewable fuel sources increases. The increased oxygen content in biodiesel fuel is believed to cause decreased particulate matter (PM) and increased nitrous oxides within its exhaust. The addition of fuel additives to further increase the oxygen content may contribute to even further benefits in exhaust composition. The aim of this study was to assess the toxicity of 10% (v/v) diethylene glycol dimethyl ether (DGDME) added as a biodiesel fuel additive. Primary human airway epithelial cells were grown at the air-liquid interface and exposed to diluted exhaust from an engine running on either grapeseed, bran, or coconut biodiesel or the same three biodiesels with 10% (v/v) DGDME added to them; mineral diesel and air were used as controls. Exhaust properties, culture permeability, epithelial cell damage, and IL-6 and IL-8 release were measured postexposure. The fuel additive DGDME caused a decrease in PM and nitrous oxide concentrations. However, exhaust exposure with DGDME also caused decreased permeability, increased epithelial cell damage, and increased release of IL-6 and IL-8 (p < 0.05). Despite the fuel additive having beneficial effects on the exhaust properties of the biodiesel, it was found to be more toxic.

New Water-Ethylene Glycol Lubricants with Stearate Ionic Liquid Crystal Additive

The main purpose of the present study is to improve the tribological performance of aqueous lubricants with the use of ecofriendly, fatty acid-derived additives. The protic ionic liquid crystal bis(2-hydroxyethyl)ammonium stearate (DES) has been added to 50:50 water+ethylene glycol (W–EG) to obtain (W–EG)+0.5%DES; (W–EG)+1%DES and (W–EG)+2%DES emulsions. The new lubricants have been studied in sapphire-AISI (American Iron and Steel Institute) 316L stainless-steel pin-on-disk sliding contacts. The addition of DES reduces the friction coefficient by up to 76% and wear rate by up to 80%, with respect to (W–EG). The best performance is found for the emulsions with the lower proportion of DES (0.5 and 1 wt.%). These results have been related to viscosity and turbidity values. Wear mechanisms have been studied by Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM/EDX) and by Raman microscopy. While W–EG shows a severe abrasive mechanism, no abrasion marks are present inside the wear track after lubrication with (W–EG)+0.5%DES, the emulsion with the lowest wear rate. After lubrication with W–EG, an increase in oxygen content is observed inside the wear track, as determined by EDX and confirmed by Raman microscopy, which shows the presence of iron oxides. The addition of DES reduces these oxidation processes.

Combustion characteristics and energy distribution of hydrogen engine under high oxygen concentration

Integrated Vehicle Fluid (IVF) system is a promised energy management system for cryogenic upper stage. The power unit of IVF is hydrogen-oxygen internal combustion engine (ICE) whose energy utilization is close to 100% in IVF system. The oxygen concentration of intake gas was gradually raised during ICE tests as a preliminary study. The power of hydrogen-oxygen ICE reaches 4 kW at 3000 r/min, which satisfies the power requirement of IVF system. At this time, the exhaust loss reaches 41.6%, the heat transfer loss is 35.9%, and the output power only accounts for 21.9%. The heat transfer loss shows a parabolic trend which first rises and then falls with increasing oxygen concentration. But the exhaust loss keeps growing with the increases in oxygen concentration and engine speed. It is significant for the design of regenerative cooling system and other subsystems in IVF system at specific engine speed.

Model-based identification and testing of appropriate strategies to minimize N2O emissions from biofilm deammonification.

Based on a one-year pilot plant operation of a two-step biofilm nitritation-anammox pilot plant, N2O mitigation strategies were identified by applying a newly developed biofilm modeling approach. Due to adapted plant operation, the N2O emission could be diminished by 75% (8.8% → 2.3% of NH4-Noxidized_AOB). The results (measurement and simulation) confirm the huge importance of denitrification as an N2O source or N2O sink, depending on the boundary conditions. A significant reduction of N2O emissions could only be achieved with a one-step deammonification system, which is related to low nitrite and HNO2 concentrations. Increased oxygen concentrations in the bulk phase are not related to decreased emissions. N2O formation by ammonium-oxidizing bacteria (AOB) just shifts deeper into the biofilm; zones with low oxygen concentrations are not avoidable in biofilm systems. Low oxygen concentrations in the bulk phase, however, result in a reduction of the total net N2O formation due to increased activity of heterotrophic bacteria directly at the source of N2O formation (outer biofilm layer). For the model-based identification of mitigation strategies, the standard modeling approaches for biofilms were expanded by including the factor-based N2O formation and emission approach. The new model 'Biofilm/N2OISAH' was successfully validated using data from pilot-scale measurement campaigns. Altogether, the investigation confirms that the employed digital model can strongly support the development of N2O mitigation strategies without the need for specialized measurement inside the biofilm.

Experimental characterization of spark ignited ammonia combustion under elevated oxygen concentrations

Due to its nature as a carbon free fuel and carrying hydrogen energy ammonia has received a lot of attention recently to be used as an alternative to fossil fuel in gas turbine and internal combustion engines. However, several barriers such as long ignition delay, slow flame speed, and low reactivity need to be overcome before its practical applications in engines. One potential approach to improve the ignition can be achieved by using oxygen enriched combustion. In this study, oxygen-enriched combustion of ammonia is tested in a constant volume combustion chamber to understand its combustion characteristics like flame velocity and heat release rates. With the help of high speed Schlieren imaging, an ammonia-oxygen flame is studied inside the combustion chamber. The influence of a wide range of oxygen concentrations from 15 to 40% are tested along with equivalence ratios ranging from 0.9 to 1.15. Ammonia when ignited at an oxygen concentration of 40% with an equivalence ratio of ϕ= 1.1 at 10 bar has a maximum flame velocity of 112.7 cm/s. Reduced oxygen concentration also negatively affects the flame velocity, introducing instabilities and causing the flame to develop asymmetrically due to buoyancy effects inside the combustion chamber. Heat release rate (HRR) curves show that increasing the oxygen concentration from 21 to 35% of the mixture can help reduce the ignition delays. Peak HRR data shows increased sensitivity to air fuel ratios with increased oxygen concentrations in the ambient gas. HRR also shows an overall positive dependence on the oxygen concentration in the ambient gas.

Experimental and kinetic modeling studies on oxidation of n-heptane under oxygen enrichment in a jet-stirred reactor

Oxygen-enriched combustion can improve thermal efficiency and reduce CO, unburned hydrocarbons and soot emissions in internal combustion engines. There are significant differences in the combustion process and pollutant emissions between oxygen-enriched and air condition. In order to develop an improved understanding of the effect of oxygen concentration on n-heptane oxidation, the jet-stirred reactor oxidation characteristics of n-heptane were experimentally tested at temperatures of 450–950 K and pressures of 1.03 atm with the residence time (τ) of 2 s, under the condition of oxygen mole fractions from 0.055 to 0.6. Meantime, the simulations were performed on CHEMKIN. Results show that, firstly, with the increase of oxygen concentration, the NTC (Negative Temperature Coefficient) effect is weakened, mainly due to the strengthening of low-temperature reaction path, which is also the reason for the improvement of ignition stability in cold-start condition of engines. Secondly, the activity of the reaction system improves with the increase of oxygen concentration. Within 500–750 K, it is due to enhancement of the low-temperature reaction path. When the temperature is higher than 750 K, the improvement is due to the enhancement of decomposition of H2O2 and addition reaction of H and O2. Thirdly, with the increase of oxygen concentration, both the generation and consumption of CO are strengthened, which leads to the tip of the diesel spray flame changing from soot area under air condition to the CO chemiluminescence.

Annealing duration dependent optical, nonlinear optical, and optical limiting properties of rare-earth doped glasses embedded with gold nanoparticles

In this work, the Eu2O3 doped B2O3 glass specimen embedded with gold nanoparticles (NPs) was designed by the process of melt-quenching and subjected for thermal treatment to understanding the efficacy of thermal dependency on the optical and nonlinear optical (NLO) characteristics. Linear optical studies have revealed a decrease trend in the energy band gap as the function of annealing duration, indicating the increase of non-bridging oxygen concentration in the glass host. The NLO properties were assessed in near-infrared region utilizing 150 fs laser pulses delivered at the rate of 80 MHz. The aperture free Z-scan measurements exhibited an increased nonlinear absorption coefficient with annealing duration. Further, the closed aperture Z-scan data depicted an increase trend in the positive nonlinear refraction with annealing duration and eventually reduced at the greater duration of annealing. The optical limiting studies demonstrated similar behaviour to the nonlinear absorption characteristics of studied glass samples. These results are related to the local field stimulated by surface plasmons of gold NPs near the Eu3+ ions during the exposure of glass to high fluence laser beam. Our results indicate that B2O3 glasses embedded with Au NPs heat-treated for 30 h at 450 °C are good candidates for nonlinear photonic, optoelectronic, and optical power limiting applications in photonics.

Effect of oxygen concentrations on the corrosion behavior of a duplex-phase FeNiCrCuAl high entropy alloy in supercritical water

The effect of oxygen concentrations on the corrosion behavior of a Co-free duplex-phase (DP) FeNiCrCuAl high entropy alloy (HEA) in supercritical water (SCW) at 550°C under 25 MPa was investigated. The weight gain increased with the increasing of oxygen concentration, but it was significantly lower than conventional alloys at the same corrosion conditions. In addition to the strip-like Al2O3 oxides, a large number of irregular Cu2O particles were deposited on the surface of samples due to the localized corrosion of Cu-rich FCC regions. The density of the oxides Cu2O and Al2O3 increased with increasing oxygen concentration. Different microstructures exhibited the different chemical compositions and structures of the oxide films. For FeCr-rich regions, in addition to strip-like Al2O3 oxides, a duplex-structure oxide film consisting of a Cr2O3 outer layer and FeCr2O4 inner layer was formed. However, a duplex-structure oxide film consisting of an Al2O3 outer layer and NiAl2O4 inner layer was formed on the NiAl-rich regions or along the Cu-rich regions. The thickness of the oxide films in FeCr-rich, NiAl-rich and Cu-rich regions gradually increased with the increasing oxygen concentration.

Optical Oxygen Sensors Show Reversible Cross-Talk and/or Degradation in the Presence of Nitrogen Dioxide.

A variety of luminescent dyes including the most common indicators for optical oxygen sensors were investigated in regard to their stability and photophysical properties in the presence of nitrogen dioxide. The dyes were immobilized in polystyrene and subjected to NO2 concentrations from 40 to 5500 ppm. The majority of dyes show fast degradation of optical properties due to the reaction with NO2. The class of phosphorescent metalloporphyrins shows the highest resistance against nitrogen dioxide. Among them, palladium(II) and platinum(II) complexes of octasubstituted sulfonylated benzoporphyrins are identified as the most stable dyes with almost no decomposition in the presence of NO2. The phosphorescence of these dyes is reversibly quenched by nitrogen dioxide. Immobilized in various polymeric matrices, the sulfonylated Pt(II) benzoporphyrin demonstrates about one order of magnitude more efficient quenching by NO2 than by molecular oxygen. Our study demonstrates that virtually all commercially available and reported optical oxygen sensors are likely to show either irreversible decomposition in the presence of nitrogen dioxide or reversible luminescence quenching. They should be used with extreme caution if NO2 is present in relatively high concentrations or it may be generated from other species such as nitric oxide. As an important consequence of nearly anoxic systems, production of nitrogen dioxide or nitric oxide may be therefore erroneously interpreted as an increase in oxygen concentration.

Avoiding oxygen-induced early fracture in titanium with high strength via entangled grains through laser powder bed fusion

Titanium (Ti) samples with oxygen contents of 0.13% (weight %) (0.13%O-Ti), 0.18% (0.18%O-Ti) and 0.24% (0.24%O-Ti) are printed through laser powder bed fusion (L-PBF) process. With increasing oxygen content, yield strength of L-PBF Ti under tensile testing increases without losing ductility, and becomes larger than that of conventionally produced Ti. Probably this is not resulted from even oxygen distribution, because nano-scale oxygen segregation is observed in 0.24%O-Ti through high-resolution scanning transmission electron microscopy (STEM). In order to get insight into fundamental mechanism of the oxygen-induced early fracture avoidance and high strength, tensile testing of L-PBF Ti is followed by quasi-in-situ electron backscatter diffraction (EBSD)/backscattered electron microscopy (BSEM). It is found that avoidance of the oxygen-induced early fracture and high strength are probably attributed to extensive entangled grains, which promotes formation of multiple slip systems and prevents the propagation of intergranular crack.

Modification of soy protein isolate using dielectric barrier discharge cold plasma assisted by modified atmosphere packaging

In this study, soy protein isolate (SPI) was treated by modified atmosphere packaging (MAP) assisted dielectric barrier discharge (DBD) cold plasma (CP) to improve its functional properties. For this reason, SPI powders were treated with DBD-CP at the oxygen ratio of 20 %, 30 %, 40 %, 50 % and 60 %, respectively. The results showed that with the increase of oxygen content, the structure of SPI was destroyed, protein macromolecule depolymerized. However, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed that the primary structure of SPI was not disrupted. In addition, when the oxygen content was greater than 40 %, the solubility, water holding capacity, gelling, emulsifying and foaming properties of SPI were significantly improved (p < 0.05). The results showed that high-oxygen packaging can increase the active particles generated during processing, thereby optimizing the structural and functional properties of SPI. Therefore, MAP can serve as a more efficient method for DBD-CP to modify soybean protein.

Oxygenation effects on temperature and dissolved oxygen at a commercial Atlantic salmon farm

As climate change continues to warm oceans and exacerbate deoxygenation, coastal ecosystems and anthropogenic activities that occur there are left vulnerable. Fish cultured in ocean net pens are increasingly subjected to oxygen stress. Aeration and oxygenation have been utilized to improve oxygen conditions in pond aquaculture; however, their use in open ocean net pens is still in its infancy. In this study, liquid oxygen was distributed through the NetOx Net system within sea cages in a commercial Atlantic salmon (Salmo salar) farm located off Saddle Island, Nova Scotia (Canada). Real-time sensors were used to measure temperature and oxygen before oxygenation, between oxygenation and the onset of de-stratification due to mixing, and after mixing had resulted in full de-stratification. Oxygenation likely resulted in the upwelling of cold deep water, lowering the cage temperature by ∼4 ℃ which in turn increased oxygen solubility and decreased fish metabolism (though no significant change in growth was observed); these factors resulted in an overall increase in oxygen concentrations by ∼1.5 mgL−1. Following de-stratification, the effects of the oxygenation system were diluted, and mixing due to oceanographic processes dominated the system. As climate change increases hypoxia in coastal regions, where aquaculture practices continue to expand, oxygenation systems will become commonplace. Therefore, it is important to understand whether they will work in an environment that is open to other elements.

Experimental investigation on spontaneous combustion oxidation characteristics and stages of coal with different metamorphic degrees.

Coal spontaneous combustion (CSC) is a major disaster threatening coal mine safety; therefore, the investigation of coal spontaneous combustion and oxidation characteristics has been a hot topic in the long term. In this paper, the experimental temperature programmed system is used to carry out the simulation experiment of coal spontaneous combustion and oxidation of three kinds of coal with different metamorphic degrees under three oxygen concentrations (9%, 15%, 21%). The effects of metamorphic degree and oxygen concentration on coal oxidation characteristics were analyzed, and the variation laws of crossing point temperature, three characteristic point temperature, and apparent activation energy were qualitatively discussed. Finally, coal oxidation reaction stages were evaluated and divided. The results show that the concentrations of CO and C2H4 are negatively correlated with the degree of deterioration but increase with the increase of oxygen concentration. High metamorphic coal corresponds to high crossing point temperature (CPT). The average error between the CPT value calculated from the BM empirical correlation and the experimental data is very small, which is 6.42%. The higher the metamorphic degree of coal, the higher the three characteristic temperature points (critical temperature, xerochasy temperature, and activity temperature). The oxidation process of the three coal samples is divided into four stages: surface oxidation, oxidation self-heating, accelerated oxidation, and deep oxidation. The apparent activation energy of each stage exhibits significant variability, with varying patterns displayed with the degree of metamorphism.

Effect of oxygen on the hydrogen storage properties of TiFe alloys

Hydrogen storage is one of the critical barriers to the hydrogen-based clean energy supply chain. TiFe alloy is a prime candidate material for stationary hydrogen storage, which can play a critical role in the deployment of variable renewable energies. However, the understanding of the hydrogen storage properties of TiFe alloy and the development of industrially deployable storage technologies based on TiFe are still in their nascent stage. The properties of TiFe alloy rely strongly on the presence of oxygen due to the strong affinity of Ti to oxygen. This work systematically investigated the effects of oxygen on the equilibrium pressure of TiFe-H intermetallic hydride. We aim to understand how the oxygen content affects the (de)hydrogenation behavior of TiFe alloys. Specifically, we found that the oxygen can dissolve in the TiFe phase and form solid solutions of TiFe-O. During the thermochemical synthesis process of TiFe, with the increase of annealing time, the Ti4Fe2O phase decreases, and the oxygen in TiFe increases. The increase of oxygen content in the TiFe results in the increase of equilibrium pressure of the TiFe alloy. It suggests that the oxygen dissolved in TiFe can destabilize the TiFe-H hydride and alter the thermodynamics of the TiFe-H system.

Paleoceanographic reconstruction of the Ediacaran Dengying Formation, Sichuan Basin, Southwest China: Implications for the origin of Precambrian microbial carbonates

Abundant microbial carbonates with well-preserved primary textures occur in the upper Ediacaran Dengying Formation in the Sichuan Basin, southwest China, providing an opportunity to study the paleoceanographic conditions and the origin of Precambrian microbial carbonates. However, paleoenvironmental studies of these microbial carbonates are relatively rare, especially with respect to the comparison between the upper and lower parts of the Dengying Formation. In this paper, we present new analyses of carbon and oxygen isotopes and major, trace, and rare earth elements (REEs) for carbonate rocks from the Dengying Formation, in order to reveal the paleoceanographic redox and salinity conditions of the seawater from which these rocks were deposited. These rocks have shale-normalized REE and Y patterns that display weak negative Ce anomalies, weak positive Eu anomalies, and moderate middle REE enrichment, indicating the suboxic seawater for their deposition. From the lower to upper parts of the Dengying Formation, negative Ce anomalies become more prominent, while positive Eu anomalies and middle REE enrichment weaken, suggesting a gradual increase in the seawater oxygen concentration. The heavier oxygen isotopes of the carbonate matrixes and fibrous cements in the second member of the lower part of the Dengying Formation reflect a higher seawater salinity, conforming to the thick evaporates in the second member. The elevated oxygen content and decreased salinity in the seawater promoted the emergence of metazoans that inhibited the growth of microbes, causing the decreasing development of microbial carbonates in the upper part of the Dengying Formation compared to the lower part.

The adsorption mode and evolution of O2 molecules on the SnO2 (221) crystal plane

Density functional theory (DFT) and electrochemical impedance spectroscopy (EIS) techniques are used to investigate the adsorption mode and evolution of O2 molecules on the SnO2 (221) crystal plane in this paper. The study shows that adsorbed O2 molecules on the crystal plane exist in two reversible modes. In the general atmosphere, O2 molecules are preferentially physically adsorbed on the crystal plane in the form of the mono-molecule, namely mode I; when the ambient oxygen concentration increases, it appears as a bi-molecular adsorption mode, namely mode II. Both modes decrease the crystal plane conductivity, but the decrease is more pronounced in mode II, which is also confirmed by EIS. In-depth exploration of the adsorption behavior of O2 molecules is conducive to better understanding and control the surface state of materials and provides a basis for material design.